feat(display): Set mono theme and add invert config

[caksoylar]

Update

This PR sets CONFIG_LV_USE_THEME_MONO by default when ZMK_DISPLAY is enabled, so that small font selection used in the built-in status screen widgets is no longer ineffective.

It also adds a new Kconfig ZMK_DISPLAY_INVERT to invert the colors used in the display from black-on-white to white-on-black, by setting the appropriate value in mono theme initialization.

Original

LVGL mono theme was getting selected by ZMK_DISPLAY but not actually used outside of the corneish_zen configuration. This change sets it by default if OLEDs or ls0xx memory displays like nice!view are used. This change could use some testing to make sure it doesn't break on OLEDs, nice!views, Adafruit memory displays etc. (Unfortunately I don't have any at the moment, tested on native_posix+SDL setup.)

Given that the theme is set correctly, we can also add an invert option by setting the dark_bg parameter of lv_theme_mono_init accordingly. The config is currently named CONFIG_ZMK_DISPLAY_INVERT but maybe it should be CONFIG_ZMK_MONO_THEME_INVERT or something else? Also it is possible that there is a better way to make this change.

[caksoylar]

One question: Should we default to LV_USE_THEME_MONO unconditionally? Right now it seems to be necessary for setting the small font via CONFIG_ZMK_LV_FONT_DEFAULT_SMALL, since it is set the ifdef block in main.c line 97. I think there might be other places where the monochrome display is assumed inherently.

In that case it can be added as select LV_USE_THEME_MONO under config ZMK_DISPLAY. If that's a good idea, I can open a separate PR for that as a fix.

[sfcgeorge]

Reviewing just to say I've been using this for a week and it's working as expected. Is there anything left to do to take this off Draft and get wider review?

[caksoylar]

On my end, the question on the previous comment is the main thing I want to clear up to figure out the best approach.

[joelspadin]

Working for me.

The config is currently named CONFIG_ZMK_DISPLAY_INVERT but maybe it should be CONFIG_ZMK_MONO_THEME_INVERT or something else?

I think what you have is fine unless mono is the only theme that will ever support being inverted.

Should we default to LV_USE_THEME_MONO unconditionally?

This seems like it would be an improvement to me, so long as it remains possible to override it to another theme. All of the most common displays to use with keyboards are monochrome.

[caksoylar]

Thanks for testing and the review @joelspadin, I changed to use the mono theme by default (using imply, so can be overridden) and simplified the init like you suggested. I also split it to two commits accordingly; I can split the PR into two if desired as well.

[petejohanson]

Just one minor code style comment. Otherwise LGTM. Thanks!

[caksoylar]

Looks like some conditional layers tests are failing but I couldn't reproduce locally 😕

Edit: Reruns after a force push seem to be succeeding OK.

[petejohanson]

Thanks!