Set some Qt settings to play nicer on High DPI displays

`labscript_utils.splash` is the first place a `QApplication` gets
created for all of our apps. So setting these settings there applies
them to all our applications, although they are also needed for the
splash screen itself to be scaled better on High DPI displays.

`AA_EnableHighDpiScaling` scales all pixel metrics to the device pixel
ratio - so this means curved edges and padding and whatnot get scaled
up, as well as the size of some pixmaps.

`AA_UseHighDpiPixmaps` means to use high DPI pixmaps for icons etc,
directly, rather than rendering them at the lower resolution and then
scaling them up (not sure why anyone would want the latter behaviour).
Strangely, high resolution pixmaps *are* used when
`AA_EnableHighDpiScaling` is *off*. It's only when it is turned on that
they get downscaled and then upscaled again and end up blocky.

Author: chrisjbillington

labscript_utils/splash.py

@@ -29,6 +29,15 @@
 Qt = QtCore.Qt
 
 
+# Set auto high-DPI scaling - this ensures pixel metrics are scaled
+# appropriately so that we don't get a weird mix of large fonts and small
+# everything else on High DPI displays:
+QtWidgets.QApplication.setAttribute(Qt.AA_EnableHighDpiScaling, True)
+# Use high res pixmaps if available, instead of rendering at low resolution and
+# upscaling:
+QtWidgets.QApplication.setAttribute(Qt.AA_UseHighDpiPixmaps, True)
+
+
 class Splash(QtWidgets.QFrame):
     w = 250
     h = 230