🌬️ Magic Sand & Smoke

Each grain first tries to fall straight down; if that cell is blocked it tries to slide diagonally into an empty space below. Repeated across many grains, this produces the angled piles and slopes you see in real granular materials.

Water also falls down, but when it cannot it spreads sideways into adjacent empty cells instead of only sliding diagonally. This lets it flow across surfaces and settle into a flat level, just like a real liquid.

Smoke cells move upward each tick with a little random sideways drift, because in reality hot smoke is less dense than the surrounding air. Cells also have a small chance to vanish each step and are cleared at the top, so the plume dissipates.

Fire cells rise, carry a decaying life value that eventually burns out, and randomly spawn smoke as they go. Water touching a flame extinguishes it. This produces short flickering flames topped by a trailing puff of smoke.

Scanning from the bottom upward, and flagging every cell that has already moved, ensures a grain cannot move several rows in a single step and that no two grains land in the same cell — giving stable, believable falling behaviour.

Beyond fun sandboxes, the same grid-based rules model granular flow in silos and avalanches, generate smoke and fluid effects in video games, and serve as teaching tools for emergence and complexity.

The genre was popularised by the 2005 Java applet "Hell of Sand" and later inspired the acclaimed 2020 game Noita, in which every pixel of the world is individually simulated.