On Fri, 21 Jun 2002, Lukas Molzberger wrote:
> Hello,
> I'm using Linux and XFree for quite some time now and I'm a big fan of it.
> However, there is one bug that has always annoyed me. When I resize a window
> under XFree then it can take a long time until the content of this window is
> redrawn.
This has little to do with the X-server. Many window managers do not
optimize window resizes well (they aren't compressing the events) and
many clients do not handle exposures very well. I don't think there's
much on the X-server side that can make up for that.
> Another thing that I've noticed is that when moving a window from left to
> right or vice versa the window is split along a line and the upper part of
> the window is drawn at a slightly different position than the lower part.
> This splitting line is always at a different position. I think this happens
> because X doesn't synchronize with the horizontal screen refresh. X should
> wait until the screen refresh is finished before changing the frame buffer so
> that only a consistent picture is brought to the screen.
> In case I got something wrong here than I would like to apologize for it.
>
Window moves shouldn't synchronize with the refresh rate because
of the performance penalty it would impose. All other rendering would
be suspended until the next retrace whenever you wanted to move a
window. This shearing effect can mostly be eliminated by sychronizing
your pointer sampling rate to the refresh rate. Just set you pointer
sample rate to 80 Hz and also your refresh rate to 80 Hz and you will
find that all mouse-driven operations will appear much smoother.
Also, given that the X-server is a user-space app. Synchronizing
blits with the retrace is typically not possible on most hardware.
Mark.
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