Creating User Interfaces for Vertex Shader Inputs

Variables declared as input to a vertex shader are often bound to predefined names (POSITION, COLOR0, COLOR1, TEXCOORD0, etc.) that are referred to as binding semantics. These predefined names implicitly specify the mapping of the inputs to particular hardware registers. Depending on the semantics that you use, either Softimage or your vertex program must supply the data for each of these variables.

A vertex attribute control is created in the property editor for each vertex shader variable that is bound to semantics such as COLOR[n], TEXCOORD[n], TANGENT, and BINORMAL. A vertex attribute control is not created for all binding semantics. If, for example, a variable is bound to the POSITION or NORMAL semantic, it will not generate a vertex attribute widget because these semantics are automatically bound by Softimage. For a list of the supported semantics, see Vertex Shader Input Semantics.

Note that per-vertex variable data can be bound to a TEXCOORD semantic even when it is not a texture coordinate. This gives you the freedom to connect a texture projection in a COLOR register or a vertex color in a TEXCOORD register (it's as you wish).

The members of a struct have semantics specified, which connect the variables in the shader code to the underlying graphics system (OpenGL/DirectX). The input structure identifies the data from the vertex buffer that will provide the shader inputs.

The following snippet of CgFX code maps the position, normal, tangent, binormal and texture coordinate data from the vertex buffer into vertex shader registers.

struct VS_Input {
 float3 Position	: POSITION;
 float4 UV	: TEXCOORD0;
 float4 Tangent	: TEXCOORD1;
 float4 Binormal	: TEXCOORD2;
 float4 Normal	: NORMAL;
};

The binding semantics dynamically generate vertex attribute widgets as displayed in this CgFx shader's property editor.

The following snippet of HLSL code maps the position, normal, tangent, binormal and texture coordinate data from the vertex buffer into vertex shader registers.

struct VS_Input
{
	float4 Position : POSITION;
	float3 Normal : NORMAL;
	float3 Tangent : TANGENT;
	float3 Binormal : BINORMAL;
	float2 TexCoords : TEXCOORD0;
};

The binding semantics dynamically generate vertex attribute widgets as displayed in this HLSL shader's property editor. Note that for HLSL, the vertex attributes must be used in the shader code, otherwise they will be culled by the compiler and not available in the property editor.