Add gamutSpace to ColorSpace

Some colorspaces such as hsluv, okhsl and okhsv need to do
gamut checking in a color space that is not their own space or
their base space. For example hsluv needs to do gamut checking in
the srgb color space.

A gamutSpace can now be specified when constructing a ColorSpace and
a gamutSpace property has beed added to ColorSpace.

If a gamutSpace is not specified the following rules are used to
assign the gamutSpace property:

- if the color space is polar use the base space
- if the color space is not polar use the current space

Polar spaces that need to gamut check themselves (hpluv) can set the
gamutSpace option to "self" to avoid gamut checking using the base
space.

src/space.js

@@ -53,6 +53,30 @@ export default class ColorSpace {
 			this.formats.color.id = this.id;
 		}
 
+		// Gamut space
+
+		if (options.gamutSpace) {
+			// Gamut space explicitly specified
+			this.gamutSpace = options.gamutSpace === "self" ? this : ColorSpace.get(options.gamutSpace);
+		}
+		else {
+			// No gamut space specified, calculate a sensible default
+			if (this.isPolar) {
+				// Do not check gamut through polar coordinates
+				this.gamutSpace = this.base;
+			}
+			else {
+				this.gamutSpace =  this;
+			}
+		}
+
+		// Optimize inGamut for unbounded spaces
+		if (this.gamutSpace.isUnbounded) {
+			this.inGamut = (coords, options) => {
+				return true;
+			};
+		}
+
 		// Other stuff
 		this.referred = options.referred;
 
@@ -68,11 +92,9 @@ export default class ColorSpace {
 	}
 
 	inGamut (coords, {epsilon = ε} = {}) {
-		if (this.isPolar) {
-			// Do not check gamut through polar coordinates
-			coords = this.toBase(coords);
-
-			return this.base.inGamut(coords, {epsilon});
+		if (!this.equals(this.gamutSpace)) {
+			coords = this.to(this.gamutSpace, coords);
+			return this.gamutSpace.inGamut(coords, {epsilon});
 		}
 
 		let coordMeta = Object.values(this.coords);

types/src/space.d.ts

@@ -37,6 +37,7 @@ export interface Options {
 	cssId?: string | undefined;
 	referred?: string | undefined;
 	formats?: Record<string, Format> | undefined;
+	gamutSpace?: "self" | string | ColorSpace | null | undefined;
 }
 
 export type Ref =
@@ -91,6 +92,7 @@ export default class ColorSpace {
 	formats: Record<string, Format>;
 	referred?: string | undefined;
 	white: White;
+	gamutSpace: ColorSpace;
 
 	from (color: Color | ColorObject): Coords;
 	from (space: string | ColorSpace, coords: Coords): Coords;