[cairo] Performance OpenGL backend

[Eric Anholt]

On Wed, 17 Feb 2010 17:17:02 +0000, Chris Wilson <chris at chris-wilson.co.uk> wrote:
> On Wed, 17 Feb 2010 12:23:48 +0100, Ralf <mock at cipsoft.com> wrote:
> > So can that actually be the case where the opengl backend is slower, 
> > when rendering many curves which
> > only fill a few pixels in the final picture or am I using the backend in 
> > the wrong way ?
> 
> No, just the common delusion that OpenGL is a panacea for all ills. In
> this case we currently create scan-lines on the CPU and then emit a vertex
> buffer containing all the opacities to be composited. Depending on the
> overhead and speed of the GPU, it is easily conceivable that simply using
> the CPU on local memory will be faster than the offload. Of course, we
> wish to improve our algorithms for the more advanced GPUs, so please note
> that the OpenGL backend is a work in progress.
> 
> If you can share your experience on how you integrated cairo-gl with
> Ogre3D, that will be great - and help us reflect on the gl backend api 
> before it is frozen. Similarly, if you can profile the bottlenecks on the
> -image and -gl (and other backends) that will be very useful as well. One
> technique you can use is to record an application trace using cairo-trace,
> and submit it for inclusion in cairo-traces so that we can tune cairo for
> your workload.
> 
> I hope you are having fun with Cairo, and together we can make it better!
> :)

Second on "we're interested in how you did the integration" -- it's the
big thing I haven't figured out how to handle yet.  Any experience you
can offer from your experiments would be useful.
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