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Date: Tue, 1 Jun 2010 12:11:36 +0100
From: Julian Pidancet <julian.pidancet@citrix.com>
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Subject: [Qemu-devel] Re: [[RfC PATCH]] linux fbdev display driver prototype.
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To: Gerd Hoffmann <kraxel@redhat.com>
Cc: "qemu-devel@nongnu.org" <qemu-devel@nongnu.org>, Stefano Stabellini <Stefano.Stabellini@eu.citrix.com>

On 05/25/2010 08:11 AM, Gerd Hoffmann wrote:
>> - You should register a Display Allocator and override the
>> create_displaysurface() method like I did in the DirectFB driver.
>> This way you save qemu a data copy. fbdev_render_32() should only be
>> used when the guest framebuffer is not compatible with the physical
>> framebuffer (guest_bpp != physical_bbp || guest_linesize !=
>> physical_linesize).
> 
> Isn't a trivial move though.  If the console is switched you must stop 
> drawing on the framebuffer.
> 
> Right now this is easy: just stop copying.  Likewise restoring the 
> screen when switching back is easy: just copy everything.
> 
> If we give out pointers to the framebuffer to other qemu code which 
> doesn't know anything about console switching we have to be quite 
> careful get things right ...
> 

When loosing the focus, you can force display surface reallocation by calling hw_invalidate(), this way you can give qemu a temporary pointer to prevent drawing on the framebuffer.
When switching back, you just have to copy the content of the temporary pointer location to the framebuffer.


Cheers, 
  Julian Pidancet