lib/rotjs-library/src/noise/simplex.js

/**
 * A simple 2d implementation of simplex noise by Ondrej Zara
 *
 * Based on a speed-improved simplex noise algorithm for 2D, 3D and 4D in Java.
 * Which is based on example code by Stefan Gustavson (stegu@itn.liu.se).
 * With Optimisations by Peter Eastman (peastman@drizzle.stanford.edu).
 * Better rank ordering method by Stefan Gustavson in 2012.
 */

/**
 * @class 2D simplex noise generator
 * @param {int} [gradients=256] Random gradients
 */
ROT.Noise.Simplex = function(gradients) {
	ROT.Noise.call(this);

	this._F2 = 0.5 * (Math.sqrt(3) - 1);
    this._G2 = (3 - Math.sqrt(3)) / 6;

	this._gradients = [
		[ 0, -1],
		[ 1, -1],
		[ 1,  0],
		[ 1,  1],
		[ 0,  1],
		[-1,  1],
		[-1,  0],
		[-1, -1]
	];

	var permutations = [];
	var count = gradients || 256;
	for (var i=0;i<count;i++) { permutations.push(i); }
	permutations = permutations.randomize();

	this._perms = [];
	this._indexes = [];

	for (var i=0;i<2*count;i++) {
		this._perms.push(permutations[i % count]);
		this._indexes.push(this._perms[i] % this._gradients.length);
	}

};
ROT.Noise.Simplex.extend(ROT.Noise);

ROT.Noise.Simplex.prototype.get = function(xin, yin) {
	var perms = this._perms;
	var indexes = this._indexes;
	var count = perms.length/2;
	var G2 = this._G2;

	var n0 =0, n1 = 0, n2 = 0, gi; // Noise contributions from the three corners

	// Skew the input space to determine which simplex cell we're in
	var s = (xin + yin) * this._F2; // Hairy factor for 2D
	var i = Math.floor(xin + s);
	var j = Math.floor(yin + s);
	var t = (i + j) * G2;
	var X0 = i - t; // Unskew the cell origin back to (x,y) space
	var Y0 = j - t;
	var x0 = xin - X0; // The x,y distances from the cell origin
	var y0 = yin - Y0;

	// For the 2D case, the simplex shape is an equilateral triangle.
	// Determine which simplex we are in.
	var i1, j1; // Offsets for second (middle) corner of simplex in (i,j) coords
	if (x0 > y0) {
		i1 = 1;
		j1 = 0;
	} else { // lower triangle, XY order: (0,0)->(1,0)->(1,1)
		i1 = 0;
		j1 = 1;
	} // upper triangle, YX order: (0,0)->(0,1)->(1,1)

	// A step of (1,0) in (i,j) means a step of (1-c,-c) in (x,y), and
	// a step of (0,1) in (i,j) means a step of (-c,1-c) in (x,y), where
	// c = (3-sqrt(3))/6
	var x1 = x0 - i1 + G2; // Offsets for middle corner in (x,y) unskewed coords
	var y1 = y0 - j1 + G2;
	var x2 = x0 - 1 + 2*G2; // Offsets for last corner in (x,y) unskewed coords
	var y2 = y0 - 1 + 2*G2;

	// Work out the hashed gradient indices of the three simplex corners
	var ii = i.mod(count);
	var jj = j.mod(count);

	// Calculate the contribution from the three corners
	var t0 = 0.5 - x0*x0 - y0*y0;
	if (t0 >= 0) {
		t0 *= t0;
		gi = indexes[ii+perms[jj]];
		var grad = this._gradients[gi];
		n0 = t0 * t0 * (grad[0] * x0 + grad[1] * y0);
	}
	
	var t1 = 0.5 - x1*x1 - y1*y1;
	if (t1 >= 0) {
		t1 *= t1;
		gi = indexes[ii+i1+perms[jj+j1]];
		var grad = this._gradients[gi];
		n1 = t1 * t1 * (grad[0] * x1 + grad[1] * y1);
	}
	
	var t2 = 0.5 - x2*x2 - y2*y2;
	if (t2 >= 0) {
		t2 *= t2;
		gi = indexes[ii+1+perms[jj+1]];
		var grad = this._gradients[gi];
		n2 = t2 * t2 * (grad[0] * x2 + grad[1] * y2);
	}

	// Add contributions from each corner to get the final noise value.
	// The result is scaled to return values in the interval [-1,1].
	return 70 * (n0 + n1 + n2);
}