Custom lighting models in Surface Shaders

When writing Surface ShadersUnity’s code generation approach that makes it much easier to write lit shaders than using low level vertex/pixel shader programs. More info
See in Glossary, you describe the properties of a surface (such as albedo color and normal), and a Lighting Model computes the lighting interaction.

There are two built-in lighting models: Lambert for diffuse lighting, and BlinnPhong for specular lighting. The Lighting.cginc file inside Unity defines these models (Windows: <unity install path>/Data/CGIncludes/Lighting.cginc; macOS: /Applications/Unity/Unity.app/Contents/CGIncludes/Lighting.cginc).

Sometimes you might want to use a custom lighting model. You can do this with Surface ShadersA small script that contains the mathematical calculations and algorithms for calculating the Color of each pixel rendered, based on the lighting input and the Material configuration. More info
See in Glossary. A lighting model is simply a couple of Cg/HLSL functions that match some conventions.

Declaring lighting models

A lighting model consists of regular functions with names that begin Lighting. You can declare them anywhere in your shader file, or one of the included files. The functions are:

1. half4 Lighting<Name> (SurfaceOutput s, UnityGI gi); Use this in forward renderingThe process of drawing graphics to the screen (or to a render texture). By default, the main camera in Unity renders its view to the screen. More info
   See in Glossary paths for light models that are not dependent on the view direction.

2. half4 Lighting<Name> (SurfaceOutput s, half3 viewDir, UnityGI gi); Use this in forward rendering pathsThe technique Unity uses to render graphics. Choosing a different path affects the performance of your game, and how lighting and shading are calculated. Some paths are more suited to different platforms and hardware than others. More info
   See in Glossary for light models that are dependent on the view direction.

3. half4 Lighting<Name>_Deferred (SurfaceOutput s, UnityGI gi, out half4 outDiffuseOcclusion, out half4 outSpecSmoothness, out half4 outNormal); Use this in deferred lighting paths.

4. half4 Lighting<Name>_PrePass (SurfaceOutput s, half4 light); Use this in light prepass (legacy deferred) lighting paths.

Note that you don’t need to declare all functions. A lighting model either uses view direction or it does not. Similarly, if the lighting model only works 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, do not declare the _Deferred or _Prepass function. This ensures that Shaders that use it only compile to forward rendering.

Custom GI

Declare the following function to customize the decoding lightmapA 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 data and probes:

1. half4 Lighting<Name>_GI (SurfaceOutput s, UnityGIInput data, inout UnityGI gi);

Note that to decode standard Unity lightmaps and SH probes, you can use the built-in DecodeLightmap and ShadeSHPerPixel functions, as seen in UnityGI_Base in the UnityGlobalIllumination.cginc file inside Unity (Windows: <unity install path>/Data/CGIncludes/UnityGlobalIllumination.cginc; macOS: /Applications/Unity/Unity.app/Contents/CGIncludes/UnityGlobalIllumination.cginc_).

Examples

See documentation on Surface Shader Lighting Examples for more information.