//-----------------------------------------------------------------------------------------------
// Computes a random Perlin noise value in the range [-1,1] based on a 2D input <position> and
// various Perlin noise parameters.
//
// <perlinNoiseGridCellSize>: Noise density. Larger values produce longer wavelength noise
// (e.g. gentle, sweeping hills).
// <numOctaves>: 0 is flat, 1 is simple smoothed noise. Values of 2+ add one or more additional
// "octave" harmonics. Each additional octave has double the frequency/density but only a
// fraction of the amplitude of the base noise.
// <persistence>: The fraction of amplitude of each subsequent octave, based on the amplitude of
// the previous octave. For example, with a persistence of 0.3, each octave is only 30% as
// strong as the previous octave.
//
float ComputePerlinNoise2D( const Vector2& position, float perlinNoiseGridCellSize, int numOctaves, float persistence )
{
float totalPerlinNoise = 0.f;
float currentOctaveAmplitude = 1.f;
float totalMaxAmplitude = 0.f;
float perlinGridFrequency = (1.f / perlinNoiseGridCellSize);
for( int octaveNumber = 0; octaveNumber < numOctaves; ++octaveNumber )
{
Vector2 perlinPosition( position.x * perlinGridFrequency, position.y * perlinGridFrequency );
Vector2 perlinPositionFloor( (float) floor( perlinPosition.x ), (float) floor( perlinPosition.y ) );
Vector2Int perlinCell( (int) perlinPositionFloor.x, (int) perlinPositionFloor.y );
Vector2 perlinPositionUV = perlinPosition - perlinPositionFloor;
Vector2 perlinPositionAntiUV( perlinPositionUV.x - 1.f, perlinPositionUV.y - 1.f );
float eastWeight = MathUtils::SmoothStep( perlinPositionUV.x );
float northWeight = MathUtils::SmoothStep(perlinPositionUV.y);
float westWeight = 1.f - eastWeight;
float southWeight = 1.f - northWeight;
Vector2 southwestNoiseGradient = GetPseudoRandomNoiseDirection2D( perlinCell.x, perlinCell.y );
Vector2 southeastNoiseGradient = GetPseudoRandomNoiseDirection2D( perlinCell.x + 1, perlinCell.y );
Vector2 northeastNoiseGradient = GetPseudoRandomNoiseDirection2D( perlinCell.x + 1, perlinCell.y + 1 );
Vector2 northwestNoiseGradient = GetPseudoRandomNoiseDirection2D( perlinCell.x, perlinCell.y + 1 );
float southwestDot = MathUtils::Dot(southwestNoiseGradient, perlinPositionUV);
float southeastDot = MathUtils::Dot(southeastNoiseGradient, Vector2(perlinPositionAntiUV.x, perlinPositionUV.y));
float northeastDot = MathUtils::Dot(northeastNoiseGradient, perlinPositionAntiUV);
float northwestDot = MathUtils::Dot(northwestNoiseGradient, Vector2(perlinPositionUV.x, perlinPositionAntiUV.y));
float southBlend = (eastWeight * southeastDot) + (westWeight * southwestDot);
float northBlend = (eastWeight * northeastDot) + (westWeight * northwestDot);
float fourWayBlend = (southWeight * southBlend) + (northWeight * northBlend);
float perlinNoiseForThisOctave = currentOctaveAmplitude * fourWayBlend;
totalPerlinNoise += perlinNoiseForThisOctave;
perlinGridFrequency *= 2.f;
totalMaxAmplitude += currentOctaveAmplitude;
currentOctaveAmplitude *= persistence;
}
if( totalMaxAmplitude != 0.f )
totalPerlinNoise /= totalMaxAmplitude;
return totalPerlinNoise;
}
//---------------------------------------------------------------------------
// Computes a random Perlin noise value based on a 2D input <position> and
// Perlin noise parameters. Recursive (for additional octaves).
//
// <perlinNoiseGridCellSize>: Noise density. Larger values produce longer
// wavelength noise (e.g. gentle, sweeping hills).
// <numOctaves>: 0 is flat, 1 is simple smoothed noise. Values of 2+ add one
// or more additional "octave" harmonics. Each additional octave has
// double the frequency/density but only a fraction of the amplitude of
// the base noise.
// <baseAmplitude>: The minimum (-amplitude) and maximum (+amplitude) values
// produced by the first octave of the noise. Note that adding
// additional octaves can push the final total Perlin noise values above
// or below the maximum base amplitude; the noise can be "normalized" by
// the caller (omitted from this function for optimization purposes) via:
// noise *= A / (A + (A * P))
// ...where A is the <baseAmplitude> and P is the <persistance>.
// <persistance>: The fraction of amplitude of each subsequent octave, based on the amplitude of the previous octave. For
// example, with a persistance of 0.3, each octave is only 30% as strong as the previous octave.
//
float ComputePerlinNoiseValueAtPosition2D( const Vector2& position, float perlinNoiseGridCellSize,
int numOctaves, float baseAmplitude, float persistance, int randomSeed )
{
int numOctavesRemaining = numOctaves;
float amplitude = baseAmplitude;
float gridSize = perlinNoiseGridCellSize;
float totalPerlinNoise = 0.0f;
while( numOctavesRemaining > 0 )
{
Vector2 perlinPosition = position / gridSize;
Vector2 perlinPositionFloor( floor( perlinPosition.x ), floor( perlinPosition.y ) );
IntVec2 perlinCell( (int) perlinPositionFloor.x, (int) perlinPositionFloor.y );
Vector2 perlinPositionUV = perlinPosition - perlinPositionFloor;
Vector2 perlinPositionAntiUV( perlinPositionUV.x - 1.f, perlinPositionUV.y - 1.f );
float eastWeight = SmoothStep( perlinPositionUV.x );
float northWeight = SmoothStep( perlinPositionUV.y );
float westWeight = 1.f - eastWeight;
float southWeight = 1.f - northWeight;
Vector2 southwestNoiseGradient = GetPseudoRandomNoiseUnitVector2D( perlinCell.x, perlinCell.y, randomSeed );
Vector2 southeastNoiseGradient = GetPseudoRandomNoiseUnitVector2D( perlinCell.x + 1, perlinCell.y, randomSeed );
Vector2 northeastNoiseGradient = GetPseudoRandomNoiseUnitVector2D( perlinCell.x + 1, perlinCell.y + 1, randomSeed );
Vector2 northwestNoiseGradient = GetPseudoRandomNoiseUnitVector2D( perlinCell.x, perlinCell.y + 1, randomSeed );
float southwestDot = DotProduct( southwestNoiseGradient, perlinPositionUV );
float southeastDot = DotProduct( southeastNoiseGradient, Vector2( perlinPositionAntiUV.x, perlinPositionUV.y ) );
float northeastDot = DotProduct( northeastNoiseGradient, perlinPositionAntiUV );
float northwestDot = DotProduct( northwestNoiseGradient, Vector2( perlinPositionUV.x, perlinPositionAntiUV.y ) );
float southBlend = (eastWeight * southeastDot) + (westWeight * southwestDot);
float northBlend = (eastWeight * northeastDot) + (westWeight * northwestDot);
float fourWayBlend = (southWeight * southBlend) + (northWeight * northBlend);
float perlinNoiseAtThisOctave = amplitude * fourWayBlend;
-- numOctavesRemaining;
totalPerlinNoise += perlinNoiseAtThisOctave;
amplitude *= persistance;
gridSize *= 0.5f;
}
return totalPerlinNoise;
}
//---------------------------------------------------------------------------
// Computes a random Perlin noise value based on a 2D input <position> and
// Perlin noise parameters. Recursive (for additional octaves).
//
// <perlinNoiseGridCellSize>: Noise density. Larger values produce longer
// wavelength noise (e.g. gentle, sweeping hills).
// <numOctaves>: 0 is flat, 1 is simple smoothed noise. Values of 2+ add one
// or more additional "octave" harmonics. Each additional octave has
// double the frequency/density but only a fraction of the amplitude of
// the base noise.
// <baseAmplitude>: The minimum (-amplitude) and maximum (+amplitude) values
// produced by the first octave of the noise. Note that adding
// additional octaves can push the final total Perlin noise values above
// or below the maximum base amplitude; the noise can be "normalized" by
// the caller (omitted from this function for optimization purposes) via:
// noise *= A / (A + (A * P))
// ...where A is the <baseAmplitude> and P is the <persistance>.
// <persistance>: The fraction of amplitude of each subsequent octave, based on the amplitude of the previous octave. For
// example, with a persistance of 0.3, each octave is only 30% as strong as the previous octave.
//
float ComputePerlinNoiseValueAtPosition2D( const Vector2& position, float perlinNoiseGridCellSize, int numOctaves, float baseAmplitude, float persistance )
{
if( numOctaves == 0 )
return 0.f;
Vector2 perlinPosition = position / perlinNoiseGridCellSize;
Vector2 perlinPositionFloor(floor(perlinPosition.x), floor(perlinPosition.y));
Vector2Int perlinCell((int)perlinPositionFloor.x, (int)perlinPositionFloor.y);
Vector2 perlinPositionUV = perlinPosition - perlinPositionFloor;
Vector2 perlinPositionAntiUV(perlinPositionUV.x - 1.f, perlinPositionUV.y - 1.f);
float eastWeight = SmoothStep(perlinPositionUV.x);
float northWeight = SmoothStep(perlinPositionUV.y);
float westWeight = 1.f - eastWeight;
float southWeight = 1.f - northWeight;
Vector2 southwestNoiseGradient = GetPseudoRandomNoiseUnitVector2D( perlinCell.x, perlinCell.y );
Vector2 southeastNoiseGradient = GetPseudoRandomNoiseUnitVector2D( perlinCell.x + 1, perlinCell.y );
Vector2 northeastNoiseGradient = GetPseudoRandomNoiseUnitVector2D( perlinCell.x + 1, perlinCell.y + 1 );
Vector2 northwestNoiseGradient = GetPseudoRandomNoiseUnitVector2D( perlinCell.x, perlinCell.y + 1 );
float southwestDot = MathUtils::Dot( southwestNoiseGradient, perlinPositionUV );
float southeastDot = MathUtils::Dot( southeastNoiseGradient, Vector2( perlinPositionAntiUV.x, perlinPositionUV.y ) );
float northeastDot = MathUtils::Dot( northeastNoiseGradient, perlinPositionAntiUV );
float northwestDot = MathUtils::Dot( northwestNoiseGradient, Vector2( perlinPositionUV.x, perlinPositionAntiUV.y ) );
float southBlend = (eastWeight * southeastDot) + (westWeight * southwestDot);
float northBlend = (eastWeight * northeastDot) + (westWeight * northwestDot);
float fourWayBlend = (southWeight * southBlend) + (northWeight * northBlend);
float perlinNoiseAtThisOctave = baseAmplitude * fourWayBlend;
float perlinNoiseFromAllHigherOctaves = ComputePerlinNoiseValueAtPosition2D( position,
0.5f * perlinNoiseGridCellSize, numOctaves - 1, baseAmplitude * persistance, persistance );
float totalPerlinNoise = perlinNoiseAtThisOctave + perlinNoiseFromAllHigherOctaves;
return totalPerlinNoise;
}
