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

[Dugger, Donald D]

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
>