--- ray/src/hd/rhdisp3.c	1997/11/20 16:43:42	3.3
+++ ray/src/hd/rhdisp3.c	1997/11/21 18:17:37	3.4
@@ -12,7 +12,12 @@ static char SCCSid[] = "$SunId$ SGI";
 #include "rhdisp.h"
 #include "view.h"
 
+struct cellist {
+	GCOORD	*cl;
+	int	n;
+};
 
+
 int
 npixels(vp, hr, vr, hp, bi)	/* compute appropriate number to evaluate */
 VIEW	*vp;
@@ -20,6 +25,8 @@ int	hr, vr;
 HOLO	*hp;
 int	bi;
 {
+	static VIEW	vdo, vlast;
+	static HOLO	*hplast;
 	GCOORD	gc[2];
 	FVECT	cp[4];
 	FVECT	ip[4];
@@ -28,9 +35,21 @@ int	bi;
 					/* compute cell corners in image */
 	if (!hdbcoord(gc, hp, bi))
 		error(CONSISTENCY, "bad beam index in npixels");
-	hdcell(cp, hp, gc+1);
+					/* has holodeck or view changed? */
+	if (hp != hplast || bcmp((char *)vp, (char *)&vlast, sizeof(VIEW))) {
+		copystruct(&vdo, vp);
+		if (sect_behind(hp, &vdo)) {	/* reverse view sense */
+			vdo.vdir[0] = -vdo.vdir[0];
+			vdo.vdir[1] = -vdo.vdir[1];
+			vdo.vdir[2] = -vdo.vdir[2];
+			setview(&vdo);
+		}
+		hplast = hp;
+		copystruct(&vlast, vp);
+	}
+	hdcell(cp, hp, gc+1);		/* find cell on image */
 	for (i = 0; i < 4; i++) {
-		viewloc(ip[i], vp, cp[i]);
+		viewloc(ip[i], &vdo, cp[i]);
 		if (ip[i][2] < 0.)
 			return(0);
 		ip[i][0] *= (double)hr;	/* scale by resolution */
@@ -118,13 +137,66 @@ char	*dp;
 }
 
 
+sect_behind(hp, vp)		/* check if section is "behind" viewpoint */
+register HOLO	*hp;
+register VIEW	*vp;
+{
+	FVECT	hcent;
+					/* compute holodeck section center */
+	VSUM(hcent, hp->orig, hp->xv[0], 0.5);
+	VSUM(hcent, hcent, hp->xv[1], 0.5);
+	VSUM(hcent, hcent, hp->xv[2], 0.5);
+					/* behind if center is behind */
+	return(DOT(vp->vdir,hcent) < DOT(vp->vdir,vp->vp));
+}
+
+
+viewpyramid(org, dir, hp, vp)	/* compute view pyramid */
+FVECT	org, dir[4];
+HOLO	*hp;
+VIEW	*vp;
+{
+	register int	i;
+					/* check view type */
+	if (vp->type == VT_PAR)
+		return(0);
+					/* in front or behind? */
+	if (!sect_behind(hp, vp)) {
+		if (viewray(org, dir[0], vp, 0., 0.) < -FTINY)
+			return(0);
+		if (viewray(org, dir[1], vp, 0., 1.) < -FTINY)
+			return(0);
+		if (viewray(org, dir[2], vp, 1., 1.) < -FTINY)
+			return(0);
+		if (viewray(org, dir[3], vp, 1., 0.) < -FTINY)
+			return(0);
+		return(1);
+	}				/* reverse pyramid */
+	if (viewray(org, dir[3], vp, 0., 0.) < -FTINY)
+		return(0);
+	if (viewray(org, dir[2], vp, 0., 1.) < -FTINY)
+		return(0);
+	if (viewray(org, dir[1], vp, 1., 1.) < -FTINY)
+		return(0);
+	if (viewray(org, dir[0], vp, 1., 0.) < -FTINY)
+		return(0);
+	for (i = 0; i < 3; i++) {
+		dir[0][i] = -dir[0][i];
+		dir[1][i] = -dir[1][i];
+		dir[2][i] = -dir[2][i];
+		dir[3][i] = -dir[3][i];
+	}
+	return(-1);
+}
+
+
 int
 addcell(gcp, cl)		/* add a cell to a list */
 GCOORD	*gcp;
-register int	*cl;
+register struct cellist	*cl;
 {
-	copystruct((GCOORD *)(cl+1) + *cl, gcp);
-	(*cl)++;
+	copystruct(cl->cl+cl->n, gcp);
+	cl->n++;
 	return(1);
 }
 
@@ -143,50 +215,46 @@ register GCOORD	*gcp1, *gcp2;
 }
 
 
-int *
-getviewcells(hp, vp)		/* get ordered cell list for section view */
+GCOORD *
+getviewcells(np, hp, vp)	/* get ordered cell list for section view */
+int	*np;		/* returned number of cells (negative if reversed) */
 register HOLO	*hp;
 VIEW	*vp;
 {
 	FVECT	org, dir[4];
-	int	n;
-	register int	*cl;
+	int	orient;
+	struct cellist	cl;
 					/* compute view pyramid */
-	if (vp->type == VT_PAR) goto viewerr;
-	if (viewray(org, dir[0], vp, 0., 0.) < -FTINY) goto viewerr;
-	if (viewray(org, dir[1], vp, 0., 1.) < -FTINY) goto viewerr;
-	if (viewray(org, dir[2], vp, 1., 1.) < -FTINY) goto viewerr;
-	if (viewray(org, dir[3], vp, 1., 0.) < -FTINY) goto viewerr;
+	*np = 0;
+	orient = viewpyramid(org, dir, hp, vp);
+	if (!orient)
+		return(NULL);
 					/* allocate enough list space */
-	n = 2*(	hp->grid[0]*hp->grid[1] +
-		hp->grid[0]*hp->grid[2] +
-		hp->grid[1]*hp->grid[2]	);
-	cl = (int *)malloc(sizeof(int) + n*sizeof(GCOORD));
-	if (cl == NULL)
+	cl.n = 2*(	hp->grid[0]*hp->grid[1] +
+			hp->grid[0]*hp->grid[2] +
+			hp->grid[1]*hp->grid[2]	);
+	cl.cl = (GCOORD *)malloc(cl.n*sizeof(GCOORD));
+	if (cl.cl == NULL)
 		goto memerr;
-	*cl = 0;
-					/* add cells within pyramid */
-	visit_cells(org, dir, hp, addcell, cl);
-	if (!*cl) {
-		free((char *)cl);
+	cl.n = 0;			/* add cells within pyramid */
+	visit_cells(org, dir, hp, addcell, &cl);
+	if (!cl.n) {
+		free((char *)cl.cl);
 		return(NULL);
 	}
+	*np = cl.n * orient;
 #if 0
 	/* We're just going to free this memory in a moment, and list is
 	 * sorted automatically by visit_cells(), so we don't need this.
 	 */
-	if (*cl < n) {			/* optimize memory use */
-		cl = (int *)realloc((char *)cl,
-				sizeof(int) + *cl*sizeof(GCOORD));
-		if (cl == NULL)
-			goto memerr;
-	}
+					/* optimize memory use */
+	cl.cl = (GCOORD *)realloc((char *)cl.cl, cl.n*sizeof(GCOORD));
+	if (cl.cl == NULL)
+		goto memerr;
 					/* sort the list */
-	qsort((char *)(cl+1), *cl, sizeof(GCOORD), cellcmp);
+	qsort((char *)cl.cl, cl.n, sizeof(GCOORD), cellcmp);
 #endif
-	return(cl);
-viewerr:
-	error(INTERNAL, "unusable view in getviewcells");
+	return(cl.cl);
 memerr:
 	error(SYSTEM, "out of memory in getviewcells");
 }