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From: Paul Brook <paul@codesourcery.com>
Subject: Re: [Qemu-devel] [PATCH] opengl rendering in the sdl window
Date: Sun, 7 Sep 2008 15:36:51 +0100
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To: qemu-devel@nongnu.org
Cc: Samuel Thibault <samuel.thibault@ens-lyon.org>

On Sunday 07 September 2008, Samuel Thibault wrote:
> Jamie Lokier, le Sun 07 Sep 2008 00:27:23 +0100, a =E9crit :
> > Samuel Thibault wrote:
> > > Jamie Lokier, le Fri 05 Sep 2008 13:02:15 +0100, a =E9crit :
> > > > 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.=
=20
Video ram tends to be high-latency, so you want to write to regular memory,=
=20
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 dat=
a=20
directly out of the guest framebuffer.

Paul