2013/10/10 Benoit Jacob <jacob.benoi...@gmail.com>
> I'll pile on what Benoit G said --- this is the kind of work that would
> require very careful performance measurements before we commit to it.
>
> Also, like Benoit said, we have seen no indication that glUseProgram is
> hurting us. General GPU "wisdom" is that switching programs is not per se
> expensive as long as one is not relinking them, and besides the general
> performance caveat with any state change, forcing to split drawing into
> multiple draw-calls, which also applies to updating uniforms, so we're not
> escaping it here.
>
> In addition to that, not all GPUs have real branching. My Sandy Bridge
> Intel chipset has real branching, but older Intel integrated GPUs don't,
> and I'd be very surprised if all of the mobile GPUs we're currently
> supporting did. To put this in perspective, in the world of discrete
> desktop NVIDIA GPUs, this was only introduced in the Geforce 6 series.
>
In fact, even on a Geforce 6, we only get full real CPU-like ("MIMD")
branching in vertex shaders, not in fragment shaders.
http://http.developer.nvidia.com/GPUGems2/gpugems2_chapter34.html
Benoit
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