#returns copy of picture rotated 90 degrees
def rotate(pic):
  w=getWidth(pic)
  h=getHeight(pic)
  pic2=makeEmptyPicture(h,w)
  for px in getPixels(pic):
    x=getX(px)
    y=getY(px)
    sourcepx=getPixel(pic2,h-y+1 ,x )
    c=getColor(px)
    setColor(sourcepx,c)
  return pic2
    


#the demo selects a picture, displays several
#successive reductions, and then several successive
#enlargements.    
def rotate_demo():
  p=makePicture(pickAFile())
  show(p)
  p=rotate(p)
  show(p)