OpenSimplex2S constructor

OpenSimplex2S(int seed)

Creates a seeded OpenSimplex2S that can be used to evaluate noise.

Implementation

OpenSimplex2S(int seed) {
  if (!_staticInitialized) {
    _staticInit();
    _staticInitialized = true;
  }

  final source = Int16List(_kSize);
  for (var i = 0; i < _kSize; i++) {
    source[i] = i;
  }
  // KdotJPG's implementation uses Java's long here. Long in Java is a
  // 64-bit two's complement integer. int in Dart is also a 64-bit two's
  // complement integer, however, *only on native* (see https://dart.dev/guides/language/numbers).
  // However, we want to support web, i.e. JavaScript, as well with this
  // package and therefore we have to use the fixnum Int64 type. See
  // https://github.com/dart-lang/sdk/issues/46852#issuecomment-894888740.
  var seed64 = Int64(seed);
  for (int i = _kSize - 1; i >= 0; i--) {
    // KdotJPG's implementation uses long literals here. We can use int
    // literals of this size as well in Dart, however, these are too big for
    // JavaScript and therefore we have to use int.parse instead.
    seed64 = seed64 * Int64.parseInt('6364136223846793005') +
        Int64.parseInt('1442695040888963407');
    // We know r cannot be bigger than 2047, so we can convert it back to an
    // int.
    var r = ((seed64 + 31) % (i + 1)).toInt();
    if (r < 0) r += i + 1;
    _perm[i] = source[r];
    _permGrad2[i] = _gradients2d[_perm[i]];
    _permGrad3[i] = _gradients3d[_perm[i]];
    _permGrad4[i] = _gradients4d[_perm[i]];
    source[r] = source[i];
  }
}