public function getNoise2D($x, $y)
{
$x += $this->offsetX;
$y += $this->offsetY;
// Skew the input space to determine which simplex cell we're in
$s = ($x + $y) * self::$F2;
// Hairy factor for 2D
$i = (int) ($x + $s);
$j = (int) ($y + $s);
$t = ($i + $j) * self::$G2;
// Unskew the cell origin back to (x,y) space
$x0 = $x - ($i - $t);
// The x,y distances from the cell origin
$y0 = $y - ($j - $t);
// For the 2D case, the simplex shape is an equilateral triangle.
// Determine which simplex we are in.
if ($x0 > $y0) {
$i1 = 1;
$j1 = 0;
} 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
$x1 = $x0 - $i1 + self::$G2;
// Offsets for middle corner in (x,y) unskewed coords
$y1 = $y0 - $j1 + self::$G2;
$x2 = $x0 + self::$G22;
// Offsets for last corner in (x,y) unskewed coords
$y2 = $y0 + self::$G22;
// Work out the hashed gradient indices of the three simplex corners
$ii = $i & 255;
$jj = $j & 255;
$n = 0;
// Calculate the contribution from the three corners
$t0 = 0.5 - $x0 * $x0 - $y0 * $y0;
if ($t0 > 0) {
$gi0 = self::$grad3[$this->perm[$ii + $this->perm[$jj]] % 12];
$n += $t0 * $t0 * $t0 * $t0 * ($gi0[0] * $x0 + $gi0[1] * $y0);
// (x,y) of grad3 used for 2D gradient
}
$t1 = 0.5 - $x1 * $x1 - $y1 * $y1;
if ($t1 > 0) {
$gi1 = self::$grad3[$this->perm[$ii + $i1 + $this->perm[$jj + $j1]] % 12];
$n += $t1 * $t1 * $t1 * $t1 * ($gi1[0] * $x1 + $gi1[1] * $y1);
}
$t2 = 0.5 - $x2 * $x2 - $y2 * $y2;
if ($t2 > 0) {
$gi2 = self::$grad3[$this->perm[$ii + 1 + $this->perm[$jj + 1]] % 12];
$n += $t2 * $t2 * $t2 * $t2 * ($gi2[0] * $x2 + $gi2[1] * $y2);
}
// Add contributions from each corner to get the noise value.
// The result is scaled to return values in the interval [-1,1].
return 70.0 * $n;
}
