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

[Fabrice Bellard <fabrice@bellard.org>]

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
> Donald.D.Dugger@intel.com
> Ph: (303)440-1368 
> 
> 
>>-----Original Message-----
>>From: qemu-devel-bounces+donald.d.dugger=intel.com@nongnu.org 
>>[mailto:qemu-devel-bounces+donald.d.dugger=intel.com@nongnu.org
>>] On Behalf Of Leonardo E. Reiter
>>Sent: Tuesday, May 09, 2006 2:29 PM
>>To: qemu-devel@nongnu.org
>>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: Donald.D.Dugger@intel.com
>>>
>>
>>-- 
>>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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