Execute Callback Reference

    RTSHADER_API bool (*RTS_Shader3_Execute)
    {
        IRTSExecutionState          *in_pExecState,
        void                        *in_pParams,
        XSI_RTS_Primitive           *in_pPrimitive,
        void                        *in_pAttributes,
        XSI_RTS_Attribute_Size      *in_pAttributesSize,
        void                        **io_pShaderInstanceData
    }
Once the shader has responded to GetAttributeList with its list of attributes, Softimage will package the values for these attributes and will pass them to the Execute function along with an array describing each attribute's size and format. Note that if an attribute was not found or was not defined on the mesh or point cloud, Softimage will pass a null pointer.
Note:
This callback is mandatory
Parameters:
in_pExecState  The execution state interface
in_pParams  The shader property page parameters
in_pPrimitive  The geometry information
in_pAttributes  The Softimage RTS Attribute data
in_pAttributesSize  The sizes of the attributes
io_pShaderInstanceData  Pointer to This shader instance user data
Returns:
Success/failure
Example:
This example builds on the one on the GetAttributeList page. Here's what the Execute function might look like for the example shader described: 
    RTSHADER_API bool MyShader_Execute
    (
        IRTSExecutionState      *in_pExecState,
        void                    *in_pParams,
        XSI_RTS_Primitive       *in_pPrimitive,
        void                    *in_pAttributes,
        eXSI_Attribute_Size     *in_pAttributesSize,
        void                    **io_pInstanceData
    )
    {
        ShaderPPG* options = (ShaderPPG*)in_pParams;

        if (options->useColor)
        {
            float* pfPositions  = ((float**)in_pAttributes)[0];
            float* pfNormals    = ((float**)in_pAttributes)[1];
            float* pfColors0    = ((float**)in_pAttributes)[2];
            float* pfColors1    = ((float**)in_pAttributes)[3];
            float* pfFoobars    = ((float**)in_pAttributes)[4];
            ...
        } else {
            float* pfPositions  = ((float**)in_pAttributes)[0];
            float* pfNormals    = ((float**)in_pAttributes)[1];
            float* pfFoobars    = ((float**)in_pAttributes)[2];
            ...
        }

        ...
    }
See also:
IRTSExecutionState, Realtime Shader Callbacks, Geometry Data, Execution Flow