pmcontrib2.c
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Created: Wed, May 1, 01:22

pmcontrib2.c
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	#ifndef lint
	static const char RCSid[] = "$Id$";
	#endif

	/*
	=========================================================================
	Photon map routines for precomputed light source contributions.
	This is the main photon distribution routine 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")
	(c) Tokyo University of Science,
	supported by the KAJIMA Foundation under the project title:
	"Reflections from Building Façades and their Glare Potential on the
	Built Environment -- Application of the Photon Flow Method using
	Annual Simulation"
	=========================================================================

	$Id$
	*/



	#include "pmapcontrib.h"
	#ifdef PMAP_CONTRIB
	#include "pmapdiag.h"
	#include "pmaprand.h"
	#include "pmapmat.h"
	#include "pmaproi.h"
	#include "pmapsrc.h"
	#include "pmapio.h"
	#include "otspecial.h"
	#if NIX
	#include <sys/mman.h>
	#include <sys/wait.h>
	#endif



	/* Defs for photon emission counter array passed by sub-processes to parent
	* via shared memory */
	typedef unsigned long PhotonContribCnt;

	/* Indices for photon emission counter array: num photons stored and num
	* emitted per source */
	#define PHOTONCNT_NUMPHOT 0
	#define PHOTONCNT_NUMEMIT(n) (1 + n)



	void distribPhotonContrib (PhotonMap* pmap, LUTAB *contribTab,
	unsigned numContribs, int contribMode, char rcOpts, unsigned numProc
	)
	{
	EmissionMap emap;
	char errmsg2 [128], shmFname [PMAP_TMPFNLEN];
	unsigned srcIdx, proc;
	int shmFile, stat, pid;
	double srcFlux, / Emitted flux per light source */
	srcDistribTarget; /* Target photon count
	per source */
	PhotonContribCnt photonCnt; / Photon emission counter array */
	unsigned photonCntSize = (sizeof(PhotonContribCnt) *
	PHOTONCNT_NUMEMIT(nsources)
	);
	FILE **contribSrcHeap = NULL;
	char **contribSrcHeapFname = NULL;
	PhotonContribSourceIdx *contribSrcOfs = NULL;
	pid_t procPids [PMAP_MAXPROC];

	if (!pmap)
	error(USER, "no contribution photon map specified");

	if (!nsources)
	error(USER, "no light sources");

	if (nsources > PMAP_MAXSRCIDX)
	error(USER, "too many light sources");

	if (!contribTab \|\| !numContribs)
	error(USER, "no modifiers specified for contribution photon map");

	/* Allocate photon flux per light source; this differs for every
	* source as all sources contribute the same number of distributed
	* photons (srcDistribTarget), hence the number of photons emitted per
	* source does not correlate with its emitted flux. The resulting flux
	* per photon is therefore adjusted individually for each source. */
	if (!(srcFlux = calloc(nsources, sizeof(double))))
	error(SYSTEM, "can't allocate source flux in distribPhotonContrib");

	/* ===================================================================
	* INITIALISATION - Set up emission and scattering funcs
	* =================================================================== */
	emap.samples = NULL;
	emap.src = NULL;
	emap.maxPartitions = MAXSPART;
	emap.partitions = (unsigned char*)malloc(emap.maxPartitions >> 1);
	if (!emap.partitions)
	error(USER, "can't allocate source partitions in distribPhotonContrib");

	/* Initialise contrib photon map */
	initPhotonMap(pmap, PMAP_TYPE_CONTRIB);
	initPmapContribTab(contribTab, contribMode);
	pmap -> contribMode = *contribMode;
	pmap -> rcOpts = rcOpts;
	initPmapContrib(pmap);
	initPhotonHeap(pmap);
	initPhotonEmissionFuncs();
	initPhotonScatterFuncs();

	/* Per-subprocess / per-source target counts */
	pmap -> distribTarget /= numProc;
	srcDistribTarget = nsources
	? (double)pmap -> distribTarget / nsources
	: 0;

	if (!pmap -> distribTarget)
	error(INTERNAL, "no photons to distribute in distribPhotonContrib");

	/* Get photon ports from modifier list */
	getPhotonPorts(photonPortList);

	/* Get photon sensor modifiers */
	getPhotonSensors(photonSensorList);

	/* Get polyhedral regions of interest */
	getPolyROIs(pmapROImodList);

	#if NIX
	/* Set up shared mem for photon counters (zeroed by ftruncate) */
	strcpy(shmFname, PMAP_TMPFNAME);
	shmFile = mkstemp(shmFname);

	if (shmFile < 0 \|\| ftruncate(shmFile, photonCntSize) < 0)
	error(SYSTEM, "failed shared mem init in distribPhotonContrib");

	photonCnt = mmap(NULL, photonCntSize,
	PROT_READ \| PROT_WRITE, MAP_SHARED, shmFile, 0
	);

	if (photonCnt == MAP_FAILED)
	error(SYSTEM, "failed mapping shared memory in distribPhotonContrib");
	#else
	/* Allocate photon counters statically on Windoze */
	if (!(photonCnt = malloc(photonCntSize)))
	error(SYSTEM, "failed trivial malloc in distribPhotonContrib");

	for (srcIdx = 0; srcIdx < PHOTONCNT_NUMEMIT(nsources); srcIdx++)
	photonCnt [srcIdx] = 0;
	#endif /* NIX */

	if (verbose) {
	sprintf(errmsg, "\nIntegrating flux from %d sources", nsources);

	if (photonPorts) {
	sprintf(errmsg2, " via %d ports", numPhotonPorts);
	strcat(errmsg, errmsg2);
	}

	strcat(errmsg, "\n");
	eputs(errmsg);
	}

	/* =============================================================
	* FLUX INTEGRATION - Get total flux emitted from sources/ports
	* ============================================================= */
	for (srcIdx = 0; srcIdx < nsources; srcIdx++) {
	unsigned portCnt = 0;
	const OBJREC *srcMod = findmaterial(source [srcIdx].so);

	srcFlux [srcIdx] = 0;
	/* Skip this source if its contributions are not sought */
	if (!lu_find(pmapContribTab, srcMod -> oname) -> data) {
	sprintf(errmsg, "ignoring contributions from source %s",
	source [srcIdx].so -> oname
	);
	error(WARNING, errmsg);
	continue;
	}

	emap.src = source + srcIdx;

	do { /* Need at least one iteration if no ports! */
	emap.port = emap.src -> sflags & SDISTANT
	? photonPorts + portCnt
	: NULL;
	photonPartition [emap.src -> so -> otype] (&emap);

	if (verbose) {
	sprintf(errmsg, "\tIntegrating flux from source %s ",
	source [srcIdx].so -> oname
	);

	if (emap.port) {
	sprintf(errmsg2, "via port %s ",
	photonPorts [portCnt].so -> oname
	);
	strcat(errmsg, errmsg2);
	}

	sprintf(errmsg2, "(%lu partitions)\n", emap.numPartitions);
	strcat(errmsg, errmsg2);
	eputs(errmsg);
	#if NIX
	fflush(stderr);
	#endif
	}

	for (emap.partitionCnt = 0;
	emap.partitionCnt < emap.numPartitions;
	emap.partitionCnt++
	) {
	initPhotonEmission(&emap, pdfSamples);
	srcFlux [srcIdx] += colorAvg(emap.partFlux);
	}

	portCnt++;
	} while (portCnt < numPhotonPorts);

	if (srcFlux [srcIdx] < FTINY) {
	sprintf(errmsg, "source %s has zero emission",
	source [srcIdx].so -> oname
	);
	error(WARNING, errmsg);
	}
	}

	/* Allocate & init per-subprocess contribution source heap files */
	contribSrcHeap = calloc(numProc, sizeof(FILE*));
	contribSrcHeapFname = calloc(numProc, sizeof(char*));
	contribSrcOfs = calloc(numProc, sizeof(PhotonContribSourceIdx));
	if (!contribSrcHeap \|\| !contribSrcHeapFname \|\| !contribSrcOfs)
	error(SYSTEM, "failed contribution source heap allocation "
	"in distribPhotonContrib()"
	);

	for (proc = 0; proc < numProc; proc++) {
	contribSrcHeapFname [proc] = malloc(PMAP_TMPFNLEN);
	if (!contribSrcHeapFname [proc])
	error(SYSTEM, "failed contribution source heap file allocation "
	"in distribPhotonContrib()"
	);

	mktemp(strcpy(contribSrcHeapFname [proc], PMAP_TMPFNAME));
	if (!(contribSrcHeap [proc] = fopen(contribSrcHeapFname [proc], "w+b")))
	error(SYSTEM, "failed opening contribution source heap file "
	"in distribPhotonContrib()"
	);
	}

	/* Record start time for progress reports */
	repStartTime = time(NULL);

	if (verbose) {
	sprintf(errmsg, "\nPhoton distribution @ %d procs\n", numProc);
	eputs(errmsg);
	}

	/* MAIN LOOP */
	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
	/* Local photon counters for this subprocess */
	unsigned long preIncPhotonCnt, numEmitted = 0,
	lastNumEmitted = 0, lastNumPhotons = 0;
	double photonFluxSum = 0; /* Accum. photon flux */

	/* Seed RNGs from PID for decorellated photon distribution */
	pmapSeed(randSeed + proc, partState);
	pmapSeed(randSeed + (proc + 1) % numProc, emitState);
	pmapSeed(randSeed + (proc + 2) % numProc, cntState);
	pmapSeed(randSeed + (proc + 3) % numProc, mediumState);
	pmapSeed(randSeed + (proc + 4) % numProc, scatterState);
	pmapSeed(randSeed + (proc + 5) % numProc, rouletteState);
	#ifdef PMAP_SIGUSR
	{
	double partNumEmit;
	unsigned long partEmitCnt;
	double srcPhotonFlux, avgPhotonFlux;
	unsigned portCnt, passCnt, prePassCnt;
	float srcPreDistrib;
	double srcNumEmit; /* # to emit from source */
	unsigned long srcNumDistrib; /* # stored */

	void sigUsrDiags()
	/* Loop diags via SIGUSR1 */
	{
	sprintf(errmsg,
	"******************* Proc %d Diags *******************\n"
	"srcIdx = %d (%s)\nportCnt = %d (%s)\npassCnt = %d\n"
	"srcFlux = %f\nsrcPhotonFlux = %f\navgPhotonFlux = %f\n"
	"partNumEmit = %f\npartEmitCnt = %lu\n\n",
	proc, srcIdx, findmaterial(source [srcIdx].so) -> oname,
	portCnt, photonPorts [portCnt].so -> oname,
	passCnt, srcFlux [srcIdx], srcPhotonFlux, avgPhotonFlux,
	partNumEmit, partEmitCnt
	);
	eputs(errmsg);
	fflush(stderr);
	}
	}
	#endif
	#ifdef PMAP_SIGUSR
	signal(SIGUSR1, sigUsrDiags);
	#endif
	#ifdef DEBUG_PMAP
	/* Output child process PID after random delay to prevent corrupted
	* console output due to race condition */
	usleep(1e6 * pmapRandom(rouletteState));
	sprintf(errmsg, "DBG Proc %d: PID = %d "
	"(waiting 10 sec to attach debugger...)\n",
	proc, getpid()
	);
	eputs(errmsg);
	#if NIX
	fflush(stderr);
	#endif
	/* Allow time for debugger to attach to child process */
	sleep(10);
	#endif
	/* =============================================================
	* 2-PASS PHOTON DISTRIBUTION
	* Pass 1 (pre): emit fraction of target photon count
	* Pass 2 (main): based on outcome of pass 1, estimate remaining
	* number of photons to emit to approximate target
	* count
	* ============================================================= */
	for (srcIdx = 0; srcIdx < nsources; srcIdx++) {
	const unsigned numEmitIdx = PHOTONCNT_NUMEMIT(srcIdx);
	/* Decorrelate shared photon counter updates to reduce
	* contention by setting unique update intervals per subproc */
	const unsigned photonCntUpdate = PMAP_CNTUPDATE + proc;
	#ifndef PMAP_SIGUSR
	unsigned portCnt, passCnt = 0, prePassCnt = 0;
	float srcPreDistrib = preDistrib;
	double srcNumEmit = 0; /* # to emit from source */
	unsigned long srcNumDistrib = pmap -> numPhotons; /* #stored */
	#else
	passCnt = prePassCnt = 0;
	srcPreDistrib = preDistrib;
	srcNumEmit = 0; /* # to emit from source */
	srcNumDistrib = pmap -> numPhotons; /* # stored */
	#endif
	if (srcFlux [srcIdx] < FTINY)
	/* Source has zero emission or was skipped in prepass
	because its contributions are not sought */
	continue;

	while (passCnt < 2) {
	if (!passCnt) {
	/* INIT PASS 1 */
	if (++prePassCnt > maxPreDistrib) {
	/* Warn if no photons contributed after sufficient
	* iterations; only output from subprocess 0 to reduce
	* console clutter */
	if (!proc) {
	sprintf(errmsg,
	"source %s: too many prepasses, skipped",
	source [srcIdx].so -> oname
	);
	error(WARNING, errmsg);
	}

	break;
	}

	/* Num to emit is fraction of target count */
	srcNumEmit = srcPreDistrib * srcDistribTarget;
	}
	else {
	/* INIT PASS 2 */
	#ifndef PMAP_SIGUSR
	double srcPhotonFlux, avgPhotonFlux;
	#endif
	/* Based on the outcome of the predistribution we can now
	* figure out how many more photons we have to emit from
	* the current source to meet the target count,
	* srcDistribTarget. This value is clamped to 0 in case
	* the target has already been exceeded in pass 1.
	* srcNumEmit and srcNumDistrib is the number of photons
	* emitted and distributed (stored) from the current
	* source in pass 1, respectively. */
	srcNumDistrib = pmap -> numPhotons - srcNumDistrib;
	srcNumEmit *= srcNumDistrib
	? max(srcDistribTarget/srcNumDistrib, 1) - 1
	: 0;

	if (!srcNumEmit)
	/* No photons left to distribute in main pass */
	break;

	srcPhotonFlux = srcFlux [srcIdx] / srcNumEmit;
	avgPhotonFlux = photonFluxSum / (srcIdx + 1);

	if (avgPhotonFlux > FTINY &&
	srcPhotonFlux / avgPhotonFlux < FTINY
	) {
	/* Skip source if its photon flux is grossly below the
	* running average, indicating negligible contributions
	* at the expense of excessive distribution time; only
	* output from subproc 0 to reduce console clutter */
	if (!proc) {
	sprintf(errmsg,
	"source %s: itsy bitsy photon flux, skipped",
	source [srcIdx].so -> oname
	);
	error(WARNING, errmsg);
	}

	srcNumEmit = 0; /* Or just break??? */
	}

	/* Update sum of photon flux per light source */
	photonFluxSum += srcPhotonFlux;
	}

	portCnt = 0;
	do { /* Need at least one iteration if no ports! */
	emap.src = source + srcIdx;
	emap.port = emap.src -> sflags & SDISTANT
	? photonPorts + portCnt
	: NULL;
	photonPartition [emap.src -> so -> otype] (&emap);

	if (verbose && !proc) {
	/* Output from subproc 0 only to avoid race condition
	* on console I/O */
	if (!passCnt)
	sprintf(errmsg, "\tPREPASS %d on source %s ",
	prePassCnt, source [srcIdx].so -> oname
	);
	else
	sprintf(errmsg, "\tMAIN PASS on source %s ",
	source [srcIdx].so -> oname
	);

	if (emap.port) {
	sprintf(errmsg2, "via port %s ",
	photonPorts [portCnt].so -> oname
	);
	strcat(errmsg, errmsg2);
	}

	sprintf(errmsg2, "(%lu partitions)\n",
	emap.numPartitions
	);
	strcat(errmsg, errmsg2);
	eputs(errmsg);
	#if NIX
	fflush(stderr);
	#endif
	}

	for (emap.partitionCnt = 0;
	emap.partitionCnt < emap.numPartitions;
	emap.partitionCnt++
	) {
	#ifndef PMAP_SIGUSR
	double partNumEmit;
	unsigned long partEmitCnt;
	#endif
	/* Get photon origin within current source partishunn
	* and build emission map */
	photonOrigin [emap.src -> so -> otype] (&emap);
	initPhotonEmission(&emap, pdfSamples);

	/* Number of photons to emit from ziss partishunn;
	* scale according to its normalised contribushunn to
	* the emitted source flux */
	partNumEmit = (srcNumEmit * colorAvg(emap.partFlux) /
	srcFlux [srcIdx]
	);
	partEmitCnt = (unsigned long)partNumEmit;

	/* Probabilistically account for fractional photons */
	if (pmapRandom(cntState) < partNumEmit - partEmitCnt)
	partEmitCnt++;

	/* Integer counter avoids FP rounding errors during
	* iteration */
	while (partEmitCnt--) {
	RAY photonRay;

	/* Emit photon according to PDF (if any). If
	* accepted, allocate associated contribution
	* origin, and trace through scene until
	* absorbed/leaked; emitPhoton() sets the emitting
	* light source index in photonRay */
	/* NOTE: rejection sampling skips incrementing the
	* emission counter (see below), thus compensating
	* for the rejected photons by increasing the photon
	* flux in proportion to the lower effective
	* emission count.
	* BUG: THIS INTERFERES WITH THE PROGRESS COUNTER
	* REPORTED TO THE PARENT, AND WITH THE
	* PREDISTRIBUTION PASS --> PHOTON DISTRIBUTION WILL
	* FINISH EARLY, WITH FEWER PHOTONS THAN TARGETTED!
	*/
	if (!emitPhoton(&emap, &photonRay))
	continue;

	newPhotonContribSource(pmap, &photonRay,
	contribSrcHeap [proc]
	);

	/* Update local emission counter */
	numEmitted++;

	/* Skip photon if it has an invalid bin. It will
	implicitly contribute zero flux, so don't bother
	tracing and storing it. However, it counts as
	emitted to avoid bias (see enclosing while() loop
	and local emission counter update above). */
	if (pmap -> lastContribSrc.srcBin < 0)
	continue;

	/* Set subprocess index in photonRay for post-
	* distrib contribution source index linearisation;
	* this is propagated with the contrib source index
	* in photonRay and set for photon hits by
	* newPhoton() */
	PMAP_SETRAYPROC(&photonRay, proc);
	tracePhoton(&photonRay);

	if (!(partEmitCnt && (numEmitted & photonCntUpdate))) {
	/* Update global counters shared with siblings
	in unique intervals to reduce overhead and
	contention;
	ALSO WHEN EMITTING FINAL PHOTON FROM THIS
	PARTITION, OTHERWISE COUNTERS WILL SKIP LAST
	UPDATE, BIASING THE PHOTON FLUX! */
	/* Shared photon counter file must be locked! */
	shmLock(shmFile, F_WRLCK);
	/* Differentially increment number emitted using
	* local counter numEmitted */
	preIncPhotonCnt = photonCnt [numEmitIdx];
	photonCnt [numEmitIdx] +=
	numEmitted - lastNumEmitted;
	lastNumEmitted = numEmitted;

	/* Check overflow using pre-increment values */
	if (photonCnt [numEmitIdx] < preIncPhotonCnt) {
	sprintf(errmsg, "photon emission counter "
	"overflow (was: %ld, is: %ld)",
	preIncPhotonCnt, photonCnt [numEmitIdx]
	);
	error(INTERNAL, errmsg);
	}

	/* Differentially increment photon counter */
	preIncPhotonCnt = photonCnt [PHOTONCNT_NUMPHOT];
	photonCnt [PHOTONCNT_NUMPHOT] +=
	pmap -> numPhotons - lastNumPhotons;
	lastNumPhotons = pmap -> numPhotons;

	/* Check for photon counter overflow (this could
	only happen before an emission counter overflow
	if the scene has an absurdly high albedo and/or
	very dense geometry) */
	if (photonCnt [PHOTONCNT_NUMPHOT] < preIncPhotonCnt) {
	sprintf(errmsg, "photon counter overflow "
	"(was: %ld, is: %ld)", preIncPhotonCnt,
	photonCnt [PHOTONCNT_NUMPHOT]
	);
	error(INTERNAL, errmsg);
	}

	/* Release lock on shared photon counter file! */
	shmLock(shmFile, F_UNLCK);
	}
	}
	#if !NIX
	/* Synchronous progress report on Windoze */
	if (!proc && photonRepTime > 0 &&
	time(NULL) >= repLastTime + photonRepTime
	) {
	unsigned s;
	repComplete = pmap -> distribTarget * numProc;
	repProgress = photonCnt [PHOTONCNT_NUMPHOT];

	for (repEmitted = 0, s = 0; s < nsources; s++)
	repEmitted += photonCnt [numEmitIdx];

	pmapDistribReport();
	}
	#endif
	}

	portCnt++;
	} while (portCnt < numPhotonPorts);

	if (pmap -> numPhotons == srcNumDistrib) {
	/* Double predistrib factor in case no photons were stored
	* for this source and redo pass 1 */
	srcPreDistrib *= 2;
	}
	else {
	/* Now do pass 2 */
	passCnt++;
	}
	}
	}

	/* Flush heap buffa one final time to prevent data corruption */
	flushPhotonHeap(pmap);
	/* Flush last contribution origin to origin heap file */
	newPhotonContribSource(pmap, NULL, contribSrcHeap [proc]);
	/* Heap files closed automatically on exit
	fclose(pmap -> heap);
	fclose(orgHeap [proc]); */
	#ifdef DEBUG_PMAP
	sprintf(
	errmsg, "Proc %d total %ld photons\n", proc, pmap -> numPhotons
	);
	eputs(errmsg);
	fflush(stderr);
	#endif
	#ifdef PMAP_SIGUSR
	signal(SIGUSR1, SIG_DFL);
	#endif
	#if NIX
	/* Terminate subprocess */
	exit(0);
	#endif
	}
	else {
	/* PARENT PROCESS CONTINUES LOOP ITERATION HERE */
	if (pid < 0)
	error(SYSTEM,
	"failed to fork subprocess in distribPhotonContrib()"
	);
	else
	/* Saves child process IDs */
	procPids [proc] = pid;
	}
	}

	#if NIX
	/* PARENT PROCESS CONTINUES HERE */
	#ifdef SIGCONT
	/* Enable progress report signal handler */
	signal(SIGCONT, pmapDistribReport);
	#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 & bail out */
	for (proc = 0; proc < numProc; proc++)
	kill(procPids [proc], SIGKILL);

	/* Unmap shared memory, squish mapped file */
	munmap(photonCnt, sizeof(*photonCnt));
	close(shmFile);
	unlink(shmFname);
	error(USER, "failed photon distribution");
	}

	--proc;
	}

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

	/* Asynchronous progress report from shared subprocess counters */
	shmLock(shmFile, F_RDLCK);
	repProgress = photonCnt [PHOTONCNT_NUMPHOT];
	pmap -> numPhotons = photonCnt [PHOTONCNT_NUMPHOT];

	for (repEmitted = 0, srcIdx = 0; srcIdx < nsources; srcIdx++) {
	repEmitted += photonCnt [PHOTONCNT_NUMEMIT(srcIdx)];
	}

	repComplete = pmap -> distribTarget * numProc;
	shmLock(shmFile, F_UNLCK);

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

	/* ================================================================
	* POST-DISTRIBUTION - Set photon flux and build kd-tree, etc.
	* ================================================================ */
	#ifdef SIGCONT
	/* Reset signal handler */
	signal(SIGCONT, SIG_DFL);
	#endif
	free(emap.samples);

	if (!pmap -> numPhotons)
	error(USER, "empty contribution photon map");

	/* Load per-subprocess contribution sources into pmap -> contribSrc */
	/* Dumb compilers apparently need the char** cast */
	pmap -> numContribSrc = buildContribSources(pmap, contribSrcHeap,
	(char**)contribSrcHeapFname, contribSrcOfs, numProc
	);
	if (!pmap -> numContribSrc)
	error(INTERNAL, "no contribution sources in contribution photon map");

	/* Set photon flux per source, skipping sources that emitted no photons
	* (for whatever reason...) */
	for (srcIdx = 0; srcIdx < nsources; srcIdx++) {
	srcFlux [srcIdx] = photonCnt [PHOTONCNT_NUMEMIT(srcIdx)]
	? srcFlux [srcIdx] / photonCnt [PHOTONCNT_NUMEMIT(srcIdx)]
	: 0;
	}
	#if NIX
	/* Photon counters no longer needed, unmap shared memory */
	munmap(photonCnt, sizeof(*photonCnt));
	close(shmFile);
	unlink(shmFname);
	#else
	free(photonCnt);
	#endif

	if (verbose) {
	eputs("\nBuilding contribution photon map...\n");
	#if NIX
	fflush(stderr);
	#endif
	}

	/* Build underlying data structure; heap is destroyed.
	XXX: Photon flux remains unchanged (i.e. normalised) in coefficient
	mode, so srcFlux is omitted */
	buildPhotonMap(pmap, pmap -> contribMode ? srcFlux : NULL,
	contribSrcOfs, numProc
	);

	/* Precompute binned photon contributions, initialising lookup table
	pmap -> preCompContribTab containing pre-modifier photon maps.
	XXX: maximum photon search radius is scaled by (number of modifiers)^2
	(initialised from squared distance to centre of gravity, CoGdist). */
	if (verbose)
	eputs("\n");
	contribPmap -> CoGdist = (numContribs numContribs);
	preComputeContrib(contribPmap, numProc);

	/* Build parent photon map and its per-modifier children */
	buildContribPhotonMap(pmap);

	/* Free per-subprocess origin heap files
	XXX: Can't we already do this BEFORE calling preComputeContrib() ?*/
	for (proc = 0; proc < numProc; proc++)
	free(contribSrcHeapFname [proc]);

	free(contribSrcHeapFname);
	free(contribSrcHeap);
	free(contribSrcOfs);

	if (verbose)
	eputs("\n");
	}

	#endif /* PMAP_CONTRIB */

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