Don't just ignore geometric nodes having zero volume/area - when doing difference/intersection, they tend to turn negative objects into positive ones. Fixes #221

11 files changed, 113 insertions, 106 deletions

diff --git a/src/CGALEvaluator.cc b/src/CGALEvaluator.cc
index a4744c2..4deb3b3 100644
--- a/src/CGALEvaluator.cc
+++ b/src/CGALEvaluator.cc
@@ -61,14 +61,16 @@ void CGALEvaluator::process(CGAL_Nef_polyhedron &target, const CGAL_Nef_polyhedr
  	if (target.dim != 2 && target.dim != 3) {
  		assert(false && "Dimension of Nef polyhedron must be 2 or 3");
  	}
-	if (src.empty()) return; // Empty polyhedron. This can happen for e.g. square([0,0])
+	if (src.isEmpty()) return; // Empty polyhedron. This can happen for e.g. square([0,0])
+	if (target.isEmpty() && op != CGE_UNION) return; // empty op <something> => empty
 	if (target.dim != src.dim) return; // If someone tries to e.g. union 2d and 3d objects
 
 	CGAL::Failure_behaviour old_behaviour = CGAL::set_error_behaviour(CGAL::THROW_EXCEPTION);
 	try {
 		switch (op) {
 		case CGE_UNION:
-			target += src;
+			if (target.isEmpty()) target = src.copy();
+			else target += src;
 			break;
 		case CGE_INTERSECTION:
 			target *= src;
@@ -110,7 +112,8 @@ CGAL_Nef_polyhedron CGALEvaluator::applyToChildren(const AbstractNode &node, CGA
 		if (!isCached(*chnode)) {
 			CGALCache::instance()->insert(this->tree.getIdString(*chnode), chN);
 		}
-		if (N.empty()) N = chN.copy();
+		// Initialize N on first iteration with first expected geometric object
+		if (N.isNull() && !N.isEmpty()) N = chN.copy();
 		else process(N, chN, op);
 
 		chnode->progress_report();
@@ -245,7 +248,6 @@ Response CGALEvaluator::visit(State &state, const TransformNode &node)
 		if (!isCached(node)) {
 			// First union all children
 			N = applyToChildren(node, CGE_UNION);
-
 			if ( matrix_contains_infinity( node.matrix ) || matrix_contains_nan( node.matrix ) ) {
 				// due to the way parse/eval works we can't currently distinguish between NaN and Inf
 				PRINT("Warning: Transformation matrix contains Not-a-Number and/or Infinity - removing object.");
@@ -253,51 +255,53 @@ Response CGALEvaluator::visit(State &state, const TransformNode &node)
 			}
 
 			// Then apply transform
-			// If there is no geometry under the transform, N will be empty and of dim 0,
-			// just just silently ignore such nodes
-			if (N.dim == 2) {
-				// Unfortunately CGAL provides no transform method for CGAL_Nef_polyhedron2
-				// objects. So we convert in to our internal 2d data format, transform it,
-				// tesselate it and create a new CGAL_Nef_polyhedron2 from it.. What a hack!
-				
-				Eigen::Matrix2f testmat;
-				testmat << node.matrix(0,0), node.matrix(0,1), node.matrix(1,0), node.matrix(1,1);
-				if (testmat.determinant() == 0) {
-					PRINT("Warning: Scaling a 2D object with 0 - removing object");
-					N.reset();
-				}
-				else {
-					CGAL_Aff_transformation2 t(
-						node.matrix(0,0), node.matrix(0,1), node.matrix(0,3),
-						node.matrix(1,0), node.matrix(1,1), node.matrix(1,3), node.matrix(3,3));
+			// If there is no geometry under the transform, N will be empty
+			// just silently ignore such nodes
+			if (!N.isNull()) {
+				if (N.dim == 2) {
+					// Unfortunately CGAL provides no transform method for CGAL_Nef_polyhedron2
+					// objects. So we convert in to our internal 2d data format, transform it,
+					// tesselate it and create a new CGAL_Nef_polyhedron2 from it.. What a hack!
 					
-					DxfData *dd = N.convertToDxfData();
-					for (size_t i=0; i < dd->points.size(); i++) {
-						CGAL_Kernel2::Point_2 p = CGAL_Kernel2::Point_2(dd->points[i][0], dd->points[i][1]);
-						p = t.transform(p);
-						dd->points[i][0] = to_double(p.x());
-						dd->points[i][1] = to_double(p.y());
+					Eigen::Matrix2f testmat;
+					testmat << node.matrix(0,0), node.matrix(0,1), node.matrix(1,0), node.matrix(1,1);
+					if (testmat.determinant() == 0) {
+						PRINT("Warning: Scaling a 2D object with 0 - removing object");
+						N.reset();
+					}
+					else {
+						CGAL_Aff_transformation2 t(
+							node.matrix(0,0), node.matrix(0,1), node.matrix(0,3),
+							node.matrix(1,0), node.matrix(1,1), node.matrix(1,3), node.matrix(3,3));
+						
+						DxfData *dd = N.convertToDxfData();
+						for (size_t i=0; i < dd->points.size(); i++) {
+							CGAL_Kernel2::Point_2 p = CGAL_Kernel2::Point_2(dd->points[i][0], dd->points[i][1]);
+							p = t.transform(p);
+							dd->points[i][0] = to_double(p.x());
+							dd->points[i][1] = to_double(p.y());
+						}
+						
+						PolySet ps;
+						ps.is2d = true;
+						dxf_tesselate(&ps, *dd, 0, true, false, 0);
+						
+						N = evaluateCGALMesh(ps);
+						delete dd;
 					}
-					
-					PolySet ps;
-					ps.is2d = true;
-					dxf_tesselate(&ps, *dd, 0, true, false, 0);
-					
-					N = evaluateCGALMesh(ps);
-					delete dd;
-				}
-			}
-			else if (N.dim == 3) {
-				if (node.matrix.matrix().determinant() == 0) {
-					PRINT("Warning: Scaling a 3D object with 0 - removing object");
-					N.reset();
 				}
-				else {
-					CGAL_Aff_transformation t(
-						node.matrix(0,0), node.matrix(0,1), node.matrix(0,2), node.matrix(0,3),
-						node.matrix(1,0), node.matrix(1,1), node.matrix(1,2), node.matrix(1,3),
-						node.matrix(2,0), node.matrix(2,1), node.matrix(2,2), node.matrix(2,3), node.matrix(3,3));
-					N.p3->transform(t);
+				else if (N.dim == 3) {
+					if (node.matrix.matrix().determinant() == 0) {
+						PRINT("Warning: Scaling a 3D object with 0 - removing object");
+						N.reset();
+					}
+					else {
+						CGAL_Aff_transformation t(
+							node.matrix(0,0), node.matrix(0,1), node.matrix(0,2), node.matrix(0,3),
+							node.matrix(1,0), node.matrix(1,1), node.matrix(1,2), node.matrix(1,3),
+							node.matrix(2,0), node.matrix(2,1), node.matrix(2,2), node.matrix(2,3), node.matrix(3,3));
+						N.p3->transform(t);
+					}
 				}
 			}
 		}
@@ -388,7 +392,7 @@ void CGALEvaluator::addToParent(const State &state, const AbstractNode &node, co
 
 CGAL_Nef_polyhedron CGALEvaluator::evaluateCGALMesh(const PolySet &ps)
 {
-	if (ps.empty()) return CGAL_Nef_polyhedron();
+	if (ps.empty()) return CGAL_Nef_polyhedron(ps.is2d ? 2 : 3);
 
 	if (ps.is2d)
 	{
diff --git a/src/CGALRenderer.cc b/src/CGALRenderer.cc
index adf1217..4357e44 100644
--- a/src/CGALRenderer.cc
+++ b/src/CGALRenderer.cc
@@ -43,7 +43,11 @@
 
 CGALRenderer::CGALRenderer(const CGAL_Nef_polyhedron &root) : root(root)
 {
-	if (root.dim == 2) {
+	if (this->root.isNull()) {
+		this->polyhedron = NULL;
+		this->polyset = NULL;
+	}
+	else if (root.dim == 2) {
 		DxfData *dd = root.convertToDxfData();
 		this->polyhedron = NULL;
 		this->polyset = new PolySet();
@@ -67,10 +71,6 @@ CGALRenderer::CGALRenderer(const CGAL_Nef_polyhedron &root) : root(root)
 		CGAL::OGL::Nef3_Converter<CGAL_Nef_polyhedron3>::convert_to_OGLPolyhedron(*this->root.p3, this->polyhedron);
 		this->polyhedron->init();
 	}
-	else {
-		this->polyhedron = NULL;
-		this->polyset = NULL;
-	}
 }
 
 CGALRenderer::~CGALRenderer()
@@ -81,6 +81,7 @@ CGALRenderer::~CGALRenderer()
 
 void CGALRenderer::draw(bool showfaces, bool showedges) const
 {
+	if (this->root.isNull()) return;
 	if (this->root.dim == 2) {
 		// Draw 2D polygons
 		glDisable(GL_LIGHTING);
diff --git a/src/CGAL_Nef_polyhedron.cc b/src/CGAL_Nef_polyhedron.cc
index ad2e4e2..8906595 100644
--- a/src/CGAL_Nef_polyhedron.cc
+++ b/src/CGAL_Nef_polyhedron.cc
@@ -61,7 +61,7 @@ CGAL_Nef_polyhedron &CGAL_Nef_polyhedron::minkowski(const CGAL_Nef_polyhedron &o
 
 int CGAL_Nef_polyhedron::weight() const
 {
-	if (this->empty()) return 0;
+	if (this->isNull()) return 0;
 
 	size_t memsize = sizeof(CGAL_Nef_polyhedron);
 	if (this->dim == 2) {
@@ -84,8 +84,7 @@ int CGAL_Nef_polyhedron::weight() const
 */
 PolySet *CGAL_Nef_polyhedron::convertToPolyset()
 {
-	if (this->empty())
-		return new PolySet();
+	if (this->isNull()) return new PolySet();
 	PolySet *ps = NULL;
 	if (this->dim == 2) {
 		ps = new PolySet();
diff --git a/src/CGAL_Nef_polyhedron.h b/src/CGAL_Nef_polyhedron.h
index e8c505b..d949a2a 100644
--- a/src/CGAL_Nef_polyhedron.h
+++ b/src/CGAL_Nef_polyhedron.h
@@ -8,12 +8,15 @@
 class CGAL_Nef_polyhedron
 {
 public:
-	CGAL_Nef_polyhedron() : dim(0) {}
+	CGAL_Nef_polyhedron(int dim = 0) : dim(dim) {}
 	CGAL_Nef_polyhedron(CGAL_Nef_polyhedron2 *p);
 	CGAL_Nef_polyhedron(CGAL_Nef_polyhedron3 *p);
 	~CGAL_Nef_polyhedron() {}
 
-	bool empty() const { return (dim == 0 || (!p2 && !p3)); }
+  // Empty means it is a geometric node which has zero area/volume
+	bool isEmpty() const { return (dim > 0 && !p2 && !p3); }
+  // Null means the node doesn't contain any geometry (for whatever reason)
+	bool isNull() const { return !p2 && !p3; }
 	void reset() { dim=0; p2.reset(); p3.reset(); }
 	CGAL_Nef_polyhedron &operator+=(const CGAL_Nef_polyhedron &other);
 	CGAL_Nef_polyhedron &operator*=(const CGAL_Nef_polyhedron &other);
diff --git a/src/PolySetCGALEvaluator.cc b/src/PolySetCGALEvaluator.cc
index 8e08e19..224e657 100644
--- a/src/PolySetCGALEvaluator.cc
+++ b/src/PolySetCGALEvaluator.cc
@@ -134,11 +134,11 @@ PolySet *PolySetCGALEvaluator::evaluatePolySet(const ProjectionNode &node)
 		if (v->modinst->isBackground()) continue;
 		CGAL_Nef_polyhedron N = this->cgalevaluator.evaluateCGALMesh(*v);
 		if (N.dim == 3) {
-			if (sum.empty()) sum = N.copy();
+			if (sum.isNull()) sum = N.copy();
 			else sum += N;
 		}
 	}
-	if (sum.empty()) return NULL;
+	if (sum.isNull()) return NULL;
 	if (!sum.p3->is_simple()) {
 		if (!node.cut_mode) {
 			PRINT("WARNING: Body of projection(cut = false) isn't valid 2-manifold! Modify your design..");
@@ -149,7 +149,7 @@ PolySet *PolySetCGALEvaluator::evaluatePolySet(const ProjectionNode &node)
 	//std::cout << sum.dump();
 	//std::cout.flush();
 
-	CGAL_Nef_polyhedron nef_poly;
+	CGAL_Nef_polyhedron nef_poly(2);
 
 	if (node.cut_mode) {
 		CGAL::Failure_behaviour old_behaviour = CGAL::set_error_behaviour(CGAL::THROW_EXCEPTION);
@@ -180,7 +180,7 @@ PolySet *PolySetCGALEvaluator::evaluatePolySet(const ProjectionNode &node)
 			}
 		}
 
-		if ( sum.p3->is_empty() ) {
+		if (sum.p3->is_empty()) {
 			CGAL::set_error_behaviour(old_behaviour);
 			PRINT("WARNING: projection() failed.");
 			return NULL;
@@ -204,7 +204,6 @@ PolySet *PolySetCGALEvaluator::evaluatePolySet(const ProjectionNode &node)
 				log << "<!-- volume end. -->\n";
 			}
 			nef_poly.p2 = zremover.output_nefpoly2d;
-			nef_poly.dim = 2;
 		}	catch (const CGAL::Failure_exception &e) {
 			PRINTB("CGAL error in projection node while flattening: %s", e.what());
 		}
@@ -284,8 +283,7 @@ PolySet *PolySetCGALEvaluator::evaluatePolySet(const ProjectionNode &node)
 					plist.push_back(p);
 			}
 			// FIXME: Should the CGAL_Nef_polyhedron2 be cached?
-			if (nef_poly.empty()) {
-				nef_poly.dim = 2;
+			if (nef_poly.isEmpty()) {
 				nef_poly.p2.reset(new CGAL_Nef_polyhedron2(plist.begin(), plist.end(), CGAL_Nef_polyhedron2::INCLUDED));
 			}
 			else {
@@ -385,18 +383,18 @@ PolySet *PolySetCGALEvaluator::evaluatePolySet(const LinearExtrudeNode &node)
 		BOOST_FOREACH (AbstractNode * v, node.getChildren()) {
 			if (v->modinst->isBackground()) continue;
 			CGAL_Nef_polyhedron N = this->cgalevaluator.evaluateCGALMesh(*v);
-			if (!N.empty()) {
+			if (!N.isNull()) {
 				if (N.dim != 2) {
 					PRINT("ERROR: linear_extrude() is not defined for 3D child objects!");
 				}
 				else {
-					if (sum.empty()) sum = N.copy();
+					if (sum.isNull()) sum = N.copy();
 					else sum += N;
 				}
 			}
 		}
 
-		if (sum.empty()) return NULL;
+		if (sum.isNull()) return NULL;
 		dxf = sum.convertToDxfData();;
 	} else {
 		dxf = new DxfData(node.fn, node.fs, node.fa, node.filename, node.layername, node.origin_x, node.origin_y, node.scale);
@@ -485,18 +483,18 @@ PolySet *PolySetCGALEvaluator::evaluatePolySet(const RotateExtrudeNode &node)
 		BOOST_FOREACH (AbstractNode * v, node.getChildren()) {
 			if (v->modinst->isBackground()) continue;
 			CGAL_Nef_polyhedron N = this->cgalevaluator.evaluateCGALMesh(*v);
-			if (!N.empty()) {
+			if (!N.isNull()) {
 				if (N.dim != 2) {
 					PRINT("ERROR: rotate_extrude() is not defined for 3D child objects!");
 				}
 				else {
-					if (sum.empty()) sum = N.copy();
+					if (sum.isNull()) sum = N.copy();
 					else sum += N;
 				}
 			}
 		}
 
-		if (sum.empty()) return NULL;
+		if (sum.isNull()) return NULL;
 		dxf = sum.convertToDxfData();
 	} else {
 		dxf = new DxfData(node.fn, node.fs, node.fa, node.filename, node.layername, node.origin_x, node.origin_y, node.scale);
@@ -511,7 +509,7 @@ PolySet *PolySetCGALEvaluator::evaluatePolySet(const CgaladvNode &node)
 {
 	CGAL_Nef_polyhedron N = this->cgalevaluator.evaluateCGALMesh(node);
 	PolySet *ps = NULL;
-	if (!N.empty()) {
+	if (!N.isNull()) {
 		ps = N.convertToPolyset();
 		if (ps) ps->convexity = node.convexity;
 	}
@@ -523,7 +521,7 @@ PolySet *PolySetCGALEvaluator::evaluatePolySet(const RenderNode &node)
 {
 	CGAL_Nef_polyhedron N = this->cgalevaluator.evaluateCGALMesh(node);
 	PolySet *ps = NULL;
-	if (!N.empty()) {
+	if (!N.isNull()) {
 		if (N.dim == 3 && !N.p3->is_simple()) {
 			PRINT("WARNING: Body of render() isn't valid 2-manifold!");
 		}
diff --git a/src/mainwin.cc b/src/mainwin.cc
index dc5b79b..dde6761 100644
--- a/src/mainwin.cc
+++ b/src/mainwin.cc
@@ -1236,35 +1236,37 @@ void MainWindow::actionRenderCGALDone(CGAL_Nef_polyhedron *root_N)
 		PolySetCache::instance()->print();
 		CGALCache::instance()->print();
 
-		if (root_N->dim == 2) {
-			PRINT("   Top level object is a 2D object:");
-			PRINTB("   Empty:      %6s", (root_N->p2->is_empty() ? "yes" : "no"));
-			PRINTB("   Plane:      %6s", (root_N->p2->is_plane() ? "yes" : "no"));
-			PRINTB("   Vertices:   %6d", root_N->p2->explorer().number_of_vertices());
-			PRINTB("   Halfedges:  %6d", root_N->p2->explorer().number_of_halfedges());
-			PRINTB("   Edges:      %6d", root_N->p2->explorer().number_of_edges());
-			PRINTB("   Faces:      %6d", root_N->p2->explorer().number_of_faces());
-			PRINTB("   FaceCycles: %6d", root_N->p2->explorer().number_of_face_cycles());
-			PRINTB("   ConnComp:   %6d", root_N->p2->explorer().number_of_connected_components());
-		}
-
-		if (root_N->dim == 3) {
-			PRINT("   Top level object is a 3D object:");
-			PRINTB("   Simple:     %6s", (root_N->p3->is_simple() ? "yes" : "no"));
-			PRINTB("   Valid:      %6s", (root_N->p3->is_valid() ? "yes" : "no"));
-			PRINTB("   Vertices:   %6d", root_N->p3->number_of_vertices());
-			PRINTB("   Halfedges:  %6d", root_N->p3->number_of_halfedges());
-			PRINTB("   Edges:      %6d", root_N->p3->number_of_edges());
-			PRINTB("   Halffacets: %6d", root_N->p3->number_of_halffacets());
-			PRINTB("   Facets:     %6d", root_N->p3->number_of_facets());
-			PRINTB("   Volumes:    %6d", root_N->p3->number_of_volumes());
+		if (!root_N->isNull()) {
+			if (root_N->dim == 2) {
+				PRINT("   Top level object is a 2D object:");
+				PRINTB("   Empty:      %6s", (root_N->p2->is_empty() ? "yes" : "no"));
+				PRINTB("   Plane:      %6s", (root_N->p2->is_plane() ? "yes" : "no"));
+				PRINTB("   Vertices:   %6d", root_N->p2->explorer().number_of_vertices());
+				PRINTB("   Halfedges:  %6d", root_N->p2->explorer().number_of_halfedges());
+				PRINTB("   Edges:      %6d", root_N->p2->explorer().number_of_edges());
+				PRINTB("   Faces:      %6d", root_N->p2->explorer().number_of_faces());
+				PRINTB("   FaceCycles: %6d", root_N->p2->explorer().number_of_face_cycles());
+				PRINTB("   ConnComp:   %6d", root_N->p2->explorer().number_of_connected_components());
+			}
+			
+			if (root_N->dim == 3) {
+				PRINT("   Top level object is a 3D object:");
+				PRINTB("   Simple:     %6s", (root_N->p3->is_simple() ? "yes" : "no"));
+				PRINTB("   Valid:      %6s", (root_N->p3->is_valid() ? "yes" : "no"));
+				PRINTB("   Vertices:   %6d", root_N->p3->number_of_vertices());
+				PRINTB("   Halfedges:  %6d", root_N->p3->number_of_halfedges());
+				PRINTB("   Edges:      %6d", root_N->p3->number_of_edges());
+				PRINTB("   Halffacets: %6d", root_N->p3->number_of_halffacets());
+				PRINTB("   Facets:     %6d", root_N->p3->number_of_facets());
+				PRINTB("   Volumes:    %6d", root_N->p3->number_of_volumes());
+			}
 		}
 
 		int s = this->progresswidget->elapsedTime() / 1000;
 		PRINTB("Total rendering time: %d hours, %d minutes, %d seconds", (s / (60*60)) % ((s / 60) % 60) % (s % 60));
 
 		this->root_N = root_N;
-		if (!this->root_N->empty()) {
+		if (!this->root_N->isNull()) {
 			this->cgalRenderer = new CGALRenderer(*this->root_N);
 			// Go to CGAL view mode
 			if (viewActionCGALGrid->isChecked()) {
diff --git a/testdata/scad/features/difference-tests.scad b/testdata/scad/features/difference-tests.scad
index 186772f..b770764 100644
--- a/testdata/scad/features/difference-tests.scad
+++ b/testdata/scad/features/difference-tests.scad
@@ -29,6 +29,7 @@ translate([24,0,0]) difference() {
   translate([0,0,6.99]) cylinder(r=4, h=4, center=true);
 }
 
+// Subtracting something from nothing
 translate([24,12,0]) difference() {
   cube([0,10,10], center=true);
   # cylinder(r=4, h=20, center=true);
diff --git a/tests/CMakeLists.txt b/tests/CMakeLists.txt
index 18f4469..87e5319 100644
--- a/tests/CMakeLists.txt
+++ b/tests/CMakeLists.txt
@@ -773,7 +773,6 @@ set_test_config(Heavy opencsgtest_minkowski3-tests
                       cgalpngtest_minkowski3-tests
                       cgalpngtest_for-tests
                       cgalpngtest_for-nested-tests
-                      cgalpngtest_difference-tests
                       cgalpngtest_intersection-tests)
 
 foreach(FILE ${EXAMPLE_FILES})
diff --git a/tests/cgalpngtest.cc b/tests/cgalpngtest.cc
index 08e539e..56861c6 100644
--- a/tests/cgalpngtest.cc
+++ b/tests/cgalpngtest.cc
@@ -153,30 +153,30 @@ int main(int argc, char **argv)
                 exit(1);
         }
 
-	CGALRenderer cgalRenderer(N);
-
+  CGALRenderer cgalRenderer(N);
+			 
 	BoundingBox bbox;
 	if (cgalRenderer.polyhedron) {
 		CGAL::Bbox_3 cgalbbox = cgalRenderer.polyhedron->bbox();
 		bbox = BoundingBox(Vector3d(cgalbbox.xmin(), cgalbbox.ymin(), cgalbbox.zmin()),
-							Vector3d(cgalbbox.xmax(), cgalbbox.ymax(), cgalbbox.zmax()));
+											 Vector3d(cgalbbox.xmax(), cgalbbox.ymax(), cgalbbox.zmax()));
 	}
 	else if (cgalRenderer.polyset) {
 		bbox = cgalRenderer.polyset->getBoundingBox();
 	}
-
+	
 	Vector3d center = getBoundingCenter(bbox);
 	double radius = getBoundingRadius(bbox);
-
+	
 	Vector3d cameradir(1, 1, -0.5);
 	Vector3d camerapos = center - radius*2*cameradir;
 	csgInfo.glview->setCamera(camerapos, center);
-
-
+	
+	
 	csgInfo.glview->setRenderer(&cgalRenderer);
 	csgInfo.glview->paintGL();
 	csgInfo.glview->save(outfile);
-
+	
 	delete root_node;
 	delete root_module;
 
diff --git a/tests/cgalstlsanitytest.cc b/tests/cgalstlsanitytest.cc
index 137f626..52cfb41 100644
--- a/tests/cgalstlsanitytest.cc
+++ b/tests/cgalstlsanitytest.cc
@@ -129,7 +129,7 @@ int main(int argc, char **argv)
 	CGAL_Nef_polyhedron N = cgalevaluator.evaluateCGALMesh(*root_node);
 
 	current_path(original_path);
-	if (!N.empty()) {
+	if (!N.isNull()) {
 		std::ofstream outfile;
 		outfile.open(outfilename);
 			
diff --git a/tests/cgaltest.cc b/tests/cgaltest.cc
index e4761db..b546286 100644
--- a/tests/cgaltest.cc
+++ b/tests/cgaltest.cc
@@ -122,7 +122,7 @@ int main(int argc, char **argv)
 	CGAL_Nef_polyhedron N = cgalevaluator.evaluateCGALMesh(*root_node);
 
 	current_path(original_path);
-	if (!N.empty()) {
+	if (!N.isNull()) {
 		export_stl(&N, std::cout);
 	}