Hey. Im looking into perlin noise at the moment, wanting to generate height maps and textures etc. i looked around on the internet and got a few things going (im only at the 1st stage of generating "pure" noise)

I found the following example



int bmp_dim = 256;
Bitmap bmp = new Bitmap(bmp_dim, bmp_dim);
Random r = new Random(); //to create a new image every time
int thisr = r.Next(0, 5000);

for(int i=0; i<bmp_dim; i++) {
for(int j=0; j<bmp_dim; j++) {

float t = Noise2d(j+thisr, i+thisr); //offset creates
//a different image every time
if(t<0) t = -t;
if(t>1) t = 1.0f;
int fin = (int)(t*255.0f); //get in color range
Color col = Color.FromArgb(fin, fin, fin);
bmp.SetPixel(j, i, col);
}
}
[attachment=6154:img.jpg]


Heres the noise function



float Noise2d(int x, int y)
{
int n;
n = x + y * 57;
n = (n<<13) ^ n;
float res = (float)( 1.0 - ( (n * (n * n * 15731 + 789221)
+ 1376312589) & 0x7fffffff ) / 1073741824.0);
return res;
}



I took out the random offset (the variable named thisr) used to make a different noise with each compilation, and just used the x/y of the current place in the loop.

Problem is my noise seems to have patterns in it, it seems to loop. see image below (horizontal pattern)
[attachment=6155:img.jpg]

I had a look into the values and they are not the same, they dont repeat exactly from what i can see, i suspect its just the differences and intervals between them

It may look small but surely it could have adverse effects if it keeps looping, I thought the idea was that its supposed to be random and totally without patterns.

the site i got the example from has a button to generate new noise and this does not occur on the website Link here


is this meant to happen, can i fix it

cheers

This is a better example, same everything but double width and height. its a lot easier to see the patterns

[attachment=6156:img.jpg]

Your Noise2d function is pretty bad. This one is much better and about as fast:
float Noise2d(int x, int y) {
unsigned n = x;
n ^= 0xaacff006;
n *= 0xdc3deee5;
n = (n<<13) | (n>>19);
n += y;
n ^= 0x0a87317a;
n *= 0x38656b5e;
n = (n<<13) | (n>>19);
n += 0xa6c5636a;
n *= 0x7d4677b3;
const float inv_2_31 = 1.0f / 2147483648.0f;
float res = 1.0f - n * inv_2_31;
return res;
}


Ah thanks,

I made the changes but the results are :

[attachment=6178:img.jpg]




Is it meant to be as stretched? I was expecting purely random noise.

I wasn't sure about converting the int x/y to unsigned. i just cast them.




thanks for the help

Hmmm... You are right. My bit mixing is a bit worse than I was hoping for. Adding a few operations at the end seems to get rid of the problem.

float Noise2d(int x, int y) {
unsigned n = x;
n ^= 0xaacff006;
n *= 0xdc3deee5;
n = (n<<13) | (n>>19);
n += y;
n ^= 0x0a87317a;
n *= 0x38656b5e;
n = (n<<13) | (n>>19);
n += 0xa6c5636a;
n *= 0x7d4677b3;
n = (n<<13) | (n>>19);
n ^= 0x57a90182;
n *= 0xe09358ab;
const float inv_2_31 = 1.0f / 2147483648.0f;
float res = 1.0f - n * inv_2_31;
return res;
}


Sorry about that.