[Bug]: Zoom rubber band lags in larger window #23968

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1. inxp

   changed the title [-]Zoom rubber band lags in larger window[Bug]: [/-] [+][Bug]: Zoom rubber band lags in larger window[/+] on Sep 20, 2022
2. QuLogic commented on Sep 20, 2022

   

   QuLogic

   on Sep 20, 2022

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   How large is large enough to be slow?
3. QuLogic

   added

   Performance

   on Sep 20, 2022
4. inxp commented on Sep 21, 2022

   

   inxp

   on Sep 21, 2022

   Last edited by inxp

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   The GIF that I posted is a window stretched over two 24" monitors, each having 1920x1080 resolution.

   For me, the lag becomes noticeable in a 1920x1080 window.

   Note that the same lag does not exist or is very low in the matplotlib 2.2.5 version with the Qt5Agg backend.

   There is no lag in TkAgg backend for any window size.

   Please try comparing the performance of rubber band in the following code between Matplotlib version 2.2.5 and 3.6.0.

   
   
   import sys
   from PyQt5.QtWidgets import QWidget, QApplication, QPushButton, QVBoxLayout
   
   from matplotlib.backends.backend_qt5agg import FigureCanvasQTAgg as FigureCanvas
   from matplotlib.backends.backend_qt5agg import NavigationToolbar2QT as NavigationToolbar
   import matplotlib.pyplot as plt
   
   import random
   
   class Window(QWidget):
       def __init__(self, parent=None):
           super(Window, self).__init__(parent)
   
           self.figure = plt.figure()
           
           data = [random.random() for i in range(10)]
   
           ax = self.figure.add_subplot(111)
   
           ax.plot(data, '*-')
   
           self.canvas = FigureCanvas(self.figure)
   
           self.toolbar = NavigationToolbar(self.canvas, self)
           
           self.canvas.draw()
   
           layout = QVBoxLayout()
           layout.addWidget(self.toolbar)
           layout.addWidget(self.canvas)
           self.setLayout(layout)
   
       
   if __name__ == '__main__':
       app = QApplication(sys.argv)
   
       main = Window()
       main.showMaximized()
   
       sys.exit(app.exec_())
   
   
   
5. inxp commented on Dec 11, 2022

   

   inxp

   on Dec 11, 2022

   Last edited by inxp

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   Update

   On further testing, I found that lag is there even when dragging legends.

   So I checked paintEvent function in FigureCanvasQTAgg of \backends\backend_qtagg.py

   The delay was mainly due to following statement in _unmultipled_rgba8888_to_premultiplied_argb32 function of cbook\__init__.py

   argb32 = np.take(rgba8888, [2, 1, 0, 3], axis=2)
   

   _unmultipled_rgba8888_to_premultiplied_argb32 function is called by paintEvent function

   The function call was added as part of #11845 commit.

   On reverting the changes done in commits #11731 and #11845, The lag was gone. Everything is working as expected.

   So I think, as window size increases it takes more time for np.take statement causing delay between subsequent paints.

   Am I doing something wrong?
6. jklymak commented on Dec 11, 2022

   

   jklymak

   on Dec 11, 2022

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   @anntzer you introduced _unmultiplied_rgba8888_to_premultiplied_argb32 in #11845, and the original issue says maybe it was an issue with qt5.1 and earlier. Given that qt5.2 is now 9 years old do we need to support 5.1 any longer and maybe this function isn't required?
7. timhoffm

   closed this as completedin #24692on Dec 11, 2022
8. QuLogic

   added this to the v3.6.3 milestone on Dec 12, 2022