Updated shaders with comments

shaders/glsl100/grayscale.fs

@@ -2,8 +2,11 @@
 
 precision mediump float;
 
+// Input vertex attributes (from vertex shader)
 varying vec2 fragTexCoord;
+varying vec4 fragColor;
 
+// Input uniform values
 uniform sampler2D texture0;
 uniform vec4 fragTintColor;
 
@@ -11,10 +14,12 @@ uniform vec4 fragTintColor;
 
 void main()
 {
-    vec4 base = texture2D(texture0, fragTexCoord)*fragTintColor;
+    // Texel color fetching from texture sampler
+    vec4 texelColor = texture(texture0, fragTexCoord)*fragTintColor*fragColor;
     
-    // Convert to grayscale using NTSC conversion weights
-    float gray = dot(base.rgb, vec3(0.299, 0.587, 0.114));
+    // Convert texel color to grayscale using NTSC conversion weights
+    float gray = dot(texelColor.rgb, vec3(0.299, 0.587, 0.114));
     
-    gl_FragColor = vec4(gray, gray, gray, fragTintColor.a);
+    // Calculate final fragment color
+    gl_FragColor = vec4(gray, gray, gray, texelColor.a);
 }