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

[Patrick Stinson]

This was recently fixed as a function of OpenGL support. I can’t find the bug report but it may be in 5-14

> On Oct 10, 2019, at 9:35 AM, Patrick Stinson <patrickkidd at gmail.com> wrote:
> 
> Looks like this is just a function of QQuickWidget, either in a layout or standalone:
> 
>     app = QApplication(sys.argv)
>     mw = QWidget()
>     w = QQuickWidget()
>     Layout = QVBoxLayout(mw)
>     Layout.addWidget(w)
>     mw.show()
>     app.exec()
> 
> 
>     app = QApplication(sys.argv)
>     mw = QQuickWidget()
>     mw.show()
>     app.exec()
> 
>> On Oct 10, 2019, at 9:29 AM, Patrick Stinson <patrickkidd at gmail.com <mailto:patrickkidd at gmail.com>> wrote:
>> 
>> Turns out simply adding a QQuickWidget as a child to QMainWindow::centralWidget causes this problem. I imagine this is because of the OpenGL buffer in QtQuick:
>> 
>>     app = QApplication(sys.argv)
>>     mw = QMainWindow()
>>     w = QQuickWidget()
>>     mw.setCentralWidget(w)
>>     mw.show()
>>     app.exec()
>> 
>> Does anyone know of a workaround for this? It makes the app look so ugly!
>> 
>>> On Oct 7, 2019, at 2:10 PM, Eric Pettersen <pett at cgl.ucsf.edu <mailto:pett at cgl.ucsf.edu>> wrote:
>>> 
>>> 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 <mailto: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 <mailto: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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>>> 
>> 
> 

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