ycocg-based colour grading test wip

src/shaders/ycocg_grading.frag

@@ -0,0 +1,31 @@
+#ifdef GL_ES
+precision mediump float;
+#endif
+
+
+varying vec4 v_color;
+varying vec2 v_texCoords;
+uniform sampler2D u_texture;
+
+mat4 rgb_to_ycocg = mat4(
+     0.25, 0.5,  0.25, 1.0,
+     1.0,  0.0, -1.0,  1.0,
+    -0.5,  1.0, -0.5,  1.0,
+     0.0,  0.0,  0.0,  1.0
+);
+
+mat4 ycocg_to_rgb = mat4(
+    1.0,  0.5, -0.5, 1.0,
+    1.0,  0.0,  0.5, 1.0,
+    1.0, -0.5, -0.5, 1.0,
+    0.0,  0.0,  0.0, 1.0
+);
+
+vec2 boolean = vec2(0.0, 1.0);
+
+void main() {
+    vec4 incolour = texture2D(u_texture, v_texCoords);
+    vec4 yog = rgb_to_ycocg * incolour; // vec4(Y, Co, Cg, A) where Y,A=[0,1]; Co,Cg=[-1,1]
+
+    gl_FragColor = ycocg_to_rgb * yog;
+}