Table of Contents Glide Programming Guide

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GLIDEPGM

2A Higher Level Color Combine Function

1In This Chapter

The Glide Utility Library is a set of utility functions that are built on top of the lower-level Glide routines presented in the preceding chapters. Many are convenience routines that provide higher-level services: functional descriptions of color, alpha, and texture combine functions, texture memory management services, and so on. Some of the Glide Utility Library functions have already been described: the routines to clip and draw triangles in Chapter Chapter 4. , the functions that create fog tables in Chapter Chapter 8. , or the functions that download mipmaps and decompression tables from .3DF files in Chapter Chapter 10. .
In this chapter, you will discover

a different way to configure the color combine, alpha combine, and texture combine units
a different way to manage texture memory
a higher level way to read and write the linear frame buffer

2A Higher Level Color Combine Function

Chapter 4 introduced the grColorCombine() function; it provides a low-level way to configure the color combine unit. The guColorCombineFunction() provides a higher level mechanism for controlling common rendering modes without manipulating individual registers within the hardware.
void guColorCombineFunction( GrColorCombineFunction_t function )

The argument, function, specifies one of fourteen color combine functions. Table Glide Utilities .1 lists the Glide constants that define the color combine function and the effects than can be achieved with that function. The default color combine function is undefined, so an application must set the color combine function before executing any rendering commands. Refer to the guColorCombineFunction() page in the Glide 2.2 Reference Manual for more information.

Table Glide Utilities .1 Color combine functions.

function	effect
GR_COLORCOMBINE_ZERO	0x00 (black) for each component
GR_COLORCOMBINE_ITRGB	Gouraud shading
GR_COLORCOMBINE_DECAL_TEXTURE	texture
GR_COLORCOMBINE_TEXTURE_TIMES_CCRGB	flat-shaded texture using the constant color set by grConstantColorValue() as the shading value
GR_COLORCOMBINE_TEXTURE_TIMES_ITRGB	Gouraud-shaded texture
GR_COLORCOMBINE_TEXTURE_TIMES_ITRGB_ADD_ALPHA	Gouraud-shaded texture + alpha
GR_COLORCOMBINE_TEXTURE_TIMES_ALPHA	texture * alpha
GR_COLORCOMBINE_TEXTURE_ADD_ITRGB	texture + iterated RGB
GR_COLORCOMBINE_TEXTURE_SUB_ITRGB	texture – iterated RGB
GR_COLORCOMBINE_CCRGB	flat shading using the constant color set by grConstantColorValue()
GR_COLORCOMBINE_CCRGB_BLEND_ITRGB_ON_TEXALPHA	blend between constant color and iterated RGB using an alpha texture, where alpha of 0 and 1 correspond to constant color and iterated RGB respectively
GR_COLORCOMBINE_DIFF_SPEC_A	texture * a + iterated RGB
GR_COLORCOMBINE_DIFF_SPEC_B	texture * iterated RGB + a
GR_COLORCOMBINE_ONE	0xFF (white) for each component

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