Sine and cosine functions applied to the brightness of a grid of blocks. Play around with the sliders, and then play around with the code inside if you like :)
Credit to @papipupepappa for the source project. I just moved the trig functions out of the draw loop to increase performance and made row/column selection automatic based on block size to exactly fill the screen. I also added a "graphic" block to the main forever loop to stabilize the rotation speed to "speed" x 30 deg./sec (at 30 fps).
