# Copy a little picture onto a background picture at x,y
# But only copy those parts of the little picture that are within the
# bounds of the background picture
def copyPicture(littlePic, bg, x, y):
  for fromX in range(1, getWidth(littlePic)):
    for fromY in range(1, getHeight(littlePic)):

      # Work out where the current pixel should be copied to
      fromPixel = getPixel(littlePic, fromX, fromY)
      destX = fromX + x
      destY = fromY + y
 
      # And copy it if it is within bounds.
      # This uses logical (true/false) variables as discussed in class
      betweenLeftAndRight = 0 < destX <= getWidth(bg)
      betweenTopAndBottom = 0 < destY <= getHeight(bg)
      if betweenLeftAndRight and betweenTopAndBottom:
        destPixel = getPixel(bg, destX, destY)
        setColor(destPixel, getColor(fromPixel)) 

# Write a frame to a file using the standard naming convention.
# We can write up to 999 frames prepending leading 0 or 00
def writeFrame(frame, stem, num):
  numText = str(num)
  if num < 100:
    numText = "0" + numText # Pre-pend leading zero
  if num < 10:
    numText = "0" + numText # Pre-pend an additional leading zero
  fileName = stem + numText
  fileName = fileName + ".jpg"
  writePictureTo(frame, getMediaPath(fileName))

# Make a list of sprites (pictures) from sequence of named files
# Note: This only works for 12 (count them) files called john_cleese_N.png
# Where N is a number between 1 and 12, inclusive. 
# Those files have to be in the media path.
def makeSprites():
  sprites = [] # Start with an empty list

  # Make each sprite in turn and add it to the list
  for spriteNum in range(1, 13): # note that runs from 1 to 12 really
    currentFile = "john_cleese_" + str(spriteNum) + ".png"
    currentSprite = makePicture(getMediaPath(currentFile))
    sprites = sprites + [currentSprite] # concatenate a 1-element list, not a picture
  return sprites

# Make the Silly Walk video
def makeSillyWalk():
  numFrames = 100
  width = 640
  height = 480

  # Variables for the cleese sprites
  speed = 4
  cleeses = makeSprites()

  # Variables for the falling weight
  weight = makePicture(getMediaPath("weight.gif"))
  dropTime = 90
  weightX = width - getWidth(weight) - 100
  startingY = -getHeight(weight)
  distanceFallen = height
  timeToFall = (numFrames - dropTime)
  fallingRate = distanceFallen/timeToFall

  # And now for something completely different: the loop that produces the frames
  for frameNum in range(numFrames):
    printNow("Processing frame number " + str(frameNum) + " out of " + str(numFrames))

    frame = makeEmptyPicture(width, height)

    # Find current sprite, cycling through the sprite list
    currentSprite = cleeses[frameNum % len(cleeses)]

    # Calculate x and y and copy sprite there
    x = frameNum * speed
    y = getHeight(frame) - getHeight(currentSprite)
    copyPicture(currentSprite, frame, x, y)

    # Drop the weight, but only if it is time
    if frameNum >= dropTime:
      weightY = startingY + fallingRate * (frameNum - dropTime)
      copyPicture(weight, frame, weightX, weightY)
      
    # Write frame to file
    writeFrame(frame, "sillyWalk", frameNum)