Image provided by: PeterPeter has sent me an email to let us know about his recent GBA Techdemo”Deformer”. Here is a description of it:

This demo uses mode 4. The principle how the effect works is pretty easy. You just have to do it once. OK. You have a texture, in this case I used a 256×256 pixels bitmap, plus a displacement map. The displacement map contains relative positions from which”coordinate”to take a pixel from the source texture. Draw the texture using the displacement map. Don’t directly use the xy coordinates to place pixels. Then just move the displacement map on the texture around to achieve the animation and never clear the framebuffer. The”tricky”part is to generate a good looking displacement map, hint: cos/sin 😉 Tested with no$gba and on hardware.

http://www.console-dev.de/demos/index.html