[PyQt] Resize flicking on QMainWindow centralWidget in python but not C++

[Patrick Stinson]

I put a qDebug() line in QMainWindow() and QOpenGLWidget(), rebuilt/installed Qt, and ran my app. I saw the line for the QMainWindow() but not QOpenGLWidget(), so that means QOpenGLWidget isn’t being run in my app. But I am still seeing the problem. Difficult to pinpoint as a reproducible report.

> On Oct 5, 2019, at 10:25 PM, Patrick Stinson <patrickkidd at gmail.com> wrote:
> 
> So it does, and changing that makes it work like the C++ example.
> 
> My own app is still showing the problem even without using QOpenGLWidget. I wonder if there is some setting somewhere that implicitly uses QOpenGLWidget….
> 
>> On Oct 5, 2019, at 5:36 PM, Eric Pettersen <pett at cgl.ucsf.edu <mailto:pett at cgl.ucsf.edu>> wrote:
>> 
>> Your Python class inherits from QOpenGLWidget.  Your C++ class inherits from QWidget.
>> 
>>> On Oct 5, 2019, at 2:10 PM, Patrick Stinson <patrickkidd at gmail.com <mailto:patrickkidd at gmail.com>> wrote:
>>> 
>>> Hello,
>>> 
>>> On MacOS, a QMainWindow with a simple painted centralWidget flickers when resizing quickly in python but not in C++. This only occurs with QMainWindow It is particularly pronounced more complex widgets, as shown in the following video:
>>> 
>>> https://youtu.be/0Qjy2wm6m9M <https://youtu.be/0Qjy2wm6m9M>
>>> 
>>> Here is the python example that shows the bug. Just run, rapidly resize the height of the widget , and observe a black flickering on the top edge of the widget as the height changes.
>>> 
>>> class Widget(QOpenGLWidget):
>>>     def paintEvent(self, e):
>>>         p = QPainter(self)
>>>         p.setBrush(Qt.red)
>>>         p.drawRect(self.rect())
>>> 
>>> app = QApplication(sys.argv)
>>> mw = QMainWindow()
>>> w = Widget()
>>> mw.setCentralWidget(w)
>>> mw.show()
>>> w.show()
>>> app.exec()
>>> 
>>> 
>>> The following 1-to-1 C++ translation shows no such behavior:
>>> 
>>> 
>>> #include <QApplication>
>>> #include <QMainWindow>
>>> #include <QWidget>
>>> #include <QPainter>
>>> 
>>> class Widget : public QWidget {
>>> public:
>>>     void paintEvent(QPaintEvent *) {
>>>         QPainter p(this);
>>>         p.setBrush(Qt::red);
>>>         p.drawRect(rect());
>>>     }
>>> };
>>> 
>>> int main(int argc, char *argv[])
>>> {
>>>     QApplication a(argc, argv);
>>>     QMainWindow mw;
>>>     QWidget *w = new Widget;
>>>     mw.setCentralWidget(w);
>>>     mw.show();
>>>     return a.exec();
>>> }
>>> 
>>> 
>>> 
>>> 
>>> 
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>> 
> 

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