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Re: [Qemu-devel] [PATCH] Add QEMU DirectFB display driver


From: Gerd Hoffmann
Subject: Re: [Qemu-devel] [PATCH] Add QEMU DirectFB display driver
Date: Thu, 20 May 2010 09:32:04 +0200
User-agent: Mozilla/5.0 (X11; U; Linux x86_64; en-US; rv:1.9.1.9) Gecko/20100430 Fedora/3.0.4-2.fc12 Thunderbird/3.0.4

On 05/19/10 18:30, Jamie Lokier wrote:
Julian Pidancet wrote:
So after all, why not implementing our own VT switching and using
directly the fbdev interface.

It's a good idea.  VT switching isn't hard to track reliably.

Indeed, only problem is that the fbdev libs usually want to do that too.

Being able to tell qemu, through the monitor, to attach/detach from a
particular VT might be a nice easy bonus too.

Yes, should be doable without too much effort.

I just checked the linux fbdev code to
find out if it provides with a blitting method that could perform
the pixel color conversion automatically for Qemu.

Unfortunately, from what I have read from the
drivers/video/cfbimgblt.c file in the linux tree, there's no such
thing, and it also means that we cannot take advantage of any kind
of hardware pixel format conversion.

I'm not sure if DirectFB provides that particular operation, but I
have the impression it's the sort of thing DirectFB is intended for: A
framebuffer, plus a variety of 2d acceleration methods (and other
things like multi-buffering, video and alpha channel overlay).

As far I know acceleration depends on the directfb kernel drivers though, i.e. in 99% of the cases (standard distro installs) those are not available and software fallbacks are active anyway. So from a performance point of view directfb doesn't buy us much. And for the pixel conversion I'd prefer see some reorganization of the existing qemu code which is spread all over the place now ...

cheers,
  Gerd




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