Re: [Qemu-devel] Reducing X communication bandwidth

[Julian Seward <jseward@acm.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