moveR (xc,yc) r =
  \(x,y) -> r (x-xc, y-yc)

frac x = x - floor x

stripes width size x =
  frac ((x-width/2)/width) < size

getPicture str =
  let im <- image str
      zoom <- slider "Scale" (0.1, 10) 1
      moveX <- slider "X motion" (-200, 200) 0
      moveY <- slider "Y motion" (-200, 200) 0
      rot   <- slider "Rotation" (-pi, pi) 0
  in translate (moveX, moveY) $ rotate rot $ uscale zoom im

fadeImage f =
  let t <- timer "Time" 1 true
      (im1x, im1y, im1) <- sizedImageD  "First image" "guineapig.jpg"
      (im2x, im2y, im2) <- sizedImageD  "Second image" "bob.jpg"
      im1m = max im1x im1y
      im2m = max im2x im2y
      im1s = translate (-1, -1) $ uscale (2/im1m) im1
      im2s = translate (-1, -1) $ uscale (2/im2m) im2
    in zoomIn 100 (f im1s im2s t)

fadeRegion r = fadeImage (\im1 im2 t -> 
                            \p -> if r t p then im1 p else im2 p)

interpolateN t n1 n2 = (1-t)*n1 + t*n2

interpolateP t (x1, y1) (x2, y2) = (interpolateN t x1 x2, interpolateN t y1 y2)

-- interpolateC is already there!