Re: [Qemu-devel] Reducing X communication bandwidth

[Fabrice Bellard <fabrice@bellard.org>]

Julian Seward wrote:
> [...]
> Anyway, QEMU from cvs is unusable like this, at least when
> running WinXP or Win2K.  The SDL layer (qemu/sdl.c) blasts
> huge numbers of pixels across the network in response to even
> the simplest graphical operations.  Notably, moving the mouse
> pointer is appalling, with an update rate of about twice per
> second, which is hopeless.
> 
> 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.
> [...]

OK for the feature.

I just want to be sure it does not slow down the case where QEMU runs 
locally (comparisons may be slower than just copying). So there should 
be a specific support to detect if shared memory is used by SDL.

Another point is that it may not be necessary to add a second frame 
buffer. By modifying the vga core a single line of memory should be 
necessary to do the comparison.

Fabrice.