adding alpha shader (it's not used)

assets/shaders/alpha.fs

@@ -0,0 +1,28 @@
+#version 330
+
+precision mediump float;
+
+// Input vertex attributes (from vertex shader)
+varying vec2 fragTexCoord;
+varying vec4 fragColor;
+
+// Input uniform values
+uniform sampler2D texture0;
+uniform vec4 colDiffuse;
+uniform float alpha;
+
+// NOTE: Add here your custom variables
+
+void main()
+{
+    // Texel color fetching from texture sampler
+    vec4 texelColor = texture2D(texture0, fragTexCoord);
+
+    // Convert texel color to grayscale using NTSC conversion weights
+
+    texelColor.a = alpha;
+
+    gl_FragColor = texelColor;
+    // Calculate final fragment color
+    //gl_FragColor = vec4(gray, gray, gray, texelColor.a);
+}