PortableGraphicsToolkit/src/pgt/maths/random/SimplexNoise.cpp
/**
* 2D Perlin simplex noise
*
*  Takes around 150ns on an AMD APU.
*
* @param[in] x float coordinate
* @param[in] y float coordinate
*
* @return Noise value in the range[-1; 1], value of 0 on all integer
* coordinates.
*/
2D Perlin simplex noise
Takes around 150ns on an AMD APU.
2D Perlin simplex noise Takes around 150ns on an AMD APU .
float SimplexNoise::noise(float x, float y) {
  float n0, n1, n2; 
  const float F2 = 0.366025403f; 
  const float G2 = 0.211324865f; 
  float s = (x + y) * F2; 
  float xs = x + s;
  float ys = y + s;
  int32_t i = fastfloor(xs);
  int32_t j = fastfloor(ys);
  float t = static_cast<float>(i + j) * G2;
  float X0 = i - t;
  float Y0 = j - t;
  float x0 = x - X0; 
  float y0 = y - Y0;
  int32_t i1,
      j1; 
  if (x0 > y0) { 
    i1 = 1;
    j1 = 0;
  } else { 
    i1 = 0;
    j1 = 1;
  }
  float x1 = x0 - i1 + G2; 
  float y1 = y0 - j1 + G2;
  float x2 =
      x0 - 1.0f + 2.0f * G2; 
  float y2 = y0 - 1.0f + 2.0f * G2;
  float t0 = 0.5f - x0 * x0 - y0 * y0;
  if (t0 < 0.0f) {
    n0 = 0.0f;
  } else {
    t0 *= t0;
    n0 = t0 * t0 * grad(hash(i + hash(j)), x0, y0);
  }
  float t1 = 0.5f - x1 * x1 - y1 * y1;
  if (t1 < 0.0f) {
    n1 = 0.0f;
  } else {
    t1 *= t1;
    n1 = t1 * t1 * grad(hash(i + i1 + hash(j + j1)), x1, y1);
  }
  float t2 = 0.5f - x2 * x2 - y2 * y2;
  if (t2 < 0.0f) {
    n2 = 0.0f;
  } else {
    t2 *= t2;
    n2 = t2 * t2 * grad(hash(i + 1 + hash(j + 1)), x2, y2);
  }
  return 45.23065f * (n0 + n1 + n2);
}
float SimplexNoise :: noise ( float x , float y ) { float n0 , n1 , n2 ; const float F2 = 0.366025403f ; const float G2 = 0.211324865f ; float s = ( x + y ) * F2 ; float xs = x + s ; float ys = y + s ; int32_t i = fastfloor ( xs ) ; int32_t j = fastfloor ( ys ) ; float t = static_cast < float > ( i + j ) * G2 ; float X0 = i - t ; float Y0 = j - t ; float x0 = x - X0 ; float y0 = y - Y0 ; int32_t i1 , j1 ; if ( x0 > y0 ) { i1 = 1 ; j1 = 0 ; } else { i1 = 0 ; j1 = 1 ; } float x1 = x0 - i1 + G2 ; float y1 = y0 - j1 + G2 ; float x2 = x0 - 1.0f + 2.0f * G2 ; float y2 = y0 - 1.0f + 2.0f * G2 ; float t0 = 0.5f - x0 * x0 - y0 * y0 ; if ( t0 < 0.0f ) { n0 = 0.0f ; } else { t0 *= t0 ; n0 = t0 * t0 * grad ( hash ( i + hash ( j ) ) , x0 , y0 ) ; } float t1 = 0.5f - x1 * x1 - y1 * y1 ; if ( t1 < 0.0f ) { n1 = 0.0f ; } else { t1 *= t1 ; n1 = t1 * t1 * grad ( hash ( i + i1 + hash ( j + j1 ) ) , x1 , y1 ) ; } float t2 = 0.5f - x2 * x2 - y2 * y2 ; if ( t2 < 0.0f ) { n2 = 0.0f ; } else { t2 *= t2 ; n2 = t2 * t2 * grad ( hash ( i + 1 + hash ( j + 1 ) ) , x2 , y2 ) ; } return 45.23065f * ( n0 + n1 + n2 ) ; }
2D Perlin simplex noise
Takes around 150ns on an AMD APU.
2D Perlin simplex noise Takes around 150ns on an AMD APU .
// Noise contributions from the three corners // Skewing/Unskewing factors for 2D // F2 = (sqrt(3) - 1) / 2 // G2 = (3 - sqrt(3)) / 6   = F2 / (1 + 2 * K) // Skew the input space to determine which simplex cell we're in // Hairy factor for 2D // Unskew the cell origin back to (x,y) space // The x,y distances from the cell origin // For the 2D case, the simplex shape is an equilateral triangle. // Determine which simplex we are in. // Offsets for second (middle) corner of simplex in (i,j) coords // lower triangle, XY order: (0,0)->(1,0)->(1,1) // 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 // Offsets for middle corner in (x,y) unskewed coords // Offsets for last corner in (x,y) unskewed coords // Calculate the contribution from the first corner // Calculate the contribution from the second corner // Calculate the contribution from the third corner // Add contributions from each corner to get the final noise value. // The result is scaled to return values in the interval [-1,1].