Qt IconEngine: Use a device pixel ratio of 1 when high-DPI pixmaps are disabled - #32221

I suspect we are using devicePixelRatio() also for other sizes like canvas/window size and event locations. Would those aspects not break when changing the behavior of devicePixelRatio()?

I suspect we are using devicePixelRatio() also for other sizes like canvas/window size and event locations. Would those aspects not break when changing the behavior of devicePixelRatio()?

This only modifies _IconEngine._devicePixelRatio(). As far as I can tell, this is only used to scale the size of the QPixMap and also is set as its devicePixelRatio:

dpr = self._devicePixelRatio()
scaled_size = QtCore.QSize(int(size.width() * dpr), int(size.height() * dpr))
pixmap = QtGui.QPixmap(scaled_size)
pixmap.setDevicePixelRatio(dpr)

On my retina display, I'm seeing the canvas and window at the correct size and events seem to still report the correct x/y coordinates.

That said:

1. I have no way to test this on Windows or Linux, where it's possible to have non-integral device pixel ratios.
2. You probably have more experience with Qt than I do!

Ok thanks for the clarification. Reviewing from the phone is not optimal as it’s harder to see all context.

The result is more complicated on Linux. If I run with QT_QPA_PLATFORM=xcb, then the resulting window is small on the 1x display and double that on the 2x display, but there is nothing wrong with the toolbar icons. If I run with QT_QPA_PLATFORM=wayland, then the resulting window is twice as big as before on the 1x display, and double that on the 2x display, but the toolbar icons are broken as in the original issue.

This PR fixes the toolbar icons in the latter case. It does not fix the inconsistency between platform libraries, which I think must have to do with the other global QApplication settings that we enable.