**I have added the corrected file to the original download**
Whoops, I've just spotted the following-
The following line should be added to the bottom of the .fx file to make it work correctly-
gl_FragColor.a = front.a;
So the bottom line's should look like this-
else
gl_FragColor.rgb = vec3(noise(p));
gl_FragColor.a = front.a;
}
resulting in -
Cheers.