Surface Shaders and rendering paths

In the Built-in Render PipelineA series of operations that take the contents of a Scene, and displays them on a screen. Unity lets you choose from pre-built render pipelines, or write your own. More info
See in Glossary, when using a Surface ShaderA program that runs on the GPU. More info
See in Glossary, how lighting is applied and which Passes of the shader are used depends on which rendering pathThe technique that a render pipeline uses to render graphics. Choosing a different rendering path affects how lighting and shading are calculated. Some rendering paths are more suited to different platforms and hardware than others. More info
See in Glossary is used. Each pass in a shader communicates its lighting type via Pass Tags.

Render pipeline compatibility

Rendering paths

• In Forward RenderingA rendering path that renders each object in one or more passes, depending on lights that affect the object. Lights themselves are also treated differently by Forward Rendering, depending on their settings and intensity. More info
  See in Glossary
  , ForwardBase and ForwardAdd passes are used.
• In Deferred ShadingA rendering path in the Built-in Render Pipeline that places no limit on the number of Lights that can affect a GameObject. All Lights are evaluated per-pixel, which means that they all interact correctly with normal maps and so on. Additionally, all Lights can have cookies and shadows. More info
  See in Glossary
  , Deferred pass is used.
• In legacy Vertex Lit, Vertex, VertexLMRGBM and VertexLM passes are used.
• In any of the above, to render ShadowsA UI component that adds a simple outline effect to graphic components such as Text or Image. It must be on the same GameObject as the graphic component. More info
  See in Glossary
  or a depth texture, ShadowCaster pass is used.

Forward Rendering path

ForwardBase pass renders ambient, lightmapsA pre-rendered texture that contains the effects of light sources on static objects in the scene. Lightmaps are overlaid on top of scene geometry to create the effect of lighting. More info
See in Glossary
, 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.