1 files changed, 7 insertions, 3 deletions

diff --git a/module.cc b/module.cc
index ea59a08..a28dd39 100644
--- a/module.cc
+++ b/module.cc
@@ -249,19 +249,23 @@ CGAL_Nef_polyhedron AbstractNode::render_cgal_nef_polyhedron() const
 
 #endif /* ENABLE_CGAL */
 
-CSGTerm *AbstractNode::render_csg_term(double m[16], QVector<CSGTerm*> *highlights) const
+CSGTerm *AbstractNode::render_csg_term(double m[16], QVector<CSGTerm*> *highlights, QVector<CSGTerm*> *background) const
 {
 	CSGTerm *t1 = NULL;
 	foreach(AbstractNode *v, children) {
-		CSGTerm *t2 = v->render_csg_term(m, highlights);
+		CSGTerm *t2 = v->render_csg_term(m, highlights, background);
 		if (t2 && !t1) {
 			t1 = t2;
 		} else if (t2 && t1) {
 			t1 = new CSGTerm(CSGTerm::UNION, t1, t2);
 		}
 	}
-	if (modinst->tag_highlight && highlights)
+	if (t1 && modinst->tag_highlight && highlights)
 		highlights->append(t1->link());
+	if (t1 && modinst->tag_background && background) {
+		background->append(t1);
+		return NULL;
+	}
 	return t1;
 }