# help with perlin noise

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Hi, I'm trying to implement 2D perlin noise in C/C++, but I'm having problems. I looked at Ken Perlin's improved noise at http://mrl.nyu.edu/~perlin/noise/ and translated it to C++. Basically this is what i came up with:
static double fade(double t) { return t * t * t * (t * (t * 6 - 15) + 10); }
static double lerp(double t, double a, double b) { return a + t * (b - a); }

static int p[512], 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 double grad(int hash, double x, double y, double z)
{

int h = hash & 15;                      // CONVERT LO 4 BITS OF HASH CODE
double 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);

}

double noise(double x, double y, double z)
{

int X = (int)floor(x) & 255,                  // FIND UNIT CUBE THAT
Y = (int)floor(y) & 255,                  // CONTAINS POINT.
Z = (int)floor(z) & 255;

x -= floor(x);                                // FIND RELATIVE X,Y,Z
y -= floor(y);                                // OF POINT IN CUBE.
z -= floor(z);
v = fade(y),                                // FOR EACH OF X,Y,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 lerp(w, lerp(v, lerp(u, grad(p[AA  ], x  , y  , z   ),  // AND ADD
grad(p[BA  ], x-1, y  , z   )), // BLENDED
lerp(u, grad(p[AB  ], x  , y-1, z   ),  // RESULTS
grad(p[BB  ], x-1, y-1, z   ))),// FROM  8
lerp(v, lerp(u, grad(p[AA+1], x  , y  , z-1 ),  // CORNERS
grad(p[BA+1], x-1, y  , z-1 )), // OF CUBE
lerp(u, grad(p[AB+1], x  , y-1, z-1 ),

}

in my main function i do : for (int i=0; i < 256 ; i++) p[256+i] = p[i] = permutation[i]; then I call the noise function giving it x,y pixel locations: disp1= noise(x,y,0); problem is I get 0 back from the noise call. Not sure what I'm doing wrong. I would appreciate any help you can give. Thanks.

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You can take a look at my translation here :

Raytracer in C++ - Perlin noise and procedural textures

I didn't have any problem with it.

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Thanks, I'll take a look at it. I think maybe my implementation of it is correct, but wrong in how I use it to generate the texture. I was just calling noise and passing it the x,y coordinates (normalized to between 0..1) of the image. I think each coordinate needs to be multiplied by frequency maybe?

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