Reimplement ColorPicker presets

[Geometror]

Reimplements the color preset functionality of the ColorPicker:

Changes:

• Reimplement color picker presets with custom Button (ColorPresetButton)
  Presets were disabled due to the way they were implemented as stated by reduz's comment: //presets should be shown using buttons or something else, this method is not a good idea (the former method was using a TextureRect for the whole palette)
• Add the overbright indicator which is already used in other places of the ColorPicker and an alpha checker board background for transparent colors
• Some small structural improvements to the code for better readability

[fire]

This design is on the right track. Something came up, maybe @groud can review.

[KoBeWi]

I get this crash when I try to remove preset:

CrashHandlerException: Program crashed
Dumping the backtrace. Please include this when reporting the bug on https://github.com/godotengine/godot/issues
[0] StyleBoxFlat::set_bg_color (C:\godot_source\scene\resources\style_box.cpp:315)
[1] ColorPresetButton::_notification (C:\godot_source\scene\gui\color_picker.cpp:1452)
[2] ColorPresetButton::_notificationv (C:\godot_source\scene\gui\color_picker.h:48)
[3] Object::notification (C:\godot_source\core\object\object.cpp:843)
[4] CanvasItem::_update_callback (C:\godot_source\scene\main\canvas_item.cpp:153)
[5] call_with_variant_args_helper<CanvasItem> (C:\godot_source\core\variant\binder_common.h:227)
[6] call_with_variant_args_dv<CanvasItem> (C:\godot_source\core\variant\binder_common.h:370)
[7] MethodBindT<CanvasItem>::call (C:\godot_source\core\object\method_bind.h:287)
[8] Object::call (C:\godot_source\core\object\object.cpp:832)
[9] Callable::call (C:\godot_source\core\variant\callable.cpp:62)
[10] MessageQueue::_call_function (C:\godot_source\core\object\message_queue.cpp:259)
[11] MessageQueue::flush (C:\godot_source\core\object\message_queue.cpp:306)
[12] Main::iteration (C:\godot_source\main\main.cpp:2521)
[13] OS_Windows::run (C:\godot_source\platform\windows\os_windows.cpp:626)
[14] widechar_main (C:\godot_source\platform\windows\godot_windows.cpp:163)
[15] _main (C:\godot_source\platform\windows\godot_windows.cpp:185)
[16] main (C:\godot_source\platform\windows\godot_windows.cpp:199)
[17] __scrt_common_main_seh (D:\a01\_work\26\s\src\vctools\crt\vcstartup\src\startup\exe_common.inl:288)
[18] BaseThreadInitThunk
-- END OF BACKTRACE --

[EricEzaM]

Looks like the destroctor runs which calls unref on a static property, so the next time draw is called on any button it crashes.

[KoBeWi]

Is there even a need for cached stylebox? They aren't very expensive. You could create them on demand to prevent having lots of unused styleboxes in every picker. Or maybe put it in theme and add checks that ensure it's StyleboxFlat (or a StyleboxTexture, which you could colorize; that would be interesting option for customization).

[KoBeWi]

You could actually avoid adding a new class if you made a flat button and used draw signal to handle custom drawing inside ColorPicker and modulate instead of pick color.

[Geometror]

Fixed the crash. (the cached stylebox was a bad last-minute decision without testing :/)
I chose to implement the presets with a custom button class because a normal button is more expensive to create (even with no text a shaped_text gets created) and it felt less hacky in general. But if adding a new class is undesired, I will change that.
The idea to make the color preset stylebox part of the theme is pretty good, I will look into that tomorrow :)

[KoBeWi]

Ah, you are right. Having a custom button is more light-weight in this case, so it's ok.

[Geometror]

• Added theming support for the ColorPresetButton (StyleBoxFlat and StyleBoxTexture are supported)
  • the foreground can be changed (StyleBoxFlat and StyleBoxTexture are supported)
  • the overbright indicator can be changed (default is white corner triangle)
  • the preset background texture can be changed (default is MiniCheckerboard)
    Now something like this is possible when using a ColorPicker in a project:
    
• Moved splitted ColorPickerButton theming in default_theme.cpp (there was one large codeblock and one line at another place in the file) Now ColorPicker, ColorPresetButton and ColorPickerButton are all at one place.
• Renamed preset_bg to sample_bg to be more descriptive (because it was only used for the sample area in the ColorPicker)/ preset_bg is now actually used for the presets
• Optimization: only update the presets when the their desired size has changed during a theme change (NOTIFICATION_THEME_CHANGED is still sent 4-8 times when selecting another node in the scene tree)

[YuriSizov]

With styling support like this I kind of think it could be made into a separate ColorPalette control, so it could be used independent from the ColorPicker.

[KoBeWi]

I think that could be done in another PR.

[KoBeWi]

Looks ok overall, but change the conditions in NOTIFICATION_DRAW like I commented.

[fire]

Thanks.

[akien-mga]

This would need a dedicated backport PR for 3.x if wanted there. Maybe also without the theme item rename to avoid breaking compat? Provided that it was working in 3.3.