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Unity Engine

Surface Shaders and rendering paths in the Built-In Render Pipeline

Understand how the rendering path affects how Unity applies lighting, and which passes Unity uses.
Read time 2 minutesLast updated 21 days ago
Important
The Built-In Render Pipeline is deprecated and will be made obsolete in a future release.
It remains supported, including bug fixes and maintenance, through the full Unity 6.7 LTS lifecycle.
For more information on migration, refer to Migrating from the Built-In Render Pipeline to the Universal Render Pipeline and Render pipeline feature comparison.
In the Built-in Render Pipeline, when using a Surface Shader, how lighting is applied and which Passes of the shader are used depends on which rendering path is used. Each pass in a shader communicates its lighting type via Pass Tags.

Render pipeline compatibility

Feature name

Universal Render Pipeline (URP)

High Definition Render Pipeline (HDRP)

Custom SRP

Built-in Render Pipeline

Surface ShadersNo

For a streamlined way of creating Shader objects in URP, see Shader Graph.		No

For a streamlined way of creating Shader objects in HDRP, see Shader Graph.		NoYes

Rendering paths

Forward Rendering path

ForwardBase
pass renders ambient, lightmaps, main directional light and not important (vertex/SH) lights at once. 
ForwardAdd
pass is used for any additive per-pixel lights; one invocation per object illuminated by such light is done. See Forward Rendering for details.
If forward rendering is used, but a shader does not have forward-suitable passes (i.e. neither 
ForwardBase
nor 
ForwardAdd
pass types are present), then that object is rendered just like it would in Vertex Lit path, see below.

Deferred Shading path

Deferred
pass renders all information needed for lighting (in built-in shaders: diffuse color, specular color, smoothness, world space normal, emission). It also adds lightmaps, reflection probes and ambient lighting into the emission channel. See Deferred Shading for details.

Legacy Vertex Lit Rendering path

Since vertex lighting is most often used on platforms that do not support programmable shaders, Unity can't create multiple shader variants internally to handle lightmapped vs. non-lightmapped cases. So to handle lightmapped and non-lightmapped objects, multiple passes have to be written explicitly.
  • Vertex
    pass is used for non-lightmapped objects. All lights are rendered at once, using a fixed function OpenGL/Direct3D lighting model (Blinn-Phong)
  • VertexLMRGBM
    pass is used for lightmapped objects, when lightmaps are RGBM encoded (PC and consoles). No real-time lighting is applied; pass is expected to combine textures with a lightmap.
  • VertexLM
    pass is used for lightmapped objects, when lightmaps are double-LDR encoded (mobile platforms). No real-time lighting is applied; pass is expected to combine textures with a lightmap.