Merge pull request #452 from metallic77/slang

improve mono mode

misc/shaders/simple_color_controls.slang

@@ -109,7 +109,7 @@ mat4 contrastMatrix(float contr)
 
 vec3 toGrayscale(vec3 color)
 {
-  float average = (color.r + color.g + color.b) / 3.0;
+  float average = dot(vec3(0.22,0.71,0.07),color);
   return vec3(average);
 }
 
@@ -150,4 +150,4 @@ void main()
     }
 
    FragColor = vec4(col,1.0);
-}
+}