--- ray/src/rt/ambient.c	1992/07/13 16:17:49	2.5
+++ ray/src/rt/ambient.c	1992/07/16 16:47:28	2.10
@@ -42,11 +42,16 @@ static AMBTREE  atrunk;		/* our ambient trunk node */
 
 static FILE  *ambfp = NULL;	/* ambient file pointer */
 
+#define  AMBFLUSH	(BUFSIZ/AMBVALSIZ)
+
 #define  newambval()	(AMBVAL *)bmalloc(sizeof(AMBVAL))
 
 #define  newambtree()	(AMBTREE *)calloc(8, sizeof(AMBTREE))
 
+extern long  ftell(), lseek();
+static int  initambfile(), avsave(), avinsert(), ambsync();
 
+
 setambres(ar)				/* set ambient resolution */
 int  ar;
 {
@@ -68,19 +73,23 @@ int  ar;
 setambient(afile)			/* initialize calculation */
 char  *afile;
 {
-	long  ftell();
+	long  headlen;
 	AMBVAL  amb;
 						/* init ambient limits */
 	setambres(ambres);
 						/* open ambient file */
 	if (afile != NULL)
 		if ((ambfp = fopen(afile, "r+")) != NULL) {
+			initambfile(0);
+			headlen = ftell(ambfp);
 			while (readambval(&amb, ambfp))
 				avinsert(&amb, &atrunk, thescene.cuorg,
 						thescene.cusize);
 							/* align */
-			fseek(ambfp, -(ftell(ambfp)%AMBVALSIZ), 1);
-		} else if ((ambfp = fopen(afile, "w")) == NULL) {
+			fseek(ambfp, -((ftell(ambfp)-headlen)%AMBVALSIZ), 1);
+		} else if ((ambfp = fopen(afile, "w+")) != NULL)
+			initambfile(1);
+		else {
 			sprintf(errmsg, "cannot open ambient file \"%s\"",
 					afile);
 			error(SYSTEM, errmsg);
@@ -264,8 +273,7 @@ int  al;
 	VCOPY(amb.gpos, gp);
 	VCOPY(amb.gdir, gd);
 						/* insert into tree */
-	avinsert(&amb, &atrunk, thescene.cuorg, thescene.cusize);
-	avsave(&amb);				/* write to file */
+	avsave(&amb);				/* and save to file */
 	return(amb.rad);
 }
 
@@ -297,23 +305,46 @@ FVECT  pv, nv;
 
 
 static
-avsave(av)				/* save an ambient value */
+initambfile(creat)		/* initialize ambient file */
+int  creat;
+{
+	extern char  *progname, *octname, VersionID[];
+
+	setbuf(ambfp, bmalloc(BUFSIZ));
+	if (creat) {			/* new file */
+		fprintf(ambfp, "%s -av %g %g %g -ab %d -aa %g ",
+				progname, colval(ambval,RED),
+				colval(ambval,GRN), colval(ambval,BLU),
+				ambounce, ambacc);
+		fprintf(ambfp, "-ad %d -as %d -ar %d %s\n",
+				ambdiv, ambssamp, ambres,
+				octname==NULL ? "" : octname);
+		fprintf(ambfp, "SOFTWARE= %s\n", VersionID);
+		fputformat(AMBFMT, ambfp);
+		putc('\n', ambfp);
+		putambmagic(ambfp);
+		fflush(ambfp);
+	} else if (checkheader(ambfp, AMBFMT, NULL) < 0 || !hasambmagic(ambfp))
+		error(USER, "bad ambient file");
+}
+
+
+static
+avsave(av)				/* insert and save an ambient value */
 AMBVAL  *av;
 {
-#ifdef  AMBFLUSH
 	static int  nunflshed = 0;
-#endif
+
+	avinsert(av, &atrunk, thescene.cuorg, thescene.cusize);
 	if (ambfp == NULL)
 		return;
 	if (writambval(av, ambfp) < 0)
 		goto writerr;
-#ifdef  AMBFLUSH
 	if (++nunflshed >= AMBFLUSH) {
-		if (fflush(ambfp) == EOF)
+		if (ambsync() == EOF)
 			goto writerr;
 		nunflshed = 0;
 	}
-#endif
 	return;
 writerr:
 	error(SYSTEM, "error writing ambient file");
@@ -355,3 +386,57 @@ double  s;
 memerr:
 	error(SYSTEM, "out of memory in avinsert");
 }
+
+
+#ifdef  NIX
+
+static
+ambsync()			/* flush ambient file */
+{
+	return(fflush(ambfp));
+}
+
+#else
+
+#include  <fcntl.h>
+#include  <sys/types.h>
+#include  <sys/stat.h>
+
+static
+ambsync()			/* synchronize ambient file */
+{
+	static FILE  *ambinp = NULL;
+	struct flock  fls;
+	struct stat  sts;
+	AMBVAL  avs;
+	long  lastpos, flen;
+	register int  n;
+				/* gain exclusive access */
+	fls.l_type = F_WRLCK;
+	fls.l_whence = 0;
+	fls.l_start = 0L;
+	fls.l_len = 0L;
+	if (fcntl(fileno(ambfp), F_SETLKW, &fls) < 0)
+		error(SYSTEM, "cannot lock ambient file");
+				/* see if file has grown */
+	lastpos = lseek(fileno(ambfp), 0L, 1);	/* get previous position */
+	if (fstat(fileno(ambfp), &sts) < 0)	/* get current length */
+		error(SYSTEM, "cannot stat ambient file");
+	flen = sts.st_size;
+	if (n = (flen - lastpos)/AMBVALSIZ) {	/* file has grown */
+		if (ambinp == NULL)		/* use duplicate file */
+			ambinp = fdopen(dup(fileno(ambfp)), "r");
+		while (n--) {			/* load contributed values */
+			readambval(&avs, ambinp);
+			avinsert(&avs,&atrunk,thescene.cuorg,thescene.cusize);
+		}				/* moves shared file pointer */
+		if (n = (flen - lastpos)%AMBVALSIZ)	/* alignment */
+			lseek(fileno(ambfp), flen-n, 0);
+	}
+	n = fflush(ambfp);			/* calls write() at last */
+	fls.l_type = F_UNLCK;			/* release file */
+	fcntl(fileno(ambfp), F_SETLKW, &fls);
+	return(n);
+}
+
+#endif