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gfxgangsta

OpenGL ETC texture + Alpha channel with fixed-function pipeline (OpenGL ES 1.1)

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Hi,

I've been doing some research on compressed texture formats, and it looks like the ETC1 format is available on most mobile devices. I'd like to use that format for my textures. The only problem is that it doesn't support an alpha channel. According to some content online, like:

http://www.malidevel...-code/index.php

There's a way to use a separate texture (also compressed as ETC) as the alpha channel. Or you can also make an ETC-compressed "atlas" that contains:

-the original texture without alpha on top
-the "alpha"-only texture on the bottom

However, the examples they give on how to combine the textures all use shaders (OpenGL ES 2.0). They grab a color component (be it R, G, or B) from the "alpha" texture and use it as the alpha value for the combined fragment color.

How can this be done on a fixed-function pipeline like OpenGL ES 1.1? I've inherited some code that has fixed-function calls all over the place and would prefer not to convert to a programmable pipeline. Is this possible without shaders?


Thanks!

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