色空間 > HLS
V = max(R,G,B) S = (V-min(R,G,B))/V if V<>0, 0 otherwise H = (G - B)/6/S, if V=R; 1/2+(B - R)/6/S, if V=G; 2/3+(R - G)/6/S, if V=B.
// clamp( abs(fract(h+vec3(0,2,1)/3) * 6 - 3) - 1, 0, 1) return ((clamp(abs(fract(h+vec3(0,2,1)/3.)*6.-3.)-1.,0.,1.)-1.)*s+1.)*v;