This script alternately "flips" and "flops" between two images, with adjustable smoothness, speed and pauses. It may be useful as an alternative to a crossfade, where you want to create movement to attract attention, or where you want to show two images with equal prominence that don't necessarily look well together (I wrote it to show two dissimilar corporate logos). Small images are less taxing on system resources and will appear smoother in operation.

It is important that:

1. The two images are square and of the same size, and
2. The difference between wdmax (maximum width of square image) and wdmin (minimum thickness edge-on image) is an exact multiple of inc (the step change); otherwise the image will flip once and disappear.

If only requiring movement in one direction, set the "ff" variable to it, and delete or change the subsequent resetting of this variable accordingly.