varying float Z;	// equal to -EC.z (dist in front of the eye)
varying vec4 Color;
varying vec3 MCposition;
varying float LightIntensity; 

uniform float NoiseScale;
uniform float NoiseFreq;
uniform float DepthFront, DepthBack;
uniform sampler3D Noise3;

const vec4 FOG = vec4( 0.5, 0.5, 0.5, 1. );

void
main( void )
{
	vec4  nv  = texture3D( Noise3, NoiseFreq*MCposition );
	float size = nv[0] + nv[1] + nv[2] + nv[3];	// [1.,3.]
	size -= 2.;					// [-1.,+1.]
	float deltaz = NoiseScale * size;

	float fogFactor = ( (Z+deltaz) - DepthFront ) / ( DepthBack - DepthFront );
	fogFactor = clamp( fogFactor, 0., 1. );
	fogFactor = smoothstep( 0., 1., fogFactor );

	Color.rgb *= LightIntensity;
	gl_FragColor = mix( Color, FOG, fogFactor );
}