Introduction to screen space ambient occlusion in URP

The Screen Space Ambient Occlusion effect darkens creases, holes, intersections and surfaces that are close to each other in real-time. In the real world, such areas tend to block out or occlude ambient light, so they appear darker.

URP implements the Screen Space Ambient Occlusion (SSAO) effect as a Renderer Feature. It works with every shader that the Universal Render Pipeline (URP) provides as well as any custom opaque Shader Graphs you create.

Note: The SSAO effect is a Renderer Feature and works independently from the post-processing effects in URP. This effect does not depend on or interact with Volumes.

The following images show a scene with the Ambient Occlusion effect turned off, on, and only the Ambient Occlusion texture.

Implementation details

The SSAO Renderer Feature uses normal vectors for calculating how exposed each point on a surface is to ambient lighting.

URP 10.0 implements the DepthNormals Pass block that generates the the normal texture _CameraNormalsTexture for the current frame. By default, the SSAO Renderer Feature uses this texture to calculate Ambient Occlusion values.

If you implement your custom SRP and if you do not want to implement the DepthNormals Pass block in your shaders, you can use the SSAO Renderer Feature and set its Source property to Depth. In this case, Unity does not use the DepthNormals Pass to generate the normal vectors, it reconstructs the normal vectors using the depth texture instead.

Selecting the option Depth in the Source property enables the Normal Quality property. The options in this property (Low, Medium, and High) determine the number of samples of the depth texture that Unity takes when reconstructing the normal vector from the depth texture. The number of samples per quality level: Low: 1, Medium: 5, High: 9.