Qwt panning broken with QT_SCREEN_SCALE_FACTORS=2

Hi,

I'm using Qwt 6.1.3 with Qt 5.10.1 (the problem has been reproduced with Qwt trunk as well).

I have a HiDPI display (dpi=192, scale factor 2). Qwt works nicely, but panner behavior is weird - it "zooms in" while dragging, so you can't see what you're actually dragging. It zooms out on mouse release.

To reproduce:
1. export QT_SCALE_FACTOR=2 (enables GUI scaling + font scaling).
(Or, set system DPI to 192 and export QT_SCREEN_SCALE_FACTORS=2, this will scale the fonts according to DPI and scale the rest of the GUI by a factor of 2).
2. Run "friedberg" or "stockchart" example.
3. Pan around with mouse middle button.

I guess it's related to displayAspectRatio property somewhere.
I can attach screenshots if needed (not sure if they would be informative though).

Thanks,
Alexander

P.S. Huge thanks for such a useful and versatile library!

I created a bug report: https://sourceforge.net/p/qwt/bugs/293/
There is already another one related to the High DPI issues: https://sourceforge.net/p/qwt/bugs/285/

Please watch the status of the bug reports - I will have time to fix those issues in the next week.

Uwe

Thanks a lot, Uwe!