[GEM-dev] Different Alpha Blending Methods in Alpha Object

[chris clepper]

On Sat, Nov 24, 2012 at 7:52 AM, Jack <jack at rybn.org> wrote:

>
> >> 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.
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