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/**
* 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);
}
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