I have a QGraphicsView where I'm allowing the user to change the zoom using CTRL-MouseWheel. The way QGraphicsView::scale(float, float) is setup it requires you to store the previous scale.

Ex:
Qt Code: 
  1. def wheelEvent(self, evt):
  2.         mods = evt.modifiers()
  3.         if mods == Qt.ControlModifier and evt.orientation() == Qt.Vertical:
  4.             # Most mouse types work in steps of 15 degrees
  5.             # in which case the delta value is a multiple of 120; 
  6.             # i.e., 120 units * 1/8 = 15 degrees
  7.             numDegrees = evt.delta() / 8
  8.             numSteps = numDegrees / 15
  9.  
  10.             newScale = self._scale + ((5*numSteps)/100.0)
  11.             if newScale > 0.0 and newScale < 5.0:
  12.                 self.resetMatrix()
  13.                 self.scale(newScale, newScale)
  14.                 self._scale = newScale
  15.             return
  16.         QtGui.QGraphicsView.wheelEvent(self, evt)
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First off... is there a better way of doing this?

This all falls apart because it relies on the fact that "self._scale" represents the current scale factor applied to the matrix. As well as a myriad of other issues that are caused by calling resetMatrix().

So I was wondering if there is a way to derive the current scale factor. I assumed there isn't since its not part of the public API... so I'm hoping someone has come up with a smarter way to zoom in/out.

By the way this works fine if I just want to zoom in/out but I'm also doing a fitToSelection() call which messes up everything.

Full code is available here in case anyone is interested:
http://www.qtcentre.org/forum/f-qt-p...iew-15739.html