pmapcontrib.c
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Created: Thu, Nov 7, 21:34

pmapcontrib.c
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	#ifndef lint
	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"
	#include "pmapdiag.h"
	#include "pmaprand.h"
	#include "pmapmat.h"
	#include "pmapsrc.h"
	#include "pmutil.h"
	#include "otspecial.h"
	#include "otypes.h"
	#include "lookup.h"



	#ifdef PMAP_CONTRIB
	/* 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;



	extern void SDdisk2square(double sq[2], double diskx, double disky);



	static int logDim (unsigned size)
	/* Return log2(sqrt(size)) = l, where size = (2^l)(2^l).
	Is there a faster way (e.g. binary search)? */
	{
	unsigned i, sz, dim;

	if (!size)
	return 0;

	for (i = 0, dim = 0, sz = size; sz >>= 2; dim++);
	return dim;
	}



	static int xy2bin (unsigned l, int x, int y)
	/* Serialise 2D coordinates in range (2^l) x (2^l) to 1D bin.
	Returns -1 if coordinates invalid */
	{
	return x < 0 \|\| y < 0
	? -1
	: (x << l) + y;
	}



	static void bin2xy (unsigned l, int bin, int x, int y)
	/* Deserialise 1D bin to 2D coordinates in range (2^l) x (2^l).
	Returns -1 if bin invalid */
	{
	/* Obviously this is faster than integer division/modulo */
	*x = bin < 0 ? -1 : bin >> l;
	*y = bin < 0 ? -1 : bin & PMAP_CONTRIB_SCDIM(l) - 1;
	}



	static int ray2bin (const RAY *ray, unsigned nbins)
	/* Map ray dir (pointing away from origin) to its 1D Shirley-Chiu bin,
	where nbins = (2^l) x (2^l) for l > 1.
	Returns -1 if mapped bin is invalid (e.g. behind plane) */
	{
	const unsigned l = logDim(nbins), scDim = PMAP_CONTRIB_SCDIM(l);
	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 function variables */
	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 */
	diskPlane [0] *= scRHS;
	diskx = DOT(ray -> rdir, diskPlane);
	disky = DOT(ray -> rdir, scUp) - dz * DOT(ray -> rdir, scUp);
	diskd2 = diskx * diskx + disky * disky; /* in-plane length^2 */
	rad = dz>FTINY ? sqrt((1 - dzdz) / diskd2) : 0; / radial factor */
	disky = rad; / diskx, disky now in range [-1, 1] */

	/* Apply Shirley-Chiu mapping of (diskx, disky) to square */
	SDdisk2square(scCoord, diskx, disky);
	/* Map Shirley-Chiu square coords to 1D bin */
	scBin [0] = scCoord [0] * scDim;
	scBin [1] = scCoord [1] * scDim;
	return xy2bin(l, 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;

	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, 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
	);
	}

	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 int coeffCompare (const void c1, const void c2)
	/* Comparison function to REVERSE sort thresholded coefficients */
	{
	const EncodedPreComputedContrib *tcoeff1 = c1,
	*tcoeff2 = c2;
	/* Use dot product as magnitude to compare _absolute_ values */
	const WAVELET_COEFF v1 = DOT(tcoeff1 -> coeff, tcoeff1 -> coeff),
	v2 = DOT(tcoeff2 -> coeff, tcoeff2 -> coeff);

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



	static int thresholdContribs (MODCONT *binnedContribs,
	PreComputedContrib *preCompContrib
	)
	/* Threshold binned detail coefficients in binnedContribs -> cbin [1..]
	by keeping the (preCompContrib -> nCompressedBins) largest and
	returning these in preContrib -> compressedBins along with their
	original bin order.
	NOTE: binnedContribs -> cbin [0] is the average wavelet coefficient
	and excluded from thresholding.
	Returns 0 on success. */
	{
	unsigned b;
	EncodedPreComputedContrib *threshCoeffs;

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

	/* Set up coefficient buffer for compression (thresholding), skipping
	* first coeff since it's the average and therefore not thresholded */
	for (b = 0; b < binnedContribs -> nbins - 1; b++) {
	/* Set up pointers to coeffs (sorted faster than 3 floats/doubles)
	and remember original bin position prior to sorting.
	NOTE: The encoded bin position preserves the offset for the
	1st coefficient i.e. the average! */
	threshCoeffs [b].coeff = (WAVELET_COEFF*)(
	&(binnedContribs -> cbin [b + 1])
	);
	threshCoeffs [b].bin = b + 1;
	}

	/* REVERSE sort coeffs by magnitude; the non-thresholded coeffs
	will then start at threshCoeffs [0] */
	qsort(threshCoeffs, binnedContribs -> nbins - 1,
	sizeof(EncodedPreComputedContrib), coeffCompare
	);

	return 0;
	}



	static int encodeContribs (MODCONT *binnedContribs,
	PreComputedContrib *preCompContrib, float compressRatio
	)
	/* Apply wavelet transform to binnedContribs -> cbin and compress
	according to compressRatio, storing thresholded and mRGBE-encoded
	coefficients in preCompContrib -> mrgbeCoeffs.
	Note that the average coefficient is not encoded, and returned
	in binnedContribs -> cbin [0].
	Returns 0 on success. */
	{
	unsigned b, i;
	EncodedPreComputedContrib *threshCoeffs;
	mRGBERange *mrgbeRange;
	mRGBE *mrgbeCoeffs;
	WAVELET_COEFF absCoeff;
	#ifdef PMAP_CONTRIB_DBG
	WaveletCoeff3 decCoeff;
	unsigned decBin, x, y;
	#endif

	if (!binnedContribs \|\| !preCompContrib \|\|
	!preCompContrib -> compressedBins \|\| !preCompContrib -> mrgbeCoeffs
	)
	/* Should be initialised by the caller! */
	return -1;

	#ifdef PMAP_CONTRIB_DBG
	#if 0
	for (b = 0; b < binnedContribs -> nbins; b++) {
	/* Set contributions to bins for debugging */
	setcolor(binnedContribs -> cbin [b], b, b, b);

	/* Dump contribs prior to encoding for debugging */
	/* printf("%.3g\t", colorAvg(binnedContribs -> cbin [b])); */
	}
	#endif
	#if 1
	for (x = 0; x < preCompContrib -> scDim; x++) {
	for (y = 0; y < preCompContrib -> scDim; y++) {
	for (i = 0; i < 3; i++) {
	/* Replace contribs with "bump" function */
	preCompContrib -> waveletMatrix [x][y][i] =
	(1. - fabs((float)x - (preCompContrib -> scDim >> 1)) /
	(preCompContrib -> scDim >> 1)
	) *
	(1. - fabs((float)y - (preCompContrib -> scDim >> 1)) /
	(preCompContrib -> scDim >> 1)
	);
	}

	#if 0
	printf("% 7.3g\t",
	colorAvg(preCompContrib -> waveletMatrix [x][y])
	);
	#endif
	}

	#if 0
	putchar('\n');
	#endif
	}

	putchar('\n');
	#endif

	/* putchar('\n'); */
	#endif

	/* Do 2D wavelet transform on preCompContrib -> waveletMatrix
	(which actually maps to binnedContribs -> cbin) */
	if (waveletXform2(preCompContrib -> waveletMatrix,
	preCompContrib -> tWaveletMatrix, preCompContrib -> l
	) < 0
	)
	error(INTERNAL, "failed wavelet transform in encodeContribs()");

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

	/* 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 (b = 0; b < preCompContrib -> nCompressedBins; b++) {
	for (i = 0; i < 3; i++) {
	#ifdef PMAP_CONTRIB_DBG
	#if 0
	/* Replace wavelet coefficient with bin for debugging, ordering
	bins linearly */
	threshCoeffs [b].coeff [i] = b + 1;
	threshCoeffs [b].bin = b + 1;
	#endif
	#endif
	absCoeff = fabs(threshCoeffs [b].coeff [i]);

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

	if (preCompContrib -> nCompressedBins == 1)
	/* Maximum compression with just 1 (!) compressed bin (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 (b = 0; b < preCompContrib -> nCompressedBins; b++) {
	mrgbeCoeffs [b] = mRGBEencode(threshCoeffs [b].coeff,
	mrgbeRange, threshCoeffs [b].bin
	);

	#ifdef PMAP_CONTRIB_DBG
	/* Encoding sanity check */
	decBin = mRGBEdecode(mrgbeCoeffs [b], mrgbeRange, decCoeff);
	#if 0
	if (decBin != threshCoeffs [b].bin \|\|
	sqrt(dist2(decCoeff, threshCoeffs [b].coeff)) > 1.7
	)
	error(CONSISTENCY, "failed sanity check in encodeContribs()");
	#endif
	for (i = 0; i < 3; i++)
	if (decCoeff [i] / threshCoeffs [b].coeff [i] < 0)
	error(CONSISTENCY,
	"coefficient sign reversal in encodeContribs()"
	);
	#endif
	}

	return 0;
	}



	static void initContribHeap (PhotonMap *pmap)
	/* Initialise precomputed contribution heap */
	{
	int fdFlags;

	if (!pmap -> contribHeap) {
	/* Open heap file for precomputed contributions */
	mktemp(strcpy(pmap -> contribHeapFname, PMAP_TMPFNAME));
	if (!(pmap -> contribHeap = fopen(pmap -> contribHeapFname, "w+b")))
	error(SYSTEM, "failed opening precomputed contribution "
	"heap file in initContribHeap()"
	);
	#ifdef F_SETFL /* XXX is there an alternative needed for Wind0z? */
	fdFlags = fcntl(fileno(pmap -> contribHeap), F_GETFL);
	fcntl(fileno(pmap -> contribHeap), F_SETFL, fdFlags \| O_APPEND);
	#endif /* ftruncate(fileno(pmap -> heap), 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 contrib = (MODCONT)lu_find(
	pmapContribTab, srcMod -> oname
	) -> data;
	Photon *photon;
	COLOR flux;
	PhotonSearchQueueNode *sqn;
	float r2, norm;
	unsigned i;

	/* Zero bins for this source modifier */
	memset(contrib -> cbin, 0, sizeof(DCOLOR) * contrib -> nbins);
	setcolor(irrad, 0, 0, 0);

	if (!contrib \|\| !pmap -> maxGather)
	/* Modifier not in LUT or zero bandwidth */
	return NULL;

	/* Lookup photons */
	pmap -> squeue.tail = 0;
	/* 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));

	/* XXX: OMIT extra normalisation factor 1/PI for ambient calc? */
	#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 ; 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 photon distance */
	scalecolor(flux, 1 - sqn -> dist2 / r2);
	#endif
	addcolor(irrad, flux);
	addcolor(contrib -> cbin [photonSrcBin(pmap, photon)], flux);
	}

	return contrib;
	}



	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 */
	free(preCompContrib -> waveletMatrix);
	freeWaveletMatrix(preCompContrib -> tWaveletMatrix,
	preCompContrib -> l
	);

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

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

	/* 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 -> compressedBins = 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 -> nBins = preCompContrib -> nCompressedBins =
	preCompContrib -> l = preCompContrib -> scDim =
	preCompContrib -> contribSize = 0;
	}



	void preComputeContrib (PhotonMap *pmap)
	/* 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 i, numPreComp;
	unsigned b, j;
	long nCompressedBins;
	PhotonIdx pIdx;
	Photon photon;
	RAY ray;
	MODCONT *binnedContribs;
	COLR mrgbeRange32 [2];
	LUENT *preCompContribNode;
	PhotonMap *preCompContribPmap, nuPmap;
	PreComputedContrib *preCompContrib;
	LUTAB lutInit = LU_SINIT(NULL, freePreCompContribNode);
	#ifdef PMAP_CONTRIB_DBG
	RAY dbgRay;
	#endif

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

	/* 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));

	/* Record start time, baby */
	repStartTime = time(NULL);
	#ifdef SIGCONT
	signal(SIGCONT, pmapPreCompReport);
	#endif
	repComplete = numPreComp = finalGather * pmap -> numPhotons;
	repProgress = 0;

	photonRay(NULL, &ray, PRIMARY, NULL);
	ray.ro = NULL;

	for (i = 0; i < numPreComp; i++) {
	/* Get random photon from stratified distribution in source heap
	* to avoid duplicates and clustering */
	pIdx = firstPhoton(pmap) + (unsigned long)(
	(i + pmapRandom(pmap -> randState)) / finalGather
	);
	getPhoton(pmap, pIdx, &photon);

	/* 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 (j = 0; j < 3; j++)
	ray.ron [j] = photon.norm [j] / 127.0;

	#ifndef PMAP_CONTRIB_DBG
	/* Get contributions at photon position; retry with another
	photon if no contribs found */
	binnedContribs = getPhotonContrib(pmap, &ray, ray.rcol);
	#else
	/* Get all contribs from same photon for debugging */
	getPhoton(pmap, 0, &photon);
	memcpy(&dbgRay, &ray, sizeof(RAY));
	VCOPY(dbgRay.rop, photon.pos);
	dbgRay.rsrc = photonSrcIdx(pmap, &photon);
	for (j = 0; j < 3; j++)
	dbgRay.ron [j] = photon.norm [j] / 127.0;
	binnedContribs = getPhotonContrib(pmap, &dbgRay, dbgRay.rcol);
	#endif

	if (binnedContribs) {
	/* Found contributions at photon position, so generate
	* precomputed photon */
	if (!(preCompContribNode = lu_find(nuPmap.preCompContribTab,
	binnedContribs -> modname)
	)
	)
	error(SYSTEM, "out of memory allocating LUT entry in "
	"preComputeContrib()"
	);

	if (!preCompContribNode -> key) {
	/* New LUT node for precomputed contribs for this modifier */
	preCompContribNode -> key = (char*)binnedContribs -> modname;
	preCompContribNode -> data = (char*)(
	preCompContribPmap = malloc(sizeof(PhotonMap))
	);

	if (preCompContribPmap) {
	/* Init new child photon map and its contributions */
	initPhotonMap(preCompContribPmap,
	PMAP_TYPE_CONTRIB_CHILD
	);
	initPhotonHeap(preCompContribPmap);
	initContribHeap(preCompContribPmap);
	preCompContrib = (PreComputedContrib*)(
	preCompContribPmap -> preCompContrib =
	malloc(sizeof(PreComputedContrib))
	);
	initPreComputedContrib(preCompContrib);
	}
	if (!preCompContribPmap \|\| !preCompContrib)
	error(SYSTEM, "out of memory allocating new photon map "
	"in preComputeContrib()"
	);

	/* Set output filename from parent photon map */
	preCompContribPmap -> fileName = nuPmap.fileName;

	/* Set contrib/coeff mode from parent photon map */
	preCompContribPmap -> contribMode = nuPmap.contribMode;

	/* Get Shirley-Chiu square & wavelet matrix resolution, bins
	per dimension, and number of bins */
	preCompContrib -> l = logDim(binnedContribs -> nbins);
	preCompContrib -> scDim = PMAP_CONTRIB_SCDIM(
	preCompContrib -> l
	);
	preCompContrib -> nBins = preCompContrib -> scDim *
	preCompContrib -> scDim;

	if (preCompContrib -> nBins != binnedContribs -> nbins)
	/* Shouldn't happen */
	error(INTERNAL,
	"bin count mismatch in preComputeContrib()"
	);

	if (preCompContrib -> nBins > 1) {
	/* BINNING ENABLED; set up wavelet xform & compression.
	Number of compressed coeffs/bins is fixed (subtract
	one as the average coefficient is not thresholded) */
	nCompressedBins = (preCompContrib -> nBins - 1) *
	(1 - compressRatio);

	if (nCompressedBins < 1) {
	error(WARNING,
	"maximum contribution compression, clamping number "
	"of bins in preComputeContrib()"
	);
	nCompressedBins = 1;
	}
	if (nCompressedBins >= preCompContrib -> nBins) {
	error(WARNING,
	"minimum contribution compression, clamping number "
	"of bins in preComputeContrib()"
	);
	nCompressedBins = preCompContrib -> nBins - 1;
	}

	preCompContrib -> nCompressedBins = nCompressedBins;

	/* Lazily allocate 2D primary wavelet matrix and map its
	rows to linear array binnedContribs -> cbin */
	if (!(preCompContrib -> waveletMatrix = calloc(
	preCompContrib -> scDim, sizeof(WaveletCoeff3*))
	)
	)
	error(SYSTEM, "out of memory allocating primary "
	"wavelet matrix in preComputeContrib()"
	);

	for (b = 0; b < preCompContrib -> scDim; b++)
	/* Point to each row in existing 1D contrib array */
	preCompContrib -> waveletMatrix [b] =
	&binnedContribs -> cbin [b * preCompContrib -> scDim];

	/* Lazily allocate transposed wavelet matrix */
	preCompContrib -> tWaveletMatrix =
	allocWaveletMatrix(preCompContrib -> l);
	if (!preCompContrib -> tWaveletMatrix)
	error(SYSTEM,
	"out of memory allocating transposed wavelet "
	"matrix in preComputeContrib()"
	);

	/* Lazily allocate thresholded detail coefficients (minus
	the average coeff) */
	preCompContrib -> compressedBins = calloc(
	preCompContrib -> nBins - 1,
	sizeof(EncodedPreComputedContrib)
	);
	/* Lazily alloc mRGBE-encoded compressed wavelet coeffs */
	preCompContrib -> mrgbeCoeffs = calloc(
	preCompContrib -> nCompressedBins, sizeof(mRGBE)
	);
	if (!preCompContrib -> compressedBins \|\|
	!preCompContrib -> mrgbeCoeffs
	)
	error(SYSTEM, "out of memory allocating compressed "
	"coefficients in preComputeContrib()"
	);

	/* Set size of compressed contributions, in bytes */
	preCompContrib -> contribSize = PMAP_CONTRIB_ENCSIZE(
	preCompContrib -> nCompressedBins
	);
	}
	}
	else {
	/* LUT node already exists for this modifier; use its data */
	preCompContribPmap = (PhotonMap*)preCompContribNode -> data;
	preCompContrib = (PreComputedContrib*)(
	preCompContribPmap -> preCompContrib
	);
	}

	if (binnedContribs -> nbins > 1) {
	/* Binning enabled; compress & encode binned contribs */
	if (encodeContribs(binnedContribs, preCompContrib,
	compressRatio
	)
	)
	error(INTERNAL, "failed contribution "
	"compression/encoding in preComputeContrib()"
	);

	/* Dump encoded bins to contrib heap file, prepended by
	mRGBE range in 32-bit RGBE. NOTE: minimum and maximum are
	reversed in the file to facilitate handling of single
	compressed bins (see below) */
	setcolr(mrgbeRange32 [0],
	preCompContrib -> mrgbeRange.max [0],
	preCompContrib -> mrgbeRange.max [1],
	preCompContrib -> mrgbeRange.max [2]
	);
	setcolr(mrgbeRange32 [1],
	preCompContrib -> mrgbeRange.min [0],
	preCompContrib -> mrgbeRange.min [1],
	preCompContrib -> mrgbeRange.min [2]
	);

	/* Dump only mRGBE maximum if 1 compressed bin (maximum
	* compression), since minimum is implicitly zero and can
	* be omitted to save space */
	putbinary(mrgbeRange32, sizeof(COLR),
	1 + (preCompContrib -> nCompressedBins > 1),
	preCompContribPmap -> contribHeap
	);

	if (putbinary(preCompContrib -> mrgbeCoeffs, sizeof(mRGBE),
	preCompContrib -> nCompressedBins,
	preCompContribPmap -> contribHeap
	) != preCompContrib -> nCompressedBins
	)
	error(SYSTEM, "failed writing to coefficients to "
	"contribution heap in preComputeContrib()"
	);
	}

	/* Set photon flux to coarsest average wavelet coefficient
	NOTE: binnedContrib -> cbin [0] ==
	preCompContrib -> waveletMatrix [0][0] ==
	preCompContrib -> tWaveletMatrix [0][0].
	IF BINNING IS DISABLED, this is the total contribution
	from all directions */
	copycolor(ray.rcol, binnedContribs -> cbin [0]);

	/* HACK: signal newPhoton() to set precomputed photon's
	contribution source from ray -> rsrc */
	/* XXX: DO WE STILL NEED THIS SHIT AFTER PRECOMP,
	SINCE CHILD PMAPS ARE PER-MODIFIER ANYWAY? */
	preCompContribPmap -> lastContribSrc.srcIdx = -2;

	/* Append photon to new heap from ray and increment total
	count for all modifiers in parent photon map */
	newPhoton(preCompContribPmap, &ray);
	nuPmap.numPhotons++;
	}

	/* Update progress */
	repProgress++;

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

	#ifdef SIGCONT
	signal(SIGCONT, SIG_DFL);
	#endif

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

	/* 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, l, nbins, nsamp, numTheta = 0, numPhi = 0;
	double t, p;
	RAY ray;
	int bin;

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

	if (!(l = atoi(argv [1]))) {
	fputs("Invalid resolution\n", stderr);
	return -1;
	}
	else nbins = PMAP_CONTRIB_SCBINS(l);

	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();
	setcontext(RCCONTEXT);
	#endif

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

	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, nbins);

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

	return 0;
	}
	#endif

	#endif /* PMAP_CONTRIB */

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