ShaderLab: Legacy BindChannels

BindChannels command allows you to specify how vertex data maps to the graphics hardware.

Note: _BindChannels has no effect when vertex programs are used, as in that case bindings are controlled by vertex shaderA program that runs on each vertex of a 3D model when the model is being rendered. More info
See in Glossary inputs. It is advisable to use programmable 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 these days instead of fixed function vertex processing.

By default, Unity figures out the bindings for you, but in some cases you want custom ones to be used.

For example you could map the primary UV set to be used in the first texture stage and the secondary UV set to be used in the second texture stage; or tell the hardware that vertex colors should be taken into account.

Syntax

BindChannels { Bind "source", target }

Specifies that vertex data source maps to hardware target.

Source can be one of:

• Vertex: vertex position
• NormalThe direction perpendicular to the surface of a mesh, represented by a Vector. Unity uses normals to determine object orientation and apply shading. More info
  See in Glossary: vertex normal
• TangentOne of two handles that controls the shape of the animation curve before and after a key. Tangents appear when a key is selected in the Curves view, or when a key is selected in the Curve Editor.
  See in Glossary: vertex tangent
• Texcoord: primary UV coordinate
• Texcoord1: secondary UV coordinate
• Color: per-vertex color

Target can be one of:

• Vertex: vertex position
• Normal: vertex normal
• Tangent: vertex tangent
• Texcoord0, Texcoord1, …: texture coordinates for corresponding texture stage
• Texcoord: texture coordinates for all texture stages
• Color: vertex color

Details

Unity places some restrictions on which sources can be mapped to which targets. Source and target must match for Vertex, Normal, Tangent and Color. Texture coordinates from the meshThe main graphics primitive of Unity. Meshes make up a large part of your 3D worlds. Unity supports triangulated or Quadrangulated polygon meshes. Nurbs, Nurms, Subdiv surfaces must be converted to polygons. More info
See in Glossary (Texcoord and Texcoord1) can be mapped into texture coordinate targets (Texcoord for all texture stages, or TexcoordN for a specific stage).

There are two typical use cases for BindChannels:

• Shaders that take vertex colors into account.
• Shaders that use two UV sets.

Examples

// Maps the first UV set to the first texture stage
// and the second UV set to the second texture stage
BindChannels {
   Bind "Vertex", vertex
   Bind "texcoord", texcoord0
   Bind "texcoord1", texcoord1
}

// Maps the first UV set to all texture stages
// and uses vertex colors
BindChannels {
   Bind "Vertex", vertex
   Bind "texcoord", texcoord
   Bind "Color", color
}