title: OpenGL paint program based on Apple's 'glPaint' on a white background - how to blend?
body: <p>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?</p>
  
  <p><strong>Edit:</strong><br>
  I don't even really transparency effects, at this point if I could draw solid lines with rounded ends I'd be happy.</p>