Unity's Rendering Pipeline
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Unity's Rendering Pipeline

Shaders define both how an object looks by itself (its material properties) and how it reacts to the light. Because lighting calculations must be built into the shader, and there are many possible light & shadow types, writing quality shaders that "just work" would be an involved task. To make it easier, Unity 3 introduces Surface Shaders, where all the lighting, shadowing, lightmapping, forward vs. deferred lighting things are taken care of automatically.

This document describes the pecularities of Unity's lighting & rendering pipeline and what happens behind the scenes of Surface Shaders.

Rendering Paths

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.

Deferred Lighting path

PrepassBase pass renders normals & specular exponent; PrepassFinal pass renders final color by combining textures, lighting & emissive material properties. All regular in-scene lighting is done separately in screen-space. See Deferred Lighting for details.

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.

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 permutations internally to handle lightmapped vs. non-lightmapped cases. So to handle lightmapped and non-lightmapped objects, multiple passes have to be written explicitly.

Page last updated: 2010-09-25