Sound on the computer is translated from waves that you hear into a series of -values, or samples, each representing the amplitude of the wave. When these -samples are sent in a stream to a sound card, an approximation of the original -wave can be recreated. The more bits used to represent the amplitude, and the -greater frequency these samples are gathered, the closer the approximated -sound is to the original, and the better the quality of sound.
This library supports both 8 and 16 bit signed and unsigned sound samples, -at frequencies ranging from 11025 Hz to 44100 Hz, depending on the -underlying hardware. If the hardware doesn't support the desired audio -format or frequency, it can be emulated if desired (See -SDL_OpenAudio())
A commonly supported audio format is 16 bits per sample at 22050 Hz.
SDL supports audio control of up to 32 local CD-ROM drives at once.
You use this API to perform all the basic functions of a CD player, -including listing the tracks, playing, stopping, and ejecting the CD-ROM. -(Currently, multi-changer CD drives are not supported.)
Before you call any of the SDL CD-ROM functions, you must first call -"SDL_Init(SDL_INIT_CDROM)", which scans the system for -CD-ROM drives, and sets the program up for audio control. Check the -return code, which should be 0, to see if there -were any errors in starting up.
After you have initialized the library, you can find out how many drives -are available using the SDL_CDNumDrives() function. -The first drive listed is the system default CD-ROM drive. After you have -chosen a drive, and have opened it with SDL_CDOpen(), -you can check the status and start playing if there's a CD in the drive.
A CD-ROM is organized into one or more tracks, each consisting of a certain -number of "frames". Each frame is ~2K in size, and at normal playing speed, -a CD plays 75 frames per second. SDL works with the number of frames on a -CD, but this can easily be converted to the more familiar minutes/seconds -format by using the FRAMES_TO_MSF() macro.
Event handling allows your application to receive input from the user. Event handling is initalised (along with video) with a call to: -
SDL_Init(SDL_INIT_VIDEO);-Internally, SDL stores all the events waiting to be handled in an event queue. Using functions like SDL_PollEvent and SDL_PeepEvents you can observe and handle waiting input events.
The key to event handling in SDL is the SDL_Event union. The event queue itself is composed of a series of SDL_Event unions, one for each waiting event. SDL_Event unions are read from the queue with the SDL_PollEvent function and it is then up to the application to process the information stored with them.
| SDL_PumpEvents | Pumps the event loop, gathering events from the input devices |
| SDL_PeepEvents | Checks the event queue for messages and optionally returns them |
| SDL_PollEvent | Polls for currently pending events |
| SDL_WaitEvent | Waits indefinitely for the next available event |
| SDL_PushEvent | Pushes an event onto the event queue |
| SDL_SetEventFilter | Sets up a filter to process all events |
| SDL_EventState | Allows you to set the state of processing certain events |
| SDL_GetKeyState | Get a snapshot of the current keyboard state |
| SDL_GetModState | Get the state of modifier keys |
| SDL_SetModState | Set the state of modifier keys |
| SDL_GetKeyName | Get the name of an SDL virtual keysym |
| SDL_EnableUNICODE | Enable UNICODE translation |
| SDL_EnableKeyRepeat | Set keyboard repeat rate |
| SDL_GetMouseState | Retrieve the current state of the mouse |
| SDL_GetRelativeMouseState | Retrieve the current state of the mouse |
| SDL_GetAppState | Get the state of the application |
| SDL_JoystickEventState | Enable/disable joystick event polling |
Before SDL can be used in a program it must be initialized with SDL_Init. SDL_Init initializes all the subsystems that the user requests (video, audio, joystick, timers and/or cdrom). Once SDL is initialized with SDL_Init subsystems can be shut down and initialized as needed using SDL_InitSubSystem and SDL_QuitSubSystem.
SDL must also be shut down before the program exits to make sure it cleans up correctly. Calling SDL_Quit shuts down all subsystems and frees any resources allocated to SDL.
SDLdoc (The SDL Documentation Project) was formed to completely rewrite the SDL documentation and to keep it continually up to date. The team consists completely of volunteers ranging from people working with SDL in their spare time to people who use SDL in their everyday working lives.
The latest version of this documentation can always be found here: http://sdldoc.csn.ul.ie Downloadable PS, man pages and html tarballs are available at http://sdldoc.csn.ul.ie/pub/
SDL_AudioSpec wanted;
- extern void fill_audio(void *udata, Uint8 *stream, int len);
-
- /* Set the audio format */
- wanted.freq = 22050;
- wanted.format = AUDIO_S16;
- wanted.channels = 2; /* 1 = mono, 2 = stereo */
- wanted.samples = 1024; /* Good low-latency value for callback */
- wanted.callback = fill_audio;
- wanted.userdata = NULL;
-
- /* Open the audio device, forcing the desired format */
- if ( SDL_OpenAudio(&wanted, NULL) < 0 ) {
- fprintf(stderr, "Couldn't open audio: %s\n", SDL_GetError());
- return(-1);
- }
- return(0); static Uint8 *audio_chunk;
- static Uint32 audio_len;
- static Uint8 *audio_pos;
-
- /* The audio function callback takes the following parameters:
- stream: A pointer to the audio buffer to be filled
- len: The length (in bytes) of the audio buffer
- */
- void fill_audio(void *udata, Uint8 *stream, int len)
- {
- /* Only play if we have data left */
- if ( audio_len == 0 )
- return;
-
- /* Mix as much data as possible */
- len = ( len > audio_len ? audio_len : len );
- SDL_MixAudio(stream, audio_pos, len, SDL_MIX_MAXVOLUME);
- audio_pos += len;
- audio_len -= len;
- }
-
- /* Load the audio data ... */
-
- ;;;;;
-
- audio_pos = audio_chunk;
-
- /* Let the callback function play the audio chunk */
- SDL_PauseAudio(0);
-
- /* Do some processing */
-
- ;;;;;
-
- /* Wait for sound to complete */
- while ( audio_len > 0 ) {
- SDL_Delay(100); /* Sleep 1/10 second */
- }
- SDL_CloseAudio();SDL is composed of eight subsystems - Audio, CDROM, Event Handling, File I/O, Joystick Handling, Threading, Timers and Video. Before you can use any of these subsystems they must be initialized by calling SDL_Init (or SDL_InitSubSystem). SDL_Init must be called before any other SDL function. It automatically initializes the Event Handling, File I/O and Threading subsystems and it takes a parameter specifying which other subsystems to initialize. So, to initialize the default subsystems and the Video subsystems you would call: -
SDL_Init ( SDL_INIT_VIDEO );-To initialize the default subsystems, the Video subsystem and the Timers subsystem you would call: -
SDL_Init ( SDL_INIT_VIDEO | SDL_INIT_TIMER );
SDL_Init is complemented by SDL_Quit (and SDL_QuitSubSystem). SDL_Quit shuts down all subsystems, including the default ones. It should always be called before a SDL application exits.
With SDL_Init and SDL_Quit firmly embedded in your programmers toolkit you can write your first and most basic SDL application. However, we must be prepare to handle errors. Many SDL functions return a value and indicates whether the function has succeeded or failed, SDL_Init, for instance, returns -1 if it could not initialize a subsystem. SDL provides a useful facility that allows you to determine exactly what the problem was, every time an error occurs within SDL an error message is stored which can be retrieved using SDL_GetError. Use this often, you can never know too much about an error.
Example 1-1. Initializing SDL
#include "SDL.h" /* All SDL App's need this */
-#include <stdio.h>
-
-int main(int argc, char *argv[]) {
-
- printf("Initializing SDL.\n");
-
- /* Initialize defaults, Video and Audio */
- if((SDL_Init(SDL_INIT_VIDEO|SDL_INIT_AUDIO)==-1)) {
- printf("Could not initialize SDL: %s.\n", SDL_GetError());
- exit(-1);
- }
-
- printf("SDL initialized.\n");
-
- printf("Quiting SDL.\n");
-
- /* Shutdown all subsystems */
- SDL_Quit();
-
- printf("Quiting....\n");
-
- exit(0);
-}
#include "SDL.h"
-
- /* Initialize SDL first */
- if ( SDL_Init(SDL_INIT_CDROM) < 0 ) {
- fprintf(stderr, "Couldn't initialize SDL: %s\n",SDL_GetError());
- exit(1);
- }
- atexit(SDL_Quit);
-
- /* Find out how many CD-ROM drives are connected to the system */
- printf("Drives available: %d\n", SDL_CDNumDrives());
- for ( i=0; i<SDL_CDNumDrives(); ++i ) {
- printf("Drive %d: \"%s\"\n", i, SDL_CDName(i));
- } SDL_CD *cdrom;
- CDstatus status;
- char *status_str;
-
- cdrom = SDL_CDOpen(0);
- if ( cdrom == NULL ) {
- fprintf(stderr, "Couldn't open default CD-ROM drive: %s\n",
- SDL_GetError());
- exit(2);
- }
-
- status = SDL_CDStatus(cdrom);
- switch (status) {
- case CD_TRAYEMPTY:
- status_str = "tray empty";
- break;
- case CD_STOPPED:
- status_str = "stopped";
- break;
- case CD_PLAYING:
- status_str = "playing";
- break;
- case CD_PAUSED:
- status_str = "paused";
- break;
- case CD_ERROR:
- status_str = "error state";
- break;
- }
- printf("Drive status: %s\n", status_str);
- if ( status >= CD_PLAYING ) {
- int m, s, f;
- FRAMES_TO_MSF(cdrom->cur_frame, &m, &s, &f);
- printf("Currently playing track %d, %d:%2.2d\n",
- cdrom->track[cdrom->cur_track].id, m, s);
- } SDL_CD *cdrom; /* Assuming this has already been set.. */
- int i;
- int m, s, f;
-
- SDL_CDStatus(cdrom);
- printf("Drive tracks: %d\n", cdrom->numtracks);
- for ( i=0; i<cdrom->numtracks; ++i ) {
- FRAMES_TO_MSF(cdrom->track[i].length, &m, &s, &f);
- if ( f > 0 )
- ++s;
- printf("\tTrack (index %d) %d: %d:%2.2d\n", i,
- cdrom->track[i].id, m, s);
- } SDL_CD *cdrom; /* Assuming this has already been set.. */
-
- // Play entire CD:
- if ( CD_INDRIVE(SDL_CDStatus(cdrom)) )
- SDL_CDPlayTracks(cdrom, 0, 0, 0, 0);
-
- // Play last track:
- if ( CD_INDRIVE(SDL_CDStatus(cdrom)) ) {
- SDL_CDPlayTracks(cdrom, cdrom->numtracks-1, 0, 0, 0);
- }
-
- // Play first and second track and 10 seconds of third track:
- if ( CD_INDRIVE(SDL_CDStatus(cdrom)) )
- SDL_CDPlayTracks(cdrom, 0, 0, 2, CD_FPS * 10);| Sam Lantinga, slouken@libsdl.org |
| Martin Donlon, akawaka@skynet.ie |
| Mattias Engdegård |
| Julian Peterson |
| Ken Jordan |
| Maxim Sobolev |
| Wesley Poole |
| Michael Vance |
| Andreas Umbach |
| Andreas Hofmeister |
#include <stdio.h>
-#include <stdlib.h>
-
-#include "SDL.h"
-
-/* This function may run in a separate event thread */
-int FilterEvents(const SDL_Event *event) {
- static int boycott = 1;
-
- /* This quit event signals the closing of the window */
- if ( (event->type == SDL_QUIT) && boycott ) {
- printf("Quit event filtered out -- try again.\n");
- boycott = 0;
- return(0);
- }
- if ( event->type == SDL_MOUSEMOTION ) {
- printf("Mouse moved to (%d,%d)\n",
- event->motion.x, event->motion.y);
- return(0); /* Drop it, we've handled it */
- }
- return(1);
-}
-
-int main(int argc, char *argv[])
-{
- SDL_Event event;
-
- /* Initialize the SDL library (starts the event loop) */
- if ( SDL_Init(SDL_INIT_VIDEO) < 0 ) {
- fprintf(stderr,
- "Couldn't initialize SDL: %s\n", SDL_GetError());
- exit(1);
- }
-
- /* Clean up on exit, exit on window close and interrupt */
- atexit(SDL_Quit);
-
- /* Ignore key events */
- SDL_EventState(SDL_KEYDOWN, SDL_IGNORE);
- SDL_EventState(SDL_KEYUP, SDL_IGNORE);
-
- /* Filter quit and mouse motion events */
- SDL_SetEventFilter(FilterEvents);
-
- /* The mouse isn't much use unless we have a display for reference */
- if ( SDL_SetVideoMode(640, 480, 8, 0) == NULL ) {
- fprintf(stderr, "Couldn't set 640x480x8 video mode: %s\n",
- SDL_GetError());
- exit(1);
- }
-
- /* Loop waiting for ESC+Mouse_Button */
- while ( SDL_WaitEvent(&event) >= 0 ) {
- switch (event.type) {
- case SDL_ACTIVEEVENT: {
- if ( event.active.state & SDL_APPACTIVE ) {
- if ( event.active.gain ) {
- printf("App activated\n");
- } else {
- printf("App iconified\n");
- }
- }
- }
- break;
-
- case SDL_MOUSEBUTTONDOWN: {
- Uint8 *keys;
-
- keys = SDL_GetKeyState(NULL);
- if ( keys[SDLK_ESCAPE] == SDL_PRESSED ) {
- printf("Bye bye...\n");
- exit(0);
- }
- printf("Mouse button pressed\n");
- }
- break;
-
- case SDL_QUIT: {
- printf("Quit requested, quitting.\n");
- exit(0);
- }
- break;
- }
- }
- /* This should never happen */
- printf("SDL_WaitEvent error: %s\n", SDL_GetError());
- exit(1);
-}The first step in using a joystick in a SDL program is to initialize the Joystick subsystems of SDL. This done by passing the SDL_INIT_JOYSTICK flag to SDL_Init. The joystick flag will usually be used in conjunction with other flags (like the video flag) because the joystick is usually used to control something.
Example 3-1. Initializing SDL with Joystick Support
if (SDL_Init( SDL_INIT_VIDEO | SDL_INIT_JOYSTICK ) < 0)
- {
- fprintf(stderr, "Couldn't initialize SDL: %s\n", SDL_GetError());
- exit(1);
- }This will attempt to start SDL with both the video and the joystick subsystems activated.
If we have reached this point then we can safely assume that the SDL library has been initialized and that the Joystick subsystem is active. We can now call some video and/or sound functions to get things going before we need the joystick. Eventually we have to make sure that there is actually a joystick to work with. It's wise to always check even if you know a joystick will be present on the system because it can also help detect when the joystick is unplugged. The function used to check for joysticks is SDL_NumJoysticks.
This function simply returns the number of joysticks available on the system. If it is at least one then we are in good shape. The next step is to determine which joystick the user wants to use. If the number of joysticks available is only one then it is safe to assume that one joystick is the one the user wants to use. SDL has a function to get the name of the joysticks as assigned by the operations system and that function is SDL_JoystickName. The joystick is specified by an index where 0 is the first joystick and the last joystick is the number returned by SDL_NumJoysticks - 1. In the demonstration a list of all available joysticks is printed to stdout.
SDL's event driven architecture makes working with joysticks a snap. Joysticks can trigger 4 different types of events: -
| SDL_JoyAxisEvent | Occurs when an axis changes |
| SDL_JoyBallEvent | Occurs when a joystick trackball's position changes |
| SDL_JoyHatEvent | Occurs when a hat's position changes |
| SDL_JoyButtonEvent | Occurs when a button is pressed or released |
Events are received from all joysticks opened. The first thing that needs to be done in order to receive joystick events is to call SDL_JoystickEventState with the SDL_ENABLE flag. Next you must open the joysticks that you want to receive envents from. This is done with the SDL_JoystickOpen function. For the example we are only interested in events from the first joystick on the system, regardless of what it may be. To receive events from it we would do this:
Example 3-3. Opening a Joystick
SDL_Joystick *joystick; - - SDL_JoystickEventState(SDL_ENABLE); - joystick = SDL_JoystickOpen(0);
If we wanted to receive events for other joysticks we would open them with calls to SDL_JoystickOpen just like we opened joystick 0, except we would store the SDL_Joystick structure they return in a different pointer. We only need the joystick pointer when we are querying the joysticks or when we are closing the joystick.
Up to this point all the code we have is used just to initialize the joysticks in order to read values at run time. All we need now is an event loop, which is something that all SDL programs should have anyway to receive the systems quit events. We must now add code to check the event loop for at least some of the above mentioned events. Let's assume our event loop looks like this: -
SDL_Event event;
- /* Other initializtion code goes here */
-
- /* Start main game loop here */
-
- while(SDL_PollEvent(&event))
- {
- switch(event.type)
- {
- case SDL_KEYDOWN:
- /* handle keyboard stuff here */
- break;
-
- case SDL_QUIT:
- /* Set whatever flags are necessary to */
- /* end the main game loop here */
- break;
- }
- }
-
- /* End loop here */
-To handle Joystick events we merely add cases for them, first we'll add axis handling code. Axis checks can get kinda of tricky because alot of the joystick events received are junk. Joystick axis have a tendency to vary just a little between polling due to the way they are designed. To compensate for this you have to set a threshold for changes and ignore the events that have'nt exceeded the threshold. 10% is usually a good threshold value. This sounds a lot more complicated than it is. Here is the Axis event handler:Example 3-4. Joystick Axis Events
case SDL_JOYAXISMOTION: /* Handle Joystick Motion */
- if ( ( event.jaxis.value < -3200 ) || (event.jaxis.value > 3200 ) )
- {
- /* code goes here */
- }
- break;Another trick with axis events is that up-down and left-right movement are two different sets of axes. The most important axis is axis 0 (left-right) and axis 1 (up-down). To handle them seperatly in the code we do the following:
Example 3-5. More Joystick Axis Events
case SDL_JOYAXISMOTION: /* Handle Joystick Motion */
- if ( ( event.jaxis.value < -3200 ) || (event.jaxis.value > 3200 ) )
- {
- if( event.jaxis.axis == 0)
- {
- /* Left-right movement code goes here */
- }
-
- if( event.jaxis.axis == 1)
- {
- /* Up-Down movement code goes here */
- }
- }
- break;Ideally the code here should use event.jaxis.value to scale something. For example lets assume you are using the joystick to control the movement of a spaceship. If the user is using an analog joystick and they push the stick a little bit they expect to move less than if they pushed it a lot. Designing your code for this situation is preferred because it makes the experience for users of analog controls better and remains the same for users of digital controls.
If your joystick has any additional axis then they may be used for other sticks or throttle controls and those axis return values too just with different event.jaxis.axis values.
Button handling is simple compared to the axis checking.
Example 3-6. Joystick Button Events
case SDL_JOYBUTTONDOWN: /* Handle Joystick Button Presses */
- if ( event.jbutton.button == 0 )
- {
- /* code goes here */
- }
- break;Button checks are simpler than axis checks because a button can only be pressed or not pressed. The SDL_JOYBUTTONDOWN event is triggered when a button is pressed and the SDL_JOYBUTTONUP event is fired when a button is released. We do have to know what button was pressed though, that is done by reading the event.jbutton.button field.
Lastly when we are through using our joysticks we should close them with a call to SDL_JoystickClose. To close our opened joystick 0 we would do this at the end of our program: -
SDL_JoystickClose(joystick);
That takes care of the controls that you can count on being on every joystick under the sun, but there are a few extra things that SDL can support. Joyballs are next on our list, they are alot like axis with a few minor differences. Joyballs store relative changes unlike the the absolute postion stored in a axis event. Also one trackball event contains both the change in x and they change in y. Our case for it is as follows:
Example 3-7. Joystick Ball Events
case SDL_JOYBALLMOTION: /* Handle Joyball Motion */
- if( event.jball.ball == 0 )
- {
- /* ball handling */
- }
- break;The above checks the first joyball on the joystick. The change in position will be stored in event.jball.xrel and event.jball.yrel.
Finally we have the hat event. Hats report only the direction they are pushed in. We check hat's position with the bitmasks: - -
| SDL_HAT_CENTERED |
| SDL_HAT_UP |
| SDL_HAT_RIGHT |
| SDL_HAT_DOWN |
| SDL_HAT_LEFT |
| SDL_HAT_RIGHTUP |
| SDL_HAT_RIGHTDOWN |
| SDL_HAT_LEFTUP |
| SDL_HAT_LEFTDOWN |
Example 3-8. Joystick Hat Events
case SDL_JOYHATMOTION: /* Handle Hat Motion */
- if ( event.jhat.value & SDL_HAT_UP )
- {
- /* Do up stuff here */
- }
-
- if ( event.jhat.value & SDL_HAT_LEFT )
- {
- /* Do left stuff here */
- }
-
- if ( event.jhat.value & SDL_HAT_RIGHTDOWN )
- {
- /* Do right and down together stuff here */
- }
- break;In addition to the queries for number of joysticks on the system and their names there are additional functions to query the capabilities of attached joysticks: -
| SDL_JoystickNumAxes | Returns the number of joysitck axes |
| SDL_JoystickNumButtons | Returns the number of joysitck buttons |
| SDL_JoystickNumBalls | Returns the number of joysitck balls |
| SDL_JoystickNumHats | Returns the number of joysitck hats |
Example 3-9. Querying Joystick Characteristics
int number_of_buttons; - SDL_Joystick *joystick; - - joystick = SDL_JoystickOpen(0); - number_of_buttons = SDL_JoystickNumButtons(joystick);
This block of code would get the number of buttons on the first joystick in the system.
It should make it a lot easier to understand this tutorial is you are familiar with the data types involved in keyboard access, so I'll explain them first.
SDLKey is an enumerated type defined in SDL/include/SDL_keysym.h and detailed here. Each SDLKey symbol represents a key, SDLK_a corresponds to the 'a' key on a keyboard, SDLK_SPACE corresponds to the space bar, and so on.
SDLMod is an enumerated type, similar to SDLKey, however it enumerates keyboard modifiers (Control, Alt, Shift). The full list of modifier symbols is here. SDLMod values can be AND'd together to represent several modifiers.
typedef struct{
- Uint8 scancode;
- SDLKey sym;
- SDLMod mod;
- Uint16 unicode;
-} SDL_keysym;The SDL_keysym structure describes a key press or a key release. The scancode field is hardware specific and should be ignored unless you know what your doing. The sym field is the SDLKey value of the key being pressed or released. The mod field describes the state of the keyboard modifiers at the time the key press or release occurred. So a value of KMOD_NUM | KMOD_CAPS | KMOD_LSHIFT would mean that Numlock, Capslock and the left shift key were all press (or enabled in the case of the lock keys). Finally, the unicode field stores the 16-bit unicode value of the key.
Note: It should be noted and understood that this field is only valid when the SDL_keysym is describing a key press, not a key release. Unicode values only make sense on a key press because the unicode value describes an international character and only key presses produce characters. More information on Unicode can be found at www.unicode.org
Note: Unicode translation must be enabled using the SDL_EnableUNICODE function.
typedef struct{
- Uint8 type;
- Uint8 state;
- SDL_keysym keysym;
-} SDL_KeyboardEvent;The SDL_KeyboardEvent describes a keyboard event (obviously). The key member of the SDL_Event union is a SDL_KeyboardEvent structure. The type field specifies whether the event is a key release (SDL_KEYUP) or a key press (SDL_KEYDOWN) event. The state is largely redundant, it reports the same information as the type field but uses different values (SDL_RELEASED and SDL_PRESSED). The keysym contains information of the key press or release that this event represents (see above).
Reading keybaord events from the event queue is quite simple (the event queue and using it is described here). We read events using SDL_PollEvent in a while() loop and check for SDL_KEYUP and SDL_KEYDOWN events using a switch statement, like so:
Example 3-10. Reading Keyboard Events
SDL_Event event;
- .
- .
- /* Poll for events. SDL_PollEvent() returns 0 when there are no */
- /* more events on the event queue, our while loop will exit when */
- /* that occurs. */
- while( SDL_PollEvent( &event ) ){
- /* We are only worried about SDL_KEYDOWN and SDL_KEYUP events */
- switch( event.type ){
- case SDL_KEYDOWN:
- printf( "Key press detected\n" );
- break;
-
- case SDL_KEYUP:
- printf( "Key release detected\n" );
- break;
-
- default:
- break;
- }
- }
- .
- .This is a very basic example. No information about the key press or release is interpreted. We will explore the other extreme out our first full example below - reporting all available information about a keyboard event.
Before we can read events SDL must be initialised with SDL_Init and a video mode must be set using SDL_SetVideoMode. There are, however, two other functions we must use to obtain all the information required. We must enable unicode translation by calling SDL_EnableUNICODE(1) and we must convert SDLKey values into something printable, using SDL_GetKeyName
Note: It is useful to note that unicode values < 0x80 translate directly a characters ASCII value. THis is used in the example below
Example 3-11. Interpreting Key Event Information
#include "SDL.h"
-
- /* Function Prototypes */
- void PrintKeyInfo( SDL_KeyboardEvent *key );
- void PrintModifiers( SDLMod mod );
-
- /* main */
- int main( int argc, char *argv[] ){
-
- SDL_Event event;
- int quit = 0;
-
- /* Initialise SDL */
- if( SDL_Init( SDL_INIT_VIDEO ) < 0){
- fprintf( stderr, "Could not initialise SDL: %s\n", SDL_GetError() );
- exit( -1 );
- }
-
- /* Set a video mode */
- if( !SDL_SetVideoMode( 320, 200, 0, 0 ) ){
- fprintf( stderr, "Could not set video mode: %s\n", SDL_GetError() );
- SDL_Quit();
- exit( -1 );
- }
-
- /* Enable Unicode translation */
- SDL_EnableUNICODE( 1 );
-
- /* Loop until an SDL_QUIT event is found */
- while( !quit ){
-
- /* Poll for events */
- while( SDL_PollEvent( &event ) ){
-
- switch( event.type ){
- /* Keyboard event */
- /* Pass the event data onto PrintKeyInfo() */
- case SDL_KEYDOWN:
- case SDL_KEYUP:
- PrintKeyInfo( &event.key );
- break;
-
- /* SDL_QUIT event (window close) */
- case SDL_QUIT:
- quit = 1;
- break;
-
- default:
- break;
- }
-
- }
-
- }
-
- /* Clean up */
- SDL_Quit();
- exit( 0 );
- }
-
- /* Print all information about a key event */
- void PrintKeyInfo( SDL_KeyboardEvent *key ){
- /* Is it a release or a press? */
- if( key->type == SDL_KEYUP )
- printf( "Release:- " );
- else
- printf( "Press:- " );
-
- /* Print the hardware scancode first */
- printf( "Scancode: 0x%02X", key->keysym.scancode );
- /* Print the name of the key */
- printf( ", Name: %s", SDL_GetKeyName( key->keysym.sym ) );
- /* We want to print the unicode info, but we need to make */
- /* sure its a press event first (remember, release events */
- /* don't have unicode info */
- if( key->type == SDL_KEYDOWN ){
- /* If the Unicode value is less than 0x80 then the */
- /* unicode value can be used to get a printable */
- /* representation of the key, using (char)unicode. */
- printf(", Unicode: " );
- if( key->keysym.unicode < 0x80 && key->keysym.unicode > 0 ){
- printf( "%c (0x%04X)", (char)key->keysym.unicode,
- key->keysym.unicode );
- }
- else{
- printf( "? (0x%04X)", key->keysym.unicode );
- }
- }
- printf( "\n" );
- /* Print modifier info */
- PrintModifiers( key->keysym.mod );
- }
-
- /* Print modifier info */
- void PrintModifiers( SDLMod mod ){
- printf( "Modifers: " );
-
- /* If there are none then say so and return */
- if( mod == KMOD_NONE ){
- printf( "None\n" );
- return;
- }
-
- /* Check for the presence of each SDLMod value */
- /* This looks messy, but there really isn't */
- /* a clearer way. */
- if( mod & KMOD_NUM ) printf( "NUMLOCK " );
- if( mod & KMOD_CAPS ) printf( "CAPSLOCK " );
- if( mod & KMOD_LCTRL ) printf( "LCTRL " );
- if( mod & KMOD_RCTRL ) printf( "RCTRL " );
- if( mod & KMOD_RSHIFT ) printf( "RSHIFT " );
- if( mod & KMOD_LSHIFT ) printf( "LSHIFT " );
- if( mod & KMOD_RALT ) printf( "RALT " );
- if( mod & KMOD_LALT ) printf( "LALT " );
- if( mod & KMOD_CTRL ) printf( "CTRL " );
- if( mod & KMOD_SHIFT ) printf( "SHIFT " );
- if( mod & KMOD_ALT ) printf( "ALT " );
- printf( "\n" );
- }I have found that people using keyboard events for games and other interactive applications don't always understand one fundemental point.
Keyboard events only take place when a keys state changes from being unpressed to pressed, and vice versa.
Imagine you have an image of an alien that you wish to move around using the cursor keys: when you pressed the left arrow key you want him to slide over to the left, and when you press the down key you want him to slide down the screen. Examine the following code; it highlights an error that many people have made. -
/* Alien screen coordinates */
- int alien_x=0, alien_y=0;
- .
- .
- /* Initialise SDL and video modes and all that */
- .
- /* Main game loop */
- /* Check for events */
- while( SDL_PollEvent( &event ) ){
- switch( event.type ){
- /* Look for a keypress */
- case SDL_KEYDOWN:
- /* Check the SDLKey values and move change the coords */
- switch( event.key.keysym.sym ){
- case SDLK_LEFT:
- alien_x -= 1;
- break;
- case SDLK_RIGHT:
- alien_x += 1;
- break;
- case SDLK_UP:
- alien_y -= 1;
- break;
- case SDLK_DOWN:
- alien_y += 1;
- break;
- default:
- break;
- }
- }
- }
- }
- .
- .
-At first glance you may think this is a perfectly reasonable piece of code for the task, but it isn't. Like I said keyboard events only occur when a key changes state, so the user would have to press and release the left cursor key 100 times to move the alien 100 pixels to the left.To get around this problem we must not use the events to change the position of the alien, we use the events to set flags which are then used in a seperate section of code to move the alien. Something like this:
Example 3-12. Proper Game Movement
/* Alien screen coordinates */
- int alien_x=0, alien_y=0;
- int alien_xvel=0, alien_yvel=0;
- .
- .
- /* Initialise SDL and video modes and all that */
- .
- /* Main game loop */
- /* Check for events */
- while( SDL_PollEvent( &event ) ){
- switch( event.type ){
- /* Look for a keypress */
- case SDL_KEYDOWN:
- /* Check the SDLKey values and move change the coords */
- switch( event.key.keysym.sym ){
- case SDLK_LEFT:
- alien_xvel = -1;
- break;
- case SDLK_RIGHT:
- alien_xvel = 1;
- break;
- case SDLK_UP:
- alien_yvel = -1;
- break;
- case SDLK_DOWN:
- alien_yvel = 1;
- break;
- default:
- break;
- }
- break;
- /* We must also use the SDL_KEYUP events to zero the x */
- /* and y velocity variables. But we must also be */
- /* careful not to zero the velocities when we shouldn't*/
- case SDL_KEYUP:
- switch( event.key.keysym.sym ){
- case SDLK_LEFT:
- /* We check to make sure the alien is moving */
- /* to the left. If it is then we zero the */
- /* velocity. If the alien is moving to the */
- /* right then the right key is still press */
- /* so we don't tocuh the velocity */
- if( alien_xvel < 0 )
- alien_xvel = 0;
- break;
- case SDLK_RIGHT:
- if( alien_xvel > 0 )
- alien_xvel = 0;
- break;
- case SDLK_UP:
- if( alien_yvel < 0 )
- alien_yvel = 0;
- break;
- case SDLK_DOWN:
- if( alien_yvel > 0 )
- alien_yvel = 0;
- break;
- default:
- break;
- }
- break;
-
- default:
- break;
- }
- }
- .
- .
- /* Update the alien position */
- alien_x += alien_xvel;
- alien_y += alien_yvel;As can be seen, we use two extra variables, alien_xvel and alien_yvel, which represent the motion of the ship, it is these variables that we update when we detect keypresses and releases.
The SDL library is designed to make it easy to write games that run on Linux, *BSD, MacOS, Win32 and BeOS using the various native high-performance media interfaces, (for video, audio, etc) and presenting a single source-code level API to your application. SDL is a fairly low level API, but using it, completely portable applications can be written with a great deal of flexibility.
#define TICK_INTERVAL 30
-
-static Uint32 next_time;
-
-Uint32 time_left(void)
-{
- Uint32 now;
-
- now = SDL_GetTicks();
- if(next_time <= now)
- return 0;
- else
- return next_time - now;
-}
-
-
-/* main game loop */
-
- next_time = SDL_GetTicks() + TICK_INTERVAL;
- while ( game_running ) {
- update_game_state();
- SDL_Delay(time_left());
- next_time += TICK_INTERVAL;
- }
Video is probably the most common thing that SDL is used for, and -so it has the most complete subsystem. Here are a few -examples to demonstrate the basics.
This is what almost all SDL programs have to do in one way or -another.
Example 2-1. Initializing the Video Display
SDL_Surface *screen;
-
- /* Initialize the SDL library */
- if( SDL_Init(SDL_INIT_VIDEO) < 0 ) {
- fprintf(stderr,
- "Couldn't initialize SDL: %s\n", SDL_GetError());
- exit(1);
- }
-
- /* Clean up on exit */
- atexit(SDL_Quit);
-
- /*
- * Initialize the display in a 640x480 8-bit palettized mode,
- * requesting a software surface
- */
- screen = SDL_SetVideoMode(640, 480, 8, SDL_SWSURFACE);
- if ( screen == NULL ) {
- fprintf(stderr, "Couldn't set 640x480x8 video mode: %s\n",
- SDL_GetError());
- exit(1);
- }If you have a preference for a certain pixel depth but will accept any -other, use SDL_SetVideoMode with SDL_ANYFORMAT as below. You can also -use SDL_VideoModeOK() to find the native video mode that is closest to -the mode you request.
Example 2-2. Initializing the Best Video Mode
/* Have a preference for 8-bit, but accept any depth */
- screen = SDL_SetVideoMode(640, 480, 8, SDL_SWSURFACE|SDL_ANYFORMAT);
- if ( screen == NULL ) {
- fprintf(stderr, "Couldn't set 640x480x8 video mode: %s\n",
- SDL_GetError());
- exit(1);
- }
- printf("Set 640x480 at %d bits-per-pixel mode\n",
- screen->format->BitsPerPixel);The following function loads and displays a BMP file given as -argument, once SDL is initialised and a video mode has been set.
Example 2-3. Loading and Displaying a BMP File
void display_bmp(char *file_name)
-{
- SDL_Surface *image;
-
- /* Load the BMP file into a surface */
- image = SDL_LoadBMP(file_name);
- if (image == NULL) {
- fprintf(stderr, "Couldn't load %s: %s\n", file_name, SDL_GetError());
- return;
- }
-
- /*
- * Palettized screen modes will have a default palette (a standard
- * 8*8*4 colour cube), but if the image is palettized as well we can
- * use that palette for a nicer colour matching
- */
- if (image->format->palette && screen->format->palette) {
- SDL_SetColors(screen, image->format->palette->colors, 0,
- image->format->palette->ncolors);
- }
-
- /* Blit onto the screen surface */
- if(SDL_BlitSurface(image, NULL, screen, NULL) < 0)
- fprintf(stderr, "BlitSurface error: %s\n", SDL_GetError());
-
- SDL_UpdateRect(screen, 0, 0, image->w, image->h);
-
- /* Free the allocated BMP surface */
- SDL_FreeSurface(image);
-}The following two functions can be used to get and set single -pixels of a surface. They are carefully written to work with any depth -currently supported by SDL. Remember to lock the surface before -calling them, and to unlock it before calling any other SDL -functions.
To convert between pixel values and their red, green, blue -components, use SDL_GetRGB() and SDL_MapRGB().
Example 2-4. getpixel()
/*
- * Return the pixel value at (x, y)
- * NOTE: The surface must be locked before calling this!
- */
-Uint32 getpixel(SDL_Surface *surface, int x, int y)
-{
- int bpp = surface->format->BytesPerPixel;
- /* Here p is the address to the pixel we want to retrieve */
- Uint8 *p = (Uint8 *)surface->pixels + y * surface->pitch + x * bpp;
-
- switch(bpp) {
- case 1:
- return *p;
-
- case 2:
- return *(Uint16 *)p;
-
- case 3:
- if(SDL_BYTEORDER == SDL_BIG_ENDIAN)
- return p[0] << 16 | p[1] << 8 | p[2];
- else
- return p[0] | p[1] << 8 | p[2] << 16;
-
- case 4:
- return *(Uint32 *)p;
-
- default:
- return 0; /* shouldn't happen, but avoids warnings */
- }
-}Example 2-5. putpixel()
/*
- * Set the pixel at (x, y) to the given value
- * NOTE: The surface must be locked before calling this!
- */
-void putpixel(SDL_Surface *surface, int x, int y, Uint32 pixel)
-{
- int bpp = surface->format->BytesPerPixel;
- /* Here p is the address to the pixel we want to set */
- Uint8 *p = (Uint8 *)surface->pixels + y * surface->pitch + x * bpp;
-
- switch(bpp) {
- case 1:
- *p = pixel;
- break;
-
- case 2:
- *(Uint16 *)p = pixel;
- break;
-
- case 3:
- if(SDL_BYTEORDER == SDL_BIG_ENDIAN) {
- p[0] = (pixel >> 16) & 0xff;
- p[1] = (pixel >> 8) & 0xff;
- p[2] = pixel & 0xff;
- } else {
- p[0] = pixel & 0xff;
- p[1] = (pixel >> 8) & 0xff;
- p[2] = (pixel >> 16) & 0xff;
- }
- break;
-
- case 4:
- *(Uint32 *)p = pixel;
- break;
- }
-}The following code uses the putpixel() function above to set a -yellow pixel in the middle of the screen.
Example 2-6. Using putpixel()
/* Code to set a yellow pixel at the center of the screen */
-
- int x, y;
- Uint32 yellow;
-
- /* Map the color yellow to this display (R=0xff, G=0xFF, B=0x00)
- Note: If the display is palettized, you must set the palette first.
- */
- yellow = SDL_MapRGB(screen->format, 0xff, 0xff, 0x00);
-
- x = screen->w / 2;
- y = screen->h / 2;
-
- /* Lock the screen for direct access to the pixels */
- if ( SDL_MUSTLOCK(screen) ) {
- if ( SDL_LockSurface(screen) < 0 ) {
- fprintf(stderr, "Can't lock screen: %s\n", SDL_GetError());
- return;
- }
- }
-
- putpixel(screen, x, y, yellow);
-
- if ( SDL_MUSTLOCK(screen) ) {
- SDL_UnlockSurface(screen);
- }
- /* Update just the part of the display that we've changed */
- SDL_UpdateRect(screen, x, y, 1, 1);
-
- return;
SDL has the ability to create and use OpenGL contexts on several platforms(Linux/X11, Win32, BeOS, MacOS Classic/Toolbox, Mac OS X, FreeBSD/X11 and Solaris/X11). This allows you to use SDL's audio, event handling, threads and times in your OpenGL applications (a function often performed by GLUT).
Initialising SDL to use OpenGL is not very different to initialising SDL normally. There are three differences; you must pass SDL_OPENGL to SDL_SetVideoMode, you must specify several GL attributes (depth buffer size, framebuffer sizes) using SDL_GL_SetAttribute and finally, if you wish to use double buffering you must specify it as a GL attribute, not by passing the SDL_DOUBLEBUF flag to SDL_SetVideoMode.
Example 2-7. Initializing SDL with OpenGL
/* Information about the current video settings. */
- const SDL_VideoInfo* info = NULL;
- /* Dimensions of our window. */
- int width = 0;
- int height = 0;
- /* Color depth in bits of our window. */
- int bpp = 0;
- /* Flags we will pass into SDL_SetVideoMode. */
- int flags = 0;
-
- /* First, initialize SDL's video subsystem. */
- if( SDL_Init( SDL_INIT_VIDEO ) < 0 ) {
- /* Failed, exit. */
- fprintf( stderr, "Video initialization failed: %s\n",
- SDL_GetError( ) );
- quit_tutorial( 1 );
- }
-
- /* Let's get some video information. */
- info = SDL_GetVideoInfo( );
-
- if( !info ) {
- /* This should probably never happen. */
- fprintf( stderr, "Video query failed: %s\n",
- SDL_GetError( ) );
- quit_tutorial( 1 );
- }
-
- /*
- * Set our width/height to 640/480 (you would
- * of course let the user decide this in a normal
- * app). We get the bpp we will request from
- * the display. On X11, VidMode can't change
- * resolution, so this is probably being overly
- * safe. Under Win32, ChangeDisplaySettings
- * can change the bpp.
- */
- width = 640;
- height = 480;
- bpp = info->vfmt->BitsPerPixel;
-
- /*
- * Now, we want to setup our requested
- * window attributes for our OpenGL window.
- * We want *at least* 5 bits of red, green
- * and blue. We also want at least a 16-bit
- * depth buffer.
- *
- * The last thing we do is request a double
- * buffered window. '1' turns on double
- * buffering, '0' turns it off.
- *
- * Note that we do not use SDL_DOUBLEBUF in
- * the flags to SDL_SetVideoMode. That does
- * not affect the GL attribute state, only
- * the standard 2D blitting setup.
- */
- SDL_GL_SetAttribute( SDL_GL_RED_SIZE, 5 );
- SDL_GL_SetAttribute( SDL_GL_GREEN_SIZE, 5 );
- SDL_GL_SetAttribute( SDL_GL_BLUE_SIZE, 5 );
- SDL_GL_SetAttribute( SDL_GL_DEPTH_SIZE, 16 );
- SDL_GL_SetAttribute( SDL_GL_DOUBLEBUFFER, 1 );
-
- /*
- * We want to request that SDL provide us
- * with an OpenGL window, in a fullscreen
- * video mode.
- *
- * EXERCISE:
- * Make starting windowed an option, and
- * handle the resize events properly with
- * glViewport.
- */
- flags = SDL_OPENGL | SDL_FULLSCREEN;
-
- /*
- * Set the video mode
- */
- if( SDL_SetVideoMode( width, height, bpp, flags ) == 0 ) {
- /*
- * This could happen for a variety of reasons,
- * including DISPLAY not being set, the specified
- * resolution not being available, etc.
- */
- fprintf( stderr, "Video mode set failed: %s\n",
- SDL_GetError( ) );
- quit_tutorial( 1 );
- }Apart from initialisation, using OpenGL within SDL is the same as using OpenGL -with any other API, e.g. GLUT. You still use all the same function calls and -data types. However if you are using a double-buffered display, then you must -use -SDL_GL_SwapBuffers() -to swap the buffers and update the display. To request double-buffering -with OpenGL, use -SDL_GL_SetAttribute -with SDL_GL_DOUBLEBUFFER, and use -SDL_GL_GetAttribute -to see if you actually got it.
A full example code listing is now presented below.
Example 2-8. SDL and OpenGL
/*
- * SDL OpenGL Tutorial.
- * (c) Michael Vance, 2000
- * briareos@lokigames.com
- *
- * Distributed under terms of the LGPL.
- */
-
-#include <SDL/SDL.h>
-#include <GL/gl.h>
-#include <GL/glu.h>
-
-#include <stdio.h>
-#include <stdlib.h>
-
-static GLboolean should_rotate = GL_TRUE;
-
-static void quit_tutorial( int code )
-{
- /*
- * Quit SDL so we can release the fullscreen
- * mode and restore the previous video settings,
- * etc.
- */
- SDL_Quit( );
-
- /* Exit program. */
- exit( code );
-}
-
-static void handle_key_down( SDL_keysym* keysym )
-{
-
- /*
- * We're only interested if 'Esc' has
- * been presssed.
- *
- * EXERCISE:
- * Handle the arrow keys and have that change the
- * viewing position/angle.
- */
- switch( keysym->sym ) {
- case SDLK_ESCAPE:
- quit_tutorial( 0 );
- break;
- case SDLK_SPACE:
- should_rotate = !should_rotate;
- break;
- default:
- break;
- }
-
-}
-
-static void process_events( void )
-{
- /* Our SDL event placeholder. */
- SDL_Event event;
-
- /* Grab all the events off the queue. */
- while( SDL_PollEvent( &event ) ) {
-
- switch( event.type ) {
- case SDL_KEYDOWN:
- /* Handle key presses. */
- handle_key_down( &event.key.keysym );
- break;
- case SDL_QUIT:
- /* Handle quit requests (like Ctrl-c). */
- quit_tutorial( 0 );
- break;
- }
-
- }
-
-}
-
-static void draw_screen( void )
-{
- /* Our angle of rotation. */
- static float angle = 0.0f;
-
- /*
- * EXERCISE:
- * Replace this awful mess with vertex
- * arrays and a call to glDrawElements.
- *
- * EXERCISE:
- * After completing the above, change
- * it to use compiled vertex arrays.
- *
- * EXERCISE:
- * Verify my windings are correct here ;).
- */
- static GLfloat v0[] = { -1.0f, -1.0f, 1.0f };
- static GLfloat v1[] = { 1.0f, -1.0f, 1.0f };
- static GLfloat v2[] = { 1.0f, 1.0f, 1.0f };
- static GLfloat v3[] = { -1.0f, 1.0f, 1.0f };
- static GLfloat v4[] = { -1.0f, -1.0f, -1.0f };
- static GLfloat v5[] = { 1.0f, -1.0f, -1.0f };
- static GLfloat v6[] = { 1.0f, 1.0f, -1.0f };
- static GLfloat v7[] = { -1.0f, 1.0f, -1.0f };
- static GLubyte red[] = { 255, 0, 0, 255 };
- static GLubyte green[] = { 0, 255, 0, 255 };
- static GLubyte blue[] = { 0, 0, 255, 255 };
- static GLubyte white[] = { 255, 255, 255, 255 };
- static GLubyte yellow[] = { 0, 255, 255, 255 };
- static GLubyte black[] = { 0, 0, 0, 255 };
- static GLubyte orange[] = { 255, 255, 0, 255 };
- static GLubyte purple[] = { 255, 0, 255, 0 };
-
- /* Clear the color and depth buffers. */
- glClear( GL_COLOR_BUFFER_BIT | GL_DEPTH_BUFFER_BIT );
-
- /* We don't want to modify the projection matrix. */
- glMatrixMode( GL_MODELVIEW );
- glLoadIdentity( );
-
- /* Move down the z-axis. */
- glTranslatef( 0.0, 0.0, -5.0 );
-
- /* Rotate. */
- glRotatef( angle, 0.0, 1.0, 0.0 );
-
- if( should_rotate ) {
-
- if( ++angle > 360.0f ) {
- angle = 0.0f;
- }
-
- }
-
- /* Send our triangle data to the pipeline. */
- glBegin( GL_TRIANGLES );
-
- glColor4ubv( red );
- glVertex3fv( v0 );
- glColor4ubv( green );
- glVertex3fv( v1 );
- glColor4ubv( blue );
- glVertex3fv( v2 );
-
- glColor4ubv( red );
- glVertex3fv( v0 );
- glColor4ubv( blue );
- glVertex3fv( v2 );
- glColor4ubv( white );
- glVertex3fv( v3 );
-
- glColor4ubv( green );
- glVertex3fv( v1 );
- glColor4ubv( black );
- glVertex3fv( v5 );
- glColor4ubv( orange );
- glVertex3fv( v6 );
-
- glColor4ubv( green );
- glVertex3fv( v1 );
- glColor4ubv( orange );
- glVertex3fv( v6 );
- glColor4ubv( blue );
- glVertex3fv( v2 );
-
- glColor4ubv( black );
- glVertex3fv( v5 );
- glColor4ubv( yellow );
- glVertex3fv( v4 );
- glColor4ubv( purple );
- glVertex3fv( v7 );
-
- glColor4ubv( black );
- glVertex3fv( v5 );
- glColor4ubv( purple );
- glVertex3fv( v7 );
- glColor4ubv( orange );
- glVertex3fv( v6 );
-
- glColor4ubv( yellow );
- glVertex3fv( v4 );
- glColor4ubv( red );
- glVertex3fv( v0 );
- glColor4ubv( white );
- glVertex3fv( v3 );
-
- glColor4ubv( yellow );
- glVertex3fv( v4 );
- glColor4ubv( white );
- glVertex3fv( v3 );
- glColor4ubv( purple );
- glVertex3fv( v7 );
-
- glColor4ubv( white );
- glVertex3fv( v3 );
- glColor4ubv( blue );
- glVertex3fv( v2 );
- glColor4ubv( orange );
- glVertex3fv( v6 );
-
- glColor4ubv( white );
- glVertex3fv( v3 );
- glColor4ubv( orange );
- glVertex3fv( v6 );
- glColor4ubv( purple );
- glVertex3fv( v7 );
-
- glColor4ubv( green );
- glVertex3fv( v1 );
- glColor4ubv( red );
- glVertex3fv( v0 );
- glColor4ubv( yellow );
- glVertex3fv( v4 );
-
- glColor4ubv( green );
- glVertex3fv( v1 );
- glColor4ubv( yellow );
- glVertex3fv( v4 );
- glColor4ubv( black );
- glVertex3fv( v5 );
-
- glEnd( );
-
- /*
- * EXERCISE:
- * Draw text telling the user that 'Spc'
- * pauses the rotation and 'Esc' quits.
- * Do it using vetors and textured quads.
- */
-
- /*
- * Swap the buffers. This this tells the driver to
- * render the next frame from the contents of the
- * back-buffer, and to set all rendering operations
- * to occur on what was the front-buffer.
- *
- * Double buffering prevents nasty visual tearing
- * from the application drawing on areas of the
- * screen that are being updated at the same time.
- */
- SDL_GL_SwapBuffers( );
-}
-
-static void setup_opengl( int width, int height )
-{
- float ratio = (float) width / (float) height;
-
- /* Our shading model--Gouraud (smooth). */
- glShadeModel( GL_SMOOTH );
-
- /* Culling. */
- glCullFace( GL_BACK );
- glFrontFace( GL_CCW );
- glEnable( GL_CULL_FACE );
-
- /* Set the clear color. */
- glClearColor( 0, 0, 0, 0 );
-
- /* Setup our viewport. */
- glViewport( 0, 0, width, height );
-
- /*
- * Change to the projection matrix and set
- * our viewing volume.
- */
- glMatrixMode( GL_PROJECTION );
- glLoadIdentity( );
- /*
- * EXERCISE:
- * Replace this with a call to glFrustum.
- */
- gluPerspective( 60.0, ratio, 1.0, 1024.0 );
-}
-
-int main( int argc, char* argv[] )
-{
- /* Information about the current video settings. */
- const SDL_VideoInfo* info = NULL;
- /* Dimensions of our window. */
- int width = 0;
- int height = 0;
- /* Color depth in bits of our window. */
- int bpp = 0;
- /* Flags we will pass into SDL_SetVideoMode. */
- int flags = 0;
-
- /* First, initialize SDL's video subsystem. */
- if( SDL_Init( SDL_INIT_VIDEO ) < 0 ) {
- /* Failed, exit. */
- fprintf( stderr, "Video initialization failed: %s\n",
- SDL_GetError( ) );
- quit_tutorial( 1 );
- }
-
- /* Let's get some video information. */
- info = SDL_GetVideoInfo( );
-
- if( !info ) {
- /* This should probably never happen. */
- fprintf( stderr, "Video query failed: %s\n",
- SDL_GetError( ) );
- quit_tutorial( 1 );
- }
-
- /*
- * Set our width/height to 640/480 (you would
- * of course let the user decide this in a normal
- * app). We get the bpp we will request from
- * the display. On X11, VidMode can't change
- * resolution, so this is probably being overly
- * safe. Under Win32, ChangeDisplaySettings
- * can change the bpp.
- */
- width = 640;
- height = 480;
- bpp = info->vfmt->BitsPerPixel;
-
- /*
- * Now, we want to setup our requested
- * window attributes for our OpenGL window.
- * We want *at least* 5 bits of red, green
- * and blue. We also want at least a 16-bit
- * depth buffer.
- *
- * The last thing we do is request a double
- * buffered window. '1' turns on double
- * buffering, '0' turns it off.
- *
- * Note that we do not use SDL_DOUBLEBUF in
- * the flags to SDL_SetVideoMode. That does
- * not affect the GL attribute state, only
- * the standard 2D blitting setup.
- */
- SDL_GL_SetAttribute( SDL_GL_RED_SIZE, 5 );
- SDL_GL_SetAttribute( SDL_GL_GREEN_SIZE, 5 );
- SDL_GL_SetAttribute( SDL_GL_BLUE_SIZE, 5 );
- SDL_GL_SetAttribute( SDL_GL_DEPTH_SIZE, 16 );
- SDL_GL_SetAttribute( SDL_GL_DOUBLEBUFFER, 1 );
-
- /*
- * We want to request that SDL provide us
- * with an OpenGL window, in a fullscreen
- * video mode.
- *
- * EXERCISE:
- * Make starting windowed an option, and
- * handle the resize events properly with
- * glViewport.
- */
- flags = SDL_OPENGL | SDL_FULLSCREEN;
-
- /*
- * Set the video mode
- */
- if( SDL_SetVideoMode( width, height, bpp, flags ) == 0 ) {
- /*
- * This could happen for a variety of reasons,
- * including DISPLAY not being set, the specified
- * resolution not being available, etc.
- */
- fprintf( stderr, "Video mode set failed: %s\n",
- SDL_GetError( ) );
- quit_tutorial( 1 );
- }
-
- /*
- * At this point, we should have a properly setup
- * double-buffered window for use with OpenGL.
- */
- setup_opengl( width, height );
-
- /*
- * Now we want to begin our normal app process--
- * an event loop with a lot of redrawing.
- */
- while( 1 ) {
- /* Process incoming events. */
- process_events( );
- /* Draw the screen. */
- draw_screen( );
- }
-
- /*
- * EXERCISE:
- * Record timings using SDL_GetTicks() and
- * and print out frames per second at program
- * end.
- */
-
- /* Never reached. */
- return 0;
-}| Next | ||
| SDL Guide |
Joysticks, and other similar input devices, have a very strong role in game playing and SDL provides comprehensive support for them. Axes, Buttons, POV Hats and trackballs are all supported.
Joystick support is initialized by passed the SDL_INIT_JOYSTICK flag to SDL_Init. Once initilized joysticks must be opened using SDL_JoystickOpen.
While using the functions describe in this secton may seem like the best way to access and read from joysticks, in most cases they aren't. Ideally joysticks should be read using the event system. To enable this, you must set the joystick event processing state with SDL_JoystickEventState. Joysticks must be opened before they can be used of course.
Note: If you are not handling the joystick via the event queue then you must explicitly request a joystick update by calling SDL_JoystickUpdate.
Note: Force Feedback is not yet support. Sam (slouken@libsdl.org) is soliciting suggestions from people with force-feedback experience on the best wat to desgin the API.
SDL_ActiveEvent is a member of the SDL_Event union and is used when an event of type SDL_ACTIVEEVENT is reported.
When the mouse leaves or enters the window area a SDL_APPMOUSEFOCUS type activation event occurs, if the mouse entered the window then gain will be 1, otherwise gain will be 0. A SDL_APPINPUTFOCUS type activation event occurs when the application loses or gains keyboard focus. This usually occurs when another application is made active. Finally, a SDL_APPACTIVE type event occurs when the application is either minimised/iconified (gain=0) or restored.
Note: This event does not occur when an application window is first created.
/* type definition for the "new" timer callback function */ -typedef Uint32 (*SDL_NewTimerCallback)(Uint32 interval, void *param);
Adds a callback function to be run after the specified number of -milliseconds has elapsed. The callback function is passed the current -timer interval and the user supplied parameter from the -SDL_AddTimer call and returns the next timer -interval. If the returned value from the callback is the same as the one -passed in, the periodic alarm continues, otherwise a new alarm is -scheduled.
To cancel a currently running timer call -SDL_RemoveTimer with the -timer ID returned from -SDL_AddTimer.
The timer callback function may run in a different thread than your -main program, and so shouldn't call any functions from within itself. -You may always call SDL_PushEvent, however.
The granularity of the timer is platform-dependent, but you should count -on it being at least 10 ms as this is the most common number. -This means that if -you request a 16 ms timer, your callback will run approximately 20 ms -later on an unloaded system. If you wanted to set a flag signaling -a frame update at 30 frames per second (every 33 ms), you might set a -timer for 30 ms (see example below). - -If you use this function, you need to pass SDL_INIT_TIMER -to SDL_Init.
typedef struct{
- int needed;
- Uint16 src_format;
- Uint16 dest_format;
- double rate_incr;
- Uint8 *buf;
- int len;
- int len_cvt;
- int len_mult;
- double len_ratio;
- void (*filters[10])(struct SDL_AudioCVT *cvt, Uint16 format);
- int filter_index;
-} SDL_AudioCVT;| needed | Set to one if the conversion is possible |
| src_format | Audio format of the source |
| dest_format | Audio format of the destination |
| rate_incr | Rate conversion increment |
| buf | Audio buffer |
| len | Length of the original audio buffer in bytes |
| len_cvt | Length of converted audio buffer in bytes (calculated) |
| len_mult | buf must be len*len_mult bytes in size(calculated) |
| len_ratio | Final audio size is len*len_ratio |
| filters[10](..) | Pointers to functions needed for this conversion |
| filter_index | Current conversion function |
The SDL_AudioCVT is used to convert audio data between different formats. A SDL_AudioCVT structure is created with the SDL_BuildAudioCVT function, while the actual conversion is done by the SDL_ConvertAudio function.
Many of the fields in the SDL_AudioCVT structure should be considered private and their function will not be discussed here.
This points to the audio data that will be used in the conversion. It is both the source and the destination, which means the converted audio data overwrites the original data. It also means that the converted data may be larger than the original data (if you were converting from 8-bit to 16-bit, for instance), so you must ensure buf is large enough. See below.
This is the length of the original audio data in bytes.
As explained above, the audio buffer needs to be big enough to store the converted data, which may be bigger than the original audio data. The length of buf should be len*len_mult.
When you have finished converting your audio data, you need to know how much of your audio buffer is valid. len*len_ratio is the size of the converted audio data in bytes. This is very similar to len_mult, however when the convert audio data is shorter than the original len_mult would be 1. len_ratio, on the other hand, would be a fractional number between 0 and 1.
typedef struct{
- int freq;
- Uint16 format;
- Uint8 channels;
- Uint8 silence;
- Uint16 samples;
- Uint32 size;
- void (*callback)(void *userdata, Uint8 *stream, int len);
- void *userdata;
-} SDL_AudioSpec;| freq | Audio frequency in samples per second |
| format | Audio data format |
| channels | Number of channels: 1 mono, 2 stereo |
| silence | Audio buffer silence value (calculated) |
| samples | Audio buffer size in samples |
| size | Audio buffer size in bytes (calculated) |
| callback(..) | Callback function for filling the audio buffer |
| userdata | Pointer the user data which is passed to the callback function |
The SDL_AudioSpec structure is used to describe the format of some audio data. This structure is used by SDL_OpenAudio and SDL_LoadWAV. While all fields are used by SDL_OpenAudio only freq, format, samples and channels are used by SDL_LoadWAV. We will detail these common members here.
| freq | The number of samples sent to the sound device every second. Common values are 11025, 22050 and 44100. The higher the better. |
| format | Specifies the size and type of each sample element -
|
| channels | The number of seperate sound channels. 1 is mono (single channel), 2 is stereo (dual channel). |
| samples | When used with SDL_OpenAudio this refers to the size of the audio buffer in samples. A sample a chunk of audio data of the size specified in format mulitplied by the number of channels. When the SDL_AudioSpec is used with SDL_LoadWAV samples is set to 4096. |
This performs a fast blit from the source surface to the destination surface.
The width and height in srcrect determine the -size of the copied rectangle. Only the position is used in the -dstrect (the width and height are ignored).
If srcrect is NULL, the -entire surface is copied. If dstrect is -NULL, then the destination position (upper left -corner) is (0, 0).
The final blit rectangle is saved in -dstrect after all clipping is performed -(srcrect is not modified).
The blit function should not be called on a locked surface.
The results of blitting operations vary greatly depending on whether SDL_SRCAPLHA is set or not. See SDL_SetAlpha for an explaination of how this affects your results. Colorkeying and alpha attributes also interact with surface blitting, as the following pseudo-code should hopefully explain. -
if (source surface has SDL_SRCALPHA set) {
- if (source surface has alpha channel (that is, format->Amask != 0))
- blit using per-pixel alpha, ignoring any colour key
- else {
- if (source surface has SDL_SRCCOLORKEY set)
- blit using the colour key AND the per-surface alpha value
- else
- blit using the per-surface alpha value
- }
-} else {
- if (source surface has SDL_SRCCOLORKEY set)
- blit using the colour key
- else
- ordinary opaque rectangular blit
-}If the blit is successful, it returns 0, -otherwise it returns -1.
If either of the surfaces were in video memory, and the blit returns --2, the video memory was lost, so it should be -reloaded with artwork and re-blitted: -
while ( SDL_BlitSurface(image, imgrect, screen, dstrect) == -2 ) {
- while ( SDL_LockSurface(image)) < 0 )
- SDL_Delay(10);
- -- Write image pixels to image->pixels --
- SDL_UnlockSurface(image);
- }
-This happens under DirectX 5.0 when the system switches away from your
-fullscreen application. Locking the surface will also fail until you
-have access to the video memory again.Before an SDL_AudioCVT structure can be used to convert audio data it must be initialized with source and destination information.
src_format and dst_format are the source and destination format of the conversion. (For information on audio formats see SDL_AudioSpec). src_channels and dst_channels are the number of channels in the source and destination formats. Finally, src_rate and dst_rate are the frequency or samples-per-second of the source and destination formats. Once again, see SDL_AudioSpec.
typedef struct{
- int id;
- CDstatus status;
- int numtracks;
- int cur_track;
- int cur_frame;
- SDL_CDtrack track[SDL_MAX_TRACKS+1];
-} SDL_CD;| id | Private drive identifier |
| status | Drive status |
| numtracks | Number of tracks on the CD |
| cur_track | Current track |
| cur_frame | Current frame offset within the track |
| track[SDL_MAX_TRACKS+1] | Array of track descriptions. (see SDL_CDtrack) |
An SDL_CD structure is returned by SDL_CDOpen. It represents an opened CDROM device and stores information on the layout of the tracks on the disc.
A frame is the base data unit of a CD. CD_FPS frames is equal to 1 second of music. SDL provides two macros for converting between time and frames: FRAMES_TO_MSF(f, M,S,F) and MSF_TO_FRAMES.
int min, sec, frame;
-int frame_offset;
-
-FRAMES_TO_MSF(cdrom->cur_frame, &min, &sec, &frame);
-printf("Current Position: %d minutes, %d seconds, %d frames\n", min, sec, frame);
-
-frame_offset=MSF_TO_FRAMES(min, sec, frame);Returns a human-readable, system-dependent identifier for the CD-ROM. drive is the index of the drive. Drive indices start to 0 and end at SDL_CDNumDrives()-1.
Opens a CD-ROM drive for access. It returns a SDL_CD structure on success, or NULL if the drive was invalid or busy. This newly opened CD-ROM becomes the default CD used when other CD functions are passed a NULL CD-ROM handle.
Drives are numbered starting with 0. -Drive 0 is the system default CD-ROM.
SDL_CD *cdrom;
-int cur_track;
-int min, sec, frame;
-SDL_Init(SDL_INIT_CDROM);
-atexit(SDL_Quit);
-
-/* Check for CD drives */
-if(!SDL_CDNumDrives()){
- /* None found */
- fprintf(stderr, "No CDROM devices available\n");
- exit(-1);
-}
-
-/* Open the default drive */
-cdrom=SDL_CDOpen(0);
-
-/* Did if open? Check if cdrom is NULL */
-if(!cdrom){
- fprintf(stderr, "Couldn't open drive: %s\n", SDL_GetError());
- exit(-1);
-}
-
-/* Print Volume info */
-printf("Name: %s\n", SDL_CDName(0));
-printf("Tracks: %d\n", cdrom->numtracks);
-for(cur_track=0;cur_track < cdrom->numtracks; cur_track++){
- FRAMES_TO_MSF(cdrom->track[cur_track].length, &min, &sec, &frame);
- printf("\tTrack %d: Length %d:%d\n", cur_track, min, sec);
-}
-
-SDL_CDClose(cdrom);SDL_CDPlayTracks plays the given CD starting at track -start_track, for ntracks tracks.
start_frame is the frame offset, from the beginning of the start_track, at which to start. nframes is the frame offset, from the beginning of the last track (start_track+ntracks), at which to end playing.
SDL_CDPlayTracks should only be called after calling -SDL_CDStatus -to get track information about the CD.
Note: Data tracks are ignored.
/* assuming cdrom is a previously opened device */ -/* Play the entire CD */ -if(CD_INDRIVE(SDL_CDStatus(cdrom))) - SDL_CDPlayTracks(cdrom, 0, 0, 0, 0); - -/* Play the first track */ -if(CD_INDRIVE(SDL_CDStatus(cdrom))) - SDL_CDPlayTracks(cdrom, 0, 0, 1, 0); - -/* Play first 15 seconds of the 2nd track */ -if(CD_INDRIVE(SDL_CDStatus(cdrom))) - SDL_CDPlayTracks(cdrom, 1, 0, 0, CD_FPS*15);-
This function returns the current status of the given drive. Status is described like so: -
typedef enum {
- CD_TRAYEMPTY,
- CD_STOPPED,
- CD_PLAYING,
- CD_PAUSED,
- CD_ERROR = -1
-} CDstatus;If the drive has a CD in it, the table of contents of the CD and current -play position of the CD will be stored in the SDL_CD structure.
The macro CD_INDRIVE is provided for convenience, -and given a status returns true if there's a disk in the drive.
Note: SDL_CDStatus also updates the SDL_CD structure passed to it.
int playTrack(int track)
-{
- int playing = 0;
-
- if ( CD_INDRIVE(SDL_CDStatus(cdrom)) ) {
- /* clamp to the actual number of tracks on the CD */
- if (track >= cdrom->numtracks) {
- track = cdrom->numtracks-1;
- }
-
- if ( SDL_CDPlayTracks(cdrom, track, 0, 1, 0) == 0 ) {
- playing = 1;
- }
- }
- return playing;
-}typedef struct{
- Uint8 id;
- Uint8 type;
- Uint32 length;
- Uint32 offset;
-} SDL_CDtrack;SDL_CDtrack stores data on each track on a CD, its fields should be pretty self explainatory. It is a member a the SDL_CD structure.
Note: Frames can be converted to standard timings. There are CD_FPS frames per second, so SDL_CDtrack.length/CD_FPS=length_in_seconds.
SDL_Color describes a color in a format independent way. You can convert a SDL_Color to a pixel value for a certain pixel format using SDL_MapRGB.
Restarts all threads that are waiting on the condition variable, cond. Returns 0 on success, or -1 on an error.
Restart one of the threads that are waiting on the condition variable, cond. Returns 0 on success of -1 on an error.
Wait on the condition variable cond and unlock the provided mutex. The mutex must the locked before entering this function. Returns 0 when it is signalled, or -1 on an error.
Wait on the condition variable cond for, at most, ms milliseconds. mut is unlocked so it must be locked when the function is called. Returns SDL_MUTEX_TIMEDOUT if the condition is not signalled in the allotted time, 0 if it was signalled or -1 on an error.
SDL_ConvertAudio takes one parameter, cvt, which was previously initilized. Initilizing a SDL_AudioCVT is a two step process. First of all, the structure must be passed to SDL_BuildAudioCVT along with source and destination format parameters. Secondly, the cvt->buf and cvt->len fields must be setup. cvt->buf should point to the audio data and cvt->len should be set to the length of the audio data in bytes. Remember, the length of the buffer pointed to by buf show be len*len_mult bytes in length.
Once the SDL_AudioCVTstructure is initilized then we can pass it to SDL_ConvertAudio, which will convert the audio data pointer to by cvt->buf. If SDL_ConvertAudio returned 0 then the conversion was completed successfully, otherwise -1 is returned.
If the conversion completed successfully then the converted audio data can be read from cvt->buf. The amount of valid, converted, audio data in the buffer is equal to cvt->len*cvt->len_ratio.
/* Converting some WAV data to hardware format */
-void my_audio_callback(void *userdata, Uint8 *stream, int len);
-
-SDL_AudioSpec *desired, *obtained;
-SDL_AudioSpec wav_spec;
-SDL_AudioCVT wav_cvt;
-Uint32 wav_len;
-Uint8 *wav_buf;
-int ret;
-
-/* Allocated audio specs */
-desired = malloc(sizeof(SDL_AudioSpec));
-obtained = malloc(sizeof(SDL_AudioSpec));
-
-/* Set desired format */
-desired->freq=22050;
-desired->format=AUDIO_S16LSB;
-desired->samples=8192;
-desired->callback=my_audio_callback;
-desired->userdata=NULL;
-
-/* Open the audio device */
-if ( SDL_OpenAudio(desired, obtained) < 0 ){
- fprintf(stderr, "Couldn't open audio: %s\n", SDL_GetError());
- exit(-1);
-}
-
-free(desired);
-
-/* Load the test.wav */
-if( SDL_LoadWAV("test.wav", &wav_spec, &wav_buf, &wav_len) == NULL ){
- fprintf(stderr, "Could not open test.wav: %s\n", SDL_GetError());
- SDL_CloseAudio();
- free(obtained);
- exit(-1);
-}
-
-/* Build AudioCVT */
-ret = SDL_BuildAudioCVT(&wav_cvt,
- wav_spec.format, wav_spec.channels, wav_spec.freq,
- obtained->format, obtained->channels, obtained->freq);
-
-/* Check that the convert was built */
-if(ret==-1){
- fprintf(stderr, "Couldn't build converter!\n");
- SDL_CloseAudio();
- free(obtained);
- SDL_FreeWAV(wav_buf);
-}
-
-/* Setup for conversion */
-wav_cvt.buf = malloc(wav_len * wav_cvt.len_mult);
-wav_cvt.len = wav_len;
-memcpy(wav_cvt.buf, wav_buf, wav_len);
-
-/* We can delete to original WAV data now */
-SDL_FreeWAV(wav_buf);
-
-/* And now we're ready to convert */
-SDL_ConvertAudio(&wav_cvt);
-
-/* do whatever */
-.
-.
-.
-.
-
Creates a new surface of the specified format, and then copies and maps -the given surface to it. If this function fails, it returns -NULL.
The flags parameter is passed to -SDL_CreateRGBSurface -and has those semantics.
This function is used internally by -SDL_DisplayFormat.
This function can only be called after SDL_Init.
SDL_cond *cond; - -cond=SDL_CreateCond(); -. -. -/* Do stuff */ - -. -. -SDL_DestroyCond(cond);
Create a cursor using the specified data and mask (in MSB format). -The cursor width must be a multiple of 8 bits.
The cursor is created in black and white according to the following: -
| Data / Mask | Resulting pixel on screen |
|---|---|
| 0 / 1 | White |
| 1 / 1 | Black |
| 0 / 0 | Transparent |
| 1 / 0 | Inverted color if possible, black if not. |
Cursors created with this function must be freed with -SDL_FreeCursor.
/* Stolen from the mailing list */
-/* Creates a new mouse cursor from an XPM */
-
-
-/* XPM */
-static const char *arrow[] = {
- /* width height num_colors chars_per_pixel */
- " 32 32 3 1",
- /* colors */
- "X c #000000",
- ". c #ffffff",
- " c None",
- /* pixels */
- "X ",
- "XX ",
- "X.X ",
- "X..X ",
- "X...X ",
- "X....X ",
- "X.....X ",
- "X......X ",
- "X.......X ",
- "X........X ",
- "X.....XXXXX ",
- "X..X..X ",
- "X.X X..X ",
- "XX X..X ",
- "X X..X ",
- " X..X ",
- " X..X ",
- " X..X ",
- " XX ",
- " ",
- " ",
- " ",
- " ",
- " ",
- " ",
- " ",
- " ",
- " ",
- " ",
- " ",
- " ",
- " ",
- "0,0"
-};
-
-static SDL_Cursor *init_system_cursor(const char *image[])
-{
- int i, row, col;
- Uint8 data[4*32];
- Uint8 mask[4*32];
- int hot_x, hot_y;
-
- i = -1;
- for ( row=0; row<32; ++row ) {
- for ( col=0; col<32; ++col ) {
- if ( col % 8 ) {
- data[i] <<= 1;
- mask[i] <<= 1;
- } else {
- ++i;
- data[i] = mask[i] = 0;
- }
- switch (image[4+row][col]) {
- case 'X':
- data[i] |= 0x01;
- mask[i] |= 0x01;
- break;
- case '.':
- mask[i] |= 0x01;
- break;
- case ' ':
- break;
- }
- }
- }
- sscanf(image[4+row], "%d,%d", &hot_x, &hot_y);
- return SDL_CreateCursor(data, mask, 32, 32, hot_x, hot_y);
-}SDL_mutex *mut;
-
-mut=SDL_CreateMutex();
-.
-.
-if(SDL_mutexP(mut)==-1){
- fprintf(stderr, "Couldn't lock mutex\n");
- exit(-1);
-}
-.
-/* Do stuff while mutex is locked */
-.
-.
-if(SDL_mutexV(mut)==-1){
- fprintf(stderr, "Couldn't unlock mutex\n");
- exit(-1);
-}
-
-SDL_DestroyMutex(mut);
Allocate an empty surface (must be called after SDL_SetVideoMode)
If depth is 8 bits an empty palette is allocated for the surface, otherwise a 'packed-pixel' SDL_PixelFormat is created using the [RGBA]mask's provided (see SDL_PixelFormat). The flags specifies the type of surface that should be created, it is an OR'd combination of the following possible values.
| SDL_SWSURFACE | SDL will create the surface in system memory. This improves the performance of pixel level access, however you may not be able to take advantage of some types of hardware blitting. |
| SDL_HWSURFACE | SDL will attempt to create the surface in video memory. This will allow SDL to take advantage of Video->Video blits (which are often accelerated). |
| SDL_SRCCOLORKEY | This flag turns on colourkeying for blits from this surface. If -SDL_HWSURFACE is also specified and colourkeyed blits -are hardware-accelerated, then SDL will attempt to place the surface in -video memory. -Use SDL_SetColorKey -to set or clear this flag after surface creation. |
| SDL_SRCALPHA | This flag turns on alpha-blending for blits from this surface. If -SDL_HWSURFACE is also specified and alpha-blending blits -are hardware-accelerated, then the surface will be placed in video memory if -possible. -Use SDL_SetAlpha to -set or clear this flag after surface creation. |
Note: If an alpha-channel is specified (that is, if Amask is -nonzero), then the SDL_SRCALPHA flag is automatically -set. You may remove this flag by calling -SDL_SetAlpha -after surface creation.
/* Create a 32-bit surface with the bytes of each pixel in R,G,B,A order,
- as expected by OpenGL for textures */
- SDL_Surface *surface;
- Uint32 rmask, gmask, bmask, amask;
-
- /* SDL interprets each pixel as a 32-bit number, so our masks must depend
- on the endianness (byte order) of the machine */
-#if SDL_BYTEORDER == SDL_BIG_ENDIAN
- rmask = 0xff000000;
- gmask = 0x00ff0000;
- bmask = 0x0000ff00;
- amask = 0x000000ff;
-#else
- rmask = 0x000000ff;
- gmask = 0x0000ff00;
- bmask = 0x00ff0000;
- amask = 0xff000000;
-#endif
-
- surface = SDL_CreateRGBSurface(SDL_SWSURFACE, width, height, 32,
- rmask, gmask, bmask, amask);
- if(surface == NULL) {
- fprintf(stderr, "CreateRGBSurface failed: %s\n", SDL_GetError());
- exit(1);
- }SDL_CreateRGBSurfaceFrom, -SDL_FreeSurface, -SDL_SetVideoMode, -SDL_LockSurface, -SDL_PixelFormat, -SDL_Surface -SDL_SetAlpha -SDL_SetColorKey
Creates an SDL_Surface from the provided pixel data.
The data stored in pixels is assumed to be of the depth specified in the parameter list. The pixel data is not copied into the SDL_Surface structure so it should not be freed until the surface has been freed with a called to SDL_FreeSurface. pitch is the length of each scanline in bytes.
See SDL_CreateRGBSurface for a more detailed description of the other parameters.
SDL_CreateSemaphore() creates a new semaphore and -initializes it with the value initial_value. -Each locking operation on the semaphore by -SDL_SemWait, -SDL_SemTryWait or -SDL_SemWaitTimeout -will atomically decrement the semaphore value. The locking operation will be blocked -if the semaphore value is not positive (greater than zero). Each unlock operation by -SDL_SemPost -will atomically increment the semaphore value.
SDL_sem *my_sem;
-
-my_sem = SDL_CreateSemaphore(INITIAL_SEM_VALUE);
-
-if (my_sem == NULL) {
- return CREATE_SEM_FAILED;
-}SDL_DestroySemaphore, -SDL_SemWait, -SDL_SemTryWait, -SDL_SemWaitTimeout, -SDL_SemPost, -SDL_SemValue
SDL_CreateThread creates a new thread of execution -that shares all of its parent's global memory, signal handlers, -file descriptors, etc, and runs the function fn -passed the void pointer data -The thread quits when this function returns.
SDL_CreateYUVOverlay creates a YUV overlay of the specified width, height and format (see SDL_Overlay for a list of available formats), for the provided display. A SDL_Overlay structure is returned.
The term 'overlay' is a misnomer since, unless the overlay is created in hardware, the contents for the display surface underneath the area where the overlay is shown will be overwritten when the overlay is displayed.
Wait a specified number of milliseconds before returning. SDL_Delay will wait at least the specified time, but possible longer due to OS scheduling.
Note: Count on a delay granularity of at least 10 ms. -Some platforms have shorter clock ticks but this is the most common.
SDL_DestroySemaphore destroys the semaphore pointed to -by sem that was created by -SDL_CreateSemaphore. -It is not safe to destroy a semaphore if there are threads currently blocked -waiting on it.
SDL_CreateSemaphore, -SDL_SemWait, -SDL_SemTryWait, -SDL_SemWaitTimeout, -SDL_SemPost, -SDL_SemValue
This function takes a surface and copies it to a new surface of the -pixel format and colors of the video framebuffer, suitable for fast -blitting onto the display surface. It calls -SDL_ConvertSurface
If you want to take advantage of hardware colorkey or alpha blit -acceleration, you should set the colorkey and alpha value before -calling this function.
If you want an alpha channel, see SDL_DisplayFormatAlpha.
This function takes a surface and copies it to a new surface of the -pixel format and colors of the video framebuffer plus an alpha channel, -suitable for fast blitting onto the display surface. It calls -SDL_ConvertSurface
If you want to take advantage of hardware colorkey or alpha blit -acceleration, you should set the colorkey and alpha value before -calling this function.
This function can be used to convert a colourkey to an alpha channel, -if the SDL_SRCCOLORKEY flag is set on the surface. -The generated surface will then be transparent (alpha=0) where the -pixels match the colourkey, and opaque (alpha=255) elsewhere.
Blit the overlay to the surface specified when it was created. The SDL_Rect structure, dstrect, specifies the position and size of the destination. If the dstrect is a larger or smaller than the overlay then the overlay will be scaled, this is optimized for 2x scaling.
Enables or disables the keyboard repeat rate. delay specifies how long the key must be pressed before it begins repeating, it then repeats at the speed specified by interval. Both delay and interval are expressed in milliseconds.
Setting delay to 0 disables key repeating completely. Good default values are SDL_DEFAULT_REPEAT_DELAY and SDL_DEFAULT_REPEAT_INTERVAL.
Enables/Disables Unicode keyboard translation.
To obtain the character codes corresponding to received keyboard events, -Unicode translation must first be turned on using this function. The -translation incurs a slight overhead for each keyboard event and is therefore -disabled by default. For each subsequently received key down event, the -unicode member of the -SDL_keysym structure -will then contain the corresponding character code, or zero for keysyms that do -not correspond to any character code.
A value of 1 for enable enables Unicode translation; -0 disables it, and -1 leaves it unchanged (useful for querying the current -translation mode).
Note that only key press events will be translated, not release events.
Not a function, set using setenv()
Several environment variables are available to modify the -behaviour of SDL. Using these variables isn't recommened and the names -and presence of these variables aren't guaranteed from one release to -the next. However, they can be very useful for debugging -purposes.
If set to 0, disable hardware acceleration in the linux fbcon driver.
Frame buffer device to use in the linux fbcon driver, instead of /dev/fb0
In the ps2gs driver, sets the SDL_ASYNCBLIT flag on the -display surface.
Selectes the video driver for SDL to use. Possible values, in the -order they are tried if this variable is not set:
If set, tries to center the SDL window when running in X11 windowed -mode, or using the CyberGrafix driver.
The openGL driver (shared library) to use for X11. Default is libGL.so.1
With XFree86, enables use of DGA mouse if set.
For X11, sets the mouse acceleration. The value should be a string -on the form:
"n/d/t"
where n and d are the -acceleration numerator/denumerators (so mouse movement is accelerated by -n/d), and -t is the threshold above which acceleration applies -(counted as number of pixels the mouse moves at once).
If set, don't attempt to use DirectColor visuals even if they are -present. (SDL will use them otherwise for gamma correction). -This is needed with older X servers when using the XVideo extension.
ID of an X11 visual to use, overriding SDL's default visual selection -algorithm. It can be in decimal or in hex (prefixed by 0x).
If set, display YUV overlay directly on the video surface if possible, -instead of on the surface passed to -SDL_CreateYUVOverlay.
If not set or set to a nonzero value, SDL will attempt to use -hardware YUV acceleration for video playback.
For X11 or Win32, contains the ID number of the window to be used by -SDL instead of creating its own window. Either in decimal or -in hex (prefixed by 0x).
If set to 0, do not use mouse relative mode in X11. The default is -to use it if the mouse is hidden and input is grabbed.
The mouse device to use for the linux fbcon driver. If not set, -SDL first tries to use GPM in repeater mode, then various other -devices (/dev/pcaux, /dev/adbmouse, /dev/mouse etc).
If set, SDL will not try to auto-detect the IMPS/2 protocol of -a PS/2 mouse but use it right away. For the fbcon and ps2gs drivers.
For the linux fbcon driver: if set to ELO, use the ELO touchscreen -controller as a pointer device
For the libvga driver: If set, do not attempt to put the keyboard in raw mode.
If set, the linux fbcon driver will not use a mouse at all.
Disable CAPS-LOCK and NUM-LOCK suppression of down+up key events, -suitable for games where the player needs these keys to do more than just toggle. -A value of 1 will effect both CAPS-LOCK and NUM-LOCK. -A value of 2 will effect only CAPS-LOCK. -A value of 3 will effect only NUM-LOCK. -All other values have no effect. -
The audio device to use, if SDL_PATH_DSP isn't set.
Selects the audio driver for SDL to use. Possible values, in the -order they are tried if this variable is not set:
| openbsd | (OpenBSD) |
| dsp | (OSS /dev/dsp: Linux, Solaris, BSD etc) |
| alsa | (Linux) |
| pulse | (PulseAudio daemon) |
| audio | (Unix style /dev/audio: SunOS, Solaris etc) |
| AL | (Irix) |
| artsc | (ARTS audio daemon) |
| esd | (esound audio daemon) |
| nas | (NAS audio daemon) |
| dma | (OSS /dev/dsp, using DMA) |
| dsound | (Win32 DirectX) |
| waveout | (Win32 WaveOut) |
| baudio | (BeOS) |
| sndmgr | (MacOS SoundManager) |
| paud | (AIX) |
| AHI | (Amiga) |
| disk | (all; output to file) |
The name of the output file for the "disk" audio driver. If not -set, the name sdlaudio.raw is used.
For the "disk" audio driver, how long to wait (in ms) before writing -a full sound buffer. The default is 150 ms.
For some audio drivers (alsa, paud, dma and dsp), don't use select() -but a timed method instead. May cure some audio problems, or cause -others.
The audio device to use. If not set, SDL tries AUDIODEV and then -a platform-dependent default value (/dev/audio on Solaris, -/dev/dsp on Linux etc).
A colon-separated list of CD-ROM devices to use, in addition to -the standard devices (typically /dev/cdrom, platform-dependent).
If set, causes every call to SDL_SetError (that -is, every time SDL signals an error) to also print an error message on -stderr.
Joystick device to use in the linux joystick driver, in addition -to the usual: /dev/js*, /dev/input/event*, /dev/input/js*
Special joystick configuration string for linux. The format is
"name numaxes numhats numballs"
where name is the name string of the joystick -(possibly in single quotes), and the rest are the number of axes, hats -and balls respectively.
typedef union{
- Uint8 type;
- SDL_ActiveEvent active;
- SDL_KeyboardEvent key;
- SDL_MouseMotionEvent motion;
- SDL_MouseButtonEvent button;
- SDL_JoyAxisEvent jaxis;
- SDL_JoyBallEvent jball;
- SDL_JoyHatEvent jhat;
- SDL_JoyButtonEvent jbutton;
- SDL_ResizeEvent resize;
- SDL_ExposeEvent expose;
- SDL_QuitEvent quit;
- SDL_UserEvent user;
- SDL_SysWMEvent syswm;
-} SDL_Event;| type | The type of event |
| active | Activation event |
| key | Keyboard event |
| motion | Mouse motion event |
| button | Mouse button event |
| jaxis | Joystick axis motion event |
| jball | Joystick trackball motion event |
| jhat | Joystick hat motion event |
| jbutton | Joystick button event |
| resize | Application window resize event |
| expose | Application window expose event |
| quit | Application quit request event |
| user | User defined event |
| syswm | Undefined window manager event |
The SDL_Event union is the core to all event handling is SDL, its probably the most important structure after SDL_Surface. SDL_Event is a union of all event structures used in SDL, using it is a simple matter of knowing which union member relates to which event type.
| Event type | Event Structure |
|---|---|
| SDL_ACTIVEEVENT | SDL_ActiveEvent |
| SDL_KEYDOWN/UP | SDL_KeyboardEvent |
| SDL_MOUSEMOTION | SDL_MouseMotionEvent |
| SDL_MOUSEBUTTONDOWN/UP | SDL_MouseButtonEvent |
| SDL_JOYAXISMOTION | SDL_JoyAxisEvent |
| SDL_JOYBALLMOTION | SDL_JoyBallEvent |
| SDL_JOYHATMOTION | SDL_JoyHatEvent |
| SDL_JOYBUTTONDOWN/UP | SDL_JoyButtonEvent |
| SDL_QUIT | SDL_QuitEvent |
| SDL_SYSWMEVENT | SDL_SysWMEvent |
| SDL_VIDEORESIZE | SDL_ResizeEvent |
| SDL_VIDEOEXPOSE | SDL_ExposeEvent |
| SDL_USEREVENT | SDL_UserEvent |
The SDL_Event structure has two uses
Reading events on the event queue
Placing events on the event queue
Reading events from the event queue is done with either SDL_PollEvent or SDL_PeepEvents. We'll use SDL_PollEvent and step through an example.
First off, we create an empty SDL_Event structure. -
SDL_Event test_event;-SDL_PollEvent removes the next event from the event queue, if there are no events on the queue it returns 0 otherwise it returns 1. We use a while loop to process each event in turn. -
while(SDL_PollEvent(&test_event)) {
-The SDL_PollEvent function take a pointer to an SDL_Event structure that is to be filled with event information. We know that if SDL_PollEvent removes an event from the queue then the event information will be placed in our test_event structure, but we also know that the type of event will be placed in the type member of test_event. So to handle each event type seperately we use a switch statement.
- switch(test_event.type) {
-We need to know what kind of events we're looking for and the event type's of those events. So lets assume we want to detect where the user is moving the mouse pointer within our application. We look through our event types and notice that SDL_MOUSEMOTION is, more than likely, the event we're looking for. A little more research tells use that SDL_MOUSEMOTION events are handled within the SDL_MouseMotionEvent structure which is the motion member of SDL_Event. We can check for the SDL_MOUSEMOTION event type within our switch statement like so:
-case SDL_MOUSEMOTION:-All we need do now is read the information out of the motion member of test_event. -
printf("We got a motion event.\n");
- printf("Current mouse position is: (%d, %d)\n", test_event.motion.x, test_event.motion.y);
- break;
- default:
- printf("Unhandled Event!\n");
- break;
- }
-}
-printf("Event queue empty.\n");It is also possible to push events onto the event queue and so use it as a two-way communication path. Both SDL_PushEvent and SDL_PeepEvents allow you to place events onto the event queue. This is usually used to place a SDL_USEREVENT on the event queue, however you could use it to post fake input events if you wished. Creating your own events is a simple matter of choosing the event type you want, setting the type member and filling the appropriate member structure with information. -
SDL_Event user_event; - -user_event.type=SDL_USEREVENT; -user_event.user.code=2; -user_event.user.data1=NULL; -user_event.user.data2=NULL; -SDL_PushEvent(&user_event);
This function allows you to set the state of processing certain event type's.
If state is set to SDL_IGNORE, -that event type will be automatically dropped from the event queue and will -not be filtered.
If state is set to SDL_ENABLE, -that event type will be processed normally.
If state is set to SDL_QUERY, -SDL_EventState will return the current processing -state of the specified event type.
A list of event type's can be found in the SDL_Event section.
SDL_ExposeEvent is a member of the SDL_Event union and is used whan an event of type SDL_VIDEOEXPOSE is reported.
A VIDEOEXPOSE event is triggered when the screen has been modified -outside of the application, usually by the window manager and needs to -be redrawn.
This function performs a fast fill of the given rectangle with -color. If dstrect -is NULL, the whole surface will be filled with -color.
The color should be a pixel of the format used by the surface, and -can be generated by the -SDL_MapRGB or SDL_MapRGBA -functions. If the color value contains an alpha value then the -destination is simply "filled" with that alpha information, no blending -takes place.
If there is a clip rectangle set on the destination (set via -SDL_SetClipRect) then this -function will clip based on the intersection of the clip rectangle and -the dstrect rectangle and the dstrect rectangle -will be modified to represent the area actually filled.
On hardware that supports double-buffering, this function sets up a flip -and returns. The hardware will wait for vertical retrace, and then swap -video buffers before the next video surface blit or lock will return. -On hardware that doesn't support double-buffering, this is equivalent -to calling SDL_UpdateRect(screen, 0, 0, 0, 0)
The SDL_DOUBLEBUF flag must have been passed to -SDL_SetVideoMode, - when -setting the video mode for this function to perform hardware flipping.
Frees the resources used by a previously created SDL_Surface. If the surface was created using -SDL_CreateRGBSurfaceFrom then the pixel data is not freed.
After a WAVE file has been opened with SDL_LoadWAV its data can eventually be freed with SDL_FreeWAV. audio_buf is a pointer to the buffer created by SDL_LoadWAV.
This function returns the current state of the application. The value returned is a bitwise combination of:
typedef enum{
- SDL_AUDIO_STOPPED,
- SDL_AUDIO_PAUSED,
- SDL_AUDIO_PLAYING
-} SDL_audiostatus;Returns either SDL_AUDIO_STOPPED, SDL_AUDIO_PAUSED or SDL_AUDIO_PLAYING depending on the current audio state.
Gets the clipping rectangle for a surface. When this surface is the -destination of a blit, only the area within the clip rectangle is -drawn into.
The rectangle pointed to by rect will be -filled with the clipping rectangle of the surface.
SDL_GetError returns a NULL terminated string containing information about the last internal SDL error.
This function retrieces a pointer to the event filter that was previously set using SDL_SetEventFilter. An SDL_EventFilter function is defined as: -
typedef int (*SDL_EventFilter)(const SDL_Event *event);
Gets the gamma translation lookup tables currently used by the display. -Each table is an array of 256 Uint16 values.
Not all display hardware is able to change gamma.
Gets a snapshot of the current keyboard state. The current state is return as a pointer to an array, the size of this array is stored in numkeys. The array is indexed by the SDLK_* symbols. A value of 1 means the key is pressed and a value of 0 means its not. The pointer returned is a pointer to an internal SDL array and should not be freed by the caller.
Note: Use SDL_PumpEvents to update the state array.
Uint8 *keystate = SDL_GetKeyState(NULL);
-if ( keystate[SDLK_RETURN] ) printf("Return Key Pressed.\n");The return value can be an OR'd combination of the SDLMod enum.
-SDL also defines the following symbols for convenience: -SDLMod
typedef enum { - KMOD_NONE = 0x0000, - KMOD_LSHIFT= 0x0001, - KMOD_RSHIFT= 0x0002, - KMOD_LCTRL = 0x0040, - KMOD_RCTRL = 0x0080, - KMOD_LALT = 0x0100, - KMOD_RALT = 0x0200, - KMOD_LMETA = 0x0400, - KMOD_RMETA = 0x0800, - KMOD_NUM = 0x1000, - KMOD_CAPS = 0x2000, - KMOD_MODE = 0x4000, -} SDLMod;
#define KMOD_CTRL (KMOD_LCTRL|KMOD_RCTRL) -#define KMOD_SHIFT (KMOD_LSHIFT|KMOD_RSHIFT) -#define KMOD_ALT (KMOD_LALT|KMOD_RALT) -#define KMOD_META (KMOD_LMETA|KMOD_RMETA)
The current button state is returned as a button bitmask, which can -be tested using the SDL_BUTTON(X) macros, and x and y are set to the -current mouse cursor position. You can pass NULL for either x or y.
SDL_PumpEvents();
-if(SDL_GetMouseState(NULL, NULL)&SDL_BUTTON(1))
- printf("Mouse Button 1(left) is pressed.\n");The current button state is returned as a button bitmask, which can -be tested using the SDL_BUTTON(X) macros, and x and y are set to the change in the mouse position since the last call to SDL_GetRelativeMouseState or since event initialization. You can pass NULL for either x or y.
Get RGB component values from a pixel stored in the specified pixel format.
This function uses the entire 8-bit [0..255] range when converting color -components from pixel formats with less than 8-bits per RGB component -(e.g., a completely white pixel in 16-bit RGB565 format would return -[0xff, 0xff, 0xff] not [0xf8, 0xfc, 0xf8]).
Get RGBA component values from a pixel stored in the specified pixel format.
This function uses the entire 8-bit [0..255] range when converting color -components from pixel formats with less than 8-bits per RGB component -(e.g., a completely white pixel in 16-bit RGB565 format would return -[0xff, 0xff, 0xff] not [0xf8, 0xfc, 0xf8]).
If the surface has no alpha component, the alpha will be returned as 0xff -(100% opaque).
Get the number of milliseconds since the SDL library initialization. -Note that this value wraps if the program runs for more than ~49 days.
This function returns a read-only pointer to information about the video -hardware. If this is called before SDL_SetVideoMode, the -vfmt member of the returned structure will contain the -pixel format of the "best" video mode.
This function returns a pointer to the current display surface. -If SDL is doing format conversion on the display surface, this -function returns the publicly visible surface, not the real video -surface.
| SDL_GL_RED_SIZE | Size of the framebuffer red component, in bits |
| SDL_GL_GREEN_SIZE | Size of the framebuffer green component, in bits |
| SDL_GL_BLUE_SIZE | Size of the framebuffer blue component, in bits |
| SDL_GL_ALPHA_SIZE | Size of the framebuffer alpha component, in bits |
| SDL_GL_DOUBLEBUFFER | 0 or 1, enable or disable double buffering |
| SDL_GL_BUFFER_SIZE | Size of the framebuffer, in bits |
| SDL_GL_DEPTH_SIZE | Size of the depth buffer, in bits |
| SDL_GL_STENCIL_SIZE | Size of the stencil buffer, in bits |
| SDL_GL_ACCUM_RED_SIZE | Size of the accumulation buffer red component, in bits |
| SDL_GL_ACCUM_GREEN_SIZE | Size of the accumulation buffer green component, in bits |
| SDL_GL_ACCUM_BLUE_SIZE | Size of the accumulation buffer blue component, in bits |
| SDL_GL_ACCUM_ALPHA_SIZE | Size of the accumulation buffer alpha component, in bits |
While you can set most OpenGL attributes normally, the attributes list above must be known before SDL sets the video mode. These attributes a set and read with SDL_GL_SetAttribute and SDL_GL_GetAttribute.
Places the value of the SDL/OpenGL attribute attr into value. This is useful after a call to SDL_SetVideoMode to check whether your attributes have been set as you expected.
Returns the address of the GL function proc, or NULL if the function is not found. If the GL library is loaded at runtime, with SDL_GL_LoadLibrary, then all GL functions must be retrieved this way. Usually this is used to retrieve function pointers to OpenGL extensions.
typedef void (*GL_ActiveTextureARB_Func)(unsigned int);
-GL_ActiveTextureARB_Func glActiveTextureARB_ptr = 0;
-int has_multitexture=1;
-.
-.
-.
-/* Get function pointer */
-glActiveTextureARB_ptr=(GL_ActiveTextureARB_Func) SDL_GL_GetProcAddress("glActiveTextureARB");
-
-/* Check for a valid function ptr */
-if(!glActiveTextureARB_ptr){
- fprintf(stderr, "Multitexture Extensions not present.\n");
- has_multitexture=0;
-}
-.
-.
-.
-.
-if(has_multitexture){
- glActiveTextureARB_ptr(GL_TEXTURE0_ARB);
- .
- .
-}
-else{
- .
- .
-}If you wish, you may load the OpenGL library at runtime, this must be done before SDL_SetVideoMode is called. The path of the GL library is passed to SDL_GL_LoadLibrary and it returns 0 on success, or -1 on an error. You must then use SDL_GL_GetProcAddress to retrieve function pointers to GL functions.
Sets the OpenGL attribute attr to value. The attributes you set don't take effect until after a call to SDL_SetVideoMode. You should use SDL_GL_GetAttribute to check the values after a SDL_SetVideoMode call.
SDL_GL_SetAttribute( SDL_GL_RED_SIZE, 5 );
-SDL_GL_SetAttribute( SDL_GL_GREEN_SIZE, 5 );
-SDL_GL_SetAttribute( SDL_GL_BLUE_SIZE, 5 );
-SDL_GL_SetAttribute( SDL_GL_DEPTH_SIZE, 16 );
-SDL_GL_SetAttribute( SDL_GL_DOUBLEBUFFER, 1 );
-if ( (screen=SDL_SetVideoMode( 640, 480, 16, SDL_OPENGL )) == NULL ) {
- fprintf(stderr, "Couldn't set GL mode: %s\n", SDL_GetError());
- SDL_Quit();
- return;
-}Note: The SDL_DOUBLEBUF flag is not required to enable double buffering when setting an OpenGL video mode. Double buffering is enabled or disabled using the SDL_GL_DOUBLEBUFFER attribute.
Initializes SDL. This should be called before all other SDL functions. The flags parameter specifies what part(s) of SDL to initialize.
| SDL_INIT_TIMER | Initializes the timer subsystem. |
| SDL_INIT_AUDIO | Initializes the audio subsystem. |
| SDL_INIT_VIDEO | Initializes the video subsystem. |
| SDL_INIT_CDROM | Initializes the cdrom subsystem. |
| SDL_INIT_JOYSTICK | Initializes the joystick subsystem. |
| SDL_INIT_EVERYTHING | Initialize all of the above. |
| SDL_INIT_NOPARACHUTE | Prevents SDL from catching fatal signals. |
| SDL_INIT_EVENTTHREAD |
After SDL has been initialized with SDL_Init you may initialize uninitialized subsystems with SDL_InitSubSystem. The flags parameter is the same as that used in SDL_Init.
/* Seperating Joystick and Video initialization. */ -SDL_Init(SDL_INIT_VIDEO); -. -. -SDL_SetVideoMode(640, 480, 16, SDL_DOUBLEBUF|SDL_FULLSCREEN); -. -/* Do Some Video stuff */ -. -. -/* Initialize the joystick subsystem */ -SDL_InitSubSystem(SDL_INIT_JOYSTICK); - -/* Do some stuff with video and joystick */ -. -. -. -/* Shut them both down */ -SDL_Quit();
typedef struct{
- Uint8 type;
- Uint8 which;
- Uint8 axis;
- Sint16 value;
-} SDL_JoyAxisEvent;SDL_JoyAxisEvent is a member of the SDL_Event union and is used when an event of type SDL_JOYAXISMOTION is reported.
A SDL_JOYAXISMOTION event occurs when ever a user moves an axis on the joystick. The field which is the index of the joystick that reported the event and axis is the index of the axis (for a more detailed explaination see the Joystick section). value is the current position of the axis.
typedef struct{
- Uint8 type;
- Uint8 which;
- Uint8 ball;
- Sint16 xrel, yrel;
-} SDL_JoyBallEvent;SDL_JoyBallEvent is a member of the SDL_Event union and is used when an event of type SDL_JOYBALLMOTION is reported.
A SDL_JOYBALLMOTION event occurs when a user moves a trackball on the joystick. The field which is the index of the joystick that reported the event and ball is the index of the trackball (for a more detailed explaination see the Joystick section). Trackballs only return relative motion, this is the change in position on the ball since it was last polled (last cycle of the event loop) and it is stored in xrel and yrel.
typedef struct{
- Uint8 type;
- Uint8 which;
- Uint8 button;
- Uint8 state;
-} SDL_JoyButtonEvent;SDL_JoyButtonEvent is a member of the SDL_Event union and is used when an event of type SDL_JOYBUTTONDOWN or SDL_JOYBUTTONUP is reported.
A SDL_JOYBUTTONDOWN or SDL_JOYBUTTONUP event occurs when ever a user presses or releases a button on a joystick. The field which is the index of the joystick that reported the event and button is the index of the button (for a more detailed explaination see the Joystick section). state is the current state or the button which is either SDL_PRESSED or SDL_RELEASED.
typedef struct{
- Uint8 type;
- Uint8 which;
- Uint8 hat;
- Uint8 value;
-} SDL_JoyHatEvent;SDL_JoyHatEvent is a member of the SDL_Event union and is used when an event of type SDL_JOYHATMOTION is reported.
A SDL_JOYHATMOTION event occurs when ever a user moves a hat on the joystick. The field which is the index of the joystick that reported the event and hat is the index of the hat (for a more detailed exlaination see the Joystick section). value is the current position of the hat. It is a logically OR'd combination of the following values (whose meanings should be pretty obvious:) :
| SDL_HAT_CENTERED |
| SDL_HAT_UP |
| SDL_HAT_RIGHT |
| SDL_HAT_DOWN |
| SDL_HAT_LEFT |
The following defines are also provided:
| SDL_HAT_RIGHTUP |
| SDL_HAT_RIGHTDOWN |
| SDL_HAT_LEFTUP |
| SDL_HAT_LEFTDOWN |
This function is used to enable or disable joystick event processing. With joystick event processing disabled you will have to update joystick states with SDL_JoystickUpdate and read the joystick information manually. state is either SDL_QUERY, SDL_ENABLE or SDL_IGNORE.
Note: Joystick event handling is prefered
If state is SDL_QUERY then the current state is returned, otherwise the new processing state is returned.
SDL Joystick Functions, -SDL_JoystickUpdate, -SDL_JoyAxisEvent, -SDL_JoyBallEvent, -SDL_JoyButtonEvent, -SDL_JoyHatEvent
SDL_JoystickGetAxis returns the current state of the given axis on the given joystick.
On most modern joysticks the X axis is usually represented by axis 0 and the Y axis by axis 1. The value returned by SDL_JoystickGetAxis is a signed integer (-32768 to 32768) representing the current position of the axis, it maybe necessary to impose certain tolerances on these values to account for jitter. It is worth noting that some joysticks use axes 2 and 3 for extra buttons.
Sint16 x_move, y_move; -SDL_Joystick *joy1; -. -. -x_move=SDL_JoystickGetAxis(joy1, 0); -y_move=SDL_JoystickGetAxis(joy1, 1);
Get the ball axis change.
Trackballs can only return relative motion since the last call to SDL_JoystickGetBall, these motion deltas a placed into dx and dy.
int delta_x, delta_y;
-SDL_Joystick *joy;
-.
-.
-.
-SDL_JoystickUpdate();
-if(SDL_JoystickGetBall(joy, 0, &delta_x, &delta_y)==-1)
- printf("TrackBall Read Error!\n");
-printf("Trackball Delta- X:%d, Y:%d\n", delta_x, delta_y);SDL_JoystickGetButton returns the current state of the given button on the given joystick.
The current state is returned as a Uint8 which is defined as an OR'd combination of one or more of the following
| SDL_HAT_CENTERED |
| SDL_HAT_UP |
| SDL_HAT_RIGHT |
| SDL_HAT_DOWN |
| SDL_HAT_LEFT |
| SDL_HAT_RIGHTUP |
| SDL_HAT_RIGHTDOWN |
| SDL_HAT_LEFTUP |
| SDL_HAT_LEFTDOWN |
Get the implementation dependent name of joystick. The index parameter refers to the N'th joystick on the system.
/* Print the names of all attached joysticks */
-int num_joy, i;
-num_joy=SDL_NumJoysticks();
-printf("%d joysticks found\n", num_joy);
-for(i=0;i<num_joy;i++)
- printf("%s\n", SDL_JoystickName(i));Opens a joystick for use within SDL. The index refers to the N'th joystick in the system. A joystick must be opened before it game be used.
SDL_Joystick *joy;
-// Check for joystick
-if(SDL_NumJoysticks()>0){
- // Open joystick
- joy=SDL_JoystickOpen(0);
-
- if(joy)
- {
- printf("Opened Joystick 0\n");
- printf("Name: %s\n", SDL_JoystickName(0));
- printf("Number of Axes: %d\n", SDL_JoystickNumAxes(joy));
- printf("Number of Buttons: %d\n", SDL_JoystickNumButtons(joy));
- printf("Number of Balls: %d\n", SDL_JoystickNumBalls(joy));
- }
- else
- printf("Couldn't open Joystick 0\n");
-
- // Close if opened
- if(SDL_JoystickOpened(0))
- SDL_JoystickClose(joy);
-}Determines whether a joystick has already been opened within the application. index refers to the N'th joystick on the system.
Updates the state(position, buttons, etc.) of all open joysticks. If joystick events have been enabled with SDL_JoystickEventState then this is called automatically in the event loop.
Table 8-1. SDL Keysym definitions
| SDLKey | ASCII value | Common name |
|---|---|---|
| SDLK_BACKSPACE | '\b' | backspace |
| SDLK_TAB | '\t' | tab |
| SDLK_CLEAR | clear | |
| SDLK_RETURN | '\r' | return |
| SDLK_PAUSE | pause | |
| SDLK_ESCAPE | '^[' | escape |
| SDLK_SPACE | ' ' | space |
| SDLK_EXCLAIM | '!' | exclaim |
| SDLK_QUOTEDBL | '"' | quotedbl |
| SDLK_HASH | '#' | hash |
| SDLK_DOLLAR | '$' | dollar |
| SDLK_AMPERSAND | '&' | ampersand |
| SDLK_QUOTE | ''' | quote |
| SDLK_LEFTPAREN | '(' | left parenthesis |
| SDLK_RIGHTPAREN | ')' | right parenthesis |
| SDLK_ASTERISK | '*' | asterisk |
| SDLK_PLUS | '+' | plus sign |
| SDLK_COMMA | ',' | comma |
| SDLK_MINUS | '-' | minus sign |
| SDLK_PERIOD | '.' | period |
| SDLK_SLASH | '/' | forward slash |
| SDLK_0 | '0' | 0 |
| SDLK_1 | '1' | 1 |
| SDLK_2 | '2' | 2 |
| SDLK_3 | '3' | 3 |
| SDLK_4 | '4' | 4 |
| SDLK_5 | '5' | 5 |
| SDLK_6 | '6' | 6 |
| SDLK_7 | '7' | 7 |
| SDLK_8 | '8' | 8 |
| SDLK_9 | '9' | 9 |
| SDLK_COLON | ':' | colon |
| SDLK_SEMICOLON | ';' | semicolon |
| SDLK_LESS | '<' | less-than sign |
| SDLK_EQUALS | '=' | equals sign |
| SDLK_GREATER | '>' | greater-than sign |
| SDLK_QUESTION | '?' | question mark |
| SDLK_AT | '@' | at |
| SDLK_LEFTBRACKET | '[' | left bracket |
| SDLK_BACKSLASH | '\' | backslash |
| SDLK_RIGHTBRACKET | ']' | right bracket |
| SDLK_CARET | '^' | caret |
| SDLK_UNDERSCORE | '_' | underscore |
| SDLK_BACKQUOTE | '`' | grave |
| SDLK_a | 'a' | a |
| SDLK_b | 'b' | b |
| SDLK_c | 'c' | c |
| SDLK_d | 'd' | d |
| SDLK_e | 'e' | e |
| SDLK_f | 'f' | f |
| SDLK_g | 'g' | g |
| SDLK_h | 'h' | h |
| SDLK_i | 'i' | i |
| SDLK_j | 'j' | j |
| SDLK_k | 'k' | k |
| SDLK_l | 'l' | l |
| SDLK_m | 'm' | m |
| SDLK_n | 'n' | n |
| SDLK_o | 'o' | o |
| SDLK_p | 'p' | p |
| SDLK_q | 'q' | q |
| SDLK_r | 'r' | r |
| SDLK_s | 's' | s |
| SDLK_t | 't' | t |
| SDLK_u | 'u' | u |
| SDLK_v | 'v' | v |
| SDLK_w | 'w' | w |
| SDLK_x | 'x' | x |
| SDLK_y | 'y' | y |
| SDLK_z | 'z' | z |
| SDLK_DELETE | '^?' | delete |
| SDLK_KP0 | keypad 0 | |
| SDLK_KP1 | keypad 1 | |
| SDLK_KP2 | keypad 2 | |
| SDLK_KP3 | keypad 3 | |
| SDLK_KP4 | keypad 4 | |
| SDLK_KP5 | keypad 5 | |
| SDLK_KP6 | keypad 6 | |
| SDLK_KP7 | keypad 7 | |
| SDLK_KP8 | keypad 8 | |
| SDLK_KP9 | keypad 9 | |
| SDLK_KP_PERIOD | '.' | keypad period |
| SDLK_KP_DIVIDE | '/' | keypad divide |
| SDLK_KP_MULTIPLY | '*' | keypad multiply |
| SDLK_KP_MINUS | '-' | keypad minus |
| SDLK_KP_PLUS | '+' | keypad plus |
| SDLK_KP_ENTER | '\r' | keypad enter |
| SDLK_KP_EQUALS | '=' | keypad equals |
| SDLK_UP | up arrow | |
| SDLK_DOWN | down arrow | |
| SDLK_RIGHT | right arrow | |
| SDLK_LEFT | left arrow | |
| SDLK_INSERT | insert | |
| SDLK_HOME | home | |
| SDLK_END | end | |
| SDLK_PAGEUP | page up | |
| SDLK_PAGEDOWN | page down | |
| SDLK_F1 | F1 | |
| SDLK_F2 | F2 | |
| SDLK_F3 | F3 | |
| SDLK_F4 | F4 | |
| SDLK_F5 | F5 | |
| SDLK_F6 | F6 | |
| SDLK_F7 | F7 | |
| SDLK_F8 | F8 | |
| SDLK_F9 | F9 | |
| SDLK_F10 | F10 | |
| SDLK_F11 | F11 | |
| SDLK_F12 | F12 | |
| SDLK_F13 | F13 | |
| SDLK_F14 | F14 | |
| SDLK_F15 | F15 | |
| SDLK_NUMLOCK | numlock | |
| SDLK_CAPSLOCK | capslock | |
| SDLK_SCROLLOCK | scrollock | |
| SDLK_RSHIFT | right shift | |
| SDLK_LSHIFT | left shift | |
| SDLK_RCTRL | right ctrl | |
| SDLK_LCTRL | left ctrl | |
| SDLK_RALT | right alt | |
| SDLK_LALT | left alt | |
| SDLK_RMETA | right meta | |
| SDLK_LMETA | left meta | |
| SDLK_LSUPER | left windows key | |
| SDLK_RSUPER | right windows key | |
| SDLK_MODE | mode shift | |
| SDLK_HELP | help | |
| SDLK_PRINT | print-screen | |
| SDLK_SYSREQ | SysRq | |
| SDLK_BREAK | break | |
| SDLK_MENU | menu | |
| SDLK_POWER | power | |
| SDLK_EURO | euro |
Table 8-2. SDL modifier definitions
| SDL Modifier | Meaning |
|---|---|
| KMOD_NONE | No modifiers applicable |
| KMOD_NUM | Numlock is down |
| KMOD_CAPS | Capslock is down |
| KMOD_LCTRL | Left Control is down |
| KMOD_RCTRL | Right Control is down |
| KMOD_RSHIFT | Right Shift is down |
| KMOD_LSHIFT | Left Shift is down |
| KMOD_RALT | Right Alt is down |
| KMOD_LALT | Left Alt is down |
| KMOD_CTRL | A Control key is down |
| KMOD_SHIFT | A Shift key is down |
| KMOD_ALT | An Alt key is down |
typedef struct{
- Uint8 type;
- Uint8 state;
- SDL_keysym keysym;
-} SDL_KeyboardEvent;SDL_KeyboardEvent is a member of the SDL_Event union and is used when an event of type SDL_KEYDOWN or SDL_KEYUP is reported.
The type and state actually report the same information, they just use different values to do it! A keyboard event occurs when a key is released (type=SDK_KEYUP or state=SDL_RELEASED) and when a key is pressed (type=SDL_KEYDOWN or state=SDL_PRESSED). The information on what key was pressed or released is in the keysym structure.
Note: Repeating SDL_KEYDOWN events will occur if key repeat is enabled (see SDL_EnableKeyRepeat).
typedef struct{
- Uint8 scancode;
- SDLKey sym;
- SDLMod mod;
- Uint16 unicode;
-} SDL_keysym;The SDL_keysym structure is used by reporting key presses and releases since it is a part of the SDL_KeyboardEvent.
The scancode field should generally be left alone, it is the hardware dependent scancode returned by the keyboard. The sym field is extremely useful. It is the SDL-defined value of the key (see SDL Key Syms. This field is very useful when you are checking for certain key presses, like so: -
.
-.
-while(SDL_PollEvent(&event)){
- switch(event.type){
- case SDL_KEYDOWN:
- if(event.key.keysym.sym==SDLK_LEFT)
- move_left();
- break;
- .
- .
- .
- }
-}
-.
-.
-mod stores the current state of the keyboard modifiers as explained in SDL_GetModState. The unicode is only used when UNICODE translation is enabled with SDL_EnableUNICODE. If unicode is non-zero then this a the UNICODE character corresponding to the keypress. If the high 9 bits of the character are 0, then this maps to the equivalent ASCII character:
-char ch;
-if ( (keysym.unicode & 0xFF80) == 0 ) {
- ch = keysym.unicode & 0x7F;
-}
-else {
- printf("An International Character.\n");
-}
-UNICODE translation does have a slight overhead so don't enable it unless its needed.SDL_KillThread gracelessly terminates the thread -associated with thread. If possible, you should -use some other form of IPC to signal the thread to quit.
Return a pointer to an array of available screen dimensions for the given -format and video flags, sorted largest to smallest. Returns -NULL if there are no dimensions available for a particular -format, or -1 if any dimension is okay for -the given format.
If format is NULL, the mode list -will be for the format returned by SDL_GetVideoInfo()->vfmt. The flag parameter is an OR'd combination of surface flags. The flags are the same as those used SDL_SetVideoMode and they play a strong role in deciding what modes are valid. For instance, if you pass SDL_HWSURFACE as a flag only modes that support hardware video surfaces will be returned.
SDL_Rect **modes;
-int i;
-.
-.
-.
-
-/* Get available fullscreen/hardware modes */
-modes=SDL_ListModes(NULL, SDL_FULLSCREEN|SDL_HWSURFACE);
-
-/* Check is there are any modes available */
-if(modes == (SDL_Rect **)0){
- printf("No modes available!\n");
- exit(-1);
-}
-
-/* Check if our resolution is restricted */
-if(modes == (SDL_Rect **)-1){
- printf("All resolutions available.\n");
-}
-else{
- /* Print valid modes */
- printf("Available Modes\n");
- for(i=0;modes[i];++i)
- printf(" %d x %d\n", modes[i]->w, modes[i]->h);
-}
-.
-.SDL_LoadWAV -This function loads a WAVE file into memory.
If this function succeeds, it returns the given -SDL_AudioSpec, -filled with the audio data format of the wave data, and sets -audio_buf to a malloc'd -buffer containing the audio data, and sets audio_len -to the length of that audio buffer, in bytes. You need to free the audio -buffer with SDL_FreeWAV when you are -done with it.
This function returns NULL and sets the SDL -error message if the wave file cannot be opened, uses an unknown data format, -or is corrupt. Currently raw, MS-ADPCM and IMA-ADPCM WAVE files are supported.
SDL_AudioSpec wav_spec;
-Uint32 wav_length;
-Uint8 *wav_buffer;
-
-/* Load the WAV */
-if( SDL_LoadWAV("test.wav", &wav_spec, &wav_buffer, &wav_length) == NULL ){
- fprintf(stderr, "Could not open test.wav: %s\n", SDL_GetError());
- exit(-1);
-}
-.
-.
-.
-/* Do stuff with the WAV */
-.
-.
-/* Free It */
-SDL_FreeWAV(wav_buffer);The lock manipulated by these functions protects the callback function. -During a LockAudio period, you can be guaranteed that the -callback function is not running. Do not call these from the callback -function or you will cause deadlock.
SDL_LockSurface sets up a surface for directly -accessing the pixels. Between calls to SDL_LockSurface -and SDL_UnlockSurface, you can write to and read from -surface->pixels, using the pixel format stored in -surface->format. Once you are done accessing the -surface, you should use SDL_UnlockSurface to release it.
Not all surfaces require locking. -If SDL_MUSTLOCK(surface) -evaluates to 0, then you can read and write to the -surface at any time, and the pixel format of the surface will not change.
No operating system or library calls should be made between lock/unlock -pairs, as critical system locks may be held during this time.
It should be noted, that since SDL 1.1.8 surface locks are recursive. This means that you can lock a surface multiple times, but each lock must have a match unlock. -
. - . - SDL_LockSurface( surface ); - . - /* Surface is locked */ - /* Direct pixel access on surface here */ - . - SDL_LockSurface( surface ); - . - /* More direct pixel access on surface */ - . - SDL_UnlockSurface( surface ); - /* Surface is still locked */ - /* Note: Is versions < 1.1.8, the surface would have been */ - /* no longer locked at this stage */ - . - SDL_UnlockSurface( surface ); - /* Surface is now unlocked */ - . - .
Much the same as SDL_LockSurface, SDL_LockYUVOverlay locks the overlay for direct access to pixel data.
Maps the RGB color value to the specified pixel format and returns the -pixel value as a 32-bit int.
If the format has a palette (8-bit) the index of the closest matching -color in the palette will be returned.
If the specified pixel format has an alpha component it will be returned -as all 1 bits (fully opaque).
A pixel value best approximating the given RGB color value for a given -pixel format. If the pixel format bpp (color depth) is less than 32-bpp -then the unused upper bits of the return value can safely be ignored -(e.g., with a 16-bpp format the return value can be assigned to a -Uint16, and similarly a Uint8 for an 8-bpp -format).
Maps the RGBA color value to the specified pixel format and returns the -pixel value as a 32-bit int.
If the format has a palette (8-bit) the index of the closest matching -color in the palette will be returned.
If the specified pixel format has no alpha component the alpha value -will be ignored (as it will be in formats with a palette).
A pixel value best approximating the given RGBA color value for a given -pixel format. If the pixel format bpp (color depth) is less than 32-bpp -then the unused upper bits of the return value can safely be ignored -(e.g., with a 16-bpp format the return value can be assigned to a -Uint16, and similarly a Uint8 for an 8-bpp -format).
This function takes two audio buffers of len bytes each -of the playing audio format and mixes them, performing addition, volume -adjustment, and overflow clipping. The volume ranges -from 0 to SDL_MIX_MAXVOLUME and should be set to the maximum -value for full audio volume. Note this does not change hardware volume. This is -provided for convenience -- you can mix your own audio data.
Note: Do not use this function for mixing together more than two streams of sample -data. The output from repeated application of this function may be distorted -by clipping, because there is no accumulator with greater range than the -input (not to mention this being an inefficient way of doing it). -Use mixing functions from SDL_mixer, OpenAL, or write your own mixer instead.
typedef struct{
- Uint8 type;
- Uint8 button;
- Uint8 state;
- Uint16 x, y;
-} SDL_MouseButtonEvent;SDL_MouseButtonEvent is a member of the SDL_Event union and is used when an event of type SDL_MOUSEBUTTONDOWN or SDL_MOUSEBUTTONUP is reported.
When a mouse button press or release is detected then number of the button pressed (from 1 to 255, with 1 usually being the left button and 2 the right) is placed into button, the position of the mouse when this event occured is stored in the x and the y fields. Like SDL_KeyboardEvent, information on whether the event was a press or a release event is stored in both the type and state fields, but this should be obvious.
typedef struct{
- Uint8 type;
- Uint8 state;
- Uint16 x, y;
- Sint16 xrel, yrel;
-} SDL_MouseMotionEvent;SDL_MouseMotionEvent is a member of the SDL_Event union and is used when an event of type SDL_MOUSEMOTION is reported.
Simply put, a SDL_MOUSEMOTION type event occurs when a user moves the mouse within the application window or when SDL_WarpMouse is called. Both the absolute (x and y) and relative (xrel and yrel) coordinates are reported along with the current button states (state). The button state can be interpreted using the SDL_BUTTON macro (see SDL_GetMouseState).
If the cursor is hidden (SDL_ShowCursor(0)) and the input is grabbed (SDL_WM_GrabInput(SDL_GRAB_ON)), then the mouse will give relative motion events even when the cursor reaches the edge fo the screen. This is currently only implemented on Windows and Linux/Unix-a-likes.
Locks the mutex, which was previously created with SDL_CreateMutex. If the mutex is already locked then SDL_mutexP will not return until it is unlocked. Returns 0 on success, or -1 on an error.
SDL also defines a macro #define SDL_LockMutex(m) SDL_mutexP(m).
Unlocks the mutex, which was previously created with SDL_CreateMutex. Returns 0 on success, or -1 on an error.
SDL also defines a macro #define SDL_UnlockMutex(m) SDL_mutexV(m).
This function opens the audio device with the desired parameters, and -returns 0 if successful, placing the actual hardware parameters in the -structure pointed to by obtained. If obtained is NULL, the audio -data passed to the callback function will be guaranteed to be in the -requested format, and will be automatically converted to the hardware -audio format if necessary. This function returns -1 if it failed -to open the audio device, or couldn't set up the audio thread.
To open the audio device a desired SDL_AudioSpec must be created. -
SDL_AudioSpec *desired; -. -. -desired = malloc(sizeof(SDL_AudioSpec));-You must then fill this structure with your desired audio specifications.
The desired audio frequency in samples-per-second.
The desired audio format (see SDL_AudioSpec)
The desired size of the audio buffer in samples. This number should be a power of two, and may be adjusted by the audio driver to a value more suitable for the hardware. Good values seem to range between 512 and 8192 inclusive, depending on the application and CPU speed. Smaller values yield faster response time, but can lead to underflow if the application is doing heavy processing and cannot fill the audio buffer in time. A stereo sample consists of both right and left channels in LR ordering. Note that the number of samples is directly related to time by the following formula: ms = (samples*1000)/freq
This should be set to a function that will be called when the audio device is ready for more data. It is passed a pointer to the audio buffer, and the length in bytes of the audio buffer. This function usually runs in a separate thread, and so you should protect data structures that it accesses by calling SDL_LockAudio and SDL_UnlockAudio in your code. The callback prototype is: -
void callback(void *userdata, Uint8 *stream, int len);-userdata is the pointer stored in userdata field of the SDL_AudioSpec. stream is a pointer to the audio buffer you want to fill with information and len is the length of the audio buffer in bytes.
This pointer is passed as the first parameter to the callback function.
SDL_OpenAudio reads these fields from the desired SDL_AudioSpec structure pass to the function and attempts to find an audio configuration matching your desired. As mentioned above, if the obtained parameter is NULL then SDL with convert from your desired audio settings to the hardware settings as it plays.
If obtained is NULL then the desired SDL_AudioSpec is your working specification, otherwise the obtained SDL_AudioSpec becomes the working specification and the desirec specification can be deleted. The data in the working specification is used when building SDL_AudioCVT's for converting loaded data to the hardware format.
SDL_OpenAudio calculates the size and silence fields for both the desired and obtained specifications. The size field stores the total size of the audio buffer in bytes, while the silence stores the value used to represent silence in the audio buffer
The audio device starts out playing silence when it's opened, and should be enabled for playing by calling SDL_PauseAudio(0) when you are ready for your audio callback function to be called. Since the audio driver may modify the requested size of the audio buffer, you should allocate any local mixing buffers after you open the audio device.
/* Prototype of our callback function */
-void my_audio_callback(void *userdata, Uint8 *stream, int len);
-
-/* Open the audio device */
-SDL_AudioSpec *desired, *obtained;
-SDL_AudioSpec *hardware_spec;
-
-/* Allocate a desired SDL_AudioSpec */
-desired = malloc(sizeof(SDL_AudioSpec));
-
-/* Allocate space for the obtained SDL_AudioSpec */
-obtained = malloc(sizeof(SDL_AudioSpec));
-
-/* 22050Hz - FM Radio quality */
-desired->freq=22050;
-
-/* 16-bit signed audio */
-desired->format=AUDIO_S16LSB;
-
-/* Mono */
-desired->channels=0;
-
-/* Large audio buffer reduces risk of dropouts but increases response time */
-desired->samples=8192;
-
-/* Our callback function */
-desired->callback=my_audio_callback;
-
-desired->userdata=NULL;
-
-/* Open the audio device */
-if ( SDL_OpenAudio(desired, obtained) < 0 ){
- fprintf(stderr, "Couldn't open audio: %s\n", SDL_GetError());
- exit(-1);
-}
-/* desired spec is no longer needed */
-free(desired);
-hardware_spec=obtained;
-.
-.
-/* Prepare callback for playing */
-.
-.
-.
-/* Start playing */
-SDL_PauseAudio(0);typedef struct{
- Uint32 format;
- int w, h;
- int planes;
- Uint16 *pitches;
- Uint8 **pixels;
- Uint32 hw_overlay:1;
-} SDL_Overlay;| format | Overlay format (see below) |
| w, h | Width and height of overlay |
| planes | Number of planes in the overlay. Usually either 1 or 3 |
| pitches | An array of pitches, one for each plane. Pitch is the length of a row in bytes. |
| pixels | An array of pointers to teh data of each plane. The overlay should be locked before these pointers are used. |
| hw_overlay | This will be set to 1 if the overlay is hardware accelerated. |
A SDL_Overlay is similar to a SDL_Surface except it stores a YUV overlay. All the fields are read only, except for pixels which should be locked before use. The format field stores the format of the overlay which is one of the following: -
#define SDL_YV12_OVERLAY 0x32315659 /* Planar mode: Y + V + U */ -#define SDL_IYUV_OVERLAY 0x56555949 /* Planar mode: Y + U + V */ -#define SDL_YUY2_OVERLAY 0x32595559 /* Packed mode: Y0+U0+Y1+V0 */ -#define SDL_UYVY_OVERLAY 0x59565955 /* Packed mode: U0+Y0+V0+Y1 */ -#define SDL_YVYU_OVERLAY 0x55595659 /* Packed mode: Y0+V0+Y1+U0 */-More information on YUV formats can be found at http://www.webartz.com/fourcc/indexyuv.htm.
| ncolors | Number of colors used in this palette |
| colors | Pointer to SDL_Color structures that make up the palette. |
Each pixel in an 8-bit surface is an index into the colors field of the SDL_Palette structure store in SDL_PixelFormat. A SDL_Palette should never need to be created manually. It is automatically created when SDL allocates a SDL_PixelFormat for a surface. The colors values of a SDL_Surfaces palette can be set with the SDL_SetColors.
This function pauses and unpauses the audio callback processing. -It should be called with pause_on=0 after opening the audio -device to start playing sound. This is so you can safely initialize -data for your callback function after opening the audio device. -Silence will be written to the audio device during the pause.
Checks the event queue for messages and optionally returns them.
If action is SDL_ADDEVENT, up to -numevents events will be added to the back of the event - queue.
If action is SDL_PEEKEVENT, up to -numevents events at the front of the event queue, -matching mask, -will be returned and will not be removed from the queue.
If action is SDL_GETEVENT, up to -numevents events at the front of the event queue, -matching mask, -will be returned and will be removed from the queue.
The mask parameter is an bitwise OR of -SDL_EVENTMASK(event_type), for all -event types you are interested in.
This function is thread-safe.
This function returns the number of events actually stored, or --1 if there was an error.
typedef struct SDL_PixelFormat {
- SDL_Palette *palette;
- Uint8 BitsPerPixel;
- Uint8 BytesPerPixel;
- Uint8 Rloss, Gloss, Bloss, Aloss;
- Uint8 Rshift, Gshift, Bshift, Ashift;
- Uint32 Rmask, Gmask, Bmask, Amask;
- Uint32 colorkey;
- Uint8 alpha;
-} SDL_PixelFormat;| palette | Pointer to the palette, or NULL if the BitsPerPixel>8 |
| BitsPerPixel | The number of bits used to represent each pixel in a surface. Usually 8, 16, 24 or 32. |
| BytesPerPixel | The number of bytes used to represent each pixel in a surface. Usually one to four. |
| [RGBA]mask | Binary mask used to retrieve individual color values |
| [RGBA]loss | Precision loss of each color component (2[RGBA]loss) |
| [RGBA]shift | Binary left shift of each color component in the pixel value |
| colorkey | Pixel value of transparent pixels |
| alpha | Overall surface alpha value |
A SDL_PixelFormat describes the format of the pixel data stored at the pixels field of a SDL_Surface. Every surface stores a SDL_PixelFormat in the format field.
If you wish to do pixel level modifications on a surface, then understanding how SDL stores its color information is essential.
8-bit pixel formats are the easiest to understand. Since its an 8-bit format, we have 8 BitsPerPixel and 1 BytesPerPixel. Since BytesPerPixel is 1, all pixels are represented by a Uint8 which contains an index into palette->colors. So, to determine the color of a pixel in a 8-bit surface: we read the color index from surface->pixels and we use that index to read the SDL_Color structure from surface->format->palette->colors. Like so: -
SDL_Surface *surface;
-SDL_PixelFormat *fmt;
-SDL_Color *color;
-Uint8 index;
-
-.
-.
-
-/* Create surface */
-.
-.
-fmt=surface->format;
-
-/* Check the bitdepth of the surface */
-if(fmt->BitsPerPixel!=8){
- fprintf(stderr, "Not an 8-bit surface.\n");
- return(-1);
-}
-
-/* Lock the surface */
-SDL_LockSurface(surface);
-
-/* Get the topleft pixel */
-index=*(Uint8 *)surface->pixels;
-color=fmt->palette->colors[index];
-
-/* Unlock the surface */
-SDL_UnlockSurface(surface);
-printf("Pixel Color-> Red: %d, Green: %d, Blue: %d. Index: %d\n",
- color->r, color->g, color->b, index);
-.
-.Pixel formats above 8-bit are an entirely different experience. They are -considered to be "TrueColor" formats and the color information is stored in the -pixels themselves, not in a palette. The mask, shift and loss fields tell us -how the color information is encoded. The mask fields allow us to isolate each -color component, the shift fields tell us the number of bits to the right of -each component in the pixel value and the loss fields tell us the number of -bits lost from each component when packing 8-bit color component in a pixel. -
/* Extracting color components from a 32-bit color value */
-SDL_PixelFormat *fmt;
-SDL_Surface *surface;
-Uint32 temp, pixel;
-Uint8 red, green, blue, alpha;
-.
-.
-.
-fmt=surface->format;
-SDL_LockSurface(surface);
-pixel=*((Uint32*)surface->pixels);
-SDL_UnlockSurface(surface);
-
-/* Get Red component */
-temp=pixel&fmt->Rmask; /* Isolate red component */
-temp=temp>>fmt->Rshift;/* Shift it down to 8-bit */
-temp=temp<<fmt->Rloss; /* Expand to a full 8-bit number */
-red=(Uint8)temp;
-
-/* Get Green component */
-temp=pixel&fmt->Gmask; /* Isolate green component */
-temp=temp>>fmt->Gshift;/* Shift it down to 8-bit */
-temp=temp<<fmt->Gloss; /* Expand to a full 8-bit number */
-green=(Uint8)temp;
-
-/* Get Blue component */
-temp=pixel&fmt->Bmask; /* Isolate blue component */
-temp=temp>>fmt->Bshift;/* Shift it down to 8-bit */
-temp=temp<<fmt->Bloss; /* Expand to a full 8-bit number */
-blue=(Uint8)temp;
-
-/* Get Alpha component */
-temp=pixel&fmt->Amask; /* Isolate alpha component */
-temp=temp>>fmt->Ashift;/* Shift it down to 8-bit */
-temp=temp<<fmt->Aloss; /* Expand to a full 8-bit number */
-alpha=(Uint8)temp;
-
-printf("Pixel Color -> R: %d, G: %d, B: %d, A: %d\n", red, green, blue, alpha);
-.
-.
-.Polls for currently pending events, and returns 1 -if there are any pending events, or 0 if there -are none available.
If event is not NULL, the next -event is removed from the queue and stored in that area.
SDL_Event event; /* Event structure */
-
-.
-.
-.
-/* Check for events */
-while(SDL_PollEvent(&event)){ /* Loop until there are no events left on the queue */
- switch(event.type){ /* Process the appropiate event type */
- case SDL_KEYDOWN: /* Handle a KEYDOWN event */
- printf("Oh! Key press\n");
- break;
- case SDL_MOUSEMOTION:
- .
- .
- .
- default: /* Report an unhandled event */
- printf("I don't know what this event is!\n");
- }
-}Pumps the event loop, gathering events from the input devices.
SDL_PumpEvents gathers all the pending input information from devices and places it on the event queue. Without calls to SDL_PumpEvents no events would ever be placed on the queue. Often calls the need for SDL_PumpEvents is hidden from the user since SDL_PollEvent and SDL_WaitEvent implicitly call SDL_PumpEvents. However, if you are not polling or waiting for events (e.g. you are filtering them), then you must call SDL_PumpEvents to force an event queue update.
Note: You can only call this function in the thread that set the video mode.
The event queue can actually be used as a two way communication channel. Not only can events be read from the queue, but the user can also push their own events onto it. event is a pointer to the event structure you wish to push onto the queue.
Note: Pushing device input events onto the queue doesn't modify the state of the device within SDL.
SDL_Quit shuts down all SDL subsystems and frees the resources allocated to them. This should always be called before you exit. For the sake of simplicity you can set SDL_Quit as your atexit call, like: -
SDL_Init(SDL_INIT_VIDEO|SDL_INIT_AUDIO); -atexit(SDL_Quit); -. -.
Note: While using atexit maybe be fine for small programs, more advanced users should shut down SDL in their own cleanup code. Plus, using atexit in a library is a sure way to crash dynamically loaded code
SDL_QuitEvent is a member of the SDL_Event union and is used whan an event of type SDL_QUIT is reported.
As can be seen, the SDL_QuitEvent structure serves no useful purpose. The event itself, on the other hand, is very important. If you filter out or ignore a quit event then it is impossible for the user to close the window. On the other hand, if you do accept a quit event then the application window will be closed, and screen updates will still report success event though the application will no longer be visible.
Note: The macro SDL_QuitRequested will return non-zero if a quit event is pending
SDL_QuitSubSystem allows you to shut down a subsystem that has been previously initialized by SDL_Init or SDL_InitSubSystem. The flags tells SDL_QuitSubSystem which subsystems to shut down, it uses the same values that are passed to SDL_Init.
A SDL_Rect defines a rectangular area of pixels. It is used by SDL_BlitSurface to define blitting regions and by several other video functions.
SDL_ResizeEvent is a member of the SDL_Event union and is used when an event of type SDL_VIDEORESIZE is reported.
When SDL_RESIZABLE is passed as a flag to SDL_SetVideoMode the user is allowed to resize the applications window. When the window is resized an SDL_VIDEORESIZE is report, with the new window width and height values stored in w and h, respectively. When an SDL_VIDEORESIZE is recieved the window should be resized to the new dimensions using SDL_SetVideoMode.
SDL_SemPost unlocks the semaphore pointed to by -sem and atomically increments the semaphores value. -Threads that were blocking on the semaphore may be scheduled after this call -succeeds.
SDL_SemPost should be called after a semaphore is locked by a successful call to -SDL_SemWait, -SDL_SemTryWait or -SDL_SemWaitTimeout.
SDL_CreateSemaphore, -SDL_DestroySemaphore, -SDL_SemWait, -SDL_SemTryWait, -SDL_SemWaitTimeout, -SDL_SemValue
SDL_SemTryWait is a non-blocking varient of -SDL_SemWait. If the value of the semaphore -pointed to by sem is positive it will atomically -decrement the semaphore value and return 0, otherwise it will return -SDL_MUTEX_TIMEDOUT instead of suspending the thread.
After SDL_SemTryWait is successful, the semaphore -can be released and its count atomically incremented by a successful call to -SDL_SemPost.
Returns 0 if the semaphore was successfully locked or -either SDL_MUTEX_TIMEDOUT or -1 -if the thread would have suspended or there was an error, respectivly.
If the semaphore was not successfully locked, the semaphore will be unchanged.
res = SDL_SemTryWait(my_sem);
-
-if (res == SDL_MUTEX_TIMEDOUT) {
- return TRY_AGAIN;
-}
-if (res == -1) {
- return WAIT_ERROR;
-}
-
-...
-
-SDL_SemPost(my_sem);SDL_CreateSemaphore, -SDL_DestroySemaphore, -SDL_SemWait, -SDL_SemWaitTimeout, -SDL_SemPost, -SDL_SemValue
SDL_SemValue() returns the current semaphore value from -the semaphore pointed to by sem.
SDL_CreateSemaphore, -SDL_DestroySemaphore, -SDL_SemWait, -SDL_SemTryWait, -SDL_SemWaitTimeout, -SDL_SemPost
SDL_SemWait() suspends the calling thread until either -the semaphore pointed to by sem has a positive value, -the call is interrupted by a signal or error. If the call is successful it -will atomically decrement the semaphore value.
After SDL_SemWait() is successful, the semaphore -can be released and its count atomically incremented by a successful call to -SDL_SemPost.
SDL_CreateSemaphore, -SDL_DestroySemaphore, -SDL_SemTryWait, -SDL_SemWaitTimeout, -SDL_SemPost, -SDL_SemValue
SDL_SemWaitTimeout() is a varient of -SDL_SemWait -with a maximum timeout value. -If the value of the semaphore pointed to by sem is -positive (greater than zero) it will atomically decrement the semaphore value -and return 0, otherwise it will wait up to timeout -milliseconds trying to lock the semaphore. This function is to be avoided if -possible since on some platforms it is implemented by polling the semaphore -every millisecond in a busy loop.
After SDL_SemWaitTimeout() is successful, the semaphore -can be released and its count atomically incremented by a successful call to -SDL_SemPost.
Returns 0 if the semaphore was successfully locked or -either SDL_MUTEX_TIMEDOUT or -1 -if the timeout period was exceeded or there was an error, respectivly.
If the semaphore was not successfully locked, the semaphore will be unchanged.
res = SDL_SemWaitTimeout(my_sem, WAIT_TIMEOUT_MILLISEC);
-
-if (res == SDL_MUTEX_TIMEDOUT) {
- return TRY_AGAIN;
-}
-if (res == -1) {
- return WAIT_ERROR;
-}
-
-...
-
-SDL_SemPost(my_sem);SDL_CreateSemaphore, -SDL_DestroySemaphore, -SDL_SemWait, -SDL_SemTryWait, -SDL_SemPost, -SDL_SemValue
Note: This function and the semantics of SDL alpha blending have changed since version 1.1.4. Up until version 1.1.5, an alpha value of 0 was considered opaque and a value of 255 was considered transparent. This has now been inverted: 0 (SDL_ALPHA_TRANSPARENT) is now considered transparent and 255 (SDL_ALPHA_OPAQUE) is now considered opaque.
SDL_SetAlpha is used for setting the per-surface alpha -value and/or enabling and disabling alpha blending.
Thesurface parameter specifies which surface whose alpha -attributes you wish to adjust. flags is used to specify -whether alpha blending should be used (SDL_SRCALPHA) and -whether the surface should use RLE acceleration for blitting -(SDL_RLEACCEL). flags can be an OR'd -combination of these two options, one of these options or 0. If -SDL_SRCALPHA is not passed as a flag then all alpha -information is ignored when blitting the surface. The -alpha parameter is the per-surface alpha value; a -surface need not have an alpha channel to use per-surface alpha and blitting -can still be accelerated with SDL_RLEACCEL.
Note: The per-surface alpha value of 128 is considered a special case and -is optimised, so it's much faster than other per-surface values.
Alpha effects surface blitting in the following ways:
| RGBA->RGB with SDL_SRCALPHA | The source is alpha-blended with the destination, using the alpha channel. SDL_SRCCOLORKEY and the per-surface alpha are ignored. |
| RGBA->RGB without SDL_SRCALPHA | The RGB data is copied from the source. The source alpha channel and the per-surface alpha value are ignored. |
| RGB->RGBA with SDL_SRCALPHA | The source is alpha-blended with the destination using the per-surface alpha -value. If SDL_SRCCOLORKEY is set, only the pixels not -matching the colorkey value are copied. The alpha channel of the copied pixels -is set to opaque. |
| RGB->RGBA without SDL_SRCALPHA | The RGB data is copied from the source and the alpha value of the copied pixels -is set to opaque. If SDL_SRCCOLORKEY is set, only the pixels -not matching the colorkey value are copied. |
| RGBA->RGBA with SDL_SRCALPHA | The source is alpha-blended with the destination using the source alpha -channel. The alpha channel in the destination surface is left untouched. -SDL_SRCCOLORKEY is ignored. |
| RGBA->RGBA without SDL_SRCALPHA | The RGBA data is copied to the destination surface. If SDL_SRCCOLORKEY is set, only the pixels not matching the colorkey value are copied. |
| RGB->RGB with SDL_SRCALPHA | The source is alpha-blended with the destination using the per-surface alpha value. If SDL_SRCCOLORKEY is set, only the pixels not matching the colorkey value are copied. |
| RGB->RGB without SDL_SRCALPHA | The RGB data is copied from the source. If SDL_SRCCOLORKEY is set, only the pixels not matching the colorkey value are copied. |
Note: Note that RGBA->RGBA blits (with SDL_SRCALPHA set) keep the alpha -of the destination surface. This means that you cannot compose two arbitrary -RGBA surfaces this way and get the result you would expect from "overlaying" -them; the destination alpha will work as a mask.
Also note that per-pixel and per-surface alpha cannot be combined; -the per-pixel alpha is always used if available
Sets the clipping rectangle for a surface. When this surface is the -destination of a blit, only the area within the clip rectangle will be -drawn into.
The rectangle pointed to by rect will be -clipped to the edges of the surface so that the clip rectangle for a -surface can never fall outside the edges of the surface.
If rect is NULL the clipping -rectangle will be set to the full size of the surface.
Sets the color key (transparent pixel) in a blittable surface and enables or - disables RLE blit acceleration.
RLE acceleration can substantially speed up blitting of images with large -horizontal runs of transparent pixels (i.e., pixels that match the -key value). The key must be of the same pixel format as the surface, SDL_MapRGB is often useful for obtaining an acceptable value.
If flag is SDL_SRCCOLORKEY then -key is the transparent pixel value in the source image of a -blit.
If flag is OR'd with -SDL_RLEACCEL then the surface will be draw using RLE -acceleration when drawn with -SDL_BlitSurface. The surface will -actually be encoded for RLE acceleration the first time -SDL_BlitSurface or -SDL_DisplayFormat is called on the -surface.
If flag is 0, this function clears -any current color key.
Sets a portion of the colormap for the given 8-bit surface.
When surface is the surface associated with the current -display, the display colormap will be updated with the requested colors. If -SDL_HWPALETTE was set in SDL_SetVideoMode flags, -SDL_SetColors will always return 1, -and the palette is guaranteed to be set the way you desire, even if the window -colormap has to be warped or run under emulation.
The color components of a -SDL_Color -structure are 8-bits in size, giving you a total of 2563 -=16777216 colors.
Palettized (8-bit) screen surfaces with the SDL_HWPALETTE -flag have two palettes, a logical palette that is used for mapping blits -to/from the surface and a physical palette (that determines how the -hardware will map the colors to the display). SDL_SetColors -modifies both palettes (if present), and is equivalent to calling -SDL_SetPalette with the -flags set to -(SDL_LOGPAL | SDL_PHYSPAL).
If surface is not a palettized surface, this function -does nothing, returning 0. If all of the colors were set -as passed to SDL_SetColors, it will return -1. If not all the color entries were set exactly as -given, it will return 0, and you should look at the -surface palette to determine the actual color palette.
/* Create a display surface with a grayscale palette */
-SDL_Surface *screen;
-SDL_Color colors[256];
-int i;
-.
-.
-.
-/* Fill colors with color information */
-for(i=0;i<256;i++){
- colors[i].r=i;
- colors[i].g=i;
- colors[i].b=i;
-}
-
-/* Create display */
-screen=SDL_SetVideoMode(640, 480, 8, SDL_HWPALETTE);
-if(!screen){
- printf("Couldn't set video mode: %s\n", SDL_GetError());
- exit(-1);
-}
-
-/* Set palette */
-SDL_SetColors(screen, colors, 0, 256);
-.
-.
-.
-.Sets the currently active cursor to -the specified one. -If the cursor is currently visible, the change will be immediately -represented on the display.
This function sets up a filter to process all events before they are posted -to the event queue. This is a very powerful and flexible feature. The filter -is prototyped as: -
typedef int (*SDL_EventFilter)(const SDL_Event *event);-If the filter returns 1, then the event will be -added to the internal queue. If it returns 0, -then the event will be dropped from the queue. This allows selective -filtering of dynamically.
There is one caveat when dealing with the SDL_QUITEVENT event type. The -event filter is only called when the window manager desires to close the -application window. If the event filter returns 1, then the window will -be closed, otherwise the window will remain open if possible. -If the quit event is generated by an interrupt signal, it will bypass the -internal queue and be delivered to the application at the next event poll.
Note: Events pushed onto the queue with SDL_PushEvent or SDL_PeepEvents do not get passed through the event filter.
Note: Be Careful! The event filter function may run in a different thread so be careful what you do within it.
Sets the "gamma function" for the display of each color component. Gamma -controls the brightness/contrast of colors displayed on the screen. -A gamma value of 1.0 is identity (i.e., no adjustment -is made).
This function adjusts the gamma based on the "gamma function" parameter, -you can directly specify lookup tables for gamma adjustment with -SDL_SetGammaRamp.
Not all display hardware is able to change gamma.
Sets the gamma lookup tables for the display for each color component. -Each table is an array of 256 Uint16 values, representing a mapping -between the input and output for that channel. The input is the index -into the array, and the output is the 16-bit gamma value at that index, -scaled to the output color precision. You may pass NULL to any of the -channels to leave them unchanged.
This function adjusts the gamma based on lookup tables, you can also -have the gamma calculated based on a "gamma function" parameter with -SDL_SetGamma.
Not all display hardware is able to change gamma.
The inverse of SDL_GetModState, SDL_SetModState allows you to impose modifier key states on your application.
Simply pass your desired modifier states into modstate. This value my be a logical OR'd combination of the following:
typedef enum {
- KMOD_NONE = 0x0000,
- KMOD_LSHIFT= 0x0001,
- KMOD_RSHIFT= 0x0002,
- KMOD_LCTRL = 0x0040,
- KMOD_RCTRL = 0x0080,
- KMOD_LALT = 0x0100,
- KMOD_RALT = 0x0200,
- KMOD_LMETA = 0x0400,
- KMOD_RMETA = 0x0800,
- KMOD_NUM = 0x1000,
- KMOD_CAPS = 0x2000,
- KMOD_MODE = 0x4000,
-} SDLMod;Sets a portion of the palette for the given 8-bit surface.
Palettized (8-bit) screen surfaces with the -SDL_HWPALETTE flag have two palettes, a logical -palette that is used for mapping blits to/from the surface and a -physical palette (that determines how the hardware will map the colors -to the display). SDL_BlitSurface -always uses the logical palette when blitting surfaces (if it has to -convert between surface pixel formats). Because of this, it is often -useful to modify only one or the other palette to achieve various -special color effects (e.g., screen fading, color flashes, screen dimming).
This function can modify either the logical or physical palette by -specifing SDL_LOGPAL or -SDL_PHYSPALthe in the flags -parameter.
When surface is the surface associated with the current -display, the display colormap will be updated with the requested colors. If -SDL_HWPALETTE was set in SDL_SetVideoMode flags, -SDL_SetPalette will always return 1, -and the palette is guaranteed to be set the way you desire, even if the window -colormap has to be warped or run under emulation.
The color components of a -SDL_Color structure -are 8-bits in size, giving you a total of -2563=16777216 colors.
If surface is not a palettized surface, this function -does nothing, returning 0. If all of the colors were set -as passed to SDL_SetPalette, it will return -1. If not all the color entries were set exactly as -given, it will return 0, and you should look at the -surface palette to determine the actual color palette.
/* Create a display surface with a grayscale palette */
- SDL_Surface *screen;
- SDL_Color colors[256];
- int i;
- .
- .
- .
- /* Fill colors with color information */
- for(i=0;i<256;i++){
- colors[i].r=i;
- colors[i].g=i;
- colors[i].b=i;
- }
-
- /* Create display */
- screen=SDL_SetVideoMode(640, 480, 8, SDL_HWPALETTE);
- if(!screen){
- printf("Couldn't set video mode: %s\n", SDL_GetError());
- exit(-1);
- }
-
- /* Set palette */
- SDL_SetPalette(screen, SDL_LOGPAL|SDL_PHYSPAL, colors, 0, 256);
- .
- .
- .
- .| SDL Library Documentation | ||
|---|---|---|
| Prev |
/* Function prototype for the timer callback function */ -typedef Uint32 (*SDL_TimerCallback)(Uint32 interval);
Set a callback to run after the specified number of milliseconds has -elapsed. The callback function is passed the current timer interval -and returns the next timer interval. If the returned value is the -same as the one passed in, the periodic alarm continues, otherwise a -new alarm is scheduled.
To cancel a currently running timer, call -SDL_SetTimer(0, NULL);
The timer callback function may run in a different thread than your -main constant, and so shouldn't call any functions from within itself.
The maximum resolution of this timer is 10 ms, which means that if -you request a 16 ms timer, your callback will run approximately 20 ms -later on an unloaded system. If you wanted to set a flag signaling -a frame update at 30 frames per second (every 33 ms), you might set a -timer for 30 ms (see example below).
If you use this function, you need to pass SDL_INIT_TIMER -to SDL_Init().
Note: This function is kept for compatibility but has been superseded -by the new timer functions -SDL_AddTimer and -SDL_RemoveTimer which support -multiple timers.
Set up a video mode with the specified width, height and bits-per-pixel.
If bpp is 0, it is treated as the -current display bits per pixel.
The flags parameter is the same as the flags field of the SDL_Surface structure. OR'd combinations of the following values are valid.
| SDL_SWSURFACE | Create the video surface in system memory |
| SDL_HWSURFACE | Create the video surface in video memory |
| SDL_ASYNCBLIT | Enables the use of asynchronous updates of the display surface. This will -usually slow down blitting on single CPU machines, but may provide a speed -increase on SMP systems. |
| SDL_ANYFORMAT | Normally, if a video surface of the requested bits-per-pixel (bpp) is not available, SDL will emulate one with a shadow surface. Passing SDL_ANYFORMAT prevents this and causes SDL to use the video surface, regardless of its pixel depth. |
| SDL_HWPALETTE | Give SDL exclusive palette access. Without this flag you may not always get the the colors you request with SDL_SetColors or SDL_SetPalette. |
| SDL_DOUBLEBUF | Enable hardware double buffering; only valid with SDL_HWSURFACE. Calling -SDL_Flip will flip the -buffers and update the screen. All drawing will take place on the surface -that is not displayed at the moment. If double buffering could not be enabled -then SDL_Flip will just perform a -SDL_UpdateRect -on the entire screen. |
| SDL_FULLSCREEN | SDL will attempt to use a fullscreen mode. If a hardware resolution change is -not possible (for whatever reason), the next higher resolution will be used and -the display window centered on a black background. |
| SDL_OPENGL | Create an OpenGL rendering context. You should have previously set OpenGL video attributes with SDL_GL_SetAttribute. |
| SDL_OPENGLBLIT | Create an OpenGL rendering context, like above, but allow normal blitting -operations. The screen (2D) surface may have an alpha channel, and -SDL_UpdateRects -must be used for updating changes to the screen surface. NOTE: This option -is kept for compatibility only, and is not recommended for -new code. |
| SDL_RESIZABLE | Create a resizable window. When the window is resized by the user a SDL_VIDEORESIZE event is generated and SDL_SetVideoMode can be called again with the new size. |
| SDL_NOFRAME | If possible, SDL_NOFRAME causes SDL to create a window with no title bar or frame decoration. Fullscreen modes automatically have this flag set. |
Note: Whatever flags SDL_SetVideoMode could satisfy are set in the flags member of the returned surface.
Note: The bpp parameter is the number of bits per pixel, -so a bpp of 24 uses the packed representation of -3 bytes/pixel. For the more common 4 bytes/pixel mode, use a -bpp of 32. Somewhat oddly, both 15 and 16 will -request a 2 bytes/pixel mode, but different pixel formats.
The framebuffer surface, or NULL if it fails. -The surface returned is freed by SDL_Quit() and should nt be freed by -the caller.
Toggle whether or not the cursor is shown on the screen. Passing SDL_ENABLE displays the cursor and passing SDL_DISABLE hides it. The current state of the mouse cursor can be queried by passing SDL_QUERY, either SDL_DISABLE or SDL_ENABLE will be returned.
The cursor starts off displayed, but can be turned off.
typedef struct SDL_Surface {
- Uint32 flags; /* Read-only */
- SDL_PixelFormat *format; /* Read-only */
- int w, h; /* Read-only */
- Uint16 pitch; /* Read-only */
- void *pixels; /* Read-write */
-
- /* clipping information */
- SDL_Rect clip_rect; /* Read-only */
-
- /* Reference count -- used when freeing surface */
- int refcount; /* Read-mostly */
-
- /* This structure also contains private fields not shown here */
-} SDL_Surface;SDL_Surface's represent areas of "graphical" -memory, memory that can be drawn to. The video framebuffer is returned -as a SDL_Surface by -SDL_SetVideoMode -and SDL_GetVideoSurface. -Most of the fields should be pretty obvious. -w and h are the -width and height of the surface in pixels. -pixels is a pointer to the actual pixel data, -the surface should be locked -before accessing this field. The clip_rect field -is the clipping rectangle as set by -SDL_SetClipRect.
The following are supported in the -flags field.
| SDL_SWSURFACE | Surface is stored in system memory |
| SDL_HWSURFACE | Surface is stored in video memory |
| SDL_ASYNCBLIT | Surface uses asynchronous blits if possible |
| SDL_ANYFORMAT | Allows any pixel-format (Display surface) |
| SDL_HWPALETTE | Surface has exclusive palette |
| SDL_DOUBLEBUF | Surface is double buffered (Display surface) |
| SDL_FULLSCREEN | Surface is full screen (Display Surface) |
| SDL_OPENGL | Surface has an OpenGL context (Display Surface) |
| SDL_OPENGLBLIT | Surface supports OpenGL blitting (Display Surface) |
| SDL_RESIZABLE | Surface is resizable (Display Surface) |
| SDL_HWACCEL | Surface blit uses hardware acceleration |
| SDL_SRCCOLORKEY | Surface use colorkey blitting |
| SDL_RLEACCEL | Colorkey blitting is accelerated with RLE |
| SDL_SRCALPHA | Surface blit uses alpha blending |
| SDL_PREALLOC | Surface uses preallocated memory |
The system window manager event contains a pointer to system-specific -information about unknown window manager events. If you enable this event -using -SDL_EventState(), -it will be generated whenever unhandled events are received from the window -manager. This can be used, for example, to implement cut-and-paste in your -application. - -
typedef struct {
- Uint8 type; /* Always SDL_SYSWMEVENT */
- SDL_SysWMmsg *msg;
- } SDL_SysWMEvent;
-
-If you want to obtain system-specific information about the window manager,
-you can fill the version member of a SDL_SysWMinfo
-structure (details can be found in SDL_syswm.h, which must be included) using the SDL_VERSION() macro found in
-SDL_version.h, and pass it to the
-function:
-Surfaces that were previously locked using SDL_LockSurface must be unlocked with SDL_UnlockSurface. Surfaces should be unlocked as soon as possible.
It should be noted that since 1.1.8, surface locks are recursive. See SDL_LockSurface.
The opposite to SDL_LockYUVOverlay. Unlocks a previously locked overlay. An overlay must be unlocked before it can be displayed.
Makes sure the given area is updated on the given screen. The rectangle must -be confined within the screen boundaries (no clipping is done).
If 'x', 'y', 'w' -and 'h' are all 0, -SDL_UpdateRect will update the -entire screen.
This function should not be called while 'screen' is -locked.
Makes sure the given list of rectangles is updated on the given screen. -The rectangles must all be confined within the screen boundaries (no -clipping is done).
This function should not be called while screen is -locked.
Note: It is adviced to call this function only once per frame, since each -call has some processing overhead. This is no restriction since you -can pass any number of rectangles each time.
The rectangles are not automatically merged or checked for overlap. In -general, the programmer can use his knowledge about his particular -rectangles to merge them in an efficient way, to avoid overdraw.
typedef struct{
- Uint8 type;
- int code;
- void *data1;
- void *data2;
-} SDL_UserEvent;SDL_UserEvent is in the user member of the structure SDL_Event. This event is unique, it is never created by SDL but only by the user. The event can be pushed onto the event queue using SDL_PushEvent. The contents of the structure members or completely up to the programmer, the only requirement is that type is a value from SDL_USEREVENT to SDL_NUMEVENTS-1 (inclusive).
SDL_Event event; - -event.type = SDL_USEREVENT; -event.user.code = my_event_code; -event.user.data1 = significant_data; -event.user.data2 = 0; -SDL_PushEvent(&event);
The buffer pointed to by namebuf is filled up to a maximum of maxlen characters (include the NULL terminator) with the name of the initialised video driver. The driver name is a simple one word identifier like "x11" or "windib".
Returns NULL if video has not been initialised with SDL_Init or a pointer to namebuf otherwise.
typedef struct{
- Uint32 hw_available:1;
- Uint32 wm_available:1;
- Uint32 blit_hw:1;
- Uint32 blit_hw_CC:1;
- Uint32 blit_hw_A:1;
- Uint32 blit_sw:1;
- Uint32 blit_sw_CC:1;
- Uint32 blit_sw_A:1;
- Uint32 blit_fill;
- Uint32 video_mem;
- SDL_PixelFormat *vfmt;
-} SDL_VideoInfo;| hw_available | Is it possible to create hardware surfaces? |
| wm_available | Is there a window manager available |
| blit_hw | Are hardware to hardware blits accelerated? |
| blit_hw_CC | Are hardware to hardware colorkey blits accelerated? |
| blit_hw_A | Are hardware to hardware alpha blits accelerated? |
| blit_sw | Are software to hardware blits accelerated? |
| blit_sw_CC | Are software to hardware colorkey blits accelerated? |
| blit_sw_A | Are software to hardware alpha blits accelerated? |
| blit_fill | Are color fills accelerated? |
| video_mem | Total amount of video memory in Kilobytes |
| vfmt | Pixel format of the video device |
This (read-only) structure is returned by SDL_GetVideoInfo. It contains information on either the 'best' available mode (if called before SDL_SetVideoMode) or the current video mode.
SDL_VideoModeOK returns 0 -if the requested mode is not supported under any bit depth, or returns the -bits-per-pixel of the closest available mode with the given width, height and requested surface flags (see SDL_SetVideoMode).
The bits-per-pixel value returned is only a suggested mode. You can usually request and bpp you want when setting the video mode and SDL will emulate that color depth with a shadow video surface.
The arguments to SDL_VideoModeOK are the same ones you -would pass to SDL_SetVideoMode
SDL_Surface *screen;
-Uint32 bpp;
-.
-.
-.
-printf("Checking mode 640x480@16bpp.\n");
-bpp=SDL_VideoModeOK(640, 480, 16, SDL_HWSURFACE);
-
-if(!bpp){
- printf("Mode not available.\n");
- exit(-1);
-}
-
-printf("SDL Recommends 640x480@%dbpp.\n", bpp);
-screen=SDL_SetVideoMode(640, 480, bpp, SDL_HWSURFACE);
-.
-.Waits indefinitely for the next available event, returning -1, or 0 if there was -an error while waiting for events.
If event is not NULL, the next -event is removed from the queue and stored in that area.
The return code for the thread function is placed in the area pointed to by -status, if status is not -NULL.
SDL_WasInit allows you to see which SDL subsytems have been initialized. flags is a bitwise OR'd combination of the subsystems you wish to check (see SDL_Init for a list of subsystem flags).
/* Here are several ways you can use SDL_WasInit() */
-
-/* Get init data on all the subsystems */
-Uint32 subsystem_init;
-
-subsystem_init=SDL_WasInit(SDL_INIT_EVERYTHING);
-
-if(subsystem_init&SDL_INIT_VIDEO)
- printf("Video is initialized.\n");
-else
- printf("Video is not initialized.\n");
-
-
-
-/* Just check for one specfic subsystem */
-
-if(SDL_WasInit(SDL_INIT_VIDEO)!=0)
- printf("Video is initialized.\n");
-else
- printf("Video is not initialized.\n");
-
-
-
-
-/* Check for two subsystems */
-
-Uint32 subsystem_mask=SDL_INIT_VIDEO|SDL_INIT_AUDIO;
-
-if(SDL_WasInit(subsystem_mask)==subsystem_mask)
- printf("Video and Audio initialized.\n");
-else
- printf("Video and Audio not initialized.\n");
Grabbing means that the mouse is confined to the application window, -and nearly all keyboard input is passed directly to the application, -and not interpreted by a window manager, if any.
When mode is SDL_GRAB_QUERY the grab mode is not changed, but the current grab mode is returned.
typedef enum {
- SDL_GRAB_QUERY,
- SDL_GRAB_OFF,
- SDL_GRAB_ON
-} SDL_GrabMode;
- If the application is running in a window managed environment SDL attempts to iconify/minimise it. If SDL_WM_IconifyWindow is successful, the application will receive a SDL_APPACTIVE loss event.
Returns non-zero on success or 0 if iconification is not support or was refused by the window manager.
Sets the icon for the display window. Win32 icons must be 32x32.
This function must be called before the first call to -SDL_SetVideoMode.
The mask is a bitmask that describes the shape of the -icon. If mask is NULL, then the shape is determined by -the colorkey of icon, if any, or makes the icon -rectangular (no transparency) otherwise.
If mask is non-NULL, it points to a bitmap with bits set -where the corresponding pixel should be visible. The format of the bitmap is as -follows: Scanlines come in the usual top-down order. Each scanline consists of -(width / 8) bytes, rounded up. The most significant bit of each byte represents -the leftmost pixel.
Toggles the application between windowed and fullscreen mode, if supported. (X11 is the only target currently supported, BeOS support is experimental).
SDL provides functions for creating threads, mutexes, semphores and condition variables.
In general, you must be very aware of concurrency and data integrity issues -when writing multi-threaded programs. Some good guidelines include: -
Don't call SDL video/event functions from separate threads
Don't use any library functions in separate threads
Don't perform any memory management in separate threads
Lock global variables which may be accessed by multiple threads
Never terminate threads, always set a flag and wait for them to quit
Think very carefully about all possible ways your code may interact
Note: SDL's threading is not implemented on MacOS, due to that lack of preemptive thread support (Mac OS X dos nt suffer from this problem)
SDL provides several cross-platform functions for dealing with time. -It provides a way to get the current time, a way to wait a little while, -and a simple timer mechanism. These functions give you two ways of moving an -object every x milliseconds: - -
Use a timer callback function. This may have the bad effect that it runs in a seperate thread or uses alarm signals, but it's easier to implement.
Or you can get the number of milliseconds passed, and move the object if, for example, 30 ms passed.
SDL presents a very simple interface to the display framebuffer. The -framebuffer is represented as an offscreen surface to which you can write -directly. If you want the screen to show what you have written, call the update function which will -guarantee that the desired portion of the screen is updated.
Before you call any of the SDL video functions, you must first call -SDL_Init(SDL_INIT_VIDEO), which initializes the video -and events in the SDL library. Check the return code, which should be -0, to see if there were any errors in starting up.
If you use both sound and video in your application, you need to call -SDL_Init(SDL_INIT_AUDIO | SDL_INIT_VIDEO) before opening the -sound device, otherwise under Win32 DirectX, you won't be able to set -full-screen display modes.
After you have initialized the library, you can start up the video display in a -number of ways. The easiest way is to pick a common screen resolution and -depth and just initialize the video, checking for errors. You will probably -get what you want, but SDL may be emulating your requested mode and converting -the display on update. The best way is to -query, for the best -video mode closest to the desired one, and then -convert -your images to that pixel format.
SDL currently supports any bit depth >= 8 bits per pixel. 8 bpp formats are -considered 8-bit palettized modes, while 12, 15, 16, 24, and 32 bits per pixel -are considered "packed pixel" modes, meaning each pixel contains the RGB color -components packed in the bits of the pixel.
After you have initialized your video mode, you can take the surface that was -returned, and write to it like any other framebuffer, calling the update -routine as you go.
When you have finished your video access and are ready to quit your -application, you should call "SDL_Quit()" to shutdown the -video and events.
SDL provides a small set of window management functions which allow applications to change their title and toggle from windowed mode to fullscreen (if available)