Simple perlin noise shader

perlin.frag

/**
 * GLSL fragment shader for the noise clouds.
 *
 * @author Ian Stewart
 *
 */

varying float LightIntensity;
varying vec3 MCposition;

uniform sampler3D Noise;
uniform vec3 SkyColor;
uniform vec3 CloudColor;

uniform int TIME_FROM_INIT;

vec3 Offset = vec3(0.0,0.0,0.0);

void main()
{
	float offset = float(TIME_FROM_INIT) *0.00005;
	Offset = vec3(-offset, offset, offset);
	vec4 noisevec	= texture3D(Noise, MCposition+Offset);
	float intensity	= (noisevec[0] + noisevec[1] + noisevec[2]
                           + noisevec[3] + 0.03125) * 1.0;
	
	vec3 color = mix(SkyColor, CloudColor, intensity) * LightIntensity;
	color = clamp(color, 0.0, 1.0);
	gl_FragData[0] 	= vec4(color, 1.0);
}

perlin.vert

/**
 * GLSL vertex shader for the noise clouds.
 *
 * @author Ian Stewart
 *
 */

varying float LightIntensity;
varying vec3 MCposition;

uniform vec3 LightPos;
uniform float Scale;

void main()
{
	gl_Position		= ftransform();
	vec3 ECposition	= vec3(gl_ModelViewMatrix * gl_Vertex);
	MCposition		= vec3(gl_Vertex) * Scale;
	vec3 tnorm		= -normalize(vec3(gl_NormalMatrix * gl_Normal));
	LightIntensity	= dot(normalize(LightPos - ECposition), tnorm) * 1.5;
	//LightIntensity = 1.5;
}