Reviewed shaders and added comments

examples/resources/shaders/glsl100/grayscale.fs

@@ -0,0 +1,25 @@
+#version 100
+
+precision mediump float;
+
+// Input vertex attributes (from vertex shader)
+varying vec2 fragTexCoord;
+varying vec4 fragColor;
+
+// Input uniform values
+uniform sampler2D texture0;
+uniform vec4 fragTintColor;
+
+// NOTE: Add here your custom variables
+
+void main()
+{
+    // Texel color fetching from texture sampler
+    vec4 texelColor = texture(texture0, fragTexCoord)*fragTintColor*fragColor;
+    
+    // Convert texel color to grayscale using NTSC conversion weights
+    float gray = dot(texelColor.rgb, vec3(0.299, 0.587, 0.114));
+    
+    // Calculate final fragment color
+    gl_FragColor = vec4(gray, gray, gray, texelColor.a);
+}