diff --git a/poly2d/f2d_tri_holes.cpp b/poly2d/f2d_tri_holes.cpp
index e8406bd..e5fc7df 100644
--- a/poly2d/f2d_tri_holes.cpp
+++ b/poly2d/f2d_tri_holes.cpp
@@ -186,31 +186,40 @@ static struct f2d *make_face(CDT::Finite_faces_iterator fit,
     const struct p2d *p, const struct p2d *holes)
 {
 	struct f2d *f;
+	const struct v2d *v[3];
 	const struct p2d *h;
-	int i;
+	int i, j;
 
-	f = alloc_type(struct f2d);
 	for (i = 0; i != 3; i++) {
 		Point point = fit->vertex(i)->point();
 		const struct v2d *m;
 
 		m = find_point(p, point.x(), point.y());
 		if (m) {
-			f->v[i] = m;
-			f->p[i] = p;
+			v[i] = m;
 			continue;
 		}
 		for (h = holes; h; h = h->next) {
 			m = find_point(h, point.x(), point.y());
 			if (!m)
 				continue;
-			f->v[i] = m;
-			f->p[i] = h;
+			v[i] = m;
 			break;
 		}
 		assert(m);
 	}
+
+	f = alloc_type(struct f2d);
+	for (i = 0; i != 3; i++) {
+		f->x[i] = v[i]->x;
+		f->y[i] = v[i]->y;
+		j = i+1;
+		if (j == 3)
+			j = 0;
+		f->side[i] = v[i]->next == v[j] || v[j]->next == v[i];
+	}
 	f->next = NULL;
+	
 	return f;
 }
 
diff --git a/poly2d/poly2d.h b/poly2d/poly2d.h
index e802386..407994f 100644
--- a/poly2d/poly2d.h
+++ b/poly2d/poly2d.h
@@ -14,6 +14,7 @@
 #ifndef POLY2D_H
 #define POLY2D_H
 
+#include <stdbool.h>
 #include <stdio.h>
 
 
@@ -30,8 +31,9 @@ struct p2d {
 };
 
 struct f2d {
-	const struct v2d *v[3];	/* vertices forming the face */
-	const struct p2d *p[3];	/* polygons vertices belong to */
+	double x[3];	/* vertices forming the face */
+	double y[3];
+	bool side[3];	/* side[i] if v[i] and v[(i+1) mod 3] are on polygon */
 	struct f2d *next;
 };