float chebyshevUpperBound()
{
	vec2 moments = texture2D(ShadowMap,ShadowCoordPostW.xy).rg;
	
	// Surface is fully lit. as the current fragment is before the light occluder
	if (ShadowCoordPostW.z <= moments.x)
		return 1.0 ;

	// The fragment is either in shadow or penumbra. We now use chebyshev's upperBound to check
	// How likely this pixel is to be lit (p_max)
	float variance = moments.y - (moments.x*moments.x);
	variance = max(variance,0.1);

	float d = ShadowCoordPostW.z - moments.x;
	float p_max = (variance / (variance + d*d));
	
	return max(p_max, 0.4);
}

//Color computation in main()
shadow = chebyshevUpperBound();
fragColor = ((ambient_color + diffuse_color * diffuse_value))*texel;
fragColor.rgb *= shadow;