Improved LCH support

LCH.go

@@ -4,24 +4,51 @@ import (
 	"math"
 )
 
-// LCH represents a color using lightness, chroma and hue (oklch).
+// LCH represents a color using lightness, chroma and hue.
 func LCH(lightness Value, chroma Value, hue Value) Color {
-	hue *= math.Pi / 180.0
-	a := chroma * math.Cos(hue)
-	b := chroma * math.Sin(hue)
+	lightness = min(max(lightness, 0), 1)
+	hue *= math.Pi / 180
+	a := math.Cos(hue)
+	b := math.Sin(hue)
 
-	r, g, b := labToRGB(lightness, a, b)
+	if !inSRGB(lightness, a, b, chroma) {
+		chroma = findChromaInSRGB(chroma, lightness, a, b, 0.01)
+	}
 
-	r = gammaCorrection(r)
-	g = gammaCorrection(g)
-	b = gammaCorrection(b)
+	a *= chroma
+	b *= chroma
+
+	r, g, b := oklabToLinearRGB(lightness, a, b)
+
+	r = sRGB(r)
+	g = sRGB(g)
+	b = sRGB(b)
 
 	return Color{r, g, b}
 }
 
-// LAB to linear sRGB
+// findChromaInSRGB tries to find the closest chroma that can be represented in sRGB color space.
+func findChromaInSRGB(chroma Value, lightness Value, a Value, b Value, precision Value) Value {
+	high := chroma
+	low := 0.0
+	chroma *= 0.5
+
+	for high-low > precision {
+		if inSRGB(lightness, a, b, chroma) {
+			low = chroma
+		} else {
+			high = chroma
+		}
+
+		chroma = (high + low) * 0.5
+	}
+
+	return chroma
+}
+
+// OKLAB to linear RGB.
 // Source: https://bottosson.github.io/posts/oklab/
-func labToRGB(lightness Value, a Value, b Value) (Value, Value, Value) {
+func oklabToLinearRGB(lightness Value, a Value, b Value) (Value, Value, Value) {
 	l := lightness + 0.3963377773761749*a + 0.21580375730991364*b
 	m := lightness - 0.10556134581565857*a - 0.0638541728258133*b
 	s := lightness - 0.08948418498039246*a - 1.2914855480194092*b
@@ -36,21 +63,3 @@ func labToRGB(lightness Value, a Value, b Value) (Value, Value, Value) {
 
 	return red, green, blue
 }
-
-// Gamma correction
-// Source: IEC 61966-2-2
-func gammaCorrection(x Value) Value {
-	if x < 0 {
-		return 0
-	}
-
-	if x <= 0.0031308 {
-		return 12.92 * x
-	}
-
-	if x < 1.0 {
-		return 1.055*math.Pow(x, 1/2.4) - 0.055
-	}
-
-	return 1.0
-}