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glReadPixels & alpha channel problem


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#1 TM   Members   -  Reputation: 122

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Posted 05 September 2001 - 04:47 AM

I''m trying to read RGBA colors from the frame buffer using glReadPixels, but all my alpha''s are 255. Anyone encountered this problem before?

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#2 zedzeek   Members   -  Reputation: 528

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Posted 05 September 2001 - 10:24 AM

does your card support destination alpha?
is your window created with destination alpha?
are u sure the alpha values of the pixels u read aint 255?

#3 TM   Members   -  Reputation: 122

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Posted 05 September 2001 - 08:08 PM

yes
yes
yes

#4 TM   Members   -  Reputation: 122

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Posted 05 September 2001 - 08:57 PM

Shit, got it!

glutInitDisplayMode(GLUT_DOUBLE | GLUT_RGBA | GLUT_ALPHA | GLUT_DEPTH | GLUT_STENCIL);

instead of

glutInitDisplayMode(GLUT_DOUBLE | GLUT_RGBA | GLUT_DEPTH | GLUT_STENCIL);

Damn!

#5 zedzeek   Members   -  Reputation: 528

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Posted 06 September 2001 - 10:53 AM

so it was
yes
no
yes
watch out not all cards support destination alpha, though i believe only the very old/bad ones dont




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