bsp construction doesn't crash any more

[dosdemo] / src / bsptree.c

diff --git a/src/bsptree.c b/src/bsptree.c
index dc8f2af..e9353d1 100644 (file)
--- a/src/bsptree.c
+++ b/src/bsptree.c
@@ -172,17 +172,38 @@ static struct bspnode *new_node(struct g3d_vertex *v, int vnum)
 static struct bspnode *add_poly_tree(struct bspnode *n, struct g3d_vertex *v, int vnum)
 {
        struct bspnode *nres;
-       int clipres, clipped_vnum;
-       struct g3d_vertex *clipped;
+       int clipres, clipres_neg, clipped_vnum, clipped_neg_vnum;
+       struct g3d_vertex *clipped, *clipped_neg;
        struct cplane negplane;
 
+       assert(vnum > 0);
+
        if(!n) {
                return new_node(v, vnum);
        }
 
-       clipped = alloca((vnum + 1) * sizeof *clipped);
+       negplane.x = n->plane.x;
+       negplane.y = n->plane.y;
+       negplane.z = n->plane.z;
+       negplane.nx = -n->plane.nx;
+       negplane.ny = -n->plane.ny;
+       negplane.nz = -n->plane.nz;
+
+       clipped = alloca((vnum * 2) * sizeof *clipped);
+       clipped_neg = alloca((vnum * 2) * sizeof *clipped_neg);
 
        clipres = clip_poly(clipped, &clipped_vnum, v, vnum, &n->plane);
+       clipres_neg = clip_poly(clipped_neg, &clipped_neg_vnum, v, vnum, &negplane);
+
+       /* detect edge cases where due to floating point imprecision, clipping
+        * by the positive plane clips the polygon, but clipping by the negative
+        * plane doesn't. If that happens, consider the polygon completely on
+        * the side indicated by -clipres_neg
+        */
+       if(clipres == 0 && clipres_neg != 0) {
+               clipres = -clipres_neg;
+       }
+
        if(clipres > 0) {
                /* polygon completely in the positive subspace */
                if(!(nres = add_poly_tree(n->front, v, vnum))) {
@@ -204,17 +225,7 @@ static struct bspnode *add_poly_tree(struct bspnode *n, struct g3d_vertex *v, in
                }
                n->front = nres;
 
-               negplane.x = n->plane.x;
-               negplane.y = n->plane.y;
-               negplane.z = n->plane.z;
-               negplane.nx = -n->plane.nx;
-               negplane.ny = -n->plane.ny;
-               negplane.nz = -n->plane.nz;
-
-               clipres = clip_poly(clipped, &clipped_vnum, v, vnum, &negplane);
-               /*assert(clipres == 0);*/
-
-               if(!(nres = add_poly_tree(n->back, clipped, clipped_vnum))) {
+               if(!(nres = add_poly_tree(n->back, clipped_neg, clipped_neg_vnum))) {
                        return 0;
                }
                n->back = nres;