opengl paint program based on Apple's 'glPaint' on a white background - how to blend?

Posted by Adam on Stack Overflow See other posts from Stack Overflow or by Adam
Published on 2010-05-08T01:23:22Z Indexed on 2010/05/08 1:28 UTC
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opengl-es

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paint

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iphone

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opengl

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blending

Trying to write a simple paint program for iPhone, and I'm using Apple's glPaint sample as a guide. The only problem is, painting doesn't work on a white background, since white + colour = white. I've tried different blending functions, but haven't been able to hit on the right combination of settings and/or brushes to make this work. I've seen similar posts about this problem but no answers. Does anyone know how this might work?

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