# Perlin Noise acting weird

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Hi there, I fixed the problems in my previous post, but I now have another problem. The noise doesnt look like perlin noise at all, here is what i get: This is my code:
#ifndef PERLIN_H
#define PERLIN_H

#include <cstdlib>
#include <cstring>
#include <SDL/SDL.H>
#include <cmath>

#define SIZE 256

void findcoord_circle(int x, int y, double radius, int degrees, double &getx, double &gety)
{
//printf("getx %f, gety %f\n",getx,gety);
getx+=(double)x;
gety+=(double)y;
//printf("getx %f, gety %f\n\n",getx,gety);
}

int g(int xcoord,int ycoord, double &x, double &y,int w)
{
srand(xcoord+(ycoord*w));
int degrees=rand()%360;
// printf("%i @ %i,%i\n",degrees,xcoord,ycoord);
findcoord_circle(xcoord,ycoord,1.0,degrees,x,y);
}

double noise(double x,double y,int seed, int w)
{
double floorx=(double)((int)x);
double floory=(double)((int)y);
//printf("%f, %f\n",floorx,floory);
//printf("x=%f, y=%f\n",x, y);
double x00,y00;
g((int)floorx,(int)floory,x00,y00,w);
double x01,y01;
g((int)floorx,(int)(floory)+1,x01,y01,w);
double x10,y10;
g((int)(floorx)+1,(int)floory,x10,y10,w);
//printf("x01= %f\n",x01);
double x11,y11;
g((int)(floorx)+1,(int)(floory)+1,x11,y11,w);
double X00=x-floorx;
double X10=x-(floorx+1.0);
double X01=x-floorx;
double X11=x-(floorx+1.0);
double Y00=y-floory;
double Y10=y-floory;
double Y01=y-(floory+1.0);
double Y11=y-(floory+1.0);
double s,t,u,v;
s=(x00*X00)+(y00*Y00);
t=(x10*X10)+(y10*Y10);
u=(x01*X01)+(y01*Y01);
v=(x11*X11)+(y11*Y11);
// printf("%f\n%f\n%f\n%f\n",s,t,u,v);
double Sx = (3*pow(x-floorx,2.0))-(2*pow(x-floorx,3.0));
double Sy = (3*pow(y-floory,2.0))-(2*pow(y-floory,3.0));
double a=s+Sx*(t-s);
double b=u+Sx*(v-u);
double z=a+Sy*(b-a);
if(z<-1.0)
z=-1.0;
if(z>1.0)
z=1.0;
return z;
}

void SetPixel ( SDL_Surface* pSurface , int x , int y , Uint8 r, Uint8 g, Uint8 b)
{
//convert color
Uint32 col = SDL_MapRGB ( pSurface->format ,r ,g ,b ) ;

//determine position
char* pPosition = ( char* ) pSurface->pixels ;

//offset by y
pPosition += ( pSurface->pitch * y ) ;

//offset by x
pPosition += ( pSurface->format->BytesPerPixel * x ) ;

//copy pixel data
memcpy ( pPosition , &col , pSurface->format->BytesPerPixel ) ;
}

SDL_Surface *Render_PerlinNoise(int w,int h,int seed,double zoom)
{
int octaves=3;
SDL_Surface *ret=SDL_CreateRGBSurface(SDL_SWSURFACE,w,h,24,0,0,0,0);
for(int y=0;y<h;y++)
{
for(int x=0;x<w;x++)
{
double getnoise = noise(((double)x)/zoom,((double)y)/zoom,seed,w);
if((getnoise<(-1.0))||(getnoise>1.0))
printf("error\n");
//getnoise=1.0/getnoise;
int color= (int)((getnoise*128.0)+128.0);
//   printf("%f ",getnoise);
SetPixel(ret,x,y,color,color,color);
}
//printf("\n");
}
return ret;
}

#endif



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Hi there,

Because no one seems te respond I'm going to ask a different question. At Ken Perlins page Making Noise, u see a nice marble effect, now I wonder, can this be achieved by simply smoothing some non-coherent noise and editing it?

Thanks

Robin

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Take a look here. Its a very good site for noise. It has the calculations for it and example at the bottom of the page.

It shows some samples of what you can do with noise, and marble is one of them.

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Thanks, I'll look into it.

Greetins

Robin

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Your color buffer is 8bit, and can only display values in the range of 0-255.

If your getnoise returns 1.0, your color result is 256, which is seen as 0(black).

change your color function from this:
int color= (int)((getnoise*128.0)+128.0);

to this
int color= (int)((getnoise*127.0)+127.0);

you lose a little range, but you dont overflow.

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