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  *   Copyright (C) 1998-2009 by authors (see AUTHORS.txt )                 *

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  *   This file is part of LuxRender.                                       *

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  *   Lux Renderer is free software; you can redistribute it and/or modify  *

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  *   This project is based on PBRT ; see http://www.pbrt.org               *

  *   Lux Renderer website : http://www.luxrender.net                       *

  ***************************************************************************/

 // initial metropolis light transport sample integrator

 // by radiance

 // TODO: add scaling of output image samples

 // erpt.cpp*

 #include "erpt.h"

 #include "dynload.h"

 #include "scene.h"

 #include "error.h"

 using namespace lux;

 #define SAMPLE_FLOATS 6

 // mutate a value in the range [0-1]

 static float mutate(const float x, const float randomValue)

 {

 	static const float s1 = 1.f / 1024.f, s2 = 1.f / 16.f;

 	float dx = s2 * powf(s1 / s2, fabsf(2.f * randomValue - 1.f));

 	if (randomValue < 0.5f) {

 		float x1 = x + dx;

 		return (x1 > 1.f) ? x1 - 1.f : x1;

 	} else {

 		float x1 = x - dx;

 		return (x1 < 0.f) ? x1 + 1.f : x1;

 	}

 }

 // mutate a value in the range [min-max]

 static float mutateScaled(const float x, const float randomValue, const float mini, const float maxi, const float range)

 {

 	float dx = range * expf(-logf(2.f * range) * fabsf(2.f * randomValue - 1.f));

 	if (randomValue < 0.5f) {

 		float x1 = x + dx;

 		return (x1 > maxi) ? x1 - maxi + mini : x1;

 	} else {

 		float x1 = x - dx;

 		return (x1 < mini) ? x1 - mini + maxi : x1;

 	}

 }

 // Metropolis method definitions

 ERPTSampler::ERPTSampler(u_int totMutations, float rng,

 	Sampler *sampler) :

  Sampler(sampler->xPixelStart, sampler->xPixelEnd,

 	sampler->yPixelStart, sampler->yPixelEnd, sampler->samplesPerPixel),

  normalSamples(0), totalSamples(0), totalTimes(0), totalMutations(totMutations),

  range(rng), baseSampler(sampler),

  baseImage(NULL), sampleImage(NULL), currentImage(NULL),

  baseTimeImage(NULL), timeImage(NULL), currentTimeImage(NULL), offset(NULL),

  numChains(0), chain(0), mutation(~0U), stamp(0),

  baseLY(0.f), quantum(0.f), weight(0.f), LY(0.f), alpha(0.f),

  totalLY(0.), sampleCount(0.)

 {

 }

 ERPTSampler::~ERPTSampler() {

 	FreeAligned(sampleImage);

 	FreeAligned(baseImage);

 	FreeAligned(timeImage);

 	FreeAligned(baseTimeImage);

 	delete baseSampler;

 }

 // Copy

 ERPTSampler* ERPTSampler::clone() const

 {

 	ERPTSampler *newSampler = new ERPTSampler(*this);

 	newSampler->baseSampler = baseSampler->clone();

 	newSampler->totalSamples = 0;

 	newSampler->sampleImage = NULL;

 	return newSampler;

 }

 static void initERPT(ERPTSampler *sampler, const Sample *sample)

 {

 	u_int i;

 	sampler->normalSamples = SAMPLE_FLOATS;

 	for (i = 0; i < sample->n1D.size(); ++i)

 		sampler->normalSamples += sample->n1D[i];

 	for (i = 0; i < sample->n2D.size(); ++i)

 		sampler->normalSamples += 2 * sample->n2D[i];

 	sampler->totalSamples = sampler->normalSamples;

 	sampler->offset = new u_int[sample->nxD.size()];

 	sampler->totalTimes = 0;

 	for (i = 0; i < sample->nxD.size(); ++i) {

 		sampler->offset[i] = sampler->totalSamples;

 		sampler->totalTimes += sample->nxD[i];

 		sampler->totalSamples += sample->dxD[i] * sample->nxD[i];

 	}

 	sampler->sampleImage = AllocAligned<float>(sampler->totalSamples);

 	sampler->baseImage = AllocAligned<float>(sampler->totalSamples);

 	sampler->timeImage = AllocAligned<int>(sampler->totalTimes);

 	sampler->baseTimeImage = AllocAligned<int>(sampler->totalTimes);

 	sampler->baseSampler->SetTsPack(sampler->tspack);

 	sampler->baseSampler->SetFilm(sampler->film);

 	sampler->mutation = ~0U;

 	// Fetch first contribution buffer from pool

 	sampler->contribBuffer = sampler->film->scene->contribPool->Next(NULL);

 }

 // interface for new ray/samples from scene

 bool ERPTSampler::GetNextSample(Sample *sample, u_int *use_pos)

 {

 	sample->sampler = this;

 	if (sampleImage == NULL) {

 		initERPT(this, sample);

 	}

 	if (mutation == ~0U) {

 		// Dade - we are at a valid checkpoint where we can stop the

 		// rendering. Check if we have enough samples per pixel in the film.

 		if (film->enoughSamplePerPixel)

 			return false;

 		const bool ret = baseSampler->GetNextSample(sample, use_pos);

 		sample->sampler = this;

 		for (u_int i = 0; i < totalTimes; ++i)

 			sample->timexD[0][i] = -1;

 		sample->stamp = 0;

 		currentImage = baseImage;

 		currentTimeImage = baseTimeImage;

 		stamp = 0;

 		return ret;

 	} else {

 		if (mutation == 0) {

 			// *** new chain ***

 			for (u_int i = 0; i < totalTimes; ++i)

 				sample->timexD[0][i] = baseTimeImage[i];

 			sample->stamp = 0;

 			currentImage = baseImage;

 			currentTimeImage = baseTimeImage;

 			stamp = 0;

 		}

 		// *** small mutation ***

 		// mutate current sample

 		sample->imageX = mutateScaled(currentImage[0], tspack->rng->floatValue(), xPixelStart, xPixelEnd, range);

 		sample->imageY = mutateScaled(currentImage[1], tspack->rng->floatValue(), yPixelStart, yPixelEnd, range);

 		sample->lensU = mutate(currentImage[2], tspack->rng->floatValue());

 		sample->lensV = mutate(currentImage[3], tspack->rng->floatValue());

 		sample->time = mutate(currentImage[4], tspack->rng->floatValue());

 		sample->wavelengths = mutate(currentImage[5], tspack->rng->floatValue());

 		for (u_int i = SAMPLE_FLOATS; i < normalSamples; ++i)

 				sample->oneD[0][i - SAMPLE_FLOATS] = mutate(currentImage[i], tspack->rng->floatValue());

 		++(sample->stamp);

 	}

 	return true;

 }

 float *ERPTSampler::GetLazyValues(Sample *sample, u_int num, u_int pos)

 {

 	const u_int size = sample->dxD[num];

 	float *data = sample->xD[num] + pos * size;

 	const int stampLimit = sample->stamp;

 	if (sample->timexD[num][pos] != stampLimit) {

 		if (sample->timexD[num][pos] == -1) {

 			baseSampler->GetLazyValues(sample, num, pos);

 			sample->timexD[num][pos] = 0;

 		} else {

 			const u_int start = offset[num] + pos * size;

 			float *image = currentImage + start;

 			for (u_int i = 0; i < size; ++i)

 				data[i] = image[i];

 		}

 		for (int &time = sample->timexD[num][pos]; time < stampLimit; ++time) {

 			for (u_int i = 0; i < size; ++i)

 				data[i] = mutate(data[i], tspack->rng->floatValue());

 		}

 	}

 	return data;

 }

 // interface for adding/accepting a new image sample.

 void ERPTSampler::AddSample(const Sample &sample)

 {

 	vector<Contribution> &newContributions(sample.contributions);

 	float newLY = 0.0f;

 	for(u_int i = 0; i < newContributions.size(); ++i)

 		newLY += newContributions[i].color.Y();

 	if (mutation == 0U || mutation == ~0U) {

 		if (weight > 0.f) {

 			// Add accumulated contribution of previous reference sample

 			weight *= quantum / LY;

 			if (!isinf(weight) && LY > 0.f) {

 				for(u_int i = 0; i < oldContributions.size(); ++i) {

 					// Radiance - added new use of contributionpool/buffers

 					if(&oldContributions && !contribBuffer->Add(&oldContributions[i], weight)) {

 						contribBuffer = film->scene->contribPool->Next(contribBuffer);

 						contribBuffer->Add(&oldContributions[i], weight);

 					}

 				}

 			}

 			weight = 0.f;

 		}

 		if (mutation == ~0U) {

 			if (!(newLY > 0.f)) {

 				newContributions.clear();

 				return;

 			}

 			contribBuffer->AddSampleCount(1.f);

 			++sampleCount;

 			totalLY += newLY;

 			const float meanIntensity = totalLY > 0. ? static_cast<float>(totalLY / sampleCount) : 1.f;

 			// calculate the number of chains on a new seed

 			quantum = newLY / meanIntensity;

 			numChains = max(1U, Floor2UInt(quantum + .5f));

 			// The following line avoids to block on a pixel

 			// if the initial sample is extremely bright

 			numChains = min(numChains, totalMutations);

 			quantum /= (numChains * totalMutations);

 			baseLY = newLY;

 			baseContributions = newContributions;

 			baseImage[0] = sample.imageX;

 			baseImage[1] = sample.imageY;

 			baseImage[2] = sample.lensU;

 			baseImage[3] = sample.lensV;

 			baseImage[4] = sample.time;

 			baseImage[5] = sample.wavelengths;

 			for (u_int i = SAMPLE_FLOATS; i < totalSamples; ++i)

 				baseImage[i] = sample.oneD[0][i - SAMPLE_FLOATS];

 			for (u_int i = 0 ; i < totalTimes; ++i)

 				baseTimeImage[i] = sample.timexD[0][i];

 			mutation = 0;

 			newContributions.clear();

 			return;

 		}

 		LY = baseLY;

 		oldContributions = baseContributions;

 	}

 	// calculate accept probability from old and new image sample

 	float accProb;

 	if (LY > 0.f)

 		accProb = min(1.f, newLY / LY);

 	else

 		accProb = 1.f;

 	float newWeight = accProb;

 	weight += 1.f - accProb;

 	// try accepting of the new sample

 	if (accProb == 1.f || tspack->rng->floatValue() < accProb) {

 		// Add accumulated contribution of previous reference sample

 		weight *= quantum / LY;

 		if (!isinf(weight) && LY > 0.f) {

 			for(u_int i = 0; i < oldContributions.size(); ++i) {

 				// Radiance - added new use of contributionpool/buffers

 				if(&oldContributions && !contribBuffer->Add(&oldContributions[i], weight)) {

 					contribBuffer = film->scene->contribPool->Next(contribBuffer);

 					contribBuffer->Add(&oldContributions[i], weight);

 				}

 			}

 		}

 		weight = newWeight;

 		LY = newLY;

 		oldContributions = newContributions;

 		// Save new contributions for reference

 		sampleImage[0] = sample.imageX;

 		sampleImage[1] = sample.imageY;

 		sampleImage[2] = sample.lensU;

 		sampleImage[3] = sample.lensV;

 		sampleImage[4] = sample.time;

 		sampleImage[5] = sample.wavelengths;

 		for (u_int i = SAMPLE_FLOATS; i < totalSamples; ++i)

 			sampleImage[i] = sample.oneD[0][i - SAMPLE_FLOATS];

 		for (u_int i = 0 ; i < totalTimes; ++i)

 			timeImage[i] = sample.timexD[0][i];

 		stamp = sample.stamp;

 		currentImage = sampleImage;

 		currentTimeImage = timeImage;

 	} else {

 		// Add contribution of new sample before rejecting it

 		newWeight *= quantum / newLY;

 		if (!isinf(newWeight) && newLY > 0.f) {

 			for(u_int i = 0; i < newContributions.size(); ++i) {

 				// Radiance - added new use of contributionpool/buffers

 				if(!contribBuffer->Add(&newContributions[i], newWeight)) {

 					contribBuffer = film->scene->contribPool->Next(contribBuffer);

 					contribBuffer->Add(&newContributions[i], newWeight);

 				}

 			}

 		}

 		// Restart from previous reference

 		for (u_int i = 0; i < totalTimes; ++i)

 			sample.timexD[0][i] = currentTimeImage[i];

 		sample.stamp = stamp;

 	}

 	if (++mutation >= totalMutations) {

 		mutation = 0;

 		if (++chain >= numChains) {

 			chain = 0;

 			mutation = ~0U;

 		}

 	}

 	newContributions.clear();

 }

 Sampler* ERPTSampler::CreateSampler(const ParamSet &params, const Film *film)

 {

 	int xStart, xEnd, yStart, yEnd;

 	film->GetSampleExtent(&xStart, &xEnd, &yStart, &yEnd);

 	int totMutations = params.FindOneInt("chainlength", 100);	// number of mutations from a given seed

 	float range = params.FindOneFloat("mutationrange", (xEnd - xStart + yEnd - yStart) / 50.f);	// maximum distance in pixel for a small mutation

 	string base = params.FindOneString("basesampler", "random");	// sampler for new chain seed

 	Sampler *sampler = MakeSampler(base, params, film);

 	if (sampler == NULL) {

 		luxError(LUX_SYSTEM, LUX_SEVERE, "ERPTSampler: Could not obtain a valid sampler");

 		return NULL;

 	}

 	return new ERPTSampler(max(totMutations, 0), range, sampler);

 }

 static DynamicLoader::RegisterSampler<ERPTSampler> r("erpt");