>> Seriously, as Chris says it's better to use shaders now, it's more
>> flexible.
> i do not agree.
> using shader, how would you do :
> GL_ONE_MINUS_SRC_COLOR
> you need the source color. a readback is not an option.

In my mind i was thinking about textures operations with the use of two
framebuffers if you need to capture the scene.
With this solution, you can determine the source and destination in your
fragment shader (as glBlendFunc) then operate on destination something
equivalent to GL_ONE_MINUS_SRC_COLOR, or i miss something and i am wrong ?
If this solution is OK, you needn't readback...

That is essentially what recent GPUs do internally for blending anyway. There hasn't been a fixed function hardware pixel pipeline for some time now. It is more complicated to do for simple geometry in a GEM patch, as Cyrille points out so it's good to have the 'old' way for that.