Does Qt provide a signal we can hook into when the window changes screens (and hence the dpi scaling)?

Looks like the easiest way is to look for screenChanged then in there check if devicePixelRatio changes:

https://forum.qt.io/topic/52296/detect-changing-devicepixelratio/4

Note that this also causes issues when just showing a plot on the lower-res screen that is attached to a retina screen laptop (the fonts are two times too large and lines two times too thick) - that is, without even changing screen. I think this is something to do with the fact that the DPI device ratio is declared to be 1 for the low-res screen. If I force _dpi_ratio to return 2 then the scaling looks correct on the low-res screen (but the mouse events are then wrong...). Can people test what the behavior is like on other OSes with mixed-resolution screens?

@QuLogic - do you have any ideas since you've worked on the DPI ratio stuff before?

@astrofrog can you check with v2.0.1?

@tacaswell - this is still an issue with 2.0.1 unfortunately

It looks like you identified at least part of the machinery we need to add (screenChanged, etc.); any chance you can have a go at implementing it?

All right, I'm going to take a look at this today. This has been bugging me for a while. Wish me luck.

This bug report here describes two problems:

1. The figure did not properly get notified on a DPI change
2. The figure is rendered with incorrect DPI settings on the low-DPI monitor if a hi-DPI monitor is available on the system as-well.

#8931 only fixes the first of the two issues. Should this bug report be reopened or a separate one be created?

@burnpanck Can you make a new issue for the second?