Perlin Noise

perlin.cpp

#include <algorithm>
#include <random>

using namespace std;

void createRandomHash(vector<uint8_t>& hash)
{
	random_device r;
	default_random_engine re(r());

	hash.resize(256);
	iota(hash.begin(), hash.end(), 0);
	shuffle(hash.begin(), hash.end(), re);
	hash.insert(hash.end(), hash.begin(), hash.end());
}

inline
uint8_t hash(const vector<uint8_t>& h, unsigned int a, unsigned int b) { return h[h[a] + b]; }

// Our easing function
inline
double fade(double t) { return t*t*t*(t*(t*6.-15.)+10.); }

inline
double lerp(double t, double a, double b) { return a + t * (b - a); }

inline
double gradient(uint8_t hash, double x, double y)
{
	return ((hash & 1) ? x : -x) + ((hash & 2) ? y : -y);
}

double noise(double x, double y)
{
	int xi = (int)x & 255;
  int yi = (int)y & 255;

	x -= (int)x;
	y -= (int)y;

	double u = fade(x);
	double v = fade(y);

	uint8_t aa = hash(xi, yi);
	uint8_t ab = hash(xi, yi+1);
	uint8_t ba = hash(xi+1, yi);
	uint8_t bb = hash(xi+1, yi+1);

	double val = lerp(v,
					  lerp(u, gradient(aa, x, y), gradient(ba, x-1, y)),
					  lerp(u, gradient(ab, x, y-1), gradient(bb, x-1, y-1)));
	
	return (val + 1.)/2.;
}


int main(int argc, char** argv)
{
	unsigned int width = 100, height = 100;
	
	for (unsigned int i=0; i<height; ++i)
	{
		for (unsigned int j=0; j<width; ++j)
		{
			double x = (double)j/(double)width;
			double y = (double)i/(double)height;
			double n = noise(10*x, 10*y);

			// 'n' is the value to assign to the pixel at (j, i)
		}
	}

  return 0;
}