perf(rpict,rtrace,rcontrib): changed shadow test to always check firs…

…t 2 sources

src/rt/source.c

@@ -1,5 +1,5 @@
 #ifndef lint
-static const char RCSid[] = "$Id: source.c,v 2.73 2020/07/03 00:42:20 greg Exp $";
+static const char RCSid[] = "$Id: source.c,v 2.74 2020/12/17 03:30:37 greg Exp $";
 #endif
 /*
  *  source.c - routines dealing with illumination sources.
@@ -477,19 +477,17 @@ direct(					/* add direct component */
 						/* compute number to check */
 	nshadcheck = pow((double)ncnts, shadcert) + .5;
 						/* modify threshold */
-	if (ncnts > MINSHADCNT)
-		ourthresh = shadthresh / r->rweight;
-	else
-		ourthresh = 0;
+	ourthresh = shadthresh / r->rweight;
 						/* test for shadows */
 	for (nhits = 0, hwt = 0.0, sn = 0; sn < ncnts;
 			hwt += (double)source[scp->sno].nhits /
 				(double)source[scp->sno].ntests,
 			sn++) {
 						/* check threshold */
-		if ((sn+nshadcheck>=ncnts ? cntord[sn].brt :
+		if (sn >= MINSHADCNT &&
+			    (sn+nshadcheck>=ncnts ? cntord[sn].brt :
 				cntord[sn].brt-cntord[sn+nshadcheck].brt)
-				< ourthresh*bright(r->rcol))
+					< ourthresh*bright(r->rcol))
 			break;
 		scp = srccnt + cntord[sn].sndx;
 						/* test for hit */

src/rt/source.h

@@ -1,4 +1,4 @@
-/* RCSid $Id: source.h,v 2.21 2020/04/06 21:09:07 greg Exp $ */
+/* RCSid $Id: source.h,v 2.22 2020/12/17 03:30:37 greg Exp $ */
 /*
  *  source.h - header file for ray tracing sources.
  *
@@ -20,7 +20,7 @@ extern "C" {
 #define  SHADCACHE	20		/* shadow cache resolution */
 #endif
 #ifndef  MINSHADCNT
-#define  MINSHADCNT	4		/* test all sources if this few */
+#define  MINSHADCNT	2		/* test at least this many shadows */
 #endif
 
 #define  SDISTANT	01		/* source distant flag */