[PyQt] QGraphicsView very slow under Linux and Mac OS X

[Clemens Brunner]

Hi,

I've also posted this question as a bug report at qt-project.org 
(https://bugreports.qt-project.org/browse/PYSIDE-151), but this is also a PyQt 
issue.

QGraphicsView is apparently very slow under Linux and Mac OS X. I've attached 
an example program (runs with PySide or PyQt). The signals should be updated 
every 25ms; the actual timer intervals are displayed on the console. Now under 
Linux and Mac OS X, the graphics get slower with increasing window size. In 
full screen, the timer intervals are around 100ms instead of 25ms on my 
machines.

This problem does not exist under Windows. Here, the intervals are not affected 
by window size, and the intervals stay at the given values. Interestingly, the 
program runs perfectly fast even in a Windows inside a VM.

Furthermore, this problem is PySide (or PyQt) specific, because this behavior 
does not occur when I use Qt from C+. In C+, the program works as expected on 
all three platforms.

Thanks,
Clemens


import sys
from PyQt4 import QtGui, QtCore, QtOpenGL

import random
import math

class SignalItem(QtGui.QGraphicsItem):
    def __init__(self, nr):
        super(SignalItem, self).__init__()
        self.setFlags(QtGui.QGraphicsItem.ItemUsesExtendedStyleOption)
        
        self.nr = nr
        self.fr = random.randint(3, 50)
        self.bg = QtGui.QColor(random.randint(200,255),random.randint(200,255),random.randint(200,255))
    
    def boundingRect(self):
        return QtCore.QRectF(0, self.nr*50, 10000, 50)
    
    def paint(self, painter, option, widget):
        painter.fillRect(option.exposedRect, self.bg)
        self.prevY = math.sin((int(option.exposedRect.left()) - 1)/float(self.fr))*10 + 25 + self.nr*50
        for x in range(int(option.exposedRect.left()), int(option.exposedRect.right())):
            y = math.sin(x/float(self.fr))*10 + 25 + self.nr*50 
            painter.drawLine(x-1, self.prevY, x, y)
            self.prevY = y


class Dummy(QtCore.QObject):
    def __init__(self):
        super(Dummy, self).__init__()
        self.scene = QtGui.QGraphicsScene()

        for i in range(40):
            item = SignalItem(i)
            self.scene.addItem(item)

        self.view = QtGui.QGraphicsView(self.scene)
        self.view.show()

        self.startTimer(25)
        self.x = 0
        self.lastTimerEvent = None

    def timerEvent(self,event):
        self.x += 1
        self.view.horizontalScrollBar().setValue(self.x)
        currentTime = QtCore.QTime.currentTime()
        if self.lastTimerEvent:
            print self.lastTimerEvent.msecsTo(currentTime)
        self.lastTimerEvent = currentTime


if __name__ == '__main__':
    app = QtGui.QApplication(sys.argv)
    d = Dummy()
    sys.exit(app.exec_())

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