There is a bug when zooming on a QCPCurve polygone,
the edges are sometimes moving, it is quiet difficult to explain this,
I should post my exe file to show this bug.
This occurs only with a polygone where one angle is less than 90 degree
and zooming on it :
Here the code to draw this polygone:
Then zoom on the vertex located at (10,10) then move the vertex
ouside the graph view, you will see the two edges moving on a wrong way.
More you are zooming more the edges are moving.