I found this optical illusion in this tweet:
The Stepping-Feet Illusion. The two rectangles appear to be moving alternately, like a pair of stepping feet – but they’re not; they're moving together at the same constant speed. Don't believe me? Watch how the illusion disappears when the stripes fade to grey… pic.twitter.com/L9NqSq7vus
— Steve Stewart-Williams (@SteveStuWill) February 7, 2020
Ten minutes later, the GeeXLab demo was coded. It’s a very simple demo: a color shader and two quads (one for the stripes and one for the feet).
The demo is available in the OpenGL 2.1 demopack in the following folder:
Load the main.xml file into GeeXLab (drag and drop is the fastest way) and that’s all.
I didn’t test, but this demo should run on all platforms (Linux, macOS and Raspberry Pi).