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

[Eric Pettersen]

We had this behavior in our own app, but it kind of went away on its own.  We came to suspect that it had to with the setting of MACOSX_DEPLOYMENT_TARGET.  I don’t know if you set that variable in your compile, but if you do you might try changing it (or not setting it) and see what happens.

—Eric

> On Oct 6, 2019, at 1:38 PM, Patrick Stinson <patrickkidd at gmail.com> wrote:
> 
> I wonder if maybe the use of QQuickWidget child widgets enables some kind of OpenGL buffer in the QMainWindoe?
> 
>> On Oct 6, 2019, at 12:25 AM, Patrick Stinson <patrickkidd at gmail.com> wrote:
>> 
>> 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 <mailto: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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