Re: [Qemu-devel] [PATCH] opengl rendering in the sdl window

[Paul Brook]

On Sunday 07 September 2008, Samuel Thibault wrote:
> Jamie Lokier, le Sun 07 Sep 2008 00:27:23 +0100, a écrit :
> > Samuel Thibault wrote:
> > > Jamie Lokier, le Fri 05 Sep 2008 13:02:15 +0100, a écrit :
> > > > Another way to map guest framebuffer to video memory is the XF86DGA
> > > > extension, which is great when you can use it.
> > >
> > > It is being deprecated and probably never works nowadays anyway :)
> >
> > That's a shame as the alternatives are all slower on old video cards.
>
> Yes, and because alternatives don't provide so much performance.
> Ideally, once switched to fullscreen you could just let the guest
> directly write to the actual video memory (particularly interesting for
> Xen and KVM).

You really don't want to have the guest writing directly to host video ram. 
Video ram tends to be high-latency, so you want to write to regular memory, 
then use a wide block transfer or DMA to copy to video ram.

If you really need zero-copy then you should have the renderer read the data 
directly out of the guest framebuffer.

Paul