Faster ray trace GMA

Ensure the initial ray cast is done with the smallest angle. This is
done by passing the origin (color with no chroma) and passing the ray
through a second color with (almost no chroma) to guide the direction.
This is done instead of casting through the origin and the current color
which often yields the greatest angle of deviation. This will actually
cause the GMA to converge on an optimal value in less iterations,
allowing us to only require 3 passes instead of 4 while still
maintaining a ∆h somewhere in the ~2 range.

apps/gamut-mapping/methods.js

@@ -70,16 +70,16 @@ const methods = {
 			return methods.raytrace.trace(mapColor);
 		},
 		trace: (mapColor) => {
-			let gamutColor = mapColor.to("p3-linear");
 			let achroma = mapColor.set("c", 0).to("p3-linear").coords;
+			let gamutColor = mapColor.set("c", 1e-8).to("p3-linear");
 			let raytrace = methods.raytrace.raytrace_box;
 
 			// Cast a ray from the zero chroma color to the target color.
 			// Trace the line to the RGB cube edge and find where it intersects.
 			// Correct L and h within the perceptual OkLCh after each attempt.
 			let light = mapColor.coords[0];
 			let hue = mapColor.coords[2];
-			for (let i = 0; i < 4; i++) {
+			for (let i = 0; i < 3; i++) {
 				if (i) {
 					const oklch = gamutColor.oklch;
 					oklch.l = light;
@@ -150,6 +150,11 @@ const methods = {
 				tnear = tfar;
 			}
 
+			// Result should be finite
+			if (!isFinite(tnear)) {
+				return [];
+			}
+
 			// Calculate nearest intersection via interpolation
 			return [
 				start[0] + direction[0] * tnear,