In Unity a Camera can generate a depth or depth+normals texture. This is a minimalistic G-buffer texture that can be used for post-processing effects or to implement custom lighting models (e.g. light pre-pass). It is also possible to build similar textures yourself, using Shader Replacement feature.
Camera’s depth texture can be turned on using Camera.depthTextureMode variable from script.
There are two possible depth texture modes:
This builds a screen-sized depth texture.
Depth texture is rendered using the same shader passes as used for shadow caster rendering (“ShadowCaster” pass type). So by extension, if a shader does not support shadow casting (i.e. there’s no shadow caster pass in the shader or any of the fallbacks), then objects using that shader will not show up in the depth texture.
Note that only “opaque” objects (that which have their materials and shaders setup to use render queue <= 2500) are rendered into the depth texture.
This builds a screen-sized 32 bit (8 bit/channel) texture, where view space normals are encoded into R&G channels, and depth is encoded in B&A channels. Normals are encoded using Stereographic projection, and depth is 16 bit value packed into two 8 bit channels.
UnityCG.cginc include file has a helper function DecodeDepthNormal to decode depth and normal from the encoded pixel value. Returned depth is in 0..1 range.
For examples on how to use the depth and normals texture, please refer to the EdgeDetection image effect in the Shader Replacement example project or Screen Space Ambient Occlusion Image Effect.
Camera inspector indicates when a camera is rendering a depth or a depth+normals texture.
The way that depth textures are requested from the camera (Camera.depthTextureMode) might mean that after you disable some effect that needed them, the camera might still continue rendering them. Particularly with multiple effects present on a camera, where each of them needs a depth texture, there’s no good way to automatically “disable” depth texture rendering if you disable the individual effects.
When implementing complex shaders or Image Effects, keep Rendering Differences Between Platforms in mind. In particular, using depth texture in an Image Effect often needs special handling on Direct3D + Anti-Aliasing.
In some cases, the depth texture might come directly from the native Z buffer. If you see artifacts in your depth texture, make sure that the shaders that use it do not write into the Z buffer (use ZWrite Off).
Depth textures can come directly from the actual depth buffer, or be rendered in a separate pass, depending on the rendering path used and the hardware. Typically when using Deferred Shading or Legacy Deferred Lighting rendering paths, the depth textures come “for free” since they are a product of the G-buffer rendering anyway.
When the DepthNormals texture is rendered in a separate pass, this is done through Shader Replacement. Hence it is important to have correct “RenderType” tag in your shaders.