in slides/webgl/asset/common/simplex.js [77:136]
noise2D: function(xin, yin) {
var permMod12 = this.permMod12;
var perm = this.perm;
var grad3 = this.grad3;
var n0 = 0; // Noise contributions from the three corners
var n1 = 0;
var n2 = 0;
// Skew the input space to determine which simplex cell we're in
var s = (xin + yin) * 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;
} // lower triangle, XY order: (0,0)->(1,0)->(1,1)
else {
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 - 1.0 + 2.0 * G2; // Offsets for last corner in (x,y) unskewed coords
var y2 = y0 - 1.0 + 2.0 * G2;
// Work out the hashed gradient indices of the three simplex corners
var ii = i & 255;
var jj = j & 255;
// Calculate the contribution from the three corners
var t0 = 0.5 - x0 * x0 - y0 * y0;
if (t0 >= 0) {
var gi0 = permMod12[ii + perm[jj]] * 3;
t0 *= t0;
n0 = t0 * t0 * (grad3[gi0] * x0 + grad3[gi0 + 1] * y0); // (x,y) of grad3 used for 2D gradient
}
var t1 = 0.5 - x1 * x1 - y1 * y1;
if (t1 >= 0) {
var gi1 = permMod12[ii + i1 + perm[jj + j1]] * 3;
t1 *= t1;
n1 = t1 * t1 * (grad3[gi1] * x1 + grad3[gi1 + 1] * y1);
}
var t2 = 0.5 - x2 * x2 - y2 * y2;
if (t2 >= 0) {
var gi2 = permMod12[ii + 1 + perm[jj + 1]] * 3;
t2 *= t2;
n2 = t2 * t2 * (grad3[gi2] * x2 + grad3[gi2 + 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 70.0 * (n0 + n1 + n2);
},