Add support for custom font colors in the TabBar

[lodetrick]

Partially Addresses: godotengine/godot-proposals#9161
Related: #88709, #106164

The inspiration for this PR was #106164 and the desire to set a custom color for the Output and Debugger tabs now that they are within a TabBar, but there is a desire to do such, as evidenced by the previous proposal.

Currently it is impossible to set colors individually for tabs in a TabBar. This PR adds support to set custom overrides for the selected, unselected, hovered, and disabled colors on a per tab basis.

[lodetrick]

Admittedly this is lot of API for a relatively simple change. I'm curious what others think about using the set_font_color_override_all() and set_font_color_override(State p_state) convention instead, perhaps using the Button.DRAW_PRESSED enum or just making a new enum that doesn't have a PRESSED_HOVER option for clarity (because the TabBar does not support pressed and hover styles at the same time). The current method names might be a bit long but I also think that they accurately convey the use of the method.

[lodetrick]

I reduced the size of the API from eight to the three functions seen below:

extends TabContainer

func _ready():
    var color = get_tab_bar().get_font_color_override(BaseButton.DRAW_DISABLED, 3)
    get_tab_bar().set_font_color_override(BaseButton.DRAW_PRESSED, 0, Color.DEEP_PINK)
    get_tab_bar().set_font_color_override_all(2, Color.YELLOW)

This should hopefully make it easier to use, and behind the scenes it is neater, using an array of Colors instead of individual variables. Feedback is welcome on the specific enum used.

Another option would be to have a TabBar::DrawMode enum with the same values but without the DRAW_PRESSED_HOVER value. I do worry that this would be too repetitive though.

[lodetrick]

I updated to use a TabBar::DrawMode enum. I also swapped the order of the arguments, so that the tab index is always first.

extends TabContainer

func _ready():
    var color = get_tab_bar().get_font_color_override(0, TabBar.DRAW_DISABLED)
    get_tab_bar().set_font_color_override(1, TabBar.DRAW_PRESSED, Color.DEEP_PINK)
    get_tab_bar().set_font_color_override_all(2, Color.YELLOW)

[KoBeWi]

While I somewhat like the new API, for the purpose of coloring bottom panel you only need DRAW_NORMAL. Currently the buttons display the default pressed and hover colors.

Also, since the user will not have access to the tabs directly, it does not even need to be exposed. If you want to set color of a dock's tab, it can be exposed as a property of EditorDock.

Docks aside, the proposal you linked does not mention tab colors, only italics text.

[lodetrick]

I can hide these so they are just for internal use for now. I can't gauge community interest in this specific feature, its creation was motivated by compatibility for the bottom panel.

[KoBeWi]

This could be replaced by a method, like _select_color(tabs[i].font_color_overrides[DrawMode::DRAW_DISABLED], theme_cache.font_disabled_color). More readable and less repetitive.

[lodetrick]

Would it make sense to make that a macro instead, as the logic is just one line? Or would an inline function make more sense.

[KoBeWi]

Methods are better than macros. You can make a static function in cpp file, we use them sometimes.

[KoBeWi]

This is primarily made for #106164, however there is some extra stuff that likely won't be needed. Though if it's internal we can easily remove it I guess. Overall looks ok.

[lodetrick]

Could you confirm that the static function has the right qualifiers? Copied below:

static inline Color _select_color(const Color &p_override_color, const Color &p_default_color) {
	return p_override_color.a > 0 ? p_override_color : p_default_color;
}