[Spice-devel] xf86-video-qxl performance

[Alon Levy]

On Fri, May 25, 2012 at 09:07:43AM +0200, Alexander Larsson wrote:
> On Wed, 2012-05-23 at 15:20 -0500, Jeremy White wrote:
> 
> > Also, as a crazy idea, has anyone considered implementing a pure
> > streaming video driver?  That is, what if we had a frame buffer driver,
> > and then a thread that fired 29 times a second to drive a theora or vp8
> > encoder, simply feeding the current frame at those intervals.
> 
> Its not crazy at all. In fact, all the times I've been pondering how to
> support modern (i.e. GPU-based) 3D acceleration to spice I've always
> ended up at this. Its not really practical to support GPUs like a set of
> remoted drawing operations, since:
> a) They are infinitely flexible (turing complete)

I don't disagree in principal, and everyone I talked to about this
agrees about your final conclusion, i.e. video streaming is the way to
go for 3d remoting, but I do imagine a protocol that would be
application specific, and by that I mean targeting several common use
cases (prominent game engines, 3d authoring apps, compositors), would
have a chance. The best thing would be of course to have a scene graph
based guest, but too bad GL/DX are immediate mode.

> b) Work on huge amounts on temporary data (textures, buffers, etc),
>    often multiple times the size of what the final rendered screen
>    size is.
> c) Its impossible (comparable to halting problem) to figure out
>    in general which part of the input sources some GPU code snippet
>    uses, or to calculate the bounding box of the result.
> 
> So, what I think we want for GPU accelerated spice is an
> eventually-losless video codec. By that I mean the fact that individual
> frames might be lossy (so it can be effective for video and games), but
> if the input is static we'd (quickly) converge on the lossless result
> (so that you can read your word documents).
> 
> If additionally we could separate each toplevel window as its own stream
> that would be even nicer, but It might be hard as these are composed to
> the final screen using the GPU.
> 
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