Added an OKHSL Lightness sorting in palette (#1126)

* added a lightness sort system

* static check

* lightness

* formatting

* more formatting

* more formatting

src/Autoload/Palettes.gd

@@ -4,7 +4,7 @@ signal palette_selected(palette_name: String)
 signal new_palette_created
 signal new_palette_imported
 
-enum SortOptions { NEW_PALETTE, REVERSE, HUE, SATURATION, VALUE, RED, GREEN, BLUE, ALPHA }
+enum SortOptions {NEW_PALETTE, REVERSE, HUE, SATURATION, VALUE, LIGHTNESS, RED, GREEN, BLUE, ALPHA}
 ## Presets for creating a new palette
 enum NewPalettePresetType {EMPTY, FROM_CURRENT_PALETTE, FROM_CURRENT_SPRITE, FROM_CURRENT_SELECTION}
 ## Color options when user creates a new palette from current sprite or selection

src/Palette/Palette.gd

@@ -287,6 +287,38 @@ func sort(option: Palettes.SortOptions) -> void:
 			sort_method = func(a: PaletteColor, b: PaletteColor): return a.color.s < b.color.s
 		Palettes.SortOptions.VALUE:
 			sort_method = func(a: PaletteColor, b: PaletteColor): return a.color.v < b.color.v
+		Palettes.SortOptions.LIGHTNESS:
+			# Code inspired from:
+			# gdlint: ignore=max-line-length
+			# https://github.com/bottosson/bottosson.github.io/blob/master/misc/colorpicker/colorconversion.js#L519
+			sort_method = func(a: PaletteColor, b: PaletteColor):
+				# function that returns OKHSL lightness
+				var lum: Callable = func(c: Color):
+					var l = 0.4122214708 * (c.r) + 0.5363325363 * (c.g) + 0.0514459929 * (c.b)
+					var m = 0.2119034982 * (c.r) + 0.6806995451 * (c.g) + 0.1073969566 * (c.b)
+					var s = 0.0883024619 * (c.r) + 0.2817188376 * (c.g) + 0.6299787005 * (c.b)
+					var l_cr = pow(l, 1 / 3.0)
+					var m_cr = pow(m, 1 / 3.0)
+					var s_cr = pow(s, 1 / 3.0)
+					var oklab_l = 0.2104542553 * l_cr + 0.7936177850 * m_cr - 0.0040720468 * s_cr
+					# calculating toe
+					var k_1 = 0.206
+					var k_2 = 0.03
+					var k_3 = (1 + k_1) / (1 + k_2)
+					return (
+						0.5
+						* (
+							k_3 * oklab_l
+							- k_1
+							+ sqrt(
+								(
+									(k_3 * oklab_l - k_1) * (k_3 * oklab_l - k_1)
+									+ 4 * k_2 * k_3 * oklab_l
+								)
+							)
+						)
+					)
+				return lum.call(a.color.srgb_to_linear()) < lum.call(b.color.srgb_to_linear())
 		Palettes.SortOptions.RED:
 			sort_method = func(a: PaletteColor, b: PaletteColor): return a.color.r < b.color.r
 		Palettes.SortOptions.GREEN:

src/Palette/PalettePanel.gd

@@ -49,6 +49,8 @@ func _ready() -> void:
 	sort_button_popup.add_item("Sort by saturation", Palettes.SortOptions.SATURATION)
 	sort_button_popup.add_item("Sort by value", Palettes.SortOptions.VALUE)
 	sort_button_popup.add_separator()
+	sort_button_popup.add_item("Sort by lightness", Palettes.SortOptions.LIGHTNESS)
+	sort_button_popup.add_separator()
 	sort_button_popup.add_item("Sort by red", Palettes.SortOptions.RED)
 	sort_button_popup.add_item("Sort by green", Palettes.SortOptions.GREEN)
 	sort_button_popup.add_item("Sort by blue", Palettes.SortOptions.BLUE)