btphystest: play with hue values.

test/front_camera_sprite.lolfx

@@ -53,13 +53,32 @@ varying vec4 pass_color;
 const float cos_45      = 0.70710678118;
 const float PI = 3.14159265358979323846264;
 
+vec3 rgb2hsv(vec3 c)
+{
+    vec4 K = vec4(0.0, -1.0 / 3.0, 2.0 / 3.0, -1.0);
+    vec4 p = c.g < c.b ? vec4(c.bg, K.wz) : vec4(c.gb, K.xy);
+    vec4 q = c.r < p.x ? vec4(p.xyw, c.r) : vec4(c.r, p.yzx);
+
+    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 hsv2rgb(vec3 c)
+{
+    vec4 K = vec4(1.0, 2.0 / 3.0, 1.0 / 3.0, 3.0);
+    vec3 p = abs(fract(c.xxx + K.xyz) * 6.0 - K.www);
+    return c.z * mix(K.xxx, clamp(p - K.xxx, 0.0, 1.0), c.y);
+}
+
 void main(void)
 {
     vec4 color = texture2D(in_texture, pass_texcoord.xy -
-                                         vec2(pass_texcoord.z * in_sprite_flip, 0.0)) *
-                                         pass_color;
+                                 vec2(pass_texcoord.z * in_sprite_flip, 0.0));
     if (color.a < 0.01)
         discard;
-    gl_FragColor = color * pass_color;
+    vec3 hsv = rgb2hsv(color.rgb);
+    hsv.x = fract(hsv.x + rgb2hsv(pass_color.rgb).x);
+    gl_FragColor = vec4(hsv2rgb(hsv), color.a);
 }