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Zeno
04-09-2001, 09:39 AM
Is there a way to use one blend function for my color values and another blend function for my alpha values? Obviously regular glBlendFunc() can't do this. I don't think register combiners have available the color of the pixel already in the color buffer, do they?

I am willing to use any extensions that might help with this, as my only other option is to render everything twice, and it's an expensive render http://www.opengl.org/discussion_boards/ubb/frown.gif

-- Zeno

mcraighead
04-09-2001, 10:01 AM
There is an extension that provides a separate color and alpha blend function, but (to the best of my knowledge) no one implements it.

- Matt

DaViper
04-10-2001, 06:33 AM
if you are willing to render twice, you can set the ColorMask one time for rendering the Colorvalues and thew other time for Alpha values

stecher
04-10-2001, 06:55 AM
Doesn't the EXT_texture_env_combine extension let you specify color and alpha blend functions separately? But I guess that will only work if you texture your geometry.

Zeno
04-10-2001, 07:10 AM
Thanks guys. I got it to work last night by doing what daViper suggested. The performance hit seems negligable http://www.opengl.org/discussion_boards/ubb/smile.gif

-- Zeno

Serge K
04-23-2001, 04:55 AM
Originally posted by mcraighead:
There is an extension that provides a separate color and alpha blend function, but (to the best of my knowledge) no one implements it.
GL_EXT_blend_func_separate (http://oss.sgi.com/projects/ogl-sample/registry/EXT/blend_func_separate.txt) is implemented in FireGL1/2/3 and Wildcat4110..5110