title: OpenGL blending with source and destination alpha
body: <p>I'm trying to render a texture with alpha to a frame buffer with alpha. I need the texture's transparency to be controlled by a combination of its own alpha, and the alpha already rendered to the frame buffer.</p>
  
  <p>ie:</p>
  
  <p>Normal transparency:</p>
  
  <p>(src_colour * src_alpha) + (dst_colour * 1-src_alpha)</p>
  
  <p>Required transparency:</p>
  
  <p>(src_colour * src_alpha * dst_alphe) + (dst_colour * 1-(src_alpha * dst_alpha))</p>
  
  <p>Can anyone figure out how to do this?</p>
  
  <p>I've been working on it for 9 hours now :-)</p>
  
  <p>I'm using OpenGL 1.0 with GL11ExtensionPack on Android, so I have access to glBlendFunc and glBlendFuncSeparate. I would prefer not to go the GLES20 route with shaders as that would require a lot of code to be rewritten.</p>
  
  <p>Thanks,
  Andrew</p>