WIP HSV lerp

scripts/util/colors.ts

@@ -59,10 +59,88 @@ function rgbaTupleLerp(colorA: RgbaTuple, colorB: RgbaTuple, alpha: number): Rgb
  * Blends two colors linearly (not HSV lerp).
  * RGB inputs are converted to RGBA with A value of 1.
  */
-function rgbaStringLerp(colorA: string, colorB: string, alpha: number): string {
+function rgbaStringLerp(colorA: string, colorB: string, alpha: number, useHsv: boolean = false): string {
 	const arrayA = rgbaStringToTuple(colorA);
 	const arrayB = rgbaStringToTuple(colorB);
-	return tupleToRgbaString(rgbaTupleLerp(arrayA, arrayB, alpha));
+	if (!useHsv) return tupleToRgbaString(rgbaTupleLerp(arrayA, arrayB, alpha));
+
+	const FromHSV: RgbaTuple = LinearRGBToHSV(arrayA) as RgbaTuple;
+	const ToHSV: RgbaTuple = LinearRGBToHSV(arrayB) as RgbaTuple;
+
+	// Take the shortest path to the new hue
+	if (Math.abs(FromHSV[0] - ToHSV[0]) > 180) {
+		if (ToHSV[0] > FromHSV[0]) {
+			FromHSV[0] += 360;
+		} else {
+			ToHSV[0] += 360;
+		}
+	}
+	const newHsv = rgbaTupleLerp(FromHSV, ToHSV, alpha);
+
+	newHsv[0] = newHsv[0] % 360;
+	if (newHsv[0] < 0) {
+		newHsv[0] += 360;
+	}
+
+	const newRgb: RgbaTuple = HSVToLinearRGB(newHsv) as RgbaTuple;
+
+	return tupleToRgbaString(newHsv);
+}
+/** Converts an HSV color to a linear space RGB color */
+function HSVToLinearRGB([h, s, v, a]: RgbaTuple): number[] {
+	// In this color, R = H, G = S, B = V
+	const Hue = h;
+	const Saturation = s;
+	const Value = v;
+
+	const HDiv60 = Hue / 60;
+	const HDiv60_Floor = Math.floor(HDiv60);
+	const HDiv60_Fraction = HDiv60 - HDiv60_Floor;
+
+	const RGBValues: RgbaTuple = [
+		Value,
+		Value * (1 - Saturation),
+		Value * (1 - HDiv60_Fraction * Saturation),
+		Value * (1 - (1 - HDiv60_Fraction) * Saturation)
+	];
+	const RGBSwizzle = [
+		[0, 3, 1],
+		[2, 0, 1],
+		[1, 0, 3],
+		[1, 2, 0],
+		[3, 1, 0],
+		[0, 1, 2]
+	];
+	const SwizzleIndex = HDiv60_Floor % 6;
+
+	return [
+		RGBValues[RGBSwizzle[SwizzleIndex][0]] * 255,
+		RGBValues[RGBSwizzle[SwizzleIndex][1]] * 255,
+		RGBValues[RGBSwizzle[SwizzleIndex][2]] * 255,
+		a
+	];
+}
+
+function LinearRGBToHSV([r, g, b, a]: RgbaTuple): number[] {
+	const RGBMin = Math.min(r, g, b);
+	const RGBMax = Math.max(r, g, b);
+	const RGBRange = RGBMax - RGBMin;
+
+	const Hue =
+		RGBMax === RGBMin
+			? 0
+			: RGBMax === r
+			? (((g - b) / RGBRange) * 60 + 360) % 360
+			: RGBMax === g
+			? ((b - r) / RGBRange) * 60 + 120
+			: RGBMax === b
+			? ((r - g) / RGBRange) * 60 + 240
+			: 0;
+
+	const Saturation = RGBMax === 0 ? 0 : RGBRange / RGBMax;
+	const Value = RGBMax / 255;
+
+	return [Hue, Saturation, Value, a];
 }
 
 /**