--- ray/src/rt/ambient.c	1996/07/09 19:37:09	2.39
+++ ray/src/rt/ambient.c	1998/06/17 13:29:55	2.44
@@ -50,13 +50,14 @@ static int  nunflshed = 0;	/* number of unflushed ambi
 #endif
 #endif
 #ifndef SORT_INTVL
-#define SORT_INTVL	(SORT_THRESH*256)
+#define SORT_INTVL	(SORT_THRESH<<1)
 #endif
 #ifndef MAX_SORT_INTVL
-#define MAX_SORT_INTVL	(SORT_INTVL<<4)
+#define MAX_SORT_INTVL	(SORT_INTVL<<6)
 #endif
 
-static COLOR  avsum = BLKCOLOR;		/* computed ambient value sum */
+static double  avsum = 0.;		/* computed ambient value sum (log) */
+static unsigned int  navsum = 0;	/* number of values in avsum */
 static unsigned int  nambvals = 0;	/* total number of indirect values */
 static unsigned int  nambshare = 0;	/* number of values from file */
 static unsigned long  ambclock = 0;	/* ambient access clock */
@@ -69,15 +70,17 @@ static long  sortintvl = SORT_INTVL;	/* time until nex
 	 * through memory on a multiprocessor, when we want to avoid
 	 * claiming our own memory (copy on write).  Go ahead anyway
 	 * if more than two thirds of our values are unshared.
+	 * Compile with -Dtracktime=0 to turn this code off.
 	 */
+#ifndef tracktime
 #define tracktime	(shm_boundary == NULL || nambvals > 3*nambshare)
+#endif
 
 #define	 AMBFLUSH	(BUFSIZ/AMBVALSIZ)
 
 #define	 newambval()	(AMBVAL *)bmalloc(sizeof(AMBVAL))
 
-extern long  ftell(), lseek();
-static int  initambfile(), avsave(), avinsert(), sortambvals();
+static int  initambfile(), avsave(), avinsert(), sortambvals(), avlmemi();
 static AMBVAL  *avstore();
 #ifdef  F_SETLKW
 static  aflock();
@@ -144,9 +147,10 @@ char  *afile;
 		pos += (long)nambvals*AMBVALSIZ;
 		flen = lseek(fileno(ambfp), 0L, 2);
 		if (flen != pos) {
-			error(WARNING,
+			sprintf(errmsg,
 			"ignoring last %ld values in ambient file (corrupted)",
 					(flen - pos)/AMBVALSIZ);
+			error(WARNING, errmsg);
 			fseek(ambfp, pos, 0);
 			ftruncate(fileno(ambfp), pos);
 		}
@@ -190,7 +194,7 @@ register RAY  *r;
 FVECT  nrm;
 {
 	static int  rdepth = 0;			/* ambient recursion */
-	double	d;
+	double	d, l;
 
 	if (ambdiv <= 0)			/* no ambient calculation */
 		goto dumbamb;
@@ -210,8 +214,9 @@ FVECT  nrm;
 			goto dumbamb;
 		return;
 	}
-						/* resort memory? */
-	sortambvals(0);
+
+	if (tracktime)				/* sort to minimize thrashing */
+		sortambvals(0);
 						/* get ambient value */
 	setcolor(acol, 0.0, 0.0, 0.0);
 	d = sumambient(acol, r, nrm, rdepth,
@@ -227,12 +232,18 @@ FVECT  nrm;
 		return;
 dumbamb:					/* return global value */
 	copycolor(acol, ambval);
-	if (ambvwt <= 0 | nambvals == 0)
+	if (ambvwt <= 0 | navsum == 0)
 		return;
-	scalecolor(acol, (double)ambvwt);
-	addcolor(acol, avsum);			/* average in computations */
-	d = 1.0/(ambvwt+nambvals);
-	scalecolor(acol, d);
+	l = bright(ambval);			/* average in computations */
+	if (l > FTINY) {
+		d = (log(l)*(double)ambvwt + avsum) /
+				(double)(ambvwt + navsum);
+		d = exp(d) / l;
+		scalecolor(acol, d);		/* apply color of ambval */
+	} else {
+		d = exp( avsum / (double)navsum );
+		setcolor(acol, d, d, d);	/* neutral color */
+	}
 }
 
 
@@ -257,7 +268,7 @@ double	s;
 					/* do this node */
 	for (av = at->alist; av != NULL; av = av->next) {
 		if (tracktime)
-			av->latick = ambclock++;
+			av->latick = ambclock;
 		/*
 		 *  Ambient level test.
 		 */
@@ -402,10 +413,10 @@ int  creat;
 	setbuf(ambfp, bmalloc(BUFSIZ+8));
 	if (creat) {			/* new file */
 		newheader("RADIANCE", ambfp);
-		fprintf(ambfp, "%s -av %g %g %g -ab %d -aa %g ",
+		fprintf(ambfp, "%s -av %g %g %g -aw %d -ab %d -aa %g ",
 				progname, colval(ambval,RED),
 				colval(ambval,GRN), colval(ambval,BLU),
-				ambounce, ambacc);
+				ambvwt, ambounce, ambacc);
 		fprintf(ambfp, "-ad %d -as %d -ar %d %s\n",
 				ambdiv, ambssamp, ambres,
 				octname==NULL ? "" : octname);
@@ -441,14 +452,19 @@ avstore(aval)				/* allocate memory and store aval */
 register AMBVAL  *aval;
 {
 	register AMBVAL  *av;
+	double	d;
 
 	if ((av = newambval()) == NULL)
 		error(SYSTEM, "out of memory in avstore");
 	copystruct(av, aval);
 	av->latick = ambclock;
 	av->next = NULL;
-	addcolor(avsum, av->val);	/* add to sum for averaging */
 	nambvals++;
+	d = bright(av->val);
+	if (d > FTINY) {		/* add to log sum for averaging */
+		avsum += log(d);
+		navsum++;
+	}
 	return(av);
 }
 
@@ -616,7 +632,7 @@ int	always;
 	AMBVAL	tav, *tap, *pnext;
 	register int	i, j;
 					/* see if it's time yet */
-	if (!always && (ambclock < lastsort+sortintvl ||
+	if (!always && (ambclock++ < lastsort+sortintvl ||
 			nambvals < SORT_THRESH))
 		return;
 	/*