title: OpenGL: Combining glBlendFunc with glAccum
body: <p>I've been working on a graphics project doing Depth of Field. The method is doing several passes, each rendering the scene with different near and far clipping-parameters, such that it renders different depth ranges at each pass.</p>
  
  <p>The idea is to apply a blur kernel on each individual layer by rendering to a texture and doing the blur on a rendered quad (with the texture). This is all fairly basic stuff. As is working fine. However, the part I can't get working is the combining of the layers:</p>
  
  <p>The color buffer is cleared with color4(0,0,0,0) before each pass is drawn. However, the accumulation does not seem to allow the usage of glBlendFunc such that it accumulates taking the alpha channel into account (i.e. glBlendFunc(GL_SRC_ALPHA, GL_SRC_ONE_MINUS_ALPHA)). </p>
  
  <p>The question is then:
    - Does the glBlendFunc affect the glAccum?
    - If not, how can I work around this?</p>
  
  <p>Based on the documentation, this doesn't seem to be the case as it is not mentioned, however it feels this is a very useful feature.</p>
  
  <p>Regards,
  R</p>