Quote Originally Posted by wysota View Post
It would not be cosmetic anymore. You can try applying an inverted transformation on the item, but this won't increase rendering speed.
Thanks for making it clear that there is no way to archieve this without triggering manual coordinate transformations, wysota. I am, however, having problems even with that. I found the thread where spud claims to know how to draw the handles of an item scale- and rotation-invariant, however, the solution is not presented in the thread.

After trying out all kinds of different transformations, I found something that seems to yield the right result, but is not consistent with the documentation:

Qt Code: 
  1. QPen pen;
  2. pen.setWidthF(5./qAbs(painter->deviceTransform().m12()));
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Qt's documentation says QTransform::m12() and m21() describe the shearing factors. They are for my (scaled, non-sheared) example however working: I get a pen with a constant size in pixels on my QGraphicsView. m11() and m22() on the other hand, which were supposed to describe the scaling, are constant zero.

So either I am doing this wrong, and this is just working by coincidence, or the documentation is wrong. I would be surprised by that though, as my intuition also says that scaling should be on the main diagonal of the transformation matrix..

I'll see if I can revive the before-mentioned old thread.