components.md

Components

This class represent a single object on the screen, being a floating rectangle or a rotating sprite.

The base abstract class has the common expected methods update and render to be implemented.

The intermediate inheritance PositionComponent adds x, y, width, height and angle to your Components, as well as some useful methods like distance and angleBetween.

The most commonly used implementation, SpriteComponent, can be created with a Sprite:

    import 'package:flame/component.dart';

    Sprite sprite = new Sprite('player.png');

    const size = 128.0;
    var player = new SpriteComponent.fromSprite(size, size, sprite); // width, height, sprite
    
    // screen coordinates
    player.x = ... // 0 by default
    player.y = ... // 0 by default
    player.angle = ... // 0 by default
    
    player.render(canvas); // it will render only if the image is loaded and the x, y, width and height parameters are not null

Every Component has a few other methods that you can optionally implement, that are used by the BaseGame class. If you are not using the base game, you can alternatively use these methods on your own game loop.

The resize method is called whenever the screen is resized, and in the beginning once when the component is added via the add method. You need to apply here any changes to the x, y, width and height of your component, or any other changes, due to the screen resizing. You can start these variables here, as the sprite won't be rendered until everything is set.

The destroy method can be implemented to return true and warn the BaseGame that your object is marked for destruction, and it will be remove after the current update loop. It will then no longer be rendered or updated.

The isHUD method can be implemented to return true (default false) to make the BaseGame ignore the camera for this element.

There are also other implementations:

• The AnimationComponent takes an Animation object and renders a cyclic animated sprite (more details about Animations here)
• The ParallaxComponent can render a parallax background with several frames
• The Box2DComponent, that has a physics engine built-in (using the Box2D port for Dart)

Animation Component

This component uses an instance of the Animation class to represent a Component that has a sprite that runs a single cyclic animation.

This will create a simple three frame animation

    List<Sprite> sprites = [0, 1, 2].map((i) => new Sprite('player_${i}.png')).toList();
    this.player = new AnimationComponent(64.0, 64.0, new Animation.spriteList(sprites, stepTime: 0.01));

If you have a spritesheet, you can use the sequenced constructor, identical to the one provided by the Animation class (check more details in the appropriate section):

    this.player = new AnimationComponent.sequenced(64.0, 64.0, 'player.png', 2);

If you are not using BaseGame, don't forget this component needs to be update'd even if static, because the animation object needs to be ticked to move the frames.

Parallax Component

This Component can be sued to render pretty backgrounds, by drawing several transparent images on top of each other, each dislocated by a tiny amount.

The rationale is that when you look at the horizon and moving, closer objects seem to move faster than distant ones.

This component simulates this effect, making a very realistic background.

Create it like so:

    this.bg = new ParallaxComponent();
    this.bg.load([ 'bg/1.png', 'bg/2.png', 'bg/3.png' ]);

Then, render it as any other component.

Like the AnimationComponent, even if your parallax is static, you must call update on this component, so it runs its animation.

Box2D Component

Flame comes with a basic integration with the Flutter implementation of Box2D.

The whole concept of a box2d's World is mapped to the Box2DComponent component; every Body should be a BodyComponent, and added directly to the Box2DComponent, and not to the game list.

So you can have HUD and other non-physics-related components in your game list, and also as many Box2DComponents as you'd like (normally one, I guess), and then add your physical entities to your Components instance. When the Component is updated, it will use box2d physics engine to properly update every child.

You can see a more complete example of box2d usage on this WIP game made by @feroult (beware, though, it uses 0.6.x version of flame, but the Box2D related apis are unchanged).