CHAPTER 6: Will It Blend? (^185)
glGetIntegerv(GL_MAX_COMBINED_TEXTURE_IMAGE_UNITS, &numberTextureUnits), where
numberTextureUnits is defined as a GLint.
To set up a pipeline to handle multitexturing, we need to tell OpenGL what textures to
use and how to mix them together. The process isn’t that much different (in theory at
least) than defining the blend functions when dealing with the alpha and color blending
operations previously. It does involve heavy use of the glTexEnvf() call, another one of
OpenGL’s wildly overloaded methods. (If you don’t believe me, check out its official
reference page on the OpenGL site.) This sets up the texture environment that defines
each stage of the multitexturing process.
Figure 6-10 illustrates the combiner chain. Each combiner refers to the previous texture
fragment (P0 or Pn) or the incoming fragment for the first combiner. It then takes a
fragment from a ‘‘source’’ texture (called S0), combines it with P0, and hands it off to the
next combiner if needed (called C1); then the cycle repeats.
Figure 6-10. The texture combiner chain
The best way to tackle this topic is like any others: go to the code. In the following
example, two textures are loaded together, bound to their respective texture units, and
merged into a single output texture. Several kinds of methods used to combine the two
images are tried with the results of each shown and examined in depth.
singke
(singke)
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