Define: Cg Tutorials Chapter 1. Introduction

[References]

1. "What is Cg?, from developer.nvidia.com"

Chapter 1. Introduction

This chapter has the following four sections:

• "What Is Cg?" introduces the Cg programming language.
• "Vertices, Fragments, and the Graphics Pipeline" describes the data flow of modern graphics hardware and explains how Cg fits into this data flow.
• "Cg's Historical Development" provides some background on how Cg was developed.
• "The Cg Environment" explains how applications go about using Cg programs through the Cg runtime and existing 3D application programming interfaces (APIs).

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2. "introduction to shader programming with Cg-3.1, from 3dgep.com"

Cg Semantics

In Cg, you use "semantics" to map data coming from the application (the C++ part) into stream variables in the shader. You can think of a semantics as an association between the vertex information sent to the rendering pipeline in C++ and the vertex data in the Shader.

In OpenGL, this mapping is performed by telling OpenGL to apply an "attribute ID" to a named parameter in a shader using the glBindAttribLocation() method.

• You then modify the value of the attribute using either the glVertexAttrib() method, 
• or specifying stream data (like a vertex stream) using glVertexAttribPointer() method. 
• Cg doesn't require that you first bind the location of  variable to an attribute ID, but instead it defines some default ID's for different stream elements..

• Cg defines the following default semantics and the default generic attribute ID’s that are bound to the semantic.

BINDING SEMANTICS NAME	CORRESPONDING DATA
POSITION, ATTR0	Input Vertex, Generic Attribute 0
BLENDWEIGHT, ATTR1	Input vertex weight, Generic Attribute 1
NORMAL, ATTR2	Input normal, Generic Attribute 2
DIFFUSE, COLOR0, ATTR3	Input primary color, Generic Attribute 3
SPECULAR, COLOR1, ATTR4	Input secondary color, Generic Attribute 4
TESSFACTOR, FOGCOORD, ATTR5	Input fog coordinate, Generic Attribute 5
PSIZE, ATTR6	Input point size, Generic Attribute 6
BLENDINDICES, ATTR7	Generic Attribute 7
TEXCOORD0-TEXCOORD7, ATTR8-ATTR15	Input texture coordinates (texcoord0-texcoord7), Generic Attributes 8-15
TANGENT, ATTR14	Generic Attribute 14
BINORMAL, ATTR15	Generic Attribute 15

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