Advanced Computer Graphics: Laboratory Project

Introduction to CgFX

Techniques

Each CgFX file usually handles a certain effect such as bump mapping or environment mapping. The CgFX file contains one or more techniques, which describes a way to achieve the effect. Each technique can then target a certain GPU generation so that a more advanced GPU can use a more complex technique, and older graphics hardware can use a simpler one. Different techniques can also be used for level-of-detail or performance fallbacks.

// Used for advanced programmable h/w, e.g. GeForceFX, GeForce series 6, Radeon X800
technique complexPixelandVertexShader
{
    ...
}
      
// Used for lower LOD or older programmable h/w, e.g. GeForce3/4, Radeon 9800
technique simplePixelandVertexShader
{
    ...
}
      
// Fallback. Used for older non-programmable h/w, e.g. GeForce2
technique fixedFunction
{
    ...
}

The application can then query which techniques are available/valid in an effect, and choose an appropriate technique at runtime. CgFX loads and validates the techniques from top to bottom. This means that if techniques are ordered by complexity/requirements, the first valid technique will be the most complex technique available on the users graphics card.

Study the techniques available at the bottom of the file 'carscene-1.fx' available in the solution view in Visual Studio. The file is physically located at:

<Working directory>/fx/

Passes

Rendering passes can be used to add complexity to a technique on for example older graphics hardware. For example, an early version of Quake3 uses up to 10 rendering passes for a single frame.

• Each technique contains one or more passes, where all geometry has to be rendered once for each pass.
• Each pass represents a set of render states and shaders to apply for a single rendering pass within the technique.
• Each pass may contain a vertex shader, a fragment shader, or use fixed-function vertex or fragment processing.

Note how passes are used in the file 'carscene-1.fx'.

Render States

Each pass contains render states such as alpha blending (BlendEnable) and depth testing (DepthTestEnable), where each state is a mapping of an OpenGL call. Refer to the Cg reference documentation for further details.

Make sure you understand how render states are used in the file 'carscene-1.fx'.

Variables and Semantics

The CgFX file also contains global and per-technique variables. The variables are usually passed as uniform parameters to functions, or as the value for a render state or texture state setting. The variables can contain a user-defined semantic, which helps applications provide the correct data to the shader without having to use/know the actual variable names.

sampler2D diffuseSampler : DIFFUSE_MAP
{
	...
};

float4x4 viewMatrix : VIEW_MATRIX;

The application can then query the CgFX file for its variables using their names or their semantics.