Performance change from X in Fedora Core 4 to Fedora Core 5

[Felix Bellaby]

Felix Bellaby wrote:
> What we should be aiming to do is avoid the generation of damage reports
> until we are ready to display the finished drawing. The compositor will
> ignore drawing operations until the damage is reported, allowing the off
> screen pixmap to act as a buffer. 

When I made this comment I was hoping that _efficient_ compositors would
be able to ignore the contents of "undamaged" sections of the off screen
pixmaps. Unfortunately, transparent, actively distorting and unmapped
windows would expose areas of windows behind them that had not been
damaged. The compositor could not accurately determine the contents of
those exposed areas from the Xcomposite pixmap if it was being used as a
back buffer.

Therefore, the approach to back buffering that I was proposing would
rely on the compositor avoiding drawing undamaged areas that it did not
need to draw (surely a good idea) _and_ finding efficient work arounds
for exposures created by transparent, actively distorting and unmapped
windows.

I am uncertain whether the compositor would be the best place to try and
work around the potentially complex effects of these exposures.

Felix