vtkAxisActor2D is not updated when window size changes

This issue was created automatically from an original Mantis Issue. Further discussion may take place here.

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If the window size changes, but the axis position remains the same, the labels are not updated as they should.

This is because in vtkAxisActor2D::BuildAxis(), if the viewport has changed, the function only checks whether the position of the actor has changed. If it is the same, the function exits, and the labels are not updated (the size of the labels should change when window size changes).

This only happens when changing the window size does not change the position of the axis.

The function should be modified to check the size of the window too.