[PyQt] CPU spin and an error when using QQuickPaintedItem

[Russell Warren]

Sorry... This is on 64 bit Linux with the latest version from pypi at this
moment.

On Nov 19, 2016 6:31 PM, "Russell Warren" <russ at perspexis.com> wrote:

> I'm having a CPU-spinning problem, together with an odd QObject::killTimer
> error, with a basic use case of QQuickPaintedItem.
>
> I've reduced the example down so that the meat of it is just this:
>
> 1. Create a QGraphicsScene with some QGraphicsItems in it
> 2. Create a QQuickPaintedItem to render the scene to QML
> 3. Call QGraphicsScene.render(painter) inside the .paint of
> QQuickPaintedItem
>
> When I do this, it superficially works as I want, but I get an error to
> stdout, and the CPU spins to 100%. Using strace it can be seen that the CPU
> is spinning on a poll(), like seen in this capture:
>
> https://i.snag.gy/I6QZvH.jpg
>
> The FDs being polled are a socket and an 'anon_inode:[eventfd]', which is
> (I think) the normal Qt event loop.
>
> The error that results is this:
>
>     $ python HeatMapProblem.py
>     QObject::killTimer: Timers cannot be stopped from another thread
>
> This timer problem is probably related, because the spinning is likely
> what would happen with a zero timeout timer.
>
> Everything *seems* like it is being done correctly from the Qt side of
> things. Is there something wrong I'm doing with PyQt?
>
> Basic code below (two files... heatmap.qml and HeatMapProblem.py).
>
> Thanks,
> Russ
>
> #####
> ### heatmap.qml
> #####
>
> import QtQuick 2.0
> import QtQuick.Window 2.2
> import Heatmap 1.0
>
> Window {
>     visible: true
>     width: 500
>     height: 500
>     MyHeatmap {
>         anchors.fill: parent
>     }
> }
>
> #####
> ### HeatMapProblem.py
> #####
> #!/usr/bin/env python
> import random
>
> from OpenGL import GL   # workaround for Nvidia issue on linux (see
> http://goo.gl/pGPgVz)
> import PyQt5.QtWidgets as QtWidgets
> from PyQt5.QtQuick import QQuickItem, QQuickPaintedItem, QQuickView
> import PyQt5.QtCore as QtCore
> import PyQt5.QtGui as QtGui
> import PyQt5.QtQml as QtQml
>
> class MyPolygon(QtWidgets.QGraphicsPolygonItem):
>     def __init__(self, PolyPoints, parent = None):
>         super(MyPolygon, self).__init__(PolyPoints, parent)
>         color = QtGui.QColor(*(random.randint(0, 128) for x in range(3)))
>         self.setBrush(QtGui.QBrush(color))
>
> class MyScene(QtWidgets.QGraphicsScene):
>     def __init__(self, parent=None):
>         super(MyScene, self).__init__(parent)
>         blackPen = QtGui.QPen(QtCore.Qt.black, 1)
>         blackPen.setCosmetic(True)
>
>         numWide = numHigh = 3
>         boxes = []
>         for x in range(numWide):
>             for y in range(numHigh):
>                 bl = (x*10,      y*10)
>                 tl = (x*10     , y*10 + 10)
>                 tr = (x*10 + 10, y*10 + 10)
>                 br = (x*10 + 10, y*10)
>                 polyDef = [bl, tl, tr, br, bl]
>                 poly = QtGui.QPolygonF([QtCore.QPointF(x, y) for (x, y)
> in polyDef])
>                 item = MyPolygon(poly, parent = None)
>                 item.setPen(blackPen) #polygon border
>                 self.addItem(item)
>
> class MyQMLScene(QQuickPaintedItem):
>     def __init__(self, parent = None):
>         super(MyQMLScene, self).__init__(parent)
>         self._Scene = MyScene(parent = self)
>
>     def paint(self, painter):
>         self._Scene.render(painter)  # NOTE: comment this out and no
> problems exist!
>         pass
>
> if __name__ == '__main__':
>     import sys
>     app = QtWidgets.QApplication(sys.argv)
>     QtQml.qmlRegisterType(MyQMLScene, "Heatmap", 1, 0, "MyHeatmap")
>     engine = QtQml.QQmlApplicationEngine()
>     engine.load("heatmap.qml")
>     sys.exit(app.exec_())
>
>
>
>
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