def flipAlongDiagonal():
  # Set up the source and target pictures
  file = pickAFile()
  pict = makePicture(file)
  wid = getWidth (pict)
  hgt = getHeight (pict)
  canvas = makeEmptyPicture(hgt, wid)
  # Now, do the actual copying--swap X & Y!
  targetX = 1
  for sourceX in range(1,getWidth(pict)):
    targetY = 1
    for sourceY in range(1,getHeight(pict)):
      color = getColor(getPixel(pict,sourceX,sourceY))
      setColor(getPixel(canvas, targetY, targetX), color)
      targetY = targetY + 1
    targetX = targetX + 1
  show(pict)
  show(canvas)
  return canvas


def rotate90():
  # Set up the source and target pictures
  file = pickAFile()
  pict = makePicture(file)
  wid = getWidth (pict)
  hgt = getHeight (pict)
  canvas = makeEmptyPicture(hgt, wid)
  # Now, do the actual copying--swap X & Y!
  targetX = 1
  for sourceX in range(1,getWidth(pict)):
    targetY = 1
    for sourceY in range(1,getHeight(pict)):
      color = getColor(getPixel(pict,sourceX,sourceY))
      setColor(getPixel(canvas, targetY, wid - targetX), color)
      targetY = targetY + 1
    targetX = targetX + 1
  show(pict)
  show(canvas)
  return canvas