Qt auto scale factor for HiDPI displays

[mabelzhang]

On HiDPI displays, Ignition menus, fonts, and buttons don't appear correctly.
I don't have a non-HiDPI display to test whether this change messes it up for non-HiDPI displays. Can someone test this?

This PR is the equivalent of setting this on the command line:

export QT_AUTO_SCREEN_SCALE_FACTOR=1

I'm putting this line in ign-gazebo as opposed to ign-gui, because this environment variable needs to be set before ignition::gui::Application is called. I tried setting it in Application() constructor in ign-gui, and that did not have an effect.

Test simply with

ign gazebo

What I did test was whether this flag needs a guard, i.e. getting the value before setting it, then restoring it afterwards. It seems a guard is not needed, because after I terminate ign gazebo, then I launch another app in the same terminal that usually doesn't do auto-scale adjustment, and it still doesn't. So seems the flag is not propagated beyond program termination.

If this gets merged, then I can also add the same line before every Application() call in ign-gui entry point https://github.com/ignitionrobotics/ign-gui/blob/master/src/ign.cc It seems to work there from brief testing.

Before the fix

For example, on such a display with Gnome auto-scaling set to 200%, Ignition menu font sizes are inconsistent. Compare the font sizes of "Show/Hide Grid" and "Cell Count", which are the same size on non-HiDPI displays.
The mouse cursor takes on the wrong shape on the run button, making it difficult to unpause physics:

When a second panel is added, the cursor is always in double-arrow for the entire length of the panel title bar, which makes closing the second panel impossible:

After the fix

Font sizes are consistent, cursor size and behavior are correct:

Signed-off-by: Mabel Zhang [email protected]

[chapulina]

I've never had DPI issues with my Ignition setup, and adding this environment doesn't seem to be changing anything. So if it fixes other setups, I think it's good to add it in!

[iche033]

how about checking to see if the env variable exists and only set the the variable if it does not? This allows users to override it if needed

[mabelzhang]

Added in 04488ee
Tested with:

$ ign gazebo

in which case the window auto scales, and

$ QT_AUTO_SCREEN_SCALE_FACTOR=0 ign gazebo

in which case the window does not auto scale, and

$ QT_AUTO_SCREEN_SCALE_FACTOR=2 ign gazebo

in which case the window auto scales, and

$ QT_AUTO_SCREEN_SCALE_FACTOR=-1 ign gazebo

in which case the window does not auto scale.