Sturdy Powder

Mud is an example of a sturdy powder.

Sturdy Powder is a behavior similar to Powder. It behaves just like powder, but elements fall straight down without being able to slide down slopes. This leads to structures with Sturdy Powder pixels forming more stable structures instead of dunes, piles or hills. An example of a sturdy powder is Mud.

Technical

The STURDYPOWDER behavior in Sandboxels' source code is described as a behavior grid:

STURDYPOWDER: [
  "XX|XX|XX",
  "XX|XX|XX",
  "XX|M1|XX",
],