How to improve QGraphicsView performance in a 2D static scene with many items? (no way to solve it?)

If understood correctly, QGraphicsView is supposed to handle million items efficiently.

In my application, I only have some few thousand and the performance is already very bad. When the View is showing the whole scene, zooming, hoverEnvents and any other stuff becomes impossible.

I have tried to create a parent-child relationship among items, and different optimization flags, but still the same result. I really hope that I'm making some stupid mistake, but after several days looking for a way to solve the problem, I did not find any solution.

I would really appreciate any help!

This reproduces my problem:

import sys
import random
from PyQt4.QtGui import * 

NO_INDEX = False
OPTIMIZE = False
ITEM_COORD_CACHE = False
ITEM_DEVICE_CACHE = False
NESTED_ITEMS = False


class TestItem(QGraphicsEllipseItem):
    def paint(self, painter, option, index):
        return QGraphicsEllipseItem.paint(self, painter, option, index)

    def hoverEnterEvent (self, e):
        self.setBrush(QBrush(QColor("orange")))

    def hoverLeaveEvent(self,e):
        self.setBrush(QBrush(None))

if __name__ == '__main__':
    n = int(sys.argv[1]) # Number of items. With 5000 I already
                           # have performance problems
    app = QApplication(sys.argv)
    scene = QGraphicsScene()

    # Populates scene
    prev = None
    for i in xrange(n):
        # Random geometry and position
        r1 = random.randint(10, 100)
        r2 = random.randint(10, 100)
        x = random.randint(0, 500)
        y = random.randint(0, 500)

        item = TestItem(x, y, r1*2, r2*2)
        item.setAcceptsHoverEvents(True)

        if NESTED_ITEMS: 
            # Creates a parent child structure among items
            if not prev:
               开发者_C百科 scene.addItem(item)
            else:
                item.setParentItem(prev)
            prev = item
        else:
            scene.addItem(item)

        if ITEM_COORD_CACHE:
            item.setCacheMode(QGraphicsItem.ItemCoordinateCache)
        elif ITEM_DEVICE_CACHE:
            item.setCacheMode(QGraphicsItem.DeviceCoordinateCache)

    # Creates View
    view = QGraphicsView(scene)
    # Sets basic Flags for nice rendering 
    view.setRenderHints(QPainter.Antialiasing or QPainter.SmoothPixmapTransform)

    if NO_INDEX:
        view.setItemIndexMethod(QGraphicsScene.NoIndex);

    if OPTIMIZE:
        view.setOptimizationFlags(QGraphicsView.DontAdjustForAntialiasing
                                  or QGraphicsView.DontClipPainter
                                  or QGraphicsView.DontSavePainterState)

    view.show()
    sys.exit(app.exec_())

• Intel(R) Xeon(R) CPU E5410 @ 2.33GHz
• nVidia Corporation G84 [Quadro FX 1700]
• Ubuntu 9.04 64 bits
• qt4 4.5.3
• python-qt4 4.6

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Basically, what you can play with are cache modes and update modes, but also the size of the bsp-tree of the scene. Also, this speech from DevDays 2010 gives some hints and tips: http://qt.nokia.com/developer/learning/online/talks/developerdays2010/tech-talks/qt-graphics-view-in-depth .