[PyQt] Pixel pushing performance

[Roberto Alsina]

On Wednesday 07 May 2008 20:16:25 Håkon Bertheussen wrote:
> Hi,
>
> I'm just getting started with PyQt, trying to implement a fairly complex
> widget in python. Unfortunately, it cannot easily be painted using
> higher level drawing primitives, meaning that I have to set individual
> pixels. I realize that this obviously has a lot of overhead compared to
> a C++ implementation, but if possible I'd like to stay in Python. Here's
> what I'm doing now:
>
>      def paintEvent(self, event):
>          canvas = QtGui.QImage(event.rect().size(),
>                                QtGui.QImage.Format_RGB32)
>          for i in xrange(0, canvas.height()):
>              for j in xrange(0, canvas.width()):
>                  canvas.setPixel(j, i, 123456)
>          painter = QtGui.QPainter()
>          painter.begin(self)
>          painter.fillRect(event.rect(), QtGui.QBrush(canvas))
>          painter.end()
>
> Obviously, in my real application the inner statement in the loop is a
> bit more complex, but even the above example is slow when the widget is
> fairly large (e.g. 300x300px). Is there a way to speed this up?

Try putting very little busywork in there instead of a setPixel (like, 
calculate a square root),and I bet that will slow enough to be noticeable, 
too.

You need to find a way not to *have* to do that, or you will need to do it 
outside python. 300x300 are 90K iterations. 90K anything takes a little 
while. 

   
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