Rewrite YUV processing pipeline.

Use a 4-channel texture instead for packed YUV data so
every pixel in the texture has all the 4:2:2 color data
available.

data/yuv.frag

@@ -7,26 +7,24 @@ uniform mat3 color_matrix;
 uniform float inv_gamma;
 uniform float blacklevel;
 
-varying vec2 top_left_uv;
-varying vec2 top_right_uv;
-varying vec2 bottom_left_uv;
-varying vec2 bottom_right_uv;
+varying vec2 texture_coord;
 
 void
 main()
 {
-    // Note the coordinates for texture samples need to be a varying, as the
-    // Mali-400 has this as a fast path allowing 32-bit floats. Otherwise
-    // they end up as 16-bit floats and that's not accurate enough.
+    // Sample format: Y,U,Y,V
+    vec4 samples = texture2D(texture, texture_coord);
+    float y = samples.x;
+    float u = samples.y-0.5;
+    float v = samples.w-0.5;
 
-    vec4 samples = vec4(texture2D(texture, top_left_uv).r,
-    texture2D(texture, top_right_uv).r,
-    texture2D(texture, bottom_left_uv).r,
-    texture2D(texture, bottom_right_uv).r);
-    vec3 color = vec3(samples.z, samples.z, samples.z);
+    vec3 rgb;
+    rgb.r = y + (1.403 * v);
+    rgb.g = y - (0.344 * u) - (0.714 * v);
+    rgb.b = y + (1.770 * u);
 
     //color *= color_matrix;
-    vec3 gamma_color = pow(color, vec3(inv_gamma));
+    vec3 gamma_color = pow(rgb, vec3(inv_gamma));
 
     gl_FragColor = vec4(gamma_color, 1);
 }