c# - 二维柏林噪声

Question

我已经完全掌握了 3D 柏林噪声的艺术，现在我正在尝试将我的相同实现用于 2D 算法。问题似乎在于选择我的渐变方向。在 3D 中，我在均匀分布的方向上使用了 16 个渐变，效果很好。在 2D 中，我想我会使用 8 个渐变。上、下、左、右、四个对角线方向。

这是我得到的:

噪声的总体外观总是正确的，但正方形的边缘并不完全匹配。我也尝试过使用其他渐变或更少的渐变，但得到了类似的结果。在另一个示例中，您可以看到边缘有时会匹配并且该区域的结果很好 -

当我不使用渐变而只是在 4 个角的每个角随机选取的值之间进行插值时，我得到了正确的结果，这让我认为是渐变部分搞砸了。

这是我的代码:

//8 different gradient directions
private Point[] grads = new Point[] { 
    new Point(0, 1), new Point(1, 1), new Point(1, 0), new Point(1, -1), 
    new Point(0, -1), new Point(-1, -1), new Point(-1, 0), new Point(-1, 1),};

//takes the dot product of a gradient and (x, y)
private float dot2D(int i, float x, float y)
{
    return
        grads[i].X * x + grads[i].Y * y;
}

public float Noise2D(float x, float y)
{
    int
        ix = (int)(x),
        iy = (int)(y);

        x  = x - ix;
        y  = y - iy;

    float
        fx  = fade(x),
        fy  = fade(y);

        ix &= 255;
        iy &= 255;

    // here is where i get the index to look up in the list of 
    // different gradients.
    // hashTable is my array of 0-255 in random order
    int
        g00 = hashTable[ix +     hashTable[iy    ]],
        g10 = hashTable[ix + 1 + hashTable[iy    ]],
        g01 = hashTable[ix +     hashTable[iy + 1]],
        g11 = hashTable[ix + 1 + hashTable[iy + 1]];

    // this takes the dot product to find the values to interpolate between
    float
        n00 = dot2D(g00 & 7, x, y),
        n10 = dot2D(g10 & 7, x, y),
        n01 = dot2D(g01 & 7, x, y),
        n11 = dot2D(g11 & 7, x, y);

    // lerp() is just normal linear interpolation
    float
        y1 = lerp(fx, n00, n10),
        y2 = lerp(fx, n01, n11);
    return
        lerp(fy, y1, y2);
}

Answer 1

我有点匆忙，但这可能会有帮助。我将 Perlin 的引用实现改编为 C#。对于 2D，只需使用具有固定 z 参数的 3D Noise() 函数。 (public static float Noise(float x, float y, float z) 接近类(class)末尾。)

using System;
using System.Collections.Generic;
using System.Linq;
using System.Text;
using Microsoft.Xna.Framework;
using System.Diagnostics;

namespace GoEngine.Content.Entities
{
    public class NoiseMaker
    {
        /// adapted from http://cs.nyu.edu/~perlin/noise/
        // JAVA REFERENCE IMPLEMENTATION OF IMPROVED NOISE - COPYRIGHT 2002 KEN PERLIN.

        private static int[] p = new int[512];
        private static int[] permutation = { 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
               };

        static NoiseMaker()
        {
            CalculateP();
        }

        private static int _octaves;
        private static int _halfLength = 256;

        public static void SetOctaves(int octaves)
        {
            _octaves = octaves;

            var len = (int)Math.Pow(2, octaves);

            permutation = new int[len];

            Reseed();
        }

        private static void CalculateP()
        {
            p = new int[permutation.Length * 2];
            _halfLength = permutation.Length;

            for (int i = 0; i < permutation.Length; i++)
                p[permutation.Length + i] = p[i] = permutation[i];
        }

        public static void Reseed()
        {
            var random = new Random();
            var perm = Enumerable.Range(0, permutation.Length).ToArray();

            for (var i = 0; i < perm.Length; i++)
            {
                var swapIndex = random.Next(perm.Length);

                var t = perm[i];

                perm[i] = perm[swapIndex];

                perm[swapIndex] = t;
            }

            permutation = perm;

            CalculateP();

        }

        public static float Noise(Vector3 position, int octaves, ref float min, ref float max)
        {
            return Noise(position.X, position.Y, position.Z, octaves, ref min, ref max);
        }

        public static float Noise(float x, float y, float z, int octaves, ref float min, ref float max)
        {

            var perlin = 0f;
            var octave = 1;

            for (var i = 0; i < octaves; i++)
            {
                var noise = Noise(x * octave, y * octave, z * octave);

                perlin += noise / octave;

                octave *= 2;
            }

            perlin = Math.Abs((float)Math.Pow(perlin,2));
            max = Math.Max(perlin, max);
            min = Math.Min(perlin, min);

            //perlin = 1f - 2 * perlin;

            return perlin;
        }

        public static float Noise(float x, float y, float z)
        {
            int X = (int)Math.Floor(x) % _halfLength;
            int Y = (int)Math.Floor(y) % _halfLength;
            int Z = (int)Math.Floor(z) % _halfLength;

            if (X < 0)
                X += _halfLength;

            if (Y < 0)
                Y += _halfLength;

            if (Z < 0)
                Z += _halfLength;

            x -= (int)Math.Floor(x);
            y -= (int)Math.Floor(y);
            z -= (int)Math.Floor(z);

            var u = Fade(x);
            var v = Fade(y);
            var w = Fade(z);

            int A = p[X] + Y, AA = p[A] + Z, AB = p[A + 1] + Z,      // HASH COORDINATES OF
                B = p[X + 1] + Y, BA = p[B] + Z, BB = p[B + 1] + Z;      // THE 8 CUBE CORNERS,


            return MathHelper.Lerp(
                    MathHelper.Lerp(
                         MathHelper.Lerp(
                            Grad(p[AA], x, y, z) // AND ADD
                            ,
                            Grad(p[BA], x - 1, y, z) // BLENDED
                            ,
                            u
                            )
                        ,
                        MathHelper.Lerp(
                            Grad(p[AB], x, y - 1, z)  // RESULTS
                            ,
                            Grad(p[BB], x - 1, y - 1, z)
                            ,
                            u
                            )
                        ,
                        v
                    )
                    ,
                    MathHelper.Lerp(
                        MathHelper.Lerp(
                            Grad(p[AA + 1], x, y, z - 1) // CORNERS
                            ,
                            Grad(p[BA + 1], x - 1, y, z - 1) // OF CUBE
                            ,
                            u
                            )
                        ,
                        MathHelper.Lerp(
                            Grad(p[AB + 1], x, y - 1, z - 1)
                            ,
                            Grad(p[BB + 1], x - 1, y - 1, z - 1)
                            ,
                            u
                            )
                        ,
                        v
                    )
                    ,
                    w
                );

        }

        static float Fade(float t) { return t * t * t * (t * (t * 6 - 15) + 10); }

        static float Grad(int hash, float x, float y, float z)
        {
            int h = hash & 15;                      // CONVERT LO 4 BITS OF HASH CODE

            float u = h < 8 ? x : y,                 // INTO 12 GRADIENT DIRECTIONS.
                   v = h < 4 ? y : h == 12 || h == 14 ? x : z;

            return ((h & 1) == 0 ? u : -u) + ((h & 2) == 0 ? v : -v);
        }

    }
}

更新

好的，我设法创建了一个有效的 2D 版本。这是类(class):

/// implements improved Perlin noise in 2D. 
/// Transcribed from http://www.siafoo.net/snippet/144?nolinenos#perlin2003
/// </summary>
public static class Noise2d
{
    private static Random _random = new Random();
    private static int[] _permutation;

    private static Vector2[] _gradients;

    static Noise2d()
    {
        CalculatePermutation(out _permutation);
        CalculateGradients(out _gradients);
    }

    private static void CalculatePermutation(out int[] p)
    {
        p = Enumerable.Range(0, 256).ToArray();

        /// shuffle the array
        for (var i = 0; i < p.Length; i++)
        {
            var source = _random.Next(p.Length);

            var t = p[i];
            p[i] = p[source];
            p[source] = t;
        }
    }

    /// <summary>
    /// generate a new permutation.
    /// </summary>
    public static void Reseed()
    {
        CalculatePermutation(out _permutation);
    }

    private static void CalculateGradients(out Vector2[] grad)
    {
        grad = new Vector2[256];

        for (var i = 0; i < grad.Length; i++)
        {
            Vector2 gradient;

            do
            {
                gradient = new Vector2((float)(_random.NextDouble() * 2 - 1), (float)(_random.NextDouble() * 2 - 1));
            }
            while (gradient.LengthSquared() >= 1);

            gradient.Normalize();

            grad[i] = gradient;
        }

    }

    private static float Drop(float t)
    {
        t = Math.Abs(t);
        return 1f - t * t * t * (t * (t * 6 - 15) + 10);
    }

    private static float Q(float u, float v)
    {
        return Drop(u) * Drop(v);
    }

    public static float Noise(float x, float y)
    {
        var cell = new Vector2((float)Math.Floor(x), (float)Math.Floor(y));

        var total = 0f;

        var corners = new[] { new Vector2(0, 0), new Vector2(0, 1), new Vector2(1, 0), new Vector2(1, 1) };

        foreach (var n in corners)
        {
            var ij = cell + n;
            var uv = new Vector2(x - ij.X, y - ij.Y);

            var index = _permutation[(int)ij.X % _permutation.Length];
            index = _permutation[(index + (int)ij.Y) % _permutation.Length];

            var grad = _gradients[index % _gradients.Length];

            total += Q(uv.X, uv.Y) * Vector2.Dot(grad, uv);
        }

        return Math.Max(Math.Min(total, 1f), -1f);
    }

}

这样调用它:

private void GenerateNoiseMap(int width, int height, ref Texture2D noiseTexture, int octaves)
    {
        var data = new float[width * height];

        /// track min and max noise value. Used to normalize the result to the 0 to 1.0 range.
        var min = float.MaxValue;
        var max = float.MinValue;

        /// rebuild the permutation table to get a different noise pattern. 
        /// Leave this out if you want to play with changing the number of octaves while 
        /// maintaining the same overall pattern.
        Noise2d.Reseed();

        var frequency = 0.5f;
        var amplitude = 1f;
        var persistence = 0.25f;

        for (var octave = 0; octave < octaves; octave++)
        {
            /// parallel loop - easy and fast.
            Parallel.For(0
                , width * height
                , (offset) =>
                {
                    var i = offset % width;
                    var j = offset / width;
                    var noise = Noise2d.Noise(i*frequency*1f/width, j*frequency*1f/height);
                    noise = data[j * width + i] += noise * amplitude;

                    min = Math.Min(min, noise);
                    max = Math.Max(max, noise);

                }
            );

            frequency *= 2;
            amplitude /= 2;
        }


        if (noiseTexture != null && (noiseTexture.Width != width || noiseTexture.Height != height))
        {
            noiseTexture.Dispose();
            noiseTexture = null;
        }
        if (noiseTexture==null)
        {
            noiseTexture = new Texture2D(Device, width, height, false, SurfaceFormat.Color);
        }

        var colors = data.Select(
            (f) =>
            {
                var norm = (f - min) / (max - min);
                return new Color(norm, norm, norm, 1);
            }
        ).ToArray();

        noiseTexture.SetData(colors);
    }

请注意，我使用了几个 XNA 结构(Vector2 和 Texture2D)，但它们的作用应该很清楚。

如果您想要更高频率(更“嘈杂”)且 Octave 音阶更少的内容，请增加 Octave 音阶循环中使用的初始频率值。

此实现使用“改进的”Perlin 噪声，它应该比标准版本快一点。您还可以查看 Simplex 噪声，它在更高维度上要快得多。