Re: [Qemu-devel] PATCH: fix bgr color mapping on qemu on Solaris/SPARC

[Jamie Lokier <jamie@shareable.org>]

Dan Sandberg wrote:
> Creating a rectangular direct output area in OpenGL is actually like 
> vitualizing a graphics card.

That is what X's XF86DGA ("Direct Graphics Adapter") feature does.
And I believe SDL already supports XF86DGA when in full screen mode.

> It is updated at native speed

Not necessarily.  When I tried using mplayer (a video player) with the
video output set to use OpenGL, it was the slowest of all options -
even slower than writing the images though X11 shared memory with a
copy-to-screen bitblt for each frame.

But then, OpenGL drivers vary considerably in their performance and quality.

> and you can select pixelformat for that 
> area independent of the host pixel format and you do not have to be 
> doing any RectangleBlit operation or causing any CPU-load - to my 
> understanding at least.

Well, OpenGL does a RectangleBlit each time it redraws the 3d
rendering area, doesn't it?  If you have hardware accelerated OpenGL
support, that shouldn't use much CPU.  But then, the same is true for
old-fashioned hardware accelerated 2d bitblt, if the pixel format is
supported.

> [...] I am not saying that any of todays possibilities in Qemu
> should be retired, rather that it could be sort of a new plug-in
> module for those who want a virtual display adapter with close to
> native graphic performance and happen to have what is needed in
> terms of graphic card and drivers.

I agree it's worth a look, because it may be faster for some people,
and because it provides access to image scaling (potentially hardware
assisted), which classic X11 bitblt does not.

It might be worth looking at mplayer's OpenGL driver, which does
something similar to what Qemu would need.

Other X features which can do similar things and may provide equal or
better performance are: Xv (used to display video, but generally
provides a resizable overlay; may or may not provide a usable pixel
format), and Xrender.

-- Jamie