Add support for manually setting subpixel hinting on outputs.

[ggreer]

Many laptop screens report unknown subpixel order. Allow users to manually set subpixel hinting to work around this.

Addresses #3163

TODO: update docs.

[RedSoxFan]

Other points:

• This needs to be reset on reload (see default_output_config)
• This should probably be added to IPC_GET_OUTPUTS

[RedSoxFan]

Also just as a note, since sway is currently in a feature freeze for the 1.0 tree, this will not make it into 1.0.

[ggreer]

ggreer@iron:~/code/sway% swaymsg -t get_outputs
Output eDP-1 'Unknown 0x06D0 0x00000000' (focused)
  Current mode: 2880x1920 @ 60.007000 Hz
  Position: 0,0
  Scale factor: 2.000000
  Subpixel hinting: rgb
  Transform: normal
  Workspace: 2
  Available modes:
    2880x1920 @ 60.007000 Hz

ggreer@zinc:~% swaymsg -t get_outputs
Output eDP-1 'Lenovo Group Limited 0x4005 0x00000000' (focused)
  Current mode: 1400x1050 @ 50.000000 Hz
  Position: 0,0
  Scale factor: 1.000000
  Subpixel hinting: rgb
  Transform: normal
  Workspace: 2
  Available modes:
    640x480 @ 59.939999 Hz
    800x600 @ 60.317001 Hz
    1024x768 @ 60.004002 Hz
    1280x1024 @ 60.020000 Hz
    1400x1050 @ 50.000000 Hz

I can also change the subpixel hinting at runtime with swaymsg output eDP-1 subpixel rgb. Some apps don't pick up the new hinting until they're restarted, but app title bars are updated immediately. The difference is extremely obvious on my laptop with a 1400x1050 screen.

[RedSoxFan]

This still needs a way for the value to reset subpixel on reload. Currently, it sets WL_OUTPUT_SUBPIXEL_UNKNOWN as part of the default output config, but apply_output_config does not call wlr_output_set_subpixel for WL_OUTPUT_SUBPIXEL_UNKNOWN. Ideally, it would reset to the value it had before any manual changes

[ggreer]

Alright. I added the code to store the original subpixel value & reset it in apply_output_config(). In testing, I can run swaymsg output eDP-1 subpixel rgb and swaymsg -t get_outputs says hinting is rgb. Then I can reload my config and swaymsg -t get_outputs says unknown (which is the original value).

[RedSoxFan]

For the most part this LGTM. I personally can't tell a difference, but I'll take your word for it that it changes. Can you just make the few small changes and squash the commits together?

[ggreer]

Alright, changes made. Before merging, I want to test this again on a lower resolution display to make sure it still behaves correctly. I'm busy for the rest of the day, so it might be as late as tomorrow before I know for sure.

[emersion]

Thanks!