ShaderLab: Pass Tags

Passes use tags to tell how and when they expect to be rendered to the 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 engine.

Syntax

    Tags { "TagName1" = "Value1" "TagName2" = "Value2" }

Specifies TagName1 to have Value1, TagName2 to have Value2. You can have as many tags as you like.

Details

Tags are basically key-value pairs. Inside a Pass tags are used to control which role this pass has in the lighting pipeline (ambient, vertex lit, pixel lit etc.) and some other options. Note that the following tags recognized by Unity must be inside Pass section and not inside SubShaderEach shader in Unity consists of a list of subshaders. When Unity has to display a mesh, it will find the shader to use, and pick the first subshader that runs on the user’s graphics card. More info
See in Glossary!

LightMode tag

LightMode tag defines Pass’ role in the lighting pipeline. See render pipeline for details. These tags are rarely used manually; most often 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 that need to interact with lighting are written as 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 and then all those details are taken care of.

Possible values for LightMode tag are:

Always: Always rendered; no lighting is applied.
ForwardBase: Used 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, ambient, main directional light, vertex/SH lights and 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 are applied.
ForwardAdd: Used in Forward rendering; additive per-pixel lights are applied, one pass per light.
Deferred: Used in Deferred ShadingA rendering path 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; renders g-buffer.
ShadowCaster: Renders object depth into the shadowmap or a depth texture.
MotionVectors: Used to calculate per-object motion vectors.
PrepassBase: Used in legacy Deferred Lighting, renders normals and specular exponent.
PrepassFinal: Used in legacy Deferred Lighting, renders final color by combining textures, lighting and emission.
Vertex: Used in legacy Vertex Lit rendering when object is not lightmapped; all vertex lights are applied.
VertexLMRGBM: Used in legacy Vertex Lit rendering when object is lightmapped; on platforms where lightmap is RGBM encoded (PC & console).
VertexLM: Used in legacy Vertex Lit rendering when object is lightmapped; on platforms where lightmap is double-LDR encoded (mobile platforms).

PassFlags tag

A pass can indicate flags that change how rendering pipeline passes data to it. This is done by using PassFlags tag, with a value that is space-separated flag names. Currently the flags supported are:

OnlyDirectional: When used in ForwardBase pass type, this flag makes it so that only the main directional light and ambient/lightprobe data is passed into the shader. This means that data of non-important lights is not passed into vertex-light or spherical harmonics shader variables. See Forward rendering for details.

RequireOptions tag

A pass can indicate that it should only be rendered when some external conditions are met. This is done by using RequireOptions tag, whose value is a string of space separated options. Currently the options supported by Unity are:

SoftVegetation: Render this pass only if Soft Vegetation is on in the Quality window.

Unity Manual