Flow Map
Texture that tells a surface which way to flow
Also known as: Flowmap · Flow map shader · Water flow map · Lava flow map · Flow map painting
Definition
A flow map is a texture that stores a direction in its red and green channels, used to move another texture along that direction over time. It lets water run around rocks, lava creep downhill, smoke swirl and cloth-like effects follow a shape, with the direction painted or generated by a tool instead of being one constant scroll. The shader blends two offset samples in a repeating cycle to avoid stretching, and gives the flowing motion without simulation.
In production
Paint flow maps in tools such as Substance Designer or a dedicated flow map painter, or generate them from a height map. Use a tileable color texture to flow, and keep the flow strength moderate to avoid visible resets. Many stylized and realistic water and lava materials use them. Because they are cheap, they are a good alternative to real fluid simulation in games.
