pmapcontrib.c
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Created: Fri, Oct 4, 18:26

pmapcontrib.c
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	#ifndef lin
	static const char RCSid[] = "$Id: pmapcontrib.c,v 2.20 2021/02/16 20:06:06 greg Exp $";
	#endif

	/*
	=========================================================================
	Photon map routines for precomputed light source contributions.
	These routines handle contribution binning, compression and encoding,
	and are used by mkpmap.

	Roland Schregle (roland.schregle@{hslu.ch, gmail.com})
	(c) Lucerne University of Applied Sciences and Arts,
	supported by the Swiss National Science Foundation
	(SNSF #147053, "Daylight Redirecting Components",
	SNSF #179067, "Light Fields for Spatio-Temporal Glare Assessment")
	=========================================================================

	$Id: pmapcontrib.c,v 2.20 2021/02/16 20:06:06 greg Exp $
	*/


	#include "pmapcontrib.h"

	#ifdef PMAP_CONTRIB
	#include "pmapdiag.h"
	#include "pmaprand.h"
	#include "pmapmat.h"
	#include "pmapsrc.h"
	#include "pmutil.h"
	#include "otspecial.h"
	#include "otypes.h"
	#include "lookup.h"
	#if NIX
	#include <sys/mman.h>
	#include <sys/wait.h>
	#endif



	/* The following are convenient placeholders interfacing to mkpmap
	and rcontrib. They can be externally set via initPmapContribTab()
	and referenced within the contrib pmap modules. These variables
	can then be safely ignored by rtrace/rpict/rvu, without annoying
	linking errors. */
	/* Global pointer to rcontrib's contribution binning LUT */
	LUTAB *pmapContribTab = NULL;
	/* Contribution/coefficient mode flag */
	int *pmapContribMode;

	#ifdef PMAP_CONTRIB_DBG
	/* Sum/num of mRGBE encoding errors for wavelet coeffs */
	static WAVELET_COEFF mrgbeDiffs = 0;
	static unsigned long mrgbeDiffCnt = 0;
	#endif



	static int ray2bin (const RAY *ray, unsigned scDim)
	/* Map ray dir (pointing away from origin) to its 1D bin in an
	(scDim x scDim) Shirley-Chiu square.
	Returns -1 if mapped bin is invalid (e.g. behind plane) */
	{
	static int scRHS, varInit = 0;
	static FVECT scNorm, scUp;
	unsigned scBin [2];
	FVECT diskPlane;
	RREAL dz, diskx, disky, rad, diskd2, scCoord [2];

	if (!varInit) {
	/* Lazy init Shirley-Chiu mapping orientation from func variables */
	/* XXX: Note inversion of normal and up vectors to match rcontrib's
	convention, since the input ray points away from its origin */
	scRHS = -varvalue(PMAP_CONTRIB_SCRHS);
	scNorm [0] = -varvalue(PMAP_CONTRIB_SCNORMX);
	scNorm [1] = -varvalue(PMAP_CONTRIB_SCNORMY);
	scNorm [2] = -varvalue(PMAP_CONTRIB_SCNORMZ);
	scUp [0] = -varvalue(PMAP_CONTRIB_SCUPX);
	scUp [1] = -varvalue(PMAP_CONTRIB_SCUPY);
	scUp [2] = -varvalue(PMAP_CONTRIB_SCUPZ);
	varInit ^= 1;
	}

	/* Map incident direction to disk */
	dz = DOT(ray -> rdir, scNorm); /* normal proj */
	if (dz > 0) {
	fcross(diskPlane, scUp, scNorm); /* y-axis in plane, perp to up */
	/* normalize(diskPlane); NEED TO NORMALISE? */
	diskPlane [0] *= scRHS;
	diskx = DOT(ray -> rdir, diskPlane);
	disky = DOT(ray -> rdir, scUp);

	/* Apply Shirley-Chiu mapping of (diskx, disky) to square */
	disk2square(scCoord, diskx, disky);
	/* Map Shirley-Chiu square coords to 1D bin */
	scBin [0] = scCoord [0] * scDim;
	scBin [1] = scCoord [1] * scDim;
	return PMAP_CONTRIB_XY2LIN(scDim, scBin [0], scBin [1]);
	}
	else return -1;
	}


	/* ------------------ CONTRIBSRC STUFF --------------------- */


	#ifndef PMAP_CONTRIB_TEST
	MODCONT addContribModifier (LUTAB contribTab, unsigned *numContribs,
	char mod, char binParm, int binCnt
	)
	/* Add light source modifier mod to contribution lookup table contribTab,
	and update numContribs. Return initialised contribution data for this
	modifier. This code adapted from rcontrib.c:addmodifier(). */
	{
	LUENT *lutEntry = lu_find(contribTab, mod);
	MODCONT *contrib;
	EPNODE *eBinVal;
	unsigned numCoeffs;

	/* Warn if potential coefficient index overflow in mRGBE encoding.
	This requires getting the number of wavelet coefficients generated
	by the transform a priori. */
	if (!(numCoeffs = padWaveletXform2(NULL, NULL, sqrt(binCnt), NULL))) {
	sprintf(errmsg, "can't determine number of wavelet coefficients "
	"for modifier %s", mod
	);
	error(INTERNAL, errmsg);
	}

	if (numCoeffs * numCoeffs > PMAP_CONTRIB_MAXCOEFFS) {
	sprintf(errmsg,
	"mRGBE data field may overflow for modifier %s; reduce -bn "
	"and/or compression if contribution precomputation fails", mod
	);
	error(WARNING, errmsg);
	}

	if (lutEntry -> data) {
	/* Reject duplicate modifiers */
	sprintf(errmsg, "duplicate light source modifier %s", mod);
	error(USER, errmsg);
	}

	if (*numContribs >= MAXMODLIST) {
	sprintf(errmsg, "too many modifiers (max. %d)", MAXMODLIST);
	error(INTERNAL, errmsg);
	}

	lutEntry -> key = mod;

	if (binCnt <= 0) {
	sprintf(errmsg, "undefined/invalid bin count for modifier %s", mod);
	error(USER, errmsg);
	}

	/* Allocate and init contributions */
	contrib = (MODCONT *)malloc(
	sizeof(MODCONT) + sizeof(DCOLOR) * (binCnt - 1)
	);
	if (!contrib)
	error(SYSTEM, "out of memory in addContribModifier()");
	contrib -> outspec = NULL;
	contrib -> modname = mod;
	contrib -> params = binParm;
	contrib -> nbins = binCnt;
	contrib -> binv = eBinVal;
	contrib -> bin0 = 0;
	memset(contrib -> cbin, 0, sizeof(DCOLOR) * binCnt);
	lutEntry -> data = lutEntry -> data = (char *)contrib;
	++(*numContribs);

	return(contrib);
	}



	void addContribModfile (LUTAB contribTab, unsigned numContribs,
	char modFile, char binParm, int binCnt
	)
	/* Add light source modifiers from file modFile to contribution lookup table
	* contribTab, and update numContribs.
	* NOTE: This code is adapted from rcontrib.c */
	{
	char *mods [MAXMODLIST];
	int i;

	/* Find file and store strings */
	i = wordfile(mods, MAXMODLIST, getpath(modFile, getrlibpath(), R_OK));
	if (i < 0) {
	sprintf(errmsg, "can't open modifier file %s", modFile);
	error(SYSTEM, errmsg);
	}
	if (*numContribs + i >= MAXMODLIST - 1) {
	sprintf(errmsg, "too many modifiers (max. %d) in file %s",
	MAXMODLIST - 1, modFile
	);
	error(INTERNAL, errmsg);
	}

	for (i = 0; mods [i]; i++)
	/* Add each modifier */
	addContribModifier(contribTab, numContribs,
	mods [i], binParm, binCnt
	);
	}



	static int contribSourceBin (LUTAB contribs, const RAY ray)
	/* Map contribution source ray to its bin for light source ray -> rsrc,
	using Shirley-Chiu disk-to-square mapping.
	Return invalid bin -1 if mapping failed. */
	{
	const SRCREC *src;
	const OBJREC *srcMod;
	const MODCONT *srcCont;
	RAY srcRay;
	int bin, i;

	/* Check we have a valid ray and contribution LUT */
	if (!ray \|\| !contribs)
	return -1;

	src = &source [ray -> rsrc];
	srcMod = findmaterial(src -> so);
	srcCont = (MODCONT*)lu_find(contribs, srcMod -> oname) -> data;

	if (!srcCont)
	/* Not interested in this source (modifier not in contrib LUT) */
	return -1;

	/* Set up shadow ray pointing to source for disk2square mapping */
	rayorigin(&srcRay, SHADOW, NULL, NULL);
	srcRay.rsrc = ray -> rsrc;
	VCOPY(srcRay.rorg, ray -> rop);
	for (i = 0; i < 3; i++)
	srcRay.rdir [i] = -ray -> rdir [i];

	if (!(src -> sflags & SDISTANT
	? sourcehit(&srcRay)
	: (*ofun[srcMod -> otype].funp)(srcMod, &srcRay)
	))
	/* (Redundant?) sanity check for valid source ray? */
	return -1;
	#if 0
	worldfunc(RCCONTEXT, &srcRay);
	#endif
	set_eparams((char*)srcCont -> params);

	if ((bin = ray2bin(&srcRay, sqrt(srcCont -> nbins))) < 0)
	error(WARNING, "Ignoring invalid bin in contribSourceBin()");

	return bin;
	}



	PhotonContribSourceIdx newPhotonContribSource (PhotonMap *pmap,
	const RAY contribSrcRay, FILE contribSrcHeap
	)
	/* Add contribution source ray for emitted contribution photon and save
	* light source index and binned direction. The current contribution
	* source is stored in pmap -> lastContribSrc. If the previous contrib
	* source spawned photons (i.e. has srcIdx >= 0), it's appended to
	* contribSrcHeap. If contribSrcRay == NULL, the current contribution
	* source is still flushed, but no new source is set. Returns updated
	* contribution source counter pmap -> numContribSrc. */
	{
	if (!pmap \|\| !contribSrcHeap)
	return 0;

	/* Check if last contribution source has spawned photons (srcIdx >= 0,
	* see newPhoton()), in which case we save it to the heap file before
	* clobbering it. (Note this is short-term storage, so we doan' need
	* da portable I/O stuff here). */
	if (pmap -> lastContribSrc.srcIdx >= 0) {
	if (!fwrite(&pmap -> lastContribSrc, sizeof(PhotonContribSource),
	1, contribSrcHeap
	))
	error(SYSTEM, "failed writing photon contrib source in "
	"newPhotonContribSource()"
	);

	pmap -> numContribSrc++;
	if (!pmap -> numContribSrc \|\|
	pmap -> numContribSrc > PMAP_MAXCONTRIBSRC
	)
	error(INTERNAL, "contribution source overflow");
	}

	if (contribSrcRay) {
	/* Mark this contribution source unused with a negative source
	index until its path spawns a photon (see newPhoton()) */
	pmap -> lastContribSrc.srcIdx = -1;

	/* Map ray to bin in anticipation that this contrib source will be
	used, since the ray will be lost once a photon is spawned */
	pmap -> lastContribSrc.srcBin = contribSourceBin(
	pmapContribTab, contribSrcRay
	);

	if (pmap -> lastContribSrc.srcBin < 0) {
	/* Warn if invalid bin, but trace photon nonetheless. It will
	count as emitted to prevent bias, but will not be stored in
	newPhoton(), as it contributes zero flux */
	sprintf(errmsg, "invalid bin for light source %s, "
	"contribution photons will be discarded",
	source [contribSrcRay -> rsrc].so -> oname
	);
	error(WARNING, errmsg);
	}
	}

	return pmap -> numContribSrc;
	}



	PhotonContribSourceIdx buildContribSources (PhotonMap *pmap,
	FILE contribSrcHeap, char contribSrcHeapFname,
	PhotonContribSourceIdx *contribSrcOfs, unsigned numHeaps
	)
	/* Consolidate per-subprocess contribution source heaps into array
	* pmap -> contribSrc. Returns offset for contribution source index
	* linearisation in pmap -> numContribSrc. The heap files in
	* contribSrcHeap are closed on return. */
	{
	PhotonContribSourceIdx heapLen;
	unsigned heap;

	if (!pmap \|\| !contribSrcHeap \|\| !contribSrcOfs \|\| !numHeaps)
	return 0;

	pmap -> numContribSrc = 0;

	for (heap = 0; heap < numHeaps; heap++) {
	contribSrcOfs [heap] = pmap -> numContribSrc;

	if (fseek(contribSrcHeap [heap], 0, SEEK_END) < 0)
	error(SYSTEM, "failed photon contrib source seek "
	"in buildContribSources()"
	);
	pmap -> numContribSrc += heapLen =
	ftell(contribSrcHeap [heap]) / sizeof(PhotonContribSource);

	if (!(pmap -> contribSrc = realloc(pmap -> contribSrc,
	pmap -> numContribSrc * sizeof(PhotonContribSource)
	)))
	error(SYSTEM, "failed photon contrib source alloc "
	"in buildContribSources()"
	);

	rewind(contribSrcHeap [heap]);
	if (fread(pmap -> contribSrc + contribSrcOfs [heap],
	sizeof(PhotonContribSource), heapLen, contribSrcHeap [heap]
	) != heapLen)
	error(SYSTEM, "failed reading photon contrib source "
	"in buildContribSources()"
	);

	fclose(contribSrcHeap [heap]);
	unlink(contribSrcHeapFname [heap]);
	}

	return pmap -> numContribSrc;
	}



	/* ----------------- CONTRIB PMAP ENCODING STUFF -------------------- */

	static void coeffSwap (PreComputedContribCoeff *c1,
	PreComputedContribCoeff *c2
	) {
	PreComputedContribCoeff tCoeff;

	tCoeff.coeff = c1 -> coeff;
	tCoeff.idx = c1 -> idx;
	c1 -> coeff = c2 -> coeff;
	c1 -> idx = c2 -> idx;
	c2 -> coeff = tCoeff.coeff;
	c2 -> idx = tCoeff.idx;
	}



	static int coeffPartition (PreComputedContribCoeff *coeffs,
	unsigned medianPos, unsigned left, unsigned right
	)
	/* REVERSE partition coefficients by magnitude, such that
	coeffs [left..medianPos] >= coeffs [medianPos+1..right].
	Returns median's position. */
	{
	unsigned long l, r, m;
	WAVELET_COEFF lVal, rVal, mVal, tVal;

	#define COEFFVAL(c) (DOT((c) -> coeff, (c) -> coeff))

	if (left < right) {
	/* Select pivot from median-of-three and move to photons [right]
	(a.k.a. Lomuto partitioning) */
	l = left;
	r = right;
	m = l + ((r - l) >> 1); /* Avoids overflow vs. (l+r) >> 1 */
	lVal = COEFFVAL(coeffs + l);
	rVal = COEFFVAL(coeffs + r);
	mVal = COEFFVAL(coeffs + m);
	if (mVal > lVal) {
	coeffSwap(coeffs + m, coeffs + l);
	tVal = mVal;
	mVal = lVal;
	lVal = tVal;
	}
	if (rVal > lVal) {
	coeffSwap(coeffs + r, coeffs + l);
	tVal = rVal;
	rVal = lVal;
	lVal = tVal;
	}
	if (mVal > rVal) {
	coeffSwap(coeffs + m, coeffs + r);
	tVal = mVal;
	mVal = rVal;
	rVal = tVal;
	}
	/* Pivot with key rVal is now in coeffs [right] */

	/* l & r converge, swapping coefficients out of (reversed) order
	with respect to pivot. The convergence point l = r is the
	pivot's final position */
	while (l < r) {
	while (l < r && COEFFVAL(coeffs + l) > rVal)
	l++;
	while (r > l && COEFFVAL(coeffs + r) <= rVal)
	r--;

	/* Coeffs out of order, must swap */
	if (l < r)
	coeffSwap(coeffs + l, coeffs + r);
	};

	/* Now l == r is pivot's final position; swap these coeffs */
	coeffSwap(coeffs + l, coeffs + right);

	/* Recurse in partition containing median */
	if (l > medianPos)
	return coeffPartition(coeffs, medianPos, left, l - 1);
	else if (l < medianPos)
	return coeffPartition(coeffs, medianPos, l + 1, right);
	else /* l == medianPos, partitioning done */
	return l;
	}
	else return left;
	}



	static int coeffIdxCompare (const void c1, const void c2)
	/* Comparison function to sort thresholded coefficients by index */
	/* TODO: scale coeffs by 2^-l to adapt to resolution/frequency l?
	(this drops higher-frequency coeffs first). */
	{
	const PreComputedContribCoeff tcoeff1 = c1, tcoeff2 = c2;
	const unsigned v1 = tcoeff1 -> idx,
	v2 = tcoeff2 -> idx;

	if (v1 < v2)
	return -1;
	else if (v1 > v2)
	return 1;
	else
	return 0;
	}



	static int thresholdContribs (PreComputedContrib *preCompContrib)
	/* Threshold wavelet detail coefficients in preCompContrib ->
	waveletMatrix [approxDim..coeffDim-1] [approxDim..coeffDim-1] (where
	approxDim = WAVELET_PADD2_APPROXDIM) by keeping the (preCompContrib ->
	nCompressedCoeffs) largest of these and returning them in
	preCompContrib -> compressedCoeffs along with their original matrix
	indices.
	NOTE: The wavelet approximation coefficients
	preCompContrib -> waveletMatrix [0..approxDim-1] [0..approxDim-1]
	are excluded from thresholding to minimise compression artefacts.
	Returns 0 on success, else -1. */
	{
	unsigned i, j, coeffDim, coeffIdx, nNzDetailCoeffs,
	nCompressedCoeffs, numThresh;
	WaveletMatrix2 waveletMatrix;
	PreComputedContribCoeff threshCoeffs, threshCoeffPtr;
	WAVELET_COEFF *coeffPtr;

	if (!preCompContrib \|\| !(coeffDim = preCompContrib -> coeffDim) \|\|
	!(threshCoeffs = preCompContrib -> compressedCoeffs) \|\|
	!(waveletMatrix = preCompContrib -> waveletMatrix)
	)
	/* Should be initialised by caller! */
	return -1;

	/* Set up coefficient buffer for compression (thresholding), skipping
	* the approximation coefficients in the upper left of waveletMatrix,
	* which are not thresholded. Also skip zero coefficients (resulting
	* from padding), since these are already implicitly thresholded. The
	* original 2D matrix indices are linearised to 1D and saved with each
	* coefficient to restore the original sparse coefficient matrix. */
	for (i = 0, threshCoeffPtr = threshCoeffs; i < coeffDim; i++) {
	/* Calc row pointer (=mult) in outer loop, inc in inner */
	coeffIdx = PMAP_CONTRIB_XY2LIN(coeffDim, i, 0);

	for (j = 0; j < coeffDim; j++, coeffIdx++) {
	if ((i >= WAVELET_PADD2_APPROXDIM \|\|
	j >= WAVELET_PADD2_APPROXDIM
	) && !coeffIsZero(waveletMatrix [i] [j])
	) {
	/* Nonzero detail coefficient; set up pointer to coeff
	(sorts faster than 3 doubles) and save original
	(linearised) matrix index */
	threshCoeffPtr -> idx = coeffIdx;
	threshCoeffPtr++ -> coeff = (WAVELET_COEFF*)&(
	waveletMatrix [i] [j]
	);
	}
	}
	}

	/* Num of nonzero detail coeffs in buffer, number actually expected */
	numThresh = threshCoeffPtr - threshCoeffs;
	nNzDetailCoeffs = WAVELET_PADD2_NUMDETAIL(
	preCompContrib -> nNonZeroCoeffs
	);
	nCompressedCoeffs = preCompContrib -> nCompressedCoeffs;

	/* If fewer nonzero detail coeff are in the threshold buffer than
	* anticipated, the loop below fills the remainder of the threshold
	* buffer with duplicates of a coefficient in the lower right of the
	* matrix, which is padding and guaranteed to be zero. This condition
	* can occur if the wavelet transform actually generated genuine zero
	* detail coefficients. Infact it's quite common if the wavelet
	* transformed contributions are quite sparse. */
	i = j = coeffDim - 1;
	coeffIdx = PMAP_CONTRIB_XY2LIN(coeffDim, i, j);
	for (coeffPtr = (WAVELET_COEFF*)(waveletMatrix [i][j]);
	numThresh < nNzDetailCoeffs;
	numThresh++
	) {
	threshCoeffPtr -> idx = coeffIdx;
	threshCoeffPtr++ -> coeff = coeffPtr;
	}

	/* Partition coeffs in reverse order, such that all coeffs in
	threshCoeffs [0..nCompressedCoeffs-1] are larger than those in
	threshCoeffs [nCompressedCoeffs..nNzDetailCoeffs-1] */
	coeffPartition(threshCoeffs, nCompressedCoeffs - 1,
	0, nNzDetailCoeffs - 1
	);

	#ifdef PMAP_CONTRIB_DBG
	/* Check coefficient partitioning */
	threshCoeffPtr = threshCoeffs + nCompressedCoeffs - 1;
	for (i = 0; i < nCompressedCoeffs; i++)
	if (COEFFVAL(threshCoeffs + i) < COEFFVAL(threshCoeffPtr))
	error(CONSISTENCY, "invalid wavelet coefficient partitioning "
	"in thresholdContribs()"
	);

	for (; i < nNzDetailCoeffs; i++)
	if (COEFFVAL(threshCoeffs + i) > COEFFVAL(threshCoeffPtr))
	error(CONSISTENCY, "invalid wavelet coefficient partitioning "
	"in thresholdContribs()"
	);
	#endif

	/* Sort partition containing nCompressedCoeffs coefficients by index
	* (ignoring the remaining coefficients since these are now dropped
	* due to tresholding) */
	qsort(threshCoeffs, nCompressedCoeffs,
	sizeof(PreComputedContribCoeff), coeffIdxCompare
	);

	return 0;
	}



	static int encodeContribs (PreComputedContrib *preCompContrib,
	float compressRatio
	)
	/* Apply wavelet transform to input matrix preCompContrib ->
	waveletMatrix and compress according to compressRatio, storing
	thresholded and mRGBE-encoded coefficients in preCompContrib ->
	mrgbeCoeffs. Note that the approximation coefficients in the upper
	left of the matrix are not encoded, and returned in
	preCompContrib -> waveletMatrix
	[0..WAVELET_PADD2_APPROXDIM-1] [0..WAVELET_PADD2_APPROXDIM-1].
	Returns 0 on success. */
	{
	unsigned i, j, k, scDim, lastCoeffIdx;
	WaveletMatrix2 waveletMatrix, tWaveletMatrix;
	PreComputedContribCoeff *threshCoeffs;
	mRGBERange *mrgbeRange;
	mRGBE *mrgbeCoeffs;
	WAVELET_COEFF absCoeff;
	#ifdef PMAP_CONTRIB_DBG
	WaveletCoeff3 decCoeff;
	unsigned decIdx;
	#endif

	if (!preCompContrib \|\| !preCompContrib -> mrgbeCoeffs \|\|
	!preCompContrib -> compressedCoeffs \|\|
	!(waveletMatrix = preCompContrib -> waveletMatrix) \|\|
	!(tWaveletMatrix = preCompContrib -> tWaveletMatrix) \|\|
	!(scDim = preCompContrib -> scDim)
	)
	/* Should be initialised by the caller! */
	return -1;

	#ifdef PMAP_CONTRIB_DBG
	for (i = 0; i < scDim; i++) {
	for (j = 0; j < scDim; j++) {
	for (k = 0; k < 3; k++) {
	#if 0
	/* Set contributions to bins for debugging */
	waveletMatrix [i] [j] [k] = PMAP_CONTRIB_VAL(
	PMAP_CONTRIB_XY2LIN(scDim, i, j)
	);
	#elif 0
	/* Replace contribs with "bump" function */
	waveletMatrix [i] [j] [k] = PMAP_CONTRIB_VAL(
	(1. - fabs(i - scDim/2. + 0.5) / (scDim/2. - 0.5)) *
	(1. - fabs(j - scDim/2. + 0.5) / (scDim/2. - 0.5))
	);
	#elif 0
	/* Inject reference contribs from rcontrib classic */
	#include "rc-ref.c"

	if (preCompContrib -> nBins != PMAP_CONTRIB_REFSIZE) {
	sprintf(errmsg, "reference contribs require %d bins",
	PMAP_CONTRIB_REFSIZE
	);
	error(USER, errmsg);
	}
	waveletMatrix [i] [j] [k] = PMAP_CONTRIB_VAL(
	refContrib [PMAP_CONTRIB_XY2LIN(scDim, i, j)] [k]
	);
	#endif
	}

	#if 0
	/* Dump contribs prior to encoding for debugging */
	printf("% 7.3g\t", colorAvg(waveletMatrix [i] [j]));
	}
	putchar('\n');
	}
	putchar('\n');
	#else
	}
	}
	#endif
	#endif

	/* Do 2D wavelet transform on preCompContrib -> waveletMatrix */
	if (padWaveletXform2(waveletMatrix, tWaveletMatrix, scDim, NULL) !=
	preCompContrib -> coeffDim
	)
	error(INTERNAL, "failed wavelet transform in encodeContribs()");

	/* Compress wavelet detail coeffs by thresholding */
	if (thresholdContribs(preCompContrib) < 0)
	error(INTERNAL, "failed wavelet compression in encodeContribs()");
	threshCoeffs = preCompContrib -> compressedCoeffs;

	/* Init per-channel coefficient range for mRGBE encoding */
	mrgbeRange = &preCompContrib -> mrgbeRange;
	setcolor(mrgbeRange -> min, FHUGE, FHUGE, FHUGE);
	setcolor(mrgbeRange -> max, 0, 0, 0);

	/* Update per-channel coefficient range */
	for (i = 0; i < preCompContrib -> nCompressedCoeffs; i++)
	for (k = 0; k < 3; k++) {
	absCoeff = fabs(threshCoeffs [i].coeff [k]);

	if (absCoeff < mrgbeRange -> min [k])
	mrgbeRange -> min [k] = absCoeff;
	if (absCoeff > mrgbeRange -> max [k])
	mrgbeRange -> max [k] = absCoeff;
	}

	if (preCompContrib -> nCompressedCoeffs == 1)
	/* Maximum compression with just 1 (!) compressed detail coeff (is
	* this even useful?), so mRGBE range is undefined since min & max
	* coincide; set minimum to 0, maximum to the single remaining
	* coefficient */
	setcolor(mrgbeRange -> min, 0, 0, 0);

	/* Init mRGBE coefficient normalisation from range */
	if (!mRGBEinit(mrgbeRange, mrgbeRange -> min, mrgbeRange -> max))
	return -1;

	mrgbeCoeffs = preCompContrib -> mrgbeCoeffs;

	/* Encode wavelet detail coefficients to mRGBE */
	for (i = lastCoeffIdx = 0; i < preCompContrib -> nCompressedCoeffs;
	lastCoeffIdx = threshCoeffs [i++].idx
	) {
	/* HACK: To reduce the likelihood of overflowing the mRGBE data
	* field with the coefficient index, it is expressed incrementally
	* w.r.t. the previously encoded coefficient's index, instead of
	* absolutely. This implies threshCoeffs must be sorted by
	* coefficient index to ensure increments are positive, and to
	* minimise their magnitude.
	* Note that an overflow cannot be predicted beforehand, e.g. by
	* mkpmap when parsing the number of bins, as this depends on the
	* sparseness of the wavelet coefficients (which in turn depends on
	* the frequency distribution of the binned contributions), and the
	* fraction of those that are dropped (i.e. the compression ratio).
	* */
	mrgbeCoeffs [i] = mRGBEencode(threshCoeffs [i].coeff,
	mrgbeRange, threshCoeffs [i].idx - lastCoeffIdx
	);
	if (!mrgbeCoeffs [i].all)
	error(INTERNAL, "failed mRGBE encoding in encodeContribs()");
	#ifdef PMAP_CONTRIB_DBG
	/* mRGBE encoding sanity check */
	decIdx = mRGBEdecode(mrgbeCoeffs [i], mrgbeRange, decCoeff);
	mrgbeDiffs += sqrt(dist2(decCoeff, threshCoeffs [i].coeff));
	mrgbeDiffCnt++;

	if (/decIdx > preCompContrib -> nCompressedCoeffs \|\| /
	decIdx != threshCoeffs [i].idx - lastCoeffIdx \|\|
	sqrt(dist2(decCoeff, threshCoeffs [i].coeff)) >
	0.1 * colorAvg(mrgbeRange -> max)
	) {
	sprintf(errmsg, "failed sanity check in encodeContribs()\n"
	"Encoded: [%.3g %.3g %.3g %d]\nDecoded: [%.3g %.3g %.3g %d]",
	threshCoeffs [i].coeff [0], threshCoeffs [i].coeff [1],
	threshCoeffs [i].coeff [2],
	threshCoeffs [i].idx - lastCoeffIdx,
	decCoeff [0], decCoeff [1], decCoeff [2], decIdx
	);
	error(CONSISTENCY, errmsg);
	}

	for (k = 0; k < 3; k++) {
	absCoeff = fabs(threshCoeffs [i].coeff [k]) > 1e-6
	? decCoeff [k] / threshCoeffs [i].coeff [k] : 0;
	if (absCoeff < 0)
	error(CONSISTENCY,
	"coefficient sign reversal in encodeContribs()"
	);
	}
	#endif
	}

	return 0;
	}



	static MODCONT getPhotonContrib (PhotonMap pmap, RAY *ray, COLOR irrad)
	/* Locate photons near ray -> rop which originated from the light source
	modifier indexed by ray -> rsrc, and accumulate their contributions
	in pmap -> srcContrib. Return total contributions in irrad and
	pointer to binned contributions (or NULL if none were found). */
	{
	const OBJREC *srcMod = findmaterial(source [ray->rsrc].so);
	MODCONT modCont = (MODCONT)lu_find(
	pmapContribTab, srcMod -> oname
	) -> data;
	Photon *photon;
	COLOR flux;
	DCOLOR *cbin;
	PhotonSearchQueueNode *sqn;
	float r2, norm;
	unsigned i, bin, numZeroBins;

	setcolor(irrad, 0, 0, 0);
	if (!modCont)
	/* Modifier not in LUT */
	return NULL;

	/* Zero bins for this source modifier */
	memset(modCont -> cbin, 0, sizeof(DCOLOR) * modCont -> nbins);
	if (!pmap -> maxGather)
	/* Zero bandwidth */
	return NULL;

	/* Lookup photons; pass light source index to filter in findPhotons()
	via pmap -> lastContribSrc */
	pmap -> lastContribSrc.srcIdx = ray -> rsrc;
	findPhotons(pmap, ray);

	/* Need at least 2 photons */
	if (pmap -> squeue.tail < 2) {
	#ifdef PMAP_NONEFOUND
	sprintf(errmsg, "no photons found on %s at (%.3f, %.3f, %.3f)",
	ray -> ro ? ray -> ro -> oname : "<null>",
	ray -> rop [0], ray -> rop [1], ray -> rop [2]
	);
	error(WARNING, errmsg);
	#endif
	return NULL;
	}

	/* Avg radius^2 between furthest two photons to improve accuracy */
	sqn = pmap -> squeue.node + 1;
	r2 = max(sqn -> dist2, (sqn + 1) -> dist2);
	r2 = 0.25 * (pmap -> maxDist2 + r2 + 2 * sqrt(pmap -> maxDist2 * r2));

	#ifdef PMAP_EPANECHNIKOV
	/* Normalise accumulated flux by Epanechnikov kernel integral in 2D
	(see Eq. 4.4, p.76 in Silverman, "Density Estimation for
	Statistics and Data Analysis", 1st Ed., 1986, and
	Wann Jensen, "Realistic Image Synthesis using Photon Mapping"),
	include RADIANCE-specific lambertian factor PI */
	norm = 2 / (PI * PI * r2);
	#else
	/* Normalise accumulated flux by search area PI * r^2, including
	RADIANCE-specific lambertian factor PI */
	norm = 1 / (PI * PI * r2);
	#endif

	/* Skip the extra photon */
	for (i = 1, numZeroBins = modCont -> nbins;
	i < pmap -> squeue.tail;
	i++, sqn++
	) {
	/* Get photon's contribution to density estimate */
	photon = getNearestPhoton(&pmap -> squeue, sqn -> idx);
	getPhotonFlux(photon, flux);
	scalecolor(flux, norm);
	#ifdef PMAP_EPANECHNIKOV
	/* Apply Epanechnikov kernel to photon flux based on distance */
	scalecolor(flux, 1 - sqn -> dist2 / r2);
	#endif
	addcolor(irrad, flux);
	cbin = &modCont -> cbin [photonSrcBin(pmap, photon)];

	/* Bin was empty (zero) before accumulating flux;
	decrement corresponding counter */
	numZeroBins -= coeffIsZero(*cbin);
	addcolor(*cbin, flux);
	}

	#ifdef PMAP_CONTRIB_WARNZEROBINS
	/* Warn if too many empty bins */
	if (numZeroBins > PMAP_CONTRIB_MAXZEROBINS * modCont -> nbins) {
	sprintf(errmsg, "empty bin ratio > %.2f at (%.3f, %.3f, %.3f) "
	"for modifier %s; contributions may be biased",
	PMAP_CONTRIB_MAXZEROBINS,
	ray -> rop [0], ray -> rop [1], ray -> rop [2],
	modCont -> modname
	);
	error(WARNING, errmsg);
	}
	#endif

	return modCont;
	}



	void freePreCompContribNode (void *p)
	/* Clean up precomputed contribution LUT entry */
	{
	PhotonMap preCompContribPmap = (PhotonMap)p;
	PreComputedContrib *preCompContrib;

	if (preCompContribPmap) {
	preCompContrib = (PreComputedContrib*)(
	preCompContribPmap -> preCompContrib
	);

	if (preCompContrib) {
	/* Free primary and transposed wavelet matrices */
	freeWaveletMatrix2(preCompContrib -> waveletMatrix,
	preCompContrib -> coeffDim
	);
	freeWaveletMatrix2(preCompContrib -> tWaveletMatrix,
	preCompContrib -> coeffDim
	);

	/* Free thresholded coefficients */
	free(preCompContrib -> compressedCoeffs);

	/* Free mRGBE encoded coefficients */
	free(preCompContrib -> mrgbeCoeffs);
	free(preCompContrib -> waveletFname);

	if (preCompContrib -> cache) {
	/* Free contribution cache */
	OOC_DeleteCache(preCompContrib -> cache);
	free(preCompContrib -> cache);
	}
	#if NIX
	if (preCompContrib -> numPhotonsShm) {
	/* Release shared memory for photon counter */
	munmap(preCompContrib -> numPhotonsShm, sizeof(unsigned long));
	close(preCompContrib -> shmFile);
	unlink(preCompContrib -> shmFname);
	}
	#endif

	#ifdef PMAP_CONTRIB_BINHISTO
	free(preCompContrib -> binHisto);
	#endif
	}

	/* Clean up precomputed contrib photon map */
	deletePhotons(preCompContribPmap);
	free(preCompContribPmap);
	}
	}



	void initPreComputedContrib (PreComputedContrib *preCompContrib)
	/* Initialise precomputed contribution container in photon map */
	{
	preCompContrib -> waveletFname = NULL;
	preCompContrib -> waveletFile = NULL;
	preCompContrib -> waveletMatrix =
	preCompContrib -> tWaveletMatrix = NULL;
	preCompContrib -> compressedCoeffs = NULL;
	setcolor(preCompContrib -> mrgbeRange.min, 0, 0, 0);
	setcolor(preCompContrib -> mrgbeRange.max, 0, 0, 0);
	setcolor(preCompContrib -> mrgbeRange.norm, 0, 0, 0);
	preCompContrib -> mrgbeCoeffs = NULL;
	preCompContrib -> scDim =
	preCompContrib -> nBins =
	preCompContrib -> coeffDim =
	preCompContrib -> nCoeffs =
	preCompContrib -> nNonZeroCoeffs =
	preCompContrib -> nCompressedCoeffs =
	preCompContrib -> contribSize = 0;
	preCompContrib -> cache = NULL;
	preCompContrib -> numPhotonsShm = NULL;
	preCompContrib -> shmFile = -1;
	#ifdef PMAP_CONTRIB_BINHISTO
	preCompContrib -> binHisto = NULL;
	#endif
	}



	static int allocPreCompContribPmap (const LUENT modContNode, void p)
	/* Allocate & init child contrib photon map for modContNode's modifier
	* and its contributions for parent photon map p. */
	{
	unsigned scDim, nBins, coeffDim, nCoeffs,
	nCompressedCoeffs, nNzDetailCoeffs;
	PhotonMap preCompContribPmap, parentPmap = (PhotonMap*)p;
	LUENT *preCompContribNode;
	PreComputedContrib *preCompContrib;
	const MODCONT modCont = (MODCONT)modContNode -> data;

	if (!modCont \|\| !parentPmap)
	return -1;

	preCompContribNode = lu_find(parentPmap -> preCompContribTab,
	modCont -> modname
	);
	if (!preCompContribNode)
	error(SYSTEM, "out of memory allocating LUT entry in "
	"allocPreCompContribPmap()"
	);

	preCompContribNode -> key = (char*)modCont -> modname;
	preCompContribNode -> data = (char*)(preCompContribPmap =
	malloc(sizeof(PhotonMap))
	);
	if (!preCompContribPmap)
	error(SYSTEM, "out of memory allocating photon map "
	"in allocPreCompContribPmap()"
	);
	initPhotonMap(preCompContribPmap, PMAP_TYPE_CONTRIB_CHILD);

	/* Set output filename from parent photon map */
	preCompContribPmap -> fileName = parentPmap -> fileName;
	/* Set contrib/coeff mode from parent photon map */
	preCompContribPmap -> contribMode = parentPmap -> contribMode;

	preCompContrib = (PreComputedContrib*)(
	preCompContribPmap -> preCompContrib =
	malloc(sizeof(PreComputedContrib))
	);
	if (!preCompContrib)
	error(SYSTEM, "out of memory allocating contributions "
	"in allocPreCompContribPmap()"
	);
	initPreComputedContrib(preCompContrib);

	#if NIX
	/* Allocate and map shared memory for photon counter */
	strcpy(preCompContrib -> shmFname, PMAP_TMPFNAME);
	preCompContrib -> shmFile = mkstemp(preCompContrib -> shmFname);
	if (preCompContrib -> shmFile < 0 \|\|
	ftruncate(preCompContrib -> shmFile, sizeof(unsigned long)) < 0
	)
	error(SYSTEM,
	"failed opening shared memory file in allocPreCompContribPmap()"
	);

	preCompContrib -> numPhotonsShm = mmap(NULL, sizeof(unsigned long),
	PROT_READ \| PROT_WRITE, MAP_SHARED, preCompContrib -> shmFile, 0
	);
	if (preCompContrib -> numPhotonsShm == MAP_FAILED)
	error(SYSTEM,
	"failed mapping shared memory in allocPreCompContribPmap()"
	);
	#endif

	/* Set Shirley-Chiu square & wavelet matrix dimensions
	(number of bins resp. coefficients). */
	preCompContrib -> scDim = scDim = sqrt(
	preCompContrib -> nBins = nBins = modCont -> nbins
	);

	if (scDim * scDim != nBins)
	/* Shouldn't happen; mkpmap took care of dis */
	error(INTERNAL, "contribution bin count not integer square "
	"in allocPreCompContribPmap()"
	);

	/* Allocate and initialise photon and contribution heaps */
	initPhotonHeap(preCompContribPmap);

	if (nBins > 1) {
	/* BINNING ENABLED; set up wavelet xform & compression.
	Get dimensions of wavelet coefficient matrix after
	boundary padding, and number of nonzero coeffs. The
	number of compressed (detail) coeffs is fixed and
	based on the number of NONZERO coeffs (minus approx,
	see NOTE below) since zero coeffs are considered
	thresholded by default.

	!!! NOTE: THE APPROX COEFFS IN THE UPPER LEFT OF
	!!! THE MATRIX ARE _NEVER_ THRESHOLDED TO MINIMISE
	!!! COMPRESSION ARTEFACTS! THEY ARE ESSENTIAL FOR
	!!! RECONSTRUCTING THE ORIGINAL CONTRIBS. */
	preCompContrib -> coeffDim = coeffDim = padWaveletXform2(
	NULL, NULL, scDim, &preCompContrib -> nNonZeroCoeffs
	);
	preCompContrib -> nCoeffs = nCoeffs = coeffDim * coeffDim;
	nNzDetailCoeffs = WAVELET_PADD2_NUMDETAIL(
	preCompContrib -> nNonZeroCoeffs
	);

	nCompressedCoeffs = (1 - compressRatio) * nNzDetailCoeffs;
	if (nCompressedCoeffs < 1) {
	error(WARNING, "maximum contribution compression, "
	"clamping number of wavelet coefficients in "
	"allocPreCompContribPmap()"
	);
	nCompressedCoeffs = 1;
	}
	if (nCompressedCoeffs >= preCompContrib -> nCoeffs) {
	error(WARNING, "minimum contribution compression, "
	"clamping number of wavelet coefficients in "
	"allocPreCompContribPmap()"
	);
	nCompressedCoeffs = nNzDetailCoeffs;
	}
	preCompContrib -> nCompressedCoeffs = nCompressedCoeffs;

	/* Lazily allocate primary & transposed wavelet coeff matrix */
	preCompContrib -> waveletMatrix = allocWaveletMatrix2(coeffDim);
	preCompContrib -> tWaveletMatrix = allocWaveletMatrix2(coeffDim);
	if (!preCompContrib -> waveletMatrix \|\|
	!preCompContrib -> tWaveletMatrix
	)
	error(SYSTEM, "out of memory allocating wavelet coefficient "
	"matrix in allocPreCompContribPmap()"
	);

	/* Lazily allocate thresholded detail coefficients */
	preCompContrib -> compressedCoeffs = calloc(nNzDetailCoeffs,
	sizeof(PreComputedContribCoeff)
	);

	/* Lazily alloc mRGBE-encoded compressed wavelet coeffs */
	preCompContrib -> mrgbeCoeffs = calloc(nCompressedCoeffs,
	sizeof(mRGBE)
	);
	if (!preCompContrib -> compressedCoeffs \|\|
	!preCompContrib -> mrgbeCoeffs
	)
	error(SYSTEM, "out of memory allocating compressed "
	"contribution buffer in allocPreCompContribPmap()"
	);

	/* Set size of compressed contributions, in bytes */
	preCompContrib -> contribSize = PMAP_CONTRIB_ENCSIZE(
	nCompressedCoeffs
	);

	#ifdef PMAP_CONTRIB_BINHISTO
	preCompContrib -> binHisto = calloc(nBins, sizeof(unsigned long));
	if (!preCompContrib -> binHisto)
	error(SYSTEM, "out of memory allocating contribution bin "
	"histogram in allocPreCompContribPmap()"
	);
	else memset(preCompContrib -> binHisto, 0,
	(size_t)nBins * sizeof(unsigned long)
	);

	preCompContrib -> minZero = nBins;
	preCompContrib -> maxZero = preCompContrib -> sumZero = 0;
	#endif
	}
	}



	static int sumNumPhotons (const LUENT preCompContribNode, void p)
	/* Set number of photons for this modifier's child contrib photon map
	* from the corresponding shared photon counter, and sum over all
	* modifiers in (unsigned long)p /
	{
	unsigned long numPhotons = (unsigned long)p;
	PhotonMap preCompContribPmap = (PhotonMap)(
	preCompContribNode -> data
	);
	const PreComputedContrib *preCompContrib;

	if (!preCompContribPmap)
	return 0;
	else preCompContrib = (PreComputedContrib*)(
	preCompContribPmap -> preCompContrib
	);

	#if NIX
	/* Lock shared photon counter file for reading */
	shmLock(preCompContrib -> shmFile, F_RDLCK);
	#endif
	*numPhotons += (preCompContribPmap -> numPhotons =
	*preCompContrib -> numPhotonsShm
	);
	#if NIX
	/* Release lock on shard photon counter file */
	shmLock(preCompContrib -> shmFile, F_UNLCK);
	#endif

	return 0;
	}



	void preComputeContrib (PhotonMap *pmap, unsigned numProc)
	/* Precompute contributions for a random subset of (finalGather *
	pmap -> numPhotons) photons, and return the per-modifier precomputed
	contribution photon maps in LUT preCompContribTab, discarding the
	original photons. */
	{
	unsigned long p, numPreComp;
	unsigned proc;
	int stat;
	pid_t pid, procPids [PMAP_MAXPROC];
	PhotonMap nuPmap;
	LUTAB lutInit = LU_SINIT(NULL, freePreCompContribNode);

	/* Init new parent photon map and set output filename */
	initPhotonMap(&nuPmap, pmap -> type);
	nuPmap.fileName = pmap -> fileName;

	/* Set contrib/coeff mode in new parent photon map */
	nuPmap.contribMode = pmap -> contribMode;

	/* Allocate and init LUT containing per-modifier child photon maps */
	if (!(nuPmap.preCompContribTab = malloc(sizeof(LUTAB))))
	error(SYSTEM,
	"out of memory allocating LUT in preComputeContrib()"
	);
	memcpy(nuPmap.preCompContribTab, &lutInit, sizeof(LUTAB));

	/* Allocate and init per-modifier child photon maps */
	lu_doall(pmapContribTab, allocPreCompContribPmap, &nuPmap);

	/* Record start time, baby */
	repStartTime = repLastTime = time(NULL);
	repComplete = numPreComp = finalGather * pmap -> numPhotons;
	repProgress = 0;

	if (verbose) {
	sprintf(errmsg,
	"\nPrecomputing contributions for %ld photons\n", numPreComp
	);
	eputs(errmsg);
	#if NIX
	fflush(stderr);
	#endif
	}

	for (proc = 0; proc < numProc; proc++) {
	#if NIX
	if (!(pid = fork())) {
	/* SUBPROCESS ENTERS HERE; opened and mmapped files inherited */
	#else
	if (1) {
	/* No subprocess under Windoze */
	#endif
	int photonOk;
	unsigned i, j, k, coeffIdx, scDim, nBins, coeffDim,
	nCoeffs, nCompressedCoeffs;
	const double pInc = finalGather > FTINY
	? 1 / finalGather : 0,
	numPhotonsPerProc =
	(double)pmap -> numPhotons / numProc,
	numPreCompPerProc =
	(double)numPreComp / numProc;
	PhotonIdx pIdx;
	Photon photon;
	MODCONT *modCont;
	LUENT *preCompContribNode;
	PhotonMap *preCompContribPmap;
	PreComputedContrib *preCompContrib;
	WaveletMatrix2 waveletMatrix;
	WaveletCoeff3 *coeffPtr;
	RAY ray;
	unsigned long lastpIdx = 0;

	photonRay(NULL, &ray, PRIMARY, NULL);
	ray.ro = NULL;
	/* Decorrelate subprocess RNGs */
	pmapSeed(randSeed + proc, pmap -> randState);

	#ifdef PMAP_CONTRIB_DBG
	/* Output child process PID after random delay to prevent
	* scrambling console output with sibling subprocs */
	usleep(1e6 * pmapRandom(rouletteState));
	sprintf(errmsg, "DBG Proc %d: PID = %d "
	"(waiting 10 sec to attach DEBUGGA...)\n",
	proc, getpid()
	);
	eputs(errmsg);
	/* Give debugga time to attach to subproc */
	sleep(10);
	#endif

	for (p = 0; p < (unsigned long)numPreCompPerProc; p++) {
	do {
	/* Get random photon from stratified distribution in
	* source heap to avoid duplicates and clustering. */
	pIdx = firstPhoton(pmap) + (unsigned long)(p * pInc +
	pmapRandom(pmap -> randState) * max(pInc - 1, 0) +
	proc * numPhotonsPerProc
	);
	getPhoton(pmap, pIdx, &photon);
	#ifdef PMAP_CONTRIB_DBG
	if (pIdx == lastpIdx) {
	sprintf(errmsg, "duplicate contrib photon "
	"(proc %d, pIdx %d)", proc, pIdx
	);
	error(WARNING, errmsg);
	}
	lastpIdx = pIdx;
	#endif
	/* Init dummy photon ray with intersection and normal at
	* photon position. Set emitting light source index from
	* origin. */
	VCOPY(ray.rop, photon.pos);
	ray.rsrc = photonSrcIdx(pmap, &photon);
	for (i = 0; i < 3; i++)
	ray.ron [i] = photon.norm [i] / 127.0;

	/* Get contributions at photon position; retry with
	another photon if no contribs found */
	modCont = getPhotonContrib(pmap, &ray, ray.rcol);
	} while (!modCont);

	/* Get preallocated LUT node for this modifier */
	preCompContribNode = lu_find(nuPmap.preCompContribTab,
	modCont -> modname
	);

	if (!preCompContribNode \|\| !preCompContribNode -> key \|\|
	!preCompContribNode -> data
	)
	error(CONSISTENCY,
	"missing LUT entry in preComputeContrib()"
	);

	preCompContribPmap = (PhotonMap*)preCompContribNode -> data;
	preCompContrib = (PreComputedContrib*)(
	preCompContribPmap -> preCompContrib
	);
	scDim = preCompContrib -> scDim;
	nBins = preCompContrib -> nBins;
	nCoeffs = preCompContrib -> nCoeffs;
	nCompressedCoeffs = preCompContrib -> nCompressedCoeffs;
	waveletMatrix = preCompContrib -> waveletMatrix;

	if (nBins > 1) { /* Binning enabled */
	char contribBuf0 [preCompContrib -> contribSize],
	*contribBuf;
	COLR rgbe32 = (COLR)contribBuf0;

	/* copy binned contribs to wavelet
	* input matrix before compressing and encoding */
	for (i = 0; i < scDim; i++) {
	/* Calculate row pointer (=multiplication) in outer
	* loop, increment in inner loop */
	coeffPtr = modCont -> cbin +
	PMAP_CONTRIB_XY2LIN(scDim, i, 0);

	#ifdef PMAP_CONTRIB_LOG
	/* Logarithmic contribs; copy & apply per element */
	for (j = 0; j < scDim; j++, coeffPtr++)
	for (k = 0; k < 3; k++)
	waveletMatrix [i] [j] [k] =
	PMAP_CONTRIB_VAL((*coeffPtr) [k]);
	#else
	/* Linear contribs; copy matrix rows */
	memcpy(waveletMatrix [i], *coeffPtr,
	scDim * WAVELET_COEFFSIZE
	);
	#endif
	}

	/* Compress and encode contribs */
	if (encodeContribs(preCompContrib, compressRatio))
	error(INTERNAL, "failed contribution "
	"compression/encoding in preComputeContrib()"
	);

	/* Encode wavelet approx coeffs in the upper left of
	* the wavelet matrix to 32-bit RGBE, and buffer them.
	* These coeffs are not thresholded to minimise
	* compression artefacts. */
	for (i = 0; i < WAVELET_PADD2_APPROXDIM; i++) {
	for (j = 0; j < WAVELET_PADD2_APPROXDIM; j++, rgbe32++) {
	setcolr(*rgbe32,
	fabs(waveletMatrix [i] [j] [0]),
	fabs(waveletMatrix [i] [j] [1]),
	fabs(waveletMatrix [i] [j] [2])
	);

	/* HACK: depending on the boundary extension mode,
	* some approx coeffs can be NEGATIVE (!), which
	* 32-bit RGBE doesn't accommodate. To get around
	* this, we sacrifice a bit in each mantissa for the
	* sign. */
	for (k = 0; k < 3; k++)
	(*rgbe32) [k] = PMAP_CONTRIB_SET_RGBE32_SGN(
	(*rgbe32) [k], waveletMatrix [i] [j] [k]
	);
	}
	}

	/* Encode wavelet detail coeff range to 32-bit RGBE, and
	* buffer it after approx coeffs.
	* NOTE: mRGBE range maximum is buffered first to
	* facilitate handling the special (but pointless) case of
	* a single compressed detail coeff; if so, the mRGBE
	* minimum is omitted, since implicitly zero. */
	setcolr(*(rgbe32++),
	preCompContrib -> mrgbeRange.max [0],
	preCompContrib -> mrgbeRange.max [1],
	preCompContrib -> mrgbeRange.max [2]
	);
	if (nCompressedCoeffs > 1)
	setcolr(*(rgbe32++),
	preCompContrib -> mrgbeRange.min [0],
	preCompContrib -> mrgbeRange.min [1],
	preCompContrib -> mrgbeRange.min [2]
	);
	contribBuf = (char*)rgbe32;

	/* Now buffa mRGBE encoded, compressed detail coeffs.
	* NOTE: we can't copy to preCompContribPmap ->
	* contribHeapBuf directly because it isn't allocated
	* until the 1st call to newPhoton() below. IMHO this is
	* cleaner and more consistent with the existing code than
	* allocating it here. */
	memcpy(contribBuf, preCompContrib -> mrgbeCoeffs,
	nCompressedCoeffs * sizeof(mRGBE)
	);

	/* Append precomputed photon to heap from ray, check if
	* photon was accepted (i.e. newPhoton() returned 0).
	* Note the locally buffered encoded contribs are passed
	* as an extra parameter. */
	ray.rsrc = proc;
	photonOk = !newPhoton(preCompContribPmap, &ray,
	contribBuf0
	);

	#ifdef PMAP_CONTRIB_BINHISTO
	{
	unsigned long numZero = 0;

	/* Update bin histogram for last photon lookup */
	for (i = 1; i < pmap -> squeue.tail; i++) {
	Photon *photon = getNearestPhoton(&pmap -> squeue,
	pmap -> squeue.node [i].idx
	);
	++preCompContrib -> binHisto [
	photonSrcBin(pmap, photon)
	];
	}

	for (i = 0; i < preCompContrib -> nBins; i++)
	numZero += (intens(modCont -> cbin [i]) < FTINY);

	preCompContrib -> sumZero += numZero;
	if (numZero < preCompContrib -> minZero)
	preCompContrib -> minZero = numZero;
	if (numZero > preCompContrib -> maxZero)
	preCompContrib -> maxZero = numZero;
	}
	#endif
	}
	else {
	/* Binning disabled; append precomputed photon to heap
	* from ray _without_ encoded contribs, check if photon
	* was accepted (i.e. newPhoton() returned 0). */
	photonOk = !newPhoton(preCompContribPmap, &ray, NULL);
	}

	/* Increment parent photon map's photon counter if photon was
	* accepted by newPhoton(). */
	nuPmap.numPhotons += photonOk;
	#if NIX
	/* Asynchronously increment shared photon counter for this
	* modifier if photon was accepted by newPhoton().
	* NOTE: write lock on memmapped file! */
	if (photonOk) {
	shmLock(preCompContrib -> shmFile, F_WRLCK);
	*preCompContrib -> numPhotonsShm += photonOk;
	shmLock(preCompContrib -> shmFile, F_UNLCK);
	}
	#else
	/* Synchronously report progress on W33nD0z */
	if (!proc && photonRepTime > 0 &&
	time(NULL) >= repLastTime + photonRepTime
	) {
	repProgress = nuPmap.numPhotons;
	pmapPreCompReport();
	}
	#endif
	} /* End precomp. photon loop */

	/* Flush heap buffa one final time to prevent data corruption */
	flushPhotonHeap(preCompContribPmap);

	#ifdef PMAP_CONTRIB_BINHISTO
	/* Print binning histogram/population count for 1st subproc */
	if (!proc) {
	printf("Binning histogram for modifier %s\n:"
	"Avg photons / bin:\n",
	preCompContribNode -> key
	);

	for (i = 0; i < preCompContrib -> nBins; i++)
	printf("%f\n", (float)preCompContrib -> binHisto [i] /
	preCompContrib -> nBins / nuPmap.numPhotons);

	printf("Empty bin ratio (avg, min, max):\t%f\t%f\t%f\n",
	(float)preCompContrib -> sumZero /
	preCompContrib -> nBins / nuPmap.numPhotons,
	(float)preCompContrib -> minZero /
	preCompContrib -> nBins,
	(float)preCompContrib -> maxZero /
	preCompContrib -> nBins
	);
	}
	#endif

	#if NIX
	#ifdef PMAP_CONTRIB_DBG
	if (mrgbeDiffCnt) {
	sprintf(errmsg,
	"DBG preComputeContrib: Avg mRGBE encoding diff = %g\n",
	mrgbeDiffs / mrgbeDiffCnt
	);
	eputs(errmsg);
	}
	sprintf(errmsg, "DBG Subproc %d exiting normally\n", proc);
	eputs(errmsg);
	#endif
	/* Terminate subprocess normally */
	exit(0);
	#endif
	} /* if (!fork()) */
	else {
	/* PARENT PROCESS CONTINUES FORKING LOOP HERE */
	if (pid < 0)
	error(SYSTEM,
	"failed to fork subprocess in preComputeContrib()"
	);
	else
	/* Save child process ID */
	procPids [proc] = pid;
	}
	} /* End forking loop */

	#if NIX
	/* PARENT PROCESS CONTINUES HERE AFTER FORKING ALL SUBPROCS */
	#ifdef SIGCONT
	/* Enable progress report signal handler */
	signal(SIGCONT, pmapPreCompReport);
	#endif
	/* Wait for subprocesses to complete while reporting progress */
	proc = numProc;
	while (proc) {
	while (waitpid(-1, &stat, WNOHANG) > 0) {
	/* Subprocess exited; check status */
	if (!WIFEXITED(stat) \|\| WEXITSTATUS(stat)) {
	/* Exited with error; terminate siblings, clean up & quit */
	for (proc = 0; proc < numProc; proc++)
	kill(procPids [proc], SIGKILL);

	cleanUpPmaps(photonMaps);
	error(USER, "failed precomputing contribution photons");
	}

	--proc;
	}

	/* Nod off for a bit and update progress */
	sleep(1);

	/* Update num photons from shared photon counters for all mods */
	nuPmap.numPhotons = 0;
	lu_doall(nuPmap.preCompContribTab, sumNumPhotons,
	&nuPmap.numPhotons
	);
	repProgress = nuPmap.numPhotons;

	if (photonRepTime > 0 && time(NULL) >= repLastTime + photonRepTime)
	pmapPreCompReport();
	#ifdef SIGCONT
	else signal(SIGCONT, pmapPreCompReport);
	#endif
	}
	#endif /* NIX */

	#ifdef SIGCONT
	/* Reset signal handler */
	signal(SIGCONT, SIG_DFL);
	#endif

	/* Trash original pmap and its leaf file, and replace with new parent,
	which now acts as container for the per-modifier child pmaps */
	unlink(pmap -> store.leafFname);
	deletePhotons(pmap);
	memcpy(pmap, &nuPmap, sizeof(PhotonMap));

	/* Bail out if no photons could be precomputed */
	if (!pmap -> numPhotons)
	error(USER,
	"no contribution photons precomputed; try increasing -am"
	);

	/* !!! NOTE: buildPreCompContribPmap() bails out if any child contrib
	* !!! pmaps are empty -- should this trigger a warning instead? */

	/* Build per-modifier precomputed photon maps from their contribution
	heaps */
	lu_doall(pmap -> preCompContribTab, buildPreCompContribPmap, NULL);
	}



	#else
	/* -------------------------------------------------------------------
	U N I T T E S T S
	------------------------------------------------------------------- */

	#include <stdio.h>
	#include <random.h>
	#include "func.h"

	int main (int argc, char *argv [])
	{
	unsigned i, scdim, nsamp, numTheta = 0, numPhi = 0;
	double t, p;
	RAY ray;
	int bin;

	if (argc < 3) {
	fprintf(stderr, "%s <scdim> <nsamp> [<var>=<value>; ..]\n",
	argv [0]
	);
	fprintf(stderr, "Default variable defs: %s\n",
	PMAP_CONTRIB_SCDEFAULTS
	);
	fputs("\nMissing Shirley-Chiu dimension scDim>1, "
	"number of samples nsamp\n",
	stderr
	);
	return -1;
	}

	if (!(scdim = atoi(argv [1]))) {
	fputs("Invalid Shirley-Chiu dimension\n", stderr);
	return -1;
	}

	if (!(nsamp = atoi(argv [2]))) {
	fputs("Invalid num samples\n", stderr);
	return -1;
	}
	else {
	numTheta = (int)(sqrt(nsamp) / 2);
	numPhi = 4* numTheta;
	}

	/* (Doan' need to) Init cal func routines for binning */
	#if 0
	initfunc();
	calcontext(RCCONTEXT);
	#endif

	/* Compile default orientation variables for contribution binning */
	scompile(PMAP_CONTRIB_SCDEFAULTS, NULL, 0);
	/* Compile custom orientation variables from command line */
	for (i = 3; i < argc; i++)
	scompile(argv [i], NULL, 0);

	puts("x\ty\tz\t\ttheta\tphi\t\tbin");
	for (i = 0; i < nsamp; i++) {
	#if 0
	/* Random */
	t = 0.5 * PI * drand48();
	p = 2 * PI * drand48();
	#else
	/* Stratified */
	t = 0.5 * PI * ((i % numTheta) + drand48()) / numTheta;
	p = 2.0 * PI * ((i / numTheta) + drand48()) / numPhi;
	#endif
	ray.rdir [0] = sin(t) * cos(p);
	ray.rdir [1] = sin(t) * sin(p);
	ray.rdir [2] = cos(t);
	bin = ray2bin(&ray, scdim);

	printf("%.3f\t%.3f\t%.3f\t-->\t%.3f\t%.3f\t-->\t%d\n",
	ray.rdir [0], ray.rdir [1], ray.rdir [2], t, p, bin
	);
	}

	return 0;
	}
	#endif

	#endif /* PMAP_CONTRIB */

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