Tell opengl use texture unit color values for arg gltexenvi

370	CHAPTER 9	Texture Mapping: Beyond the Basics
370

	Function
GL_REPLACE GL_MODULATE GL_ADD GL_ADD_SIGNED GL_INTERPOLATE GL_SUBTRACT

TABLE 9.5	Texture Combiner Sources

ment variable GL_TEXTURE_ENV_COLOR

GL_PRIMARY_COLOR

glTexEnvi(GL_TEXTURE_ENV, GL_SOURCE0_RGB, GL_TEXTURE0);

You also have some additional control over what values are used from a given source for each argument. To set these operands, you use the constant GL_OPERANDx_RGB or
GL_OPERANDx_ALPHA, where x is 0, 1, or 2. The valid operands and their meanings are given in Table 9.6.

		Point Sprites	371

Constant
GL_SRC_COLOR	The color values from the source. This may not be used with

GL_OPERANDx_ALPHA.

	One’s complement (1-value) of the alpha values from the source.

For example, if you have two textures loaded on the first two texture units, and you want to multiply the color values from both textures during the texture application, you would set it up as shown here:

// Tell OpenGL to use texture unit 0’s color values for Arg0

glTexEnvi(GL_TEXTURE_ENV, GL_SOURCE0_RGB, GL_TEXTURE0);

Finally, with texture combiners, you can also specify a constant RGB or alpha scaling factor. The default parameters for these are as shown here:

glTexEnvf(GL_TEXTURE_ENV, GL_RGB_SCALE, 1.0f);