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From: Julian Seward <jseward@acm.org>
Subject: Re: [Qemu-devel] Reducing X communication bandwidth
Date: Sun, 11 Jul 2004 12:22:02 +0100
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	<Pine.LNX.4.58.0407111151100.14752@wgmdd8.biozentrum.uni-wuerzburg.de>
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To: Johannes Schindelin <Johannes.Schindelin@gmx.de>
Cc: qemu-devel@nongnu.org

On Sunday 11 July 2004 10:53, Johannes Schindelin wrote:
> Hi,
>
> On Sat, 10 Jul 2004, Julian Seward wrote:
> > The attached patch against sdl.c fixes this.  It keeps a shadow
> > copy of video memory.  When a request arrives at sdl_update()
> > to redraw an area, the area is compared against the shadow copy,
> > and only the parts that have really changed are passed to
> > SDL_UpdateRect().  The comparison is done at a granularity of
> > 32x32 chunks of pixels.
>
> Why does this remind me of VNC? In fact, that kind of application is the
> exact reason I started my VNC patch. It could also be useful as a Windows
> 98 Terminal Server...

Exactly -- I got the idea from VNC.  First I noticed that using qemu
just as a remote X client gave appalling performance *but* when you
run it on a remote VNC server and connect with vncviewer, the results
is quite usable.  That immediately suggests that vnc found a lot of
redundant screen updates and did not bother to send them over the
network, and at that point I started hacking :-)

J