/** \brief Compute occlusion from the current view direction to the
* given sample region.
*
* \param sampleRegion - parallelogram region over which to sample the map
* \param sampleOpts - set of sampling options
* \param numSamples - number of samples to take for the region.
* \param outSamps[0] - Return parameter; amount of occlusion over the
* sample region in the viewing direction for this map.
*/
void sample(const Sq3DSampleQuad& sampleQuad,
const CqShadowSampleOptions& sampleOpts,
TqFloat* outSamps) const
{
// Get depths of sample positions.
Sq3DSampleQuad quadLightCoord = sampleQuad;
quadLightCoord.transform(m_currToLight);
// Get texture coordinates of sample positions.
Sq3DSampleQuad texQuad3D = sampleQuad;
texQuad3D.transform(m_currToRaster);
// Copy into (x,y) coordinates of texQuad and scale by the filter width.
SqSampleQuad texQuad = texQuad3D;
texQuad.scaleWidth(sampleOpts.sWidth(), sampleOpts.tWidth());
// Get the EWA filter weight functor. We use a relatively low edge cutoff
// of 2, since we want to avoid taking samples which don't contribute much
// to the average. This problem would be a relative non-issue if we did
// proper importance sampling.
//
/// \todo Investigate proper importance sampling to reduce the variance in
/// shadow sampling?
CqEwaFilterFactory ewaFactory(texQuad, m_pixels.width(),
m_pixels.height(), sampleOpts.sBlur(), sampleOpts.tBlur(), 2);
CqEwaFilter ewaWeights = ewaFactory.createFilter();
/** \todo Optimization: Cull the query if it's outside the [min,max] depth
* range of the support. Being able to determine the range from the tiles
* covered by the filter support will be a big advantage.
*/
SqFilterSupport support = ewaWeights.support();
if(support.intersectsRange(0, m_pixels.width(), 0, m_pixels.height()))
{
if(sampleOpts.depthApprox() == DApprox_Constant)
{
// Functor which approximates the surface depth using a constant.
CqConstDepthApprox depthFunc(quadLightCoord.center().z());
applyPCF(m_pixels, sampleOpts, support, ewaWeights, depthFunc, outSamps);
}
else
{
// Get a functor which approximates the surface depth across the filter
// support with a linear approximation. This deduced depth will be
// compared with the depths from the stored texture buffer.
quadLightCoord.copy2DCoords(texQuad);
CqSampleQuadDepthApprox depthFunc(quadLightCoord, m_pixels.width(),
m_pixels.height());
applyPCF(m_pixels, sampleOpts, support, ewaWeights, depthFunc, outSamps);
}
}
else
{
// If the filter support lies wholly outside the texture, return
// fully visible == 0.
*outSamps = 0;
}
}
/** \brief Compute occlusion from the current view direction to the
* given sample region.
*
* \param sampleRegion - parallelogram region over which to sample the map
* \param sampleOpts - set of sampling options
* \param numSamples - number of samples to take for the region.
* \param outSamps[0] - Return parameter; amount of occlusion over the
* sample region in the viewing direction for this map.
*/
void sample(const Sq3DSamplePllgram& sampleRegion,
const CqShadowSampleOptions& sampleOpts,
const TqInt numSamples, TqFloat* outSamps)
{
// filter weights
CqConstFilter filterWeights;
// Use constant depth approximation for the surface for maximum
// sampling speed. We use the depth from the camera to the centre
// of the sample region.
CqConstDepthApprox depthFunc((m_currToLight*sampleRegion.c).z());
// Determine rough filter support. This results in a
// texture-aligned box, so doesn't do proper anisotropic filtering.
// For occlusion this isn't visible anyway because of the large
// amount of averaging. We also want the filter setup to be as
// fast as possible.
// CqVector3D side1 = m_currToRasterVec*sampleRegion.s1;
// CqVector3D side2 = m_currToRasterVec*sampleRegion.s2;
// CqVector3D center = m_currToRaster*sampleRegion.c;
// TqFloat sWidthOn2 = max(side1.x(), side2.x())*m_pixels.width()/2;
// TqFloat tWidthOn2 = max(side1.y(), side2.y())*m_pixels.height()/2;
// TODO: Fix the above calculation so that the width is actually
// taken into account properly.
CqVector3D center = m_currToRaster*sampleRegion.c;
TqFloat sWidthOn2 = 0.5*(sampleOpts.sBlur()*m_pixels.width());
TqFloat tWidthOn2 = 0.5*(sampleOpts.tBlur()*m_pixels.height());
SqFilterSupport support(
lround(center.x()-sWidthOn2), lround(center.x()+sWidthOn2) + 1,
lround(center.y()-tWidthOn2), lround(center.y()+tWidthOn2) + 1);
// percentage closer accumulator
CqPcfAccum<CqConstFilter, CqConstDepthApprox> accumulator(
filterWeights, depthFunc, sampleOpts.startChannel(),
sampleOpts.biasLow(), sampleOpts.biasHigh(), outSamps);
// accumulate occlusion over the filter support.
filterTextureNowrapStochastic(accumulator, m_pixels, support, numSamples);
}
void CqOcclusionSampler::sample(const Sq3DSamplePllgram& samplePllgram,
const CqVector3D& normal, const CqShadowSampleOptions& sampleOpts,
TqFloat* outSamps) const
{
assert(sampleOpts.numChannels() == 1);
// Unit normal indicating the hemisphere to sample for occlusion.
CqVector3D N = normal;
N.Unit();
const TqFloat sampNumMult = 4.0 * sampleOpts.numSamples() / m_maps.size();
// Accumulate the total occlusion over all directions. Here we use an
// importance sampling approach: we decide how many samples each map should
// have based on it's relative importance as measured by the map weight.
TqFloat totOcc = 0;
TqInt totNumSamples = 0;
TqFloat maxWeight = 0;
TqViewVec::const_iterator maxWeightMap = m_maps.begin();
for(TqViewVec::const_iterator map = m_maps.begin(), end = m_maps.end();
map != end; ++map)
{
TqFloat weight = (*map)->weight(N);
if(weight > 0)
{
// Compute the number of samples to use. Assuming that the shadow
// maps are spread evenly over the sphere, we have an area of
//
// 4*PI / m_maps.size()
//
// steradians per map. The density of sample points per steradian
// should be
//
// sampleOpts.numSamples() * weight / PI
//
// Therefore the expected number of samples per map is
TqFloat numSampFlt = sampNumMult*weight;
// This isn't an integer though, so we take the floor,
TqInt numSamples = lfloor(numSampFlt);
// TODO: Investigate performance impact of using RandomFloat() here.
if(m_random.RandomFloat() < numSampFlt - numSamples)
{
// And increment with a probability equal to the extra fraction
// of samples that the current map should have.
++numSamples;
}
if(numSamples > 0)
{
// Compute amount of occlusion from the current view.
TqFloat occ = 0;
(*map)->sample(samplePllgram, sampleOpts, numSamples, &occ);
// Accumulate into total occlusion and weight.
totOcc += occ*numSamples;
totNumSamples += numSamples;
}
if(weight > maxWeight)
{
maxWeight = weight;
maxWeightMap = map;
}
}
}
// The algorithm above sometimes results in no samples being computed for
// low total sample numbers. Here we attempt to allow very small numbers
// of samples to be useful by sampling the most highly weighted map if no
// samples have been taken
if(totNumSamples == 0 && maxWeight > 0)
{
TqFloat occ = 0;
(*maxWeightMap)->sample(samplePllgram, sampleOpts, 1, &occ);
totOcc += occ;
totNumSamples += 1;
}
// Normalize the sample
*outSamps = totOcc / totNumSamples;
}
