[Octave-bug-tracker] [bug #44416] Qt toolkit OpenGL could possibly have separate painter thread

[Dan Sebald]

URL:
  <http://savannah.gnu.org/bugs/?44416>

                 Summary: Qt toolkit OpenGL could possibly have separate
painter thread
                 Project: GNU Octave
            Submitted by: sebald
            Submitted on: Tue 03 Mar 2015 08:58:10 PM GMT
                Category: Plotting with OpenGL
                Severity: 3 - Normal
                Priority: 5 - Normal
              Item Group: Feature Request
                  Status: None
             Assigned to: None
         Originator Name: 
        Originator Email: 
             Open/Closed: Open
         Discussion Lock: Any
                 Release: dev
        Operating System: Any

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Details:

I've noticed that Qt toolkit has OpenGL operating in main thread, as the
general rule is that GUI must run in the main thread.  However, the
consequence of that is that if large amounts of data are being displayed in a
plot, e.g.,


image(32*rand(20, 5000))


that the refresh in that plot window takes a great deal of CPU resources from
the rest of the GUI so that the main window is in graphics limbo when that
plot may be redrawing.  (Try dragging the main window around on top of the
figure and watch.)

The gnuplot toolkit doesn't do this because it is outboard.  The FLTK toolkit,
although also using OpenGL, doesn't either.  The GUI main window remains
usable regardless of the activity in the plot window.

I'm noting here that Qt developers have recently added a few exceptions to
"must be in main thread rule", and that it may be possible to put QPainter in
its own thread with Qt 4.8 and greater:

http://blog.qt.io/blog/2011/06/03/threaded-opengl-in-4-8/

As I understand, that should fix this screen-refresh issue for Qt graphics
toolkit.




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