Re: [Qemu-devel] [PATCH]Fix for minor video corruption under Windows

[Fabrice Bellard]

Hi,

I think the proper fix must be done in the BIOS (set VRAM to 0xFF at 
cirrus mode init). I made a patch for that but I must test it a little more.

Fabrice.

Dugger, Donald D wrote:
> Leo-
>
> Yeah, I started there but it turns out there are multiple reasons why
> that is the wrong place to fix things:
>
> 1)  `hw/vga.c' only knows about resolution changes, the bug also appears
> if you change the pixel size, e.g. 24 bpp to 16 bpp.
>
> 2)  Technically, because of the lazy screen update, your change would be
> too late.  To improve performance the vga code is only called
> periodically, not after every VRAM change.  It is theoretically possible
> for the target to change video mode, assume VRAM got reset, do a bitblt
> from non-visible VRAM to visible VRAM and then have the `hw/vga.c' code
> get called, overwriting the changes done to visible VRAM.
>
> --
> Don Dugger
> "Censeo Toto nos in Kansa esse decisse." - D. Gale
> address@hidden
> Ph: (303)440-1368 
>
>
> > -----Original Message-----
> > From: address@hidden 
> > [mailto:address@hidden
> > ] On Behalf Of Leonardo E. Reiter
> > Sent: Tuesday, May 09, 2006 2:29 PM
> > To: address@hidden
> > Subject: Re: [Qemu-devel] [PATCH]Fix for minor video 
> > corruption under Windows
> >
> > Donald...
> >
> > thanks... I actually posted a patch to fix this sometime ago, but your 
> > patch seems more thorough and probably more correct.  Just FYI, I 
> > attached my patch again.  I will test your patch as well.
> >
> > Thanks again,
> >
> > Leo Reiter
> >
> > Donald D. Dugger wrote:
> >
> > > If you change the video resolution while running a Windows 
> >
> > XP image such that
> >
> > > it uses fewer bytes of VRAM (either by using fewer bytes per 
> >
> > pixel or by
> >
> > > lowering the resolution) then some window backgrounds will 
> >
> > become corrupted.
> >
> > > This happens because the Windows XP Cirrus Logic driver 
> >
> > assumes that VRAM is
> >
> > > initialized to 0xff whenever the video mode switches between 
> >
> > VGA and SVGA.
> >
> > > This patch fixes this problem by resetting VRAM whenever a 
> >
> > VGA/SVGA mode switch
> >
> > > occurs.
> > >
> > > Signed-off-by: address@hidden
> >
> > --
> > Leonardo E. Reiter
> > Vice President of Product Development, CTO
> >
> > Win4Lin, Inc.
> > Virtual Computing that means Business
> > Main: +1 512 339 7979
> > Fax: +1 512 532 6501
> > http://www.win4lin.com
>
>
>
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