What is Ambient occlusion?
Ambient occlusion (AO) approximates how much ambient light reaches each point on a surface, darkening creases, corners and contact points to add depth.
In real life, the inside of a crease or the gap under a sofa is darker than an open surface, because less light from the surroundings reaches it. Ambient occlusion reproduces that effect. It's one of the cheapest ways to make a render look grounded.
Two kinds of AO
- Baked AO maps are stored as a texture. In glTF they usually share the "ORM" texture with roughness and metalness. They're free at runtime but only cover the object's own creases.
- Screen-space AO (SSAO) is computed every frame from the depth buffer, so it also shadows the contact between separate objects, like a cup on a table. It costs some performance.
Don't overdo it
Heavy AO makes everything look dirty. Use a subtle amount so creases read without turning black. Also make sure AO isn't painted into the base colour texture as well, or you'll get double shadows.
Related: PBR materials and texture baking.
Written with AI assistance and reviewed by the Renderlyst team. Corrections welcome at alishbakhalid766@gmail.com.