Plasma
The demo effect above all others. Waves of sine fields melt into psychedelic color that never repeats, with four palettes and a ripple on every click.
If the demo scene has one sacred effect, this is it. Four fields of sine waves overlap and interfere, and out of the interference comes an endless slow storm of color that folds into itself and never repeats. The palette cycles on top of the motion, so even the colors are always on their way somewhere else. It is computed the way the classics did it, with precalculated distance maps and a sine lookup table, not a single trig call per pixel, rendered in fat retro pixels. The buttons switch between four moods, neon, lava, ocean and vapor. Click anywhere in the field and a disturbance ripples out from your fingertip, bending the plasma into rings before it heals itself.