View Full Version : Alpha channel affectation
11-29-2000, 03:15 AM
I need to affect, change or clear the Alpha componant.
I know it works cause I can see the result on the screen with BLEND but why the glReadPixels always give me a value equal to 255 !?!?
what format do you use in the glreadpixel function ???
11-29-2000, 04:47 AM
I'm using the format GL_RGBA
11-29-2000, 07:30 PM
Looks like similar problem :
glReadPixels on GeForce2 (http://www.opengl.org/discussion_boards/ubb/Forum3/HTML/001365.html) .
> I know it works cause I can see the result on the screen with BLEND
??? What do you mean?
Alpha blending works without alpha channel in the color buffer (if you don't use _DST_ALPHA).
11-30-2000, 12:58 AM
>> I know it works cause I can see the result >>on the screen with BLEND
>??? What do you mean?
I made an operation with glblendfunc using the alpha componant and it works.
I just can't read something different than 255 with glReadPixels
I'm on a SGI o2
11-30-2000, 03:52 AM
Does your pixel format include a destination alpha buffer? If not, then obviously, the alpha is not being read back because it doesn't exist.
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