cam.py

# Point-and-shoot camera for Raspberry Pi w/camera and Adafruit PiTFT.
# This must run as root (sudo python cam.py) due to framebuffer, etc.
#
# Adafruit invests time and resources providing this open source code, 
# please support Adafruit and open-source development by purchasing 
# products from Adafruit, thanks!
#
# http://www.adafruit.com/products/998  (Raspberry Pi Model B)
# http://www.adafruit.com/products/1367 (Raspberry Pi Camera Board)
# http://www.adafruit.com/products/1601 (PiTFT Mini Kit)
# This can also work with the Model A board and/or the Pi NoIR camera.
#
# Prerequisite tutorials: aside from the basic Raspbian setup and
# enabling the camera in raspi-config, you should configure WiFi (if
# using wireless with the Dropbox upload feature) and read these:
# PiTFT setup (the tactile switch buttons are not required for this
# project, but can be installed if you want them for other things):
# http://learn.adafruit.com/adafruit-pitft-28-inch-resistive-touchscreen-display-raspberry-pi
# Dropbox setup (if using the Dropbox upload feature):
# http://raspi.tv/2013/how-to-use-dropbox-with-raspberry-pi
#
# Written by Phil Burgess / Paint Your Dragon for Adafruit Industries.
# BSD license, all text above must be included in any redistribution.

import atexit
import cPickle as pickle
import errno
import fnmatch
import io
import os
import picamera
import pygame
import stat
import threading
import time
import yuv2rgb
from pygame.locals import *
from subprocess import call  
import smbus

# UI classes ---------------------------------------------------------------

# Small resistive touchscreen is best suited to simple tap interactions.
# Importing a big widget library seemed a bit overkill.  Instead, a couple
# of rudimentary classes are sufficient for the UI elements:

# Icon is a very simple bitmap class, just associates a name and a pygame
# image (PNG loaded from icons directory) for each.
# There isn't a globally-declared fixed list of Icons.  Instead, the list
# is populated at runtime from the contents of the 'icons' directory.

class Icon:

	def __init__(self, name):
	  self.name = name
	  try:
	    self.bitmap = pygame.image.load(iconPath + '/' + name + '.png')
	  except:
	    pass

# Button is a simple tappable screen region.  Each has:
#  - bounding rect ((X,Y,W,H) in pixels)
#  - optional background color and/or Icon (or None), always centered
#  - optional foreground Icon, always centered
#  - optional single callback function
#  - optional single value passed to callback
# Occasionally Buttons are used as a convenience for positioning Icons
# but the taps are ignored.  Stacking order is important; when Buttons
# overlap, lowest/first Button in list takes precedence when processing
# input, and highest/last Button is drawn atop prior Button(s).  This is
# used, for example, to center an Icon by creating a passive Button the
# width of the full screen, but with other buttons left or right that
# may take input precedence (e.g. the Effect labels & buttons).
# After Icons are loaded at runtime, a pass is made through the global
# buttons[] list to assign the Icon objects (from names) to each Button.

class Button:

	def __init__(self, rect, **kwargs):
	  self.rect     = rect # Bounds
	  self.color    = None # Background fill color, if any
	  self.iconBg   = None # Background Icon (atop color fill)
	  self.iconFg   = None # Foreground Icon (atop background)
	  self.bg       = None # Background Icon name
	  self.fg       = None # Foreground Icon name
	  self.callback = None # Callback function
	  self.value    = None # Value passed to callback
	  for key, value in kwargs.iteritems():
	    if   key == 'color': self.color    = value
	    elif key == 'bg'   : self.bg       = value
	    elif key == 'fg'   : self.fg       = value
	    elif key == 'cb'   : self.callback = value
	    elif key == 'value': self.value    = value

	def selected(self, pos):
	  x1 = self.rect[0]
	  y1 = self.rect[1]
	  x2 = x1 + self.rect[2] - 1
	  y2 = y1 + self.rect[3] - 1
	  if ((pos[0] >= x1) and (pos[0] <= x2) and
	      (pos[1] >= y1) and (pos[1] <= y2)):
	    if self.callback:
	      if self.value is None: self.callback()
	      else:                  self.callback(self.value)
	    return True
	  return False

	def draw(self, screen):
	  if self.color:
	    screen.fill(self.color, self.rect)
	  if self.iconBg:
	    screen.blit(self.iconBg.bitmap,
	      (self.rect[0]+(self.rect[2]-self.iconBg.bitmap.get_width())/2,
	       self.rect[1]+(self.rect[3]-self.iconBg.bitmap.get_height())/2))
	  if self.iconFg:
	    screen.blit(self.iconFg.bitmap,
	      (self.rect[0]+(self.rect[2]-self.iconFg.bitmap.get_width())/2,
	       self.rect[1]+(self.rect[3]-self.iconFg.bitmap.get_height())/2))

	def setBg(self, name):
	  if name is None:
	    self.iconBg = None
	  else:
	    for i in icons:
	      if name == i.name:
	        self.iconBg = i
	        break


# UI callbacks -------------------------------------------------------------
# These are defined before globals because they're referenced by items in
# the global buttons[] list.

def isoCallback(n): # Pass 1 (next ISO) or -1 (prev ISO)
	global isoMode
	setIsoMode((isoMode + n) % len(isoData))

def settingCallback(n): # Pass 1 (next setting) or -1 (prev setting)
	global screenMode
	screenMode += n
	if screenMode < 4:               screenMode = len(buttons) - 1
	elif screenMode >= len(buttons): screenMode = 4

def fxCallback(n): # Pass 1 (next effect) or -1 (prev effect)
	global fxMode
	setFxMode((fxMode + n) % len(fxData))

def quitCallback(): # Quit confirmation button
	saveSettings()
	raise SystemExit

def viewCallback(n): # Viewfinder buttons
	global loadIdx, scaled, screenMode, screenModePrior, settingMode, storeMode

	if n is 0:   # Gear icon (settings)
	  screenMode = settingMode # Switch to last settings mode
	elif n is 1: # Play icon (image playback)
	  if scaled: # Last photo is already memory-resident
	    loadIdx         = saveIdx
	    screenMode      =  0 # Image playback
	    screenModePrior = -1 # Force screen refresh
	  else:      # Load image
	    r = imgRange(pathData[storeMode])
	    if r: showImage(r[1]) # Show last image in directory
	    else: screenMode = 2  # No images
	else: # Rest of screen = shutter
	  takePicture()

def doneCallback(): # Exit settings
	global screenMode, settingMode
	if screenMode > 3:
	  settingMode = screenMode
	  saveSettings()
	screenMode = 3 # Switch back to viewfinder mode

def imageCallback(n): # Pass 1 (next image), -1 (prev image) or 0 (delete)
	global screenMode
	if n is 0:
	  screenMode = 1 # Delete confirmation
	else:
	  showNextImage(n)

def deleteCallback(n): # Delete confirmation
	global loadIdx, scaled, screenMode, storeMode
	screenMode      =  0
	screenModePrior = -1
	if n is True:
	  os.remove(pathData[storeMode] + '/IMG_' + '%04d' % loadIdx + '.JPG')
	  if(imgRange(pathData[storeMode])):
	    screen.fill(0)
	    pygame.display.update()
	    showNextImage(-1)
	  else: # Last image deleteted; go to 'no images' mode
	    screenMode = 2
	    scaled     = None
	    loadIdx    = -1

def storeModeCallback(n): # Radio buttons on storage settings screen
	global storeMode
	buttons[4][storeMode + 3].setBg('radio3-0')
	storeMode = n
	buttons[4][storeMode + 3].setBg('radio3-1')

def sizeModeCallback(n): # Radio buttons on size settings screen
	global sizeMode
	buttons[5][sizeMode + 3].setBg('radio3-0')
	sizeMode = n
	buttons[5][sizeMode + 3].setBg('radio3-1')
	camera.resolution = sizeData[sizeMode][1]
#	camera.crop       = sizeData[sizeMode][2]


# Global stuff -------------------------------------------------------------

screenMode      =  3      # Current screen mode; default = viewfinder
screenModePrior = -1      # Prior screen mode (for detecting changes)
settingMode     =  4      # Last-used settings mode (default = storage)
storeMode       =  0      # Storage mode; default = Photos folder
storeModePrior  = -1      # Prior storage mode (for detecting changes)
sizeMode        =  0      # Image size; default = Large
fxMode          =  0      # Image effect; default = Normal
isoMode         =  0      # ISO settingl default = Auto
iconPath        = 'icons' # Subdirectory containing UI bitmaps (PNG format)
saveIdx         = -1      # Image index for saving (-1 = none set yet)
loadIdx         = -1      # Image index for loading
scaled          = None    # pygame Surface w/last-loaded image

#Address for Batterymeter I2C
fuelAddress = 0x60

# To use Dropbox uploader, must have previously run the dropbox_uploader.sh
# script to set up the app key and such.  If this was done as the normal pi
# user, set upconfig to the .dropbox_uploader config file in that account's
# home directory.  Alternately, could run the setup script as root and
# delete the upconfig line below.
uploader        = '/home/pi/Dropbox-Uploader/dropbox_uploader.sh'
upconfig        = '/home/pi/.dropbox_uploader'

sizeData = [ # Camera parameters for different size settings
 # Full res      Viewfinder  Crop window
 [(2592, 1944), (320, 240), (0.0   , 0.0   , 1.0   , 1.0   )], # Large
 [(1920, 1080), (320, 180), (0.1296, 0.2222, 0.7408, 0.5556)], # Med
 [(1440, 1080), (320, 240), (0.2222, 0.2222, 0.5556, 0.5556)]] # Small

isoData = [ # Values for ISO settings [ISO value, indicator X position]
 [  0,  27], [100,  64], [200,  97], [320, 137],
 [400, 164], [500, 197], [640, 244], [800, 297]]

# A fixed list of image effects is used (rather than polling
# camera.IMAGE_EFFECTS) because the latter contains a few elements
# that aren't valid (at least in video_port mode) -- e.g. blackboard,
# whiteboard, posterize (but posterise, British spelling, is OK).
# Others have no visible effect (or might require setting add'l
# camera parameters for which there's no GUI yet) -- e.g. saturation,
# colorbalance, colorpoint.
fxData = [
  'none', 'sketch', 'gpen', 'pastel', 'watercolor', 'oilpaint', 'hatch',
  'negative', 'colorswap', 'posterise', 'denoise', 'blur', 'film',
  'washedout', 'emboss', 'cartoon', 'solarize' ]

pathData = [
  '/home/pi/Photos',     # Path for storeMode = 0 (Photos folder)
  '/boot/DCIM/CANON999', # Path for storeMode = 1 (Boot partition)
  '/home/pi/Photos']     # Path for storeMode = 2 (Dropbox)

icons = [] # This list gets populated at startup

# buttons[] is a list of lists; each top-level list element corresponds
# to one screen mode (e.g. viewfinder, image playback, storage settings),
# and each element within those lists corresponds to one UI button.
# There's a little bit of repetition (e.g. prev/next buttons are
# declared for each settings screen, rather than a single reusable
# set); trying to reuse those few elements just made for an ugly
# tangle of code elsewhere.

buttons = [
  # Screen mode 0 is photo playback
  [Button((  0,188,320, 52), bg='done' , cb=doneCallback),
   Button((  0,  0, 80, 52), bg='prev' , cb=imageCallback, value=-1),
   Button((240,  0, 80, 52), bg='next' , cb=imageCallback, value= 1),
   Button(( 88, 70,157,102)), # 'Working' label (when enabled)
   Button((148,129, 22, 22)), # Spinner (when enabled)
   Button((121,  0, 78, 52), bg='trash', cb=imageCallback, value= 0)],

  # Screen mode 1 is delete confirmation
  [Button((  0,35,320, 33), bg='delete'),
   Button(( 32,86,120,100), bg='yn', fg='yes',
    cb=deleteCallback, value=True),
   Button((168,86,120,100), bg='yn', fg='no',
    cb=deleteCallback, value=False)],

  # Screen mode 2 is 'No Images'
  [Button((0,  0,320,240), cb=doneCallback), # Full screen = button
   Button((0,188,320, 52), bg='done'),       # Fake 'Done' button
   Button((0, 53,320, 80), bg='empty')],     # 'Empty' message

  # Screen mode 3 is viewfinder / snapshot
  [Button((  0,188,156, 52), bg='gear', cb=viewCallback, value=0),
   Button((164,188,156, 52), bg='play', cb=viewCallback, value=1),
   Button((  0,  0,320,240)           , cb=viewCallback, value=2),
   Button(( 88, 51,157,102)),  # 'Working' label (when enabled)
   Button((148, 110,22, 22))], # Spinner (when enabled)

  # Remaining screens are settings modes

  # Screen mode 4 is storage settings
  [Button((  0,188,320, 52), bg='done', cb=doneCallback),
   Button((  0,  0, 80, 52), bg='prev', cb=settingCallback, value=-1),
   Button((240,  0, 80, 52), bg='next', cb=settingCallback, value= 1),
   Button((  2, 60,100,120), bg='radio3-1', fg='store-folder',
    cb=storeModeCallback, value=0),
   Button((110, 60,100,120), bg='radio3-0', fg='store-boot',
    cb=storeModeCallback, value=1),
   Button((218, 60,100,120), bg='radio3-0', fg='store-dropbox',
    cb=storeModeCallback, value=2),
   Button((  0, 10,320, 35), bg='storage')],

  # Screen mode 5 is size settings
  [Button((  0,188,320, 52), bg='done', cb=doneCallback),
   Button((  0,  0, 80, 52), bg='prev', cb=settingCallback, value=-1),
   Button((240,  0, 80, 52), bg='next', cb=settingCallback, value= 1),
   Button((  2, 60,100,120), bg='radio3-1', fg='size-l',
    cb=sizeModeCallback, value=0),
   Button((110, 60,100,120), bg='radio3-0', fg='size-m',
    cb=sizeModeCallback, value=1),
   Button((218, 60,100,120), bg='radio3-0', fg='size-s',
    cb=sizeModeCallback, value=2),
   Button((  0, 10,320, 29), bg='size')],

  # Screen mode 6 is graphic effect
  [Button((  0,188,320, 52), bg='done', cb=doneCallback),
   Button((  0,  0, 80, 52), bg='prev', cb=settingCallback, value=-1),
   Button((240,  0, 80, 52), bg='next', cb=settingCallback, value= 1),
   Button((  0, 70, 80, 52), bg='prev', cb=fxCallback     , value=-1),
   Button((240, 70, 80, 52), bg='next', cb=fxCallback     , value= 1),
   Button((  0, 67,320, 91), bg='fx-none'),
   Button((  0, 11,320, 29), bg='fx')],

  # Screen mode 7 is ISO
  [Button((  0,188,320, 52), bg='done', cb=doneCallback),
   Button((  0,  0, 80, 52), bg='prev', cb=settingCallback, value=-1),
   Button((240,  0, 80, 52), bg='next', cb=settingCallback, value= 1),
   Button((  0, 70, 80, 52), bg='prev', cb=isoCallback    , value=-1),
   Button((240, 70, 80, 52), bg='next', cb=isoCallback    , value= 1),
   Button((  0, 79,320, 33), bg='iso-0'),
   Button((  9,134,302, 26), bg='iso-bar'),
   Button(( 17,157, 21, 19), bg='iso-arrow'),
   Button((  0, 10,320, 29), bg='iso')],

  # Screen mode 8 is quit confirmation
  [Button((  0,188,320, 52), bg='done'   , cb=doneCallback),
   Button((  0,  0, 80, 52), bg='prev'   , cb=settingCallback, value=-1),
   Button((240,  0, 80, 52), bg='next'   , cb=settingCallback, value= 1),
   Button((110, 60,100,120), bg='quit-ok', cb=quitCallback),
   Button((  0, 10,320, 35), bg='quit')],

  # Screen mode 9 is Battery information 
  [Button((  0,188,320, 52), bg='done'   , cb=doneCallback),
   Button((  0,  0, 80, 52), bg='prev'   , cb=settingCallback, value=-1),
   Button((240,  0, 80, 52), bg='next'   , cb=settingCallback, value= 1),
   Button((110, 60,100,120), bg='battery-full'),
   Button((  0, 10,320, 35), bg='quit')]
]


# Assorted utility functions -----------------------------------------------

def setFxMode(n):
	global fxMode
	fxMode = n
	camera.image_effect = fxData[fxMode]
	buttons[6][5].setBg('fx-' + fxData[fxMode])

def setIsoMode(n):
	global isoMode
	isoMode    = n
	camera.ISO = isoData[isoMode][0]
	buttons[7][5].setBg('iso-' + str(isoData[isoMode][0]))
	buttons[7][7].rect = ((isoData[isoMode][1] - 10,) +
	  buttons[7][7].rect[1:])

def saveSettings():
	try:
	  outfile = open('cam.pkl', 'wb')
	  # Use a dictionary (rather than pickling 'raw' values) so
	  # the number & order of things can change without breaking.
	  d = { 'fx'    : fxMode,
	        'iso'   : isoMode,
	        'size'  : sizeMode,
	        'store' : storeMode }
	  pickle.dump(d, outfile)
	  outfile.close()
	except:
	  pass

def loadSettings():
	try:
	  infile = open('cam.pkl', 'rb')
	  d      = pickle.load(infile)
	  infile.close()
	  if 'fx'    in d: setFxMode(   d['fx'])
	  if 'iso'   in d: setIsoMode(  d['iso'])
	  if 'size'  in d: sizeModeCallback( d['size'])
	  if 'store' in d: storeModeCallback(d['store'])
	except:
	  pass

# Scan files in a directory, locating JPEGs with names matching the
# software's convention (IMG_XXXX.JPG), returning a tuple with the
# lowest and highest indices (or None if no matching files).
def imgRange(path):
	min = 9999
	max = 0
	try:
	  for file in os.listdir(path):
	    if fnmatch.fnmatch(file, 'IMG_[0-9][0-9][0-9][0-9].JPG'):
	      i = int(file[4:8])
	      if(i < min): min = i
	      if(i > max): max = i
	finally:
	  return None if min > max else (min, max)

# Busy indicator.  To use, run in separate thread, set global 'busy'
# to False when done.
def spinner():
	global busy, screenMode, screenModePrior

	buttons[screenMode][3].setBg('working')
	buttons[screenMode][3].draw(screen)
	pygame.display.update()

	busy = True
	n    = 0
	while busy is True:
	  buttons[screenMode][4].setBg('work-' + str(n))
	  buttons[screenMode][4].draw(screen)
	  pygame.display.update()
	  n = (n + 1) % 5
	  time.sleep(0.15)

	buttons[screenMode][3].setBg(None)
	buttons[screenMode][4].setBg(None)
	screenModePrior = -1 # Force refresh

def takePicture():
	global busy, gid, loadIdx, saveIdx, scaled, sizeMode, storeMode, storeModePrior, uid

	if not os.path.isdir(pathData[storeMode]):
	  try:
	    os.makedirs(pathData[storeMode])
	    # Set new directory ownership to pi user, mode to 755
	    os.chown(pathData[storeMode], uid, gid)
	    os.chmod(pathData[storeMode],
	      stat.S_IRUSR | stat.S_IWUSR | stat.S_IXUSR |
	      stat.S_IRGRP | stat.S_IXGRP |
	      stat.S_IROTH | stat.S_IXOTH)
	  except OSError as e:
	    # errno = 2 if can't create folder
	    print errno.errorcode[e.errno]
	    return

	# If this is the first time accessing this directory,
	# scan for the max image index, start at next pos.
	if storeMode != storeModePrior:
	  r = imgRange(pathData[storeMode])
	  if r is None:
	    saveIdx = 1
	  else:
	    saveIdx = r[1] + 1
	    if saveIdx > 9999: saveIdx = 0
	  storeModePrior = storeMode

	# Scan for next available image slot
	while True:
	  filename = pathData[storeMode] + '/IMG_' + '%04d' % saveIdx + '.JPG'
	  if not os.path.isfile(filename): break
	  saveIdx += 1
	  if saveIdx > 9999: saveIdx = 0

	t = threading.Thread(target=spinner)
	t.start()

	scaled = None
	camera.resolution = sizeData[sizeMode][0]
	camera.crop       = sizeData[sizeMode][2]
	try:
	  camera.capture(filename, use_video_port=False, format='jpeg',
	    thumbnail=None)
	  # Set image file ownership to pi user, mode to 644
	  # os.chown(filename, uid, gid) # Not working, why?
	  os.chmod(filename,
	    stat.S_IRUSR | stat.S_IWUSR | stat.S_IRGRP | stat.S_IROTH)
	  img    = pygame.image.load(filename)
	  scaled = pygame.transform.scale(img, sizeData[sizeMode][1])
	  if storeMode == 2: # Dropbox
	    if upconfig:
	      cmd = uploader + ' -f ' + upconfig + ' upload ' + filename + ' Photos'
	    else:
	      cmd = uploader + ' upload ' + filename + ' Photos'
	    call ([cmd], shell=True)

	finally:
	  # Add error handling/indicator (disk full, etc.)
	  camera.resolution = sizeData[sizeMode][1]
	  camera.crop       = (0.0, 0.0, 1.0, 1.0)

	busy = False
	t.join()

	if scaled:
	  if scaled.get_height() < 240: # Letterbox
	    screen.fill(0)
	  screen.blit(scaled,
	    ((320 - scaled.get_width() ) / 2,
	     (240 - scaled.get_height()) / 2))
	  pygame.display.update()
	  time.sleep(2.5)
	  loadIdx = saveIdx

def showNextImage(direction):
	global busy, loadIdx

	t = threading.Thread(target=spinner)
	t.start()

	n = loadIdx
	while True:
	  n += direction
	  if(n > 9999): n = 0
	  elif(n < 0):  n = 9999
	  if os.path.exists(pathData[storeMode]+'/IMG_'+'%04d'%n+'.JPG'):
	    showImage(n)
	    break

	busy = False
	t.join()

def showImage(n):
	global busy, loadIdx, scaled, screenMode, screenModePrior, sizeMode, storeMode

	t = threading.Thread(target=spinner)
	t.start()

	img      = pygame.image.load(
	            pathData[storeMode] + '/IMG_' + '%04d' % n + '.JPG')
	scaled   = pygame.transform.scale(img, sizeData[sizeMode][1])
	loadIdx  = n

	busy = False
	t.join()

	screenMode      =  0 # Photo playback
	screenModePrior = -1 # Force screen refresh

# Functions for displaying battery information. 

#Define SMBus for I2C communication. 
bus = smbus.SMBus(0)

#Functions for Fuel I2C
POWER_ON_RESET = 0x54
SOC = 0x04
QUICK_START = 0x40

#Send command to Fuel
def fuelPerformCommand(command, value):
    global fuelAddress, bus
    bus.write_byte_data(fuelAddress, command, value)

#Setup and reset fuel meter
def setupFuelMeter():
    fuelPerformCommand(POWER_ON_RESET, 0x00)
    fuelPerformCommand(QUICK_START, 0x00)

def readBatteryLevel():
    global fuelAddress, bus
    percentage = 0
    return percentage

def updateBatteryMeter():
    level = readBatteryLevel()
    if(level > 80):
	    buttons[9][3].setBg('battery-full')
    elif(level > 60):
	    buttons[9][3].setBg('battery-80')
    elif(level > 40):
	    buttons[9][3].setBg('battery-60')
    elif(level > 20):
	    buttons[9][3].setBg('battery-40')
    else:
	    buttons[9][3].setBg('battery-20')


# Initialization -----------------------------------------------------------

# Init framebuffer/touchscreen environment variables
os.putenv('SDL_VIDEODRIVER', 'fbcon')
os.putenv('SDL_FBDEV'      , '/dev/fb1')
os.putenv('SDL_MOUSEDRV'   , 'TSLIB')
os.putenv('SDL_MOUSEDEV'   , '/dev/input/touchscreen')

# Get user & group IDs for file & folder creation
# (Want these to be 'pi' or other user, not root)
s = os.getenv("SUDO_UID")
uid = int(s) if s else os.getuid()
s = os.getenv("SUDO_GID")
gid = int(s) if s else os.getgid()

# Buffers for viewfinder data
rgb = bytearray(320 * 240 * 3)
yuv = bytearray(320 * 240 * 3 / 2)

# Init pygame and screen
pygame.init()
pygame.mouse.set_visible(False)
screen = pygame.display.set_mode((0,0), pygame.FULLSCREEN)

# Init camera and set up default values
camera            = picamera.PiCamera()
atexit.register(camera.close)
camera.resolution = sizeData[sizeMode][1]
#camera.crop       = sizeData[sizeMode][2]
camera.crop       = (0.0, 0.0, 1.0, 1.0)
# Leave raw format at default YUV, don't touch, don't set to RGB!

# Load all icons at startup.
for file in os.listdir(iconPath):
  if fnmatch.fnmatch(file, '*.png'):
    icons.append(Icon(file.split('.')[0]))

# Assign Icons to Buttons, now that they're loaded
for s in buttons:        # For each screenful of buttons...
  for b in s:            #  For each button on screen...
    for i in icons:      #   For each icon...
      if b.bg == i.name: #    Compare names; match?
        b.iconBg = i     #     Assign Icon to Button
        b.bg     = None  #     Name no longer used; allow garbage collection
      if b.fg == i.name:
        b.iconFg = i
        b.fg     = None

loadSettings() # Must come last; fiddles with Button/Icon states

setupFuelMeter() # Initalise Fuel Meter PCB

# Main loop ----------------------------------------------------------------

while(True):

  # Process touchscreen input
  while True:
    for event in pygame.event.get():
      if(event.type is MOUSEBUTTONDOWN):
        pos = pygame.mouse.get_pos()
        for b in buttons[screenMode]:
          if b.selected(pos): break
    # If in viewfinder or settings modes, stop processing touchscreen
    # and refresh the display to show the live preview.  In other modes
    # (image playback, etc.), stop and refresh the screen only when
    # screenMode changes.
    if screenMode >= 3 or screenMode != screenModePrior: break

  # Refresh display
  if screenMode >= 3: # Viewfinder or settings modes
    stream = io.BytesIO() # Capture into in-memory stream
    camera.capture(stream, use_video_port=True, format='raw')
    stream.seek(0)
    stream.readinto(yuv)  # stream -> YUV buffer
    stream.close()
    yuv2rgb.convert(yuv, rgb, sizeData[sizeMode][1][0],
      sizeData[sizeMode][1][1])
    img = pygame.image.frombuffer(rgb[0:
      (sizeData[sizeMode][1][0] * sizeData[sizeMode][1][1] * 3)],
      sizeData[sizeMode][1], 'RGB')
    if screenMode == 9: 
        updateBatteryMeter() 
  elif screenMode < 2: # Playback mode or delete confirmation
    img = scaled       # Show last-loaded image
  else:                # 'No Photos' mode
    img = None         # You get nothing, good day sir

  if img is None or img.get_height() < 240: # Letterbox, clear background
    screen.fill(0)
  if img:
    screen.blit(img,
      ((320 - img.get_width() ) / 2,
       (240 - img.get_height()) / 2))

  # Overlay buttons on display and update
  for i,b in enumerate(buttons[screenMode]):
    b.draw(screen)
  pygame.display.update()

  screenModePrior = screenMode