Devlog: simulating ash depth without simulating ash

Ashfall Drift needs the road surface to feel like it deforms under the car. A real deformable terrain system was never going to fit our performance target, so we built something that is wrong in ways players do not notice.

The cheat

Ash depth is a single channel in a low-resolution texture painted along the road spline. The car samples it at four points and the value feeds grip, particle density and audio. Nothing moves; the surface is static geometry with a scrolling normal offset.

• One 256×64 depth strip per road segment
• Four sample points per vehicle, not per wheel
• Grip, particles and audio all read the same channel
• No physics write-back, so no allocation per frame

Where it breaks

Two cars crossing the same patch do not affect each other, and a long drift does not leave a persistent trough. We tried persistent troughs for six weeks. They looked better in screenshots and made the game harder to read in motion, so they are gone.

If the honest version of a system makes the game less legible, the honest version is the wrong system.

[ENGINEER NAME], Technical Director

Null Harbor reuses the same channel trick for tidal wetness, which is the only reason that game has a water line at all.