PutImage vs BackgroundPixmap (was Re: Open Shared Memory and Render Pictures)

Michael Titke michael.tiedtke at o2online.de
Sun Aug 7 18:26:37 UTC 2016

On 07/08/2016 18:02, Thomas L├╝bking wrote:
> On Sat, Aug 06, 2016 at 05:18:43PM +0200, Michael Titke wrote:
>> 16 ms ? Usually a hollywood frame needs to be done within 40 ms
> But your screen refreshes at snappy 60Hz and not some choppy 24fps :-)
> To be more serious, we clamped resizing to 30fps in kwin (for clients
> which didn't support the XSYNC protocol) to lower the load on the
> client. Reason was that no human being can reasonably control sizes at
> that speed anyway and it's still "smooth enough".
>> Maybe those old WindowMaker routines from the nineties with the one 
>> pixel bitblt inverse frame ... ;-)
> Still supported by some WMs. Pace is naturally unbeatable.
>> Actually the terminal emulators seem to perform better visually: they 
>> only resize when the resize would add or remove a
>> row or column from the matrix.
After another review that was only XTerm to perform well: some Gnome 
Terminal repaints with white during the overloaded window resizes and 
konsole prefers to show you the composited frame shadows and the 
background of the last resizes for a glimpse.

> That's for the baseincrement size hint. Every client can make use of
> that but it's oc. very reasonable for clients which display rows and
> comlums of chars.
>> frequency events will exhibit some sort flickering effect especially
>> because the window in the frame buffer / on screen is erased by the 
>> drawing routine of the client when the server already
>> did that for the expose event.
> BackingStore, SaveUnder and/or compositors eleminate that problem.
My preliminary solution was the background pixmap of what was drawn 
where the backing store needs to be readjusted to the actual window 
size. That would have been another great opportunity to run into the 
shared memory segment limit and see the desktop come to a halt. Thanks 
to cgroup terminating the session is enough to get a working desktop 
back but the list of shared segments of my mischiefed stress test 
remained in the system data structures and that rebooting attitude ...
That's then the render extension, inter client communication protocol 
and xsync as the next extensions to implement. Thank you for the 
property and xsync hints!

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