--- ray/src/rt/raytrace.c	1994/01/13 09:45:11	2.11
+++ ray/src/rt/raytrace.c	1994/12/21 09:10:23	2.17
@@ -34,6 +34,8 @@ OBJREC  Lamb = {
 	{0, 5, NULL, Lambfa}, NULL,
 };					/* a Lambertian surface */
 
+OBJREC  Aftplane;			/* aft clipping plane object */
+
 static int  raymove(), checkset(), checkhit();
 
 #define  MAXLOOP	128		/* modifier loop detection */
@@ -67,6 +69,7 @@ double  rw;
 		r->rweight = ro->rweight * rw;
 		r->crtype = ro->crtype | (r->rtype = rt);
 		VCOPY(r->rorg, ro->rop);
+		r->rmax = 0.0;
 	}
 	rayclear(r);
 	return(r->rlvl <= maxdepth && r->rweight >= minweight ? 0 : -1);
@@ -95,10 +98,13 @@ RAY  *r;
 
 	if (localhit(r, &thescene))
 		gotmat = raycont(r);
-	else if (sourcehit(r))
+	else if (r->ro == &Aftplane) {
+		r->ro = NULL;
+		r->rot = FHUGE;
+	} else if (sourcehit(r))
 		gotmat = rayshade(r, r->ro->omod);
 
-	if (!gotmat)
+	if (r->ro != NULL && !gotmat)
 		objerror(r->ro, USER, "material not found");
 
 	if (trace != NULL)
@@ -125,6 +131,8 @@ register RAY  *r;
 
 	if (rayorigin(&tr, r, TRANS, 1.0) == 0) {
 		VCOPY(tr.rdir, r->rdir);
+		if (r->rmax > FTINY)
+			tr.rmax = r->rmax - r->rot;
 		rayvalue(&tr);
 		copycolor(r->rcol, tr.rcol);
 		r->rt = r->rot + tr.rt;
@@ -156,7 +164,7 @@ int  mod;
 			if (irr_ignore(m->otype)) {
 				depth--;
 				raytrans(r);
-				return;
+				return(1);
 			}
 			if (!islight(m->otype))
 				m = &Lamb;
@@ -200,7 +208,6 @@ OBJECT  fore, back;
 double  coef;
 {
 	RAY  fr, br;
-	COLOR  ctmp;
 	int  foremat, backmat;
 	register int  i;
 					/* clip coefficient */
@@ -208,43 +215,42 @@ double  coef;
 		coef = 1.0;
 	else if (coef < 0.0)
 		coef = 0.0;
+					/* compute foreground and background */
+	foremat = backmat = -1;
 					/* foreground */
 	copystruct(&fr, r);
-	fr.pert[0] = fr.pert[1] = fr.pert[2] = 0.0;
-	setcolor(fr.pcol, 1.0, 1.0, 1.0);
-	setcolor(fr.rcol, 0.0, 0.0, 0.0);
 	if (fore != OVOID && coef > FTINY)
 		foremat = rayshade(&fr, fore);
-	else
-		foremat = 0;
 					/* background */
 	copystruct(&br, r);
-	br.pert[0] = br.pert[1] = br.pert[2] = 0.0;
-	setcolor(br.pcol, 1.0, 1.0, 1.0);
-	setcolor(br.rcol, 0.0, 0.0, 0.0);
 	if (back != OVOID && coef < 1.0-FTINY)
 		backmat = rayshade(&br, back);
-	else
-		backmat = foremat;
 					/* check */
-	if ((backmat==0) != (foremat==0))
+	if (foremat < 0)
+		if (backmat < 0)
+			foremat = backmat = 0;
+		else
+			foremat = backmat;
+	else if (backmat < 0)
+		backmat = foremat;
+	if ((foremat==0) != (backmat==0))
 		objerror(r->ro, USER, "mixing material with non-material");
-					/* sum perturbations */
+					/* mix perturbations */
 	for (i = 0; i < 3; i++)
-		r->pert[i] += coef*fr.pert[i] + (1.0-coef)*br.pert[i];
-					/* multiply pattern colors */
+		r->pert[i] = coef*fr.pert[i] + (1.0-coef)*br.pert[i];
+					/* mix pattern colors */
 	scalecolor(fr.pcol, coef);
 	scalecolor(br.pcol, 1.0-coef);
-	copycolor(ctmp, fr.pcol);
-	addcolor(ctmp, br.pcol);
-	multcolor(r->pcol, ctmp);
-					/* sum returned ray values */
-	scalecolor(fr.rcol, coef);
-	scalecolor(br.rcol, 1.0-coef);
-	addcolor(r->rcol, fr.rcol);
-	addcolor(r->rcol, br.rcol);
-	if (foremat)
+	copycolor(r->pcol, fr.pcol);
+	addcolor(r->pcol, br.pcol);
+					/* mix returned ray values */
+	if (foremat) {
+		scalecolor(fr.rcol, coef);
+		scalecolor(br.rcol, 1.0-coef);
+		copycolor(r->rcol, fr.rcol);
+		addcolor(r->rcol, br.rcol);
 		r->rt = bright(fr.rcol) > bright(br.rcol) ? fr.rt : br.rt;
+	}
 					/* return value tells if material */
 	return(foremat);
 }
@@ -355,6 +361,14 @@ register CUBE  *scene;
 	}
 	if (sflags == 0)
 		error(CONSISTENCY, "zero ray direction in localhit");
+					/* start off assuming nothing hit */
+	if (r->rmax > FTINY) {		/* except aft plane if one */
+		r->ro = &Aftplane;
+		r->rot = r->rmax;
+		for (i = 0; i < 3; i++)
+			r->rop[i] = r->rorg[i] + r->rot*r->rdir[i];
+	}
+					/* find global cube entrance point */
 	t = 0.0;
 	if (!incube(scene, curpos)) {
 					/* find distance to entry */
@@ -372,6 +386,8 @@ register CUBE  *scene;
 				t = dt;	/* farthest face is the one */
 		}
 		t += FTINY;		/* fudge to get inside cube */
+		if (t >= r->rot)	/* clipped already */
+			return(0);
 					/* advance position */
 		for (i = 0; i < 3; i++)
 			curpos[i] += r->rdir[i]*t;
@@ -380,7 +396,8 @@ register CUBE  *scene;
 			return(0);
 	}
 	cxset[0] = 0;
-	return(raymove(curpos, cxset, sflags, r, scene) == RAYHIT);
+	return(raymove(curpos, cxset, sflags, r, scene) == RAYHIT &&
+			r->ro != &Aftplane);
 }