Re: [Qemu-devel] [PATCH] Reducing X communication bandwidth, take 2

[Julian Seward <jseward@acm.org>]

On Friday 16 March 2007 18:40, Anthony Liguori wrote:
> Hi Julian,
>
> Julian Seward wrote:
> > Here is a somewhat revised version of a patch I first made nearly
> > three years ago.  The original thread is
> >
> > http://lists.gnu.org/archive/html/qemu-devel/2004-07/msg00263.html
> >
> > It still uses a shadow frame buffer.  Fabrice mentioned this is not
> > necessary
>
> I thought about this a little and here's what I came up with.
>
> I think we could change vga_draw_line* so that as part of the drawing
> process, it compared the newly generated pixel with the previous pixel
> value and returned back the min, max x-coordinate that changed.
>
> Since we tend to only extend the vertical dirty range by a couple
> pixels, this should be a relatively cheap way of reducing the size of
> the update region.

Sounds plausible - having said that, I have no familiarity with the VGA
code.  Also sounds like a cleaner solution than mine.

Is there something which guarantees that the vertical dirty range only
overshoots by some small number of pixels?  (thinking more about it ..
it doesn't matter - finding min/max that changed for each line will also
make it possible to identify the vertical limits of the change).

Will this work also for the CL542x adaptor?  (Does that fall in the category
of vga?)  My current hack works for with/without -std-vga and I think 
that's because it lives "underneath" both, in the connection to SDL.

J