`cosmic::theme::Button` doesn't provide a way to due fully custom theming per button

[ids1024]

Prototyping an Iced version of the keyboard view for the Configurator, it's necessary to set the background color for each key to a certain RGB value. But cosmic::theme::Button::Custom uses fn(_: &Theme) -> Appearance, so it can't just be passed an Appearance, or a closure that captures the color for the button.

Not sure how to best do this:

• A variant taking just an Appearance. Though it should probably be possible to make this dependent on light/dark theme.
• Use boxed Fn instead of plain fn
• I don't think a type generic with an Fn bound would fit here.

This is perhaps a limitation of Iced's theming system, since as far as I'm aware it doesn't provide a way to completely override the theme for specialized elements other than with a custom widget.

[mmstick]

You can make a static function for each color variant. May need a helper function for creating a custom variant in this way, as some other widgets currently have to make it easier to define.

[ids1024]

As currently implemented the colors are specified as RGB values per-key per-keyboard (to match the look of keyboards like Launch). In json files.

[mmstick]

Then yeah, there are some widgets already using a Box so it would make sense to opt for that for increased flexibility

[ids1024]

Hm. Currently all of these types in cosmic::theme are Clone + Copy. A boxed trait can be neither. Most Iced widgets don't require their style types to be clonable, but the iced_style::text::StyleSheet::Style requires Style: Default + Copy.

Arc<dyn Fn()> or Rc<dyn Fn()> would be Clone but not Copy.

Having to use boxing here (every time view is called), or reference counting, doesn't seem ideal. Though the overhead is probably not really significant...

[FreeFull]

If the Color itself is Copy, then you can just use a move closure to avoid capturing a reference to it.