CreateTex3D.cs

using UnityEngine;
using UnityEditor;
using System.Collections;

public class CreateTex3D : EditorWindow
{
	[MenuItem("sugi.cho/Window/CreatePerlin3DTexture")]
	public static void Init ()
	{
		EditorWindow window = EditorWindow.GetWindow (typeof(CreateTex3D));
		window.title = "3DNoise";
	}

	int 
		count = 0,
		size = 256;
	IEnumerator coroutine;

	void OnGUI ()
	{
		if (count > 0) {
			float progress = (float)count / (float)(size * size * size);
			EditorGUI.ProgressBar (Rect.MinMaxRect (0, 0, position.width, 25f), progress, (progress * 100f).ToString ("000.0") + "%");
			if (GUI.Button (Rect.MinMaxRect (0, position.height - 25f, position.width, position.height), "Cancel")) {
				count = 0;
				EditorApplication.update -= Process;
				coroutine = null;
			}
			return;
		}
		size = EditorGUILayout.IntField (size);
		if (GUILayout.Button ("Create")) {
			count = 0;
			coroutine = ProcessCoroutine ();
			EditorApplication.update += Process;
		}
	}

	void Process ()
	{
		if (!coroutine.MoveNext ()) {
			count = 0;
			EditorApplication.update -= Process;
			coroutine = null;
		}
	}

	IEnumerator ProcessCoroutine ()
	{
		Color[] cs = new Color[size * size * size];
		int i = 0;
		for (int z = 0; z < size; z++) {
			for (int y = 0; y < size; y++) {
				for (int x = 0; x < size; x++) {
					Color c = Color.red;
					Vector3 v = new Vector3 (5f * ((float)x / size), 5f * ((float)y / size), 5f * ((float)z / size));

					c.r = GetFbmLoop (v, 1);
					c.g = GetFbmLoop (v, 2);
					c.b = GetFbmLoop (v, 3);
					c.a = GetFbmLoop (v, 4);

					cs [i] = c;
					count = i++;
					if (i % 100 == 0)
						yield return 0;
				}
			}
		}
		Texture3D t3d = new Texture3D (size, size, size, TextureFormat.ARGB32, false);
		t3d.SetPixels (cs);
		t3d.Apply ();

		AssetDatabase.CreateAsset (t3d, "Assets/perlin3d_" + size + ".asset");
		AssetDatabase.SaveAssets ();
		AssetDatabase.Refresh ();

		Selection.activeObject = t3d;
		count = 0;
	}


	float GetFbmLoop (Vector3 v, int octave)
	{

		Vector3 v1 = v;
		v1.x -= 5f;
		
		float
		f = GetLoopY (v, octave),
		f1 = GetLoopY (v1, octave);
		f = Mathf.Lerp (f, f1, v.x / 5f);

		return f / 2f + 0.5f;
	}

	float GetLoopY (Vector3 v, int octave)
	{

		Vector3 v1 = v;
		v1.y -= 5f;
		
		float
		f = GetLoopZ (v, octave),
		f1 = GetLoopZ (v1, octave);
		f = Mathf.Lerp (f, f1, v.y / 5f);
		
		return f;
	}

	float GetLoopZ (Vector3 v, int octave)
	{
		
		Vector3 v1 = v;
		v1.z -= 5f;
		
		float
		f = Perlin.Fbm (v, octave),
		f1 = Perlin.Fbm (v1, octave);
		f = Mathf.Lerp (f, f1, v.z / 5f);
		
		return f;
	}
}

FullscreenNoise.shader

Shader "Custom/FullscreenNoise" {
	Properties {
		_MainTex ("Base (RGB)", 2D) = "white" {}
		_N3D ("noise 3Dtexture", 3D) = "gray" {}
	}
	CGINCLUDE
		#include "UnityCG.cginc"
 		
 		sampler3D _N3D;
		sampler2D _MainTex;
		half4 _MainTex_TexelSize;
			
		half4 frag(v2f_img i) : COLOR{
			return tex3D(_N3D, float3(i.uv, _Time.x)).r*2-1;
		}
	ENDCG
	
	SubShader {
		ZTest Always Cull Off ZWrite Off
		Fog { Mode off }
 
		pass{
			CGPROGRAM
			#pragma fragmentoption ARB_precision_hint_fastest
			#pragma vertex vert_img
			#pragma fragment frag
			ENDCG
		}
	} 
}

Perlin.cs

using UnityEngine;

//
// A Perlin noise class for Unity
// By Keijiro Takahashi, 2013
// https://github.com/keijiro/unity-perlin
//
// Based on the original implementation by Ken Perlin
// http://mrl.nyu.edu/~perlin/noise/
//

public static class Perlin
{
    #region Noise functions
    public static float Noise (float x)
    {
        var X = Mathf.FloorToInt (x) & 0xff;
        x -= Mathf.Floor (x);
        return Lerp (Fade (x), Grad(X, x), Grad (X + 1, x - 1));
    }

    public static float Noise (float x, float y)
    {
        var X = Mathf.FloorToInt (x) & 0xff;
        var Y = Mathf.FloorToInt (y) & 0xff;
        x -= Mathf.Floor (x);
        y -= Mathf.Floor (y);
        var u = Fade (x);
        var v = Fade (y);
        var A = (perm [X    ] + Y) & 0xff;
        var B = (perm [X + 1] + Y) & 0xff;
        return Lerp (v, Lerp (u, Grad (A    , x, y    ), Grad (B,     x - 1, y    )),
                        Lerp (u, Grad (A + 1, x, y - 1), Grad (B + 1, x - 1, y - 1)));
    }

    public static float Noise (Vector2 coord)
    {
        return Noise (coord.x, coord.y);
    }

    public static float Noise (float x, float y, float z)
    {
        var X = Mathf.FloorToInt (x) & 0xff;
        var Y = Mathf.FloorToInt (y) & 0xff;
        var Z = Mathf.FloorToInt (z) & 0xff;
        x -= Mathf.Floor (x);
        y -= Mathf.Floor (y);
        z -= Mathf.Floor (z);
        var u = Fade (x);
        var v = Fade (y);
        var w = Fade (z);
        var A  = (perm [X    ] + Y) & 0xff;
        var B  = (perm [X + 1] + Y) & 0xff;
        var AA = (perm [A    ] + Z) & 0xff;
        var BA = (perm [B    ] + Z) & 0xff;
        var AB = (perm [A + 1] + Z) & 0xff;
        var BB = (perm [B + 1] + Z) & 0xff;
        return Lerp (w, Lerp (v, Lerp (u, Grad (AA    , x    , y    , z    ), Grad (BA    , x - 1, y    , z    )),
                                 Lerp (u, Grad (AB    , x    , y - 1, z    ), Grad (BB    , x - 1, y - 1, z    ))),
                        Lerp (v, Lerp (u, Grad (AA + 1, x    , y    , z - 1), Grad (BA + 1, x - 1, y    , z - 1)),
                                 Lerp (u, Grad (AB + 1, x    , y - 1, z - 1), Grad (BB + 1, x - 1, y - 1, z - 1))));
    }

    public static float Noise (Vector3 coord)
    {
        return Noise (coord.x, coord.y, coord.z);
    }
    #endregion

    #region fBm functions
    public static float Fbm (float x, int octave)
    {
        var f = 0.0f;
        var w = 0.5f;
        for (var i = 0; i < octave; i++) {
            f += w * Noise (x);
            x *= 2.0f;
            w *= 0.5f;
        }
        return f;
    }
    
    public static float Fbm (Vector2 coord, int octave)
    {
        var f = 0.0f;
        var w = 0.5f;
        for (var i = 0; i < octave; i++) {
            f += w * Noise (coord);
            coord *= 2.0f;
            w *= 0.5f;
        }
        return f;
    }
    
    public static float Fbm (Vector3 coord, int octave)
    {
        var f = 0.0f;
        var w = 0.5f;
        for (var i = 0; i < octave; i++) {
            f += w * Noise (coord);
            coord *= 2.0f;
            w *= 0.5f;
        }
        return f;
    }
    #endregion

    #region Private functions
    static float Fade (float t)
    {
        return t * t * t * (t * (t * 6 - 15) + 10);
    }
    
    static float Lerp (float t, float a, float b)
    {
        return a + t * (b - a);
    }
    
    static float Grad (int i, float x)
    {
        return (perm [i] & 1) != 0 ? x : -x;
    }

    static float Grad (int i, float x, float y)
    {
        var h = perm [i];
        return ((h & 1) != 0 ? x : -x) + ((h & 2) != 0 ? y : -y);
    }
    
    static float Grad (int i, float x, float y, float z)
    {
        var h = perm [i] & 15;
        var u = h < 8 ? x : y;
        var v = h < 4 ? y : (h == 12 || h == 14 ? x : z);
        return ((h & 1) != 0 ? u : -u) + ((h & 2) != 0 ? v : -v);
    }

    static int[] perm = {
        151,160,137,91,90,15,
        131,13,201,95,96,53,194,233,7,225,140,36,103,30,69,142,8,99,37,240,21,10,23,
        190, 6,148,247,120,234,75,0,26,197,62,94,252,219,203,117,35,11,32,57,177,33,
        88,237,149,56,87,174,20,125,136,171,168, 68,175,74,165,71,134,139,48,27,166,
        77,146,158,231,83,111,229,122,60,211,133,230,220,105,92,41,55,46,245,40,244,
        102,143,54, 65,25,63,161, 1,216,80,73,209,76,132,187,208, 89,18,169,200,196,
        135,130,116,188,159,86,164,100,109,198,173,186, 3,64,52,217,226,250,124,123,
        5,202,38,147,118,126,255,82,85,212,207,206,59,227,47,16,58,17,182,189,28,42,
        223,183,170,213,119,248,152, 2,44,154,163, 70,221,153,101,155,167, 43,172,9,
        129,22,39,253, 19,98,108,110,79,113,224,232,178,185, 112,104,218,246,97,228,
        251,34,242,193,238,210,144,12,191,179,162,241, 81,51,145,235,249,14,239,107,
        49,192,214, 31,181,199,106,157,184, 84,204,176,115,121,50,45,127, 4,150,254,
        138,236,205,93,222,114,67,29,24,72,243,141,128,195,78,66,215,61,156,180,
        151
    };
    #endregion
}

ShowMat.cs

using UnityEngine;
using System.Collections;

public class ShowMat : MonoBehaviour
{
	public Material mat;
	void OnRenderImage (RenderTexture s, RenderTexture d)
	{
		Graphics.Blit (s, d, mat);
	}
}