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

1 files changed, 51 insertions, 47 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)
 	{