From 86e54bd373974dfc775fca51435248045a7cc6ed Mon Sep 17 00:00:00 2001
From: hellerve <veit@veitheller.de>
Date: Mon, 5 Jun 2017 21:17:55 -0400
Subject: [PATCH] basic: added ryb example

---
 basic/ryb_and_beyond.glsl | 49 +++++++++++++++++++++++++++++++++++++++
 1 file changed, 49 insertions(+)
 create mode 100644 basic/ryb_and_beyond.glsl

diff --git a/basic/ryb_and_beyond.glsl b/basic/ryb_and_beyond.glsl
new file mode 100644
index 0000000..44c6ecf
--- /dev/null
+++ b/basic/ryb_and_beyond.glsl
@@ -0,0 +1,49 @@
+#ifdef GL_ES
+precision mediump float;
+#endif
+
+#define TAU 6.28318530718
+
+uniform vec2 u_resolution;
+
+vec3 hsb2rgb( in 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);
+}
+
+float scale_with(float hue, vec2 begin, vec2 end) {
+    return (((end.y-begin.y)/(end.x-begin.x))*(hue-begin.x)+begin.y);
+}
+
+// if you find the right values for bbend and ebend, you can scale parts of the color spectrum
+float scale(float hue) {
+    vec2 bbend = vec2(0.250,0.330);
+    vec2 ebend = vec2(0.340,0.390);
+    
+    if (hue < bbend.x) {
+        return scale_with(hue, vec2(0,0), bbend);
+    } else if (hue < ebend.x) {
+        return scale_with(hue, bbend, ebend);
+    }
+    return scale_with(hue, ebend, vec2(1.0, 1.0));
+}
+
+void main(){
+    vec2 st = gl_FragCoord.xy/u_resolution;
+    vec3 color = vec3(0.0);
+
+    // Use polar coordinates instead of cartesian
+    vec2 toCenter = vec2(0.5)-st;
+    float angle = atan(toCenter.y, toCenter.x)/TAU;
+    float radius = length(toCenter)*2.0;
+  
+    // Map the angle (-PI to PI) to the Hue (from 0 to 1)
+    // and the Saturation to the radius
+    color = hsb2rgb(vec3(scale(angle+0.5)+0.5,radius,1.0));
+
+    gl_FragColor = vec4(color,1.0);
+}