[PyQt] Paint sync issue with OpenGL widget inside MDI area

[c c]

Tom,

That looks like an X rayed gentleman sausage! 

Rob

> On 20 Jan 2016, at 17:29, Thomas Robitaille <thomas.robitaille at gmail.com> wrote:
> 
> Hi everyone,
> 
> I am trying to add an OpenGL widget in an application I am working on
> in order to display data. However, I'm running into an issue which is
> that if I try and add the OpenGL widget to an MDI area, there is a
> very noticeable spatial lag between where the Qt window is drawn and
> the OpenGL canvas when dragging the MDI window around. Here's a short
> screencast demonstrating this problem:
> 
> https://www.youtube.com/watch?v=wBg8SRpa580&feature=youtu.be
> 
> I see this effect even with the following simple example:
> 
>    import numpy as np
> 
>    from PyQt4 import QtGui, QtOpenGL
> 
>    qtapp = QtGui.QApplication([''])
> 
>    viewer = QtOpenGL.QGLWidget()
>    viewer.resize(600,600)
> 
>    widget = QtGui.QMainWindow()
> 
>    mdi = QtGui.QMdiArea()
>    widget.setCentralWidget(mdi)
> 
>    sub = QtGui.QMdiSubWindow()
>    sub.setWidget(viewer)
>    mdi.addSubWindow(sub)
>    sub.resize(600,600)
> 
>    widget.show()
> 
>    qtapp.exec_()
> 
> Even though nothing is drawn in the OpenGL canvas, if you move the
> sub-window from side to side, you'll see that the OpenGL canvas tends
> to move ahead of the Qt sub-window.
> 
> Does anyone know how to avoid this issue?
> 
> Thanks!
> Tom
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