GaussQuadratureTetrahedron::GaussQuadratureTetrahedron(size_t order)
{
GaussLegendre quadRule = GaussLegendre(order);
GaussJacobi10 quadRule10 = GaussJacobi10(order);
GaussJacobi20 quadRule20 = GaussJacobi20(order);
m_order = std::min(quadRule.order(), std::min(quadRule10.order(), quadRule20.order()));
m_numPoints = quadRule.size() * quadRule10.size() * quadRule20.size();
position_type* pvPoint = new position_type[m_numPoints];
weight_type* pvWeight = new weight_type[m_numPoints];
size_t cnt = 0;
for(size_t i = 0; i < quadRule20.size(); i++) {
for(size_t j = 0; j < quadRule10.size(); j++) {
for(size_t k = 0; k < quadRule.size(); k++, cnt++) {
pvPoint[cnt][0] = quadRule20.point(i)[0];
pvPoint[cnt][1] = (1.0 - quadRule20.point(i)[0] ) * quadRule10.point(j)[0];
pvPoint[cnt][2] = (1.0 - quadRule20.point(i)[0]) * (1.0 - quadRule10.point(j)[0]) * quadRule.point(k)[0];
pvWeight[cnt] = quadRule20.weight(i) * quadRule10.weight(j) * quadRule.weight(k);
}
}
}
m_pvPoint = pvPoint;
m_pvWeight = pvWeight;
};
/**
* Integrate down the centre of this unknown
* This will not take into account changes
* in the jacobian across the extent of the basis
* function
*/
static
typename UnknownT::NumberT
integrate(
const UnknownT& unknown,
const CoordinatesInterface<DIM,
typename UnknownT::NumberT>& geom,
const int direction)
{
GaussLegendre<UnknownT::ORDER, NumberT> quad;
ValueT integral(0.0);
for (auto interval1D :
unknown.linearIntervals1D(direction)) {
NumberT intervalMin = interval1D.minimum(0);
NumberT intervalMax = interval1D.maximum(0);
auto nodes = quad.nodes(intervalMin, intervalMax);
auto weights = quad.weights(intervalMin, intervalMax);
auto location = unknown.centres();
for (std::size_t j = 0; j < nodes.size(); ++j) {
location[direction] = nodes[j];
integral += weights[j] *
unknown.value(direction, nodes[j]) *
geom.jacobian(direction, nodes[j]);
}
}
return integral;
}
static
typename UnknownT::NumberT
integrateComplex(
const UnknownT& unknown,
const CoordinatesInterface<DIM,
typename UnknownT::NumberT>& geom,
const std::vector<int>& directions
)
{
static const int QUAD_ORDER = UnknownT::ORDER + 1;
static const int NUM = GaussLegendre<QUAD_ORDER, NumberT>::NUM;
assert(DIM > 1);
// integrate the the copy along direction
GaussLegendre<QUAD_ORDER, NumberT> quad;
std::array<int, DIM> indexSizes;
indexSizes.fill(int(quad.size()));
auto indices = MathsUtilities::allPermutations<DIM>(indexSizes);
// The integral of the unknown in the directions
// we to integrate in
ValueT integral(0.0);
for (auto interval : unknown.intervals()) {
auto minima = interval.minima();
auto maxima = interval.maxima();
auto nodes = QuadratureOps<DIM, QUAD_ORDER, NumberT>::
nodes(quad, minima, maxima);
auto weights = QuadratureOps<DIM, QUAD_ORDER, NumberT>::
weights(quad, minima, maxima);
for (auto index : indices) {
auto locationArray = ContainerUtilities::
select<DIM, NUM, NumberT>(nodes, index);
auto allWeights = ContainerUtilities::
select<DIM, NUM, NumberT>(weights, index);
Vector<DIM, NumberT> location(locationArray);
assert(interval.isInside(location));
auto directionWeights = ContainerUtilities::
select<DIM, NumberT>(allWeights, directions);
auto weight = ContainerUtilities::
product<NumberT>(directionWeights);
integral += weight *
unknown.value(directions, location) *
geom.jacobian(Contravariant<DIM, NumberT>(location));
}
}
static_assert(NUM > 0, "NUM must be greater than zero");
return integral / NUM;
}
static
typename std::array<typename GaussLegendre<ORDER, T>::NodesAndWeights, DIM>
nodesWeightsPairs(
const Vector<DIM, T>& mins,
const Vector<DIM, T>& maxs
)
{
GaussLegendre<ORDER, T> quad;
std::array<GaussLegendre<ORDER, T>, DIM> allNodesAndWeights;
for (int i = 0; i < DIM; ++i) {
assert(maxs[i] > mins[i]);
allNodesAndWeights[i] = quad.weights(mins[i], maxs[i]);
}
return allNodesAndWeights;
}
GaussQuadratureQuadrilateral::GaussQuadratureQuadrilateral(size_t order)
{
GaussLegendre quadRule = GaussLegendre(order);
m_order = std::min(quadRule.order(), quadRule.order());
m_numPoints = quadRule.size() * quadRule.size();
position_type* pvPoint = new position_type[m_numPoints];
weight_type* pvWeight = new weight_type[m_numPoints];
size_t cnt = 0;
for(size_t i = 0; i < quadRule.size(); i ++) {
for(size_t j = 0; j < quadRule.size(); j++, cnt++) {
pvPoint[cnt][0] = quadRule.point(i)[0];
pvPoint[cnt][1] = quadRule.point(j)[0];
pvWeight[cnt] = quadRule.weight(i) * quadRule.weight(j);
}
}
m_pvPoint = pvPoint;
m_pvWeight = pvWeight;
};
static
std::array<std::array<T, ORDER+1>, DIM>
weights(const GaussLegendre<ORDER, T>& quad,
const Vector<DIM, T>& mins,
const Vector<DIM, T>& maxs)
{
std::array<std::array<T, ORDER+1>, DIM> allWeights;
for (uint i = 0; i < DIM; ++i) {
assert(maxs[i] > mins[i]);
allWeights[i] = quad.weights(mins[i], maxs[i]);
}
return allWeights;
}
void HairBcsdf::precomputeAzimuthalDistributions()
{
const int Resolution = PrecomputedAzimuthalLobe::AzimuthalResolution;
std::unique_ptr<Vec3f[]> valuesR (new Vec3f[Resolution*Resolution]);
std::unique_ptr<Vec3f[]> valuesTT (new Vec3f[Resolution*Resolution]);
std::unique_ptr<Vec3f[]> valuesTRT(new Vec3f[Resolution*Resolution]);
// Ideally we could simply make this a constexpr, but MSVC does not support that yet (boo!)
#define NumPoints 140
GaussLegendre<NumPoints> integrator;
const auto points = integrator.points();
const auto weights = integrator.weights();
// Cache the gammaI across all integration points
std::array<float, NumPoints> gammaIs;
for (int i = 0; i < NumPoints; ++i)
gammaIs[i] = std::asin(points[i]);
// Precompute the Gaussian detector and sample it into three 1D tables.
// This is the only part of the precomputation that is actually approximate.
// 2048 samples are enough to support the lowest roughness that the BCSDF
// can reliably simulate
const int NumGaussianSamples = 2048;
std::unique_ptr<float[]> Ds[3];
for (int p = 0; p < 3; ++p) {
Ds[p].reset(new float[NumGaussianSamples]);
for (int i = 0; i < NumGaussianSamples; ++i)
Ds[p][i] = D(_betaR, i/(NumGaussianSamples - 1.0f)*TWO_PI);
}
// Simple wrapped linear interpolation of the precomputed table
auto approxD = [&](int p, float phi) {
float u = std::abs(phi*(INV_TWO_PI*(NumGaussianSamples - 1)));
int x0 = int(u);
int x1 = x0 + 1;
u -= x0;
return Ds[p][x0 % NumGaussianSamples]*(1.0f - u) + Ds[p][x1 % NumGaussianSamples]*u;
};
// Here follows the actual precomputation of the azimuthal scattering functions
// The scattering functions are parametrized with the azimuthal angle phi,
// and the cosine of the half angle, cos(thetaD).
// This parametrization makes the azimuthal function relatively smooth and allows using
// really low resolutions for the table (64x64 in this case) without any visual
// deviation from ground truth, even at the lowest supported roughness setting
for (int y = 0; y < Resolution; ++y) {
float cosHalfAngle = y/(Resolution - 1.0f);
// Precompute reflection Fresnel factor and reduced absorption coefficient
float iorPrime = std::sqrt(Eta*Eta - (1.0f - cosHalfAngle*cosHalfAngle))/cosHalfAngle;
float cosThetaT = std::sqrt(1.0f - (1.0f - cosHalfAngle*cosHalfAngle)*sqr(1.0f/Eta));
Vec3f sigmaAPrime = _sigmaA/cosThetaT;
// Precompute gammaT, f_t and internal absorption across all integration points
std::array<float, NumPoints> fresnelTerms, gammaTs;
std::array<Vec3f, NumPoints> absorptions;
for (int i = 0; i < NumPoints; ++i) {
gammaTs[i] = std::asin(clamp(points[i]/iorPrime, -1.0f, 1.0f));
fresnelTerms[i] = Fresnel::dielectricReflectance(1.0f/Eta, cosHalfAngle*std::cos(gammaIs[i]));
absorptions[i] = std::exp(-sigmaAPrime*2.0f*std::cos(gammaTs[i]));
}
for (int phiI = 0; phiI < Resolution; ++phiI) {
float phi = TWO_PI*phiI/(Resolution - 1.0f);
float integralR = 0.0f;
Vec3f integralTT(0.0f);
Vec3f integralTRT(0.0f);
// Here follows the integration across the fiber width, h.
// Since we were able to precompute most of the factors that
// are constant w.r.t phi for a given h,
// we don't have to do much work here.
for (int i = 0; i < integrator.numSamples(); ++i) {
float fR = fresnelTerms[i];
Vec3f T = absorptions[i];
float AR = fR;
Vec3f ATT = (1.0f - fR)*(1.0f - fR)*T;
Vec3f ATRT = ATT*fR*T;
integralR += weights[i]*approxD(0, phi - Phi(gammaIs[i], gammaTs[i], 0))*AR;
integralTT += weights[i]*approxD(1, phi - Phi(gammaIs[i], gammaTs[i], 1))*ATT;
integralTRT += weights[i]*approxD(2, phi - Phi(gammaIs[i], gammaTs[i], 2))*ATRT;
}
valuesR [phiI + y*Resolution] = Vec3f(0.5f*integralR);
valuesTT [phiI + y*Resolution] = 0.5f*integralTT;
valuesTRT[phiI + y*Resolution] = 0.5f*integralTRT;
}
}
// Hand the values off to the helper class to construct sampling CDFs and so forth
_nR .reset(new PrecomputedAzimuthalLobe(std::move(valuesR)));
_nTT .reset(new PrecomputedAzimuthalLobe(std::move(valuesTT)));
_nTRT.reset(new PrecomputedAzimuthalLobe(std::move(valuesTRT)));
}
