basic: added hsb illustration; utilities: added hsb utilities

utilities/hsb.glsl

@@ -0,0 +1,23 @@
+vec3 rgb2hsb(vec3 c){
+    vec4 K = vec4(0.0, -1.0 / 3.0, 2.0 / 3.0, -1.0);
+    vec4 p = mix(vec4(c.bg, K.wz), 
+                 vec4(c.gb, K.xy), 
+                 step(c.b, c.g));
+    vec4 q = mix(vec4(p.xyw, c.r), 
+                 vec4(c.r, p.yzx), 
+                 step(p.x, c.r));
+    float d = q.x - min(q.w, q.y);
+    float e = 1.0e-10;
+    return vec3(abs(q.z + (q.w - q.y) / (6.0 * d + e)), 
+                d / (q.x + e), 
+                q.x);
+}
+
+vec3 hsb2rgb(vec3 c){
+    vec3 rgb = clamp(abs(mod(c.x*6.0+vec3(0.0,4.0,2.0),
+                             6.0)-3.0)-1.0, 
+                     0.0, 
+                     1.0 );
+    rgb = rgb*rgb*(3.0-2.0*rgb);
+    return c.z * mix(vec3(1.0), rgb, c.y);
+}