This is the engine itself: the same field behind every page here, taking orders from you instead of from the page.
A grid of fourteen-pixel cells, a heat buffer that decays on its own, and stamps that write heat into it. Density sets how many cells survive inside a cloud. The seed redraws the clouds without touching the mechanics.
The figure needs a mouse: move the pointer below and the cursor becomes that shape. A touch screen has no pointer, so nothing happens there.
Controls
How many cells survive inside a cloud.
Seed
7.31
Figure
The shape the cursor turns into inside this area.