Correct pruning of polygons

src/output_object.cpp

@@ -119,14 +119,52 @@ Geometry buildWayGeometry(OSMStore &osmStore, OutputObject const &oo, const Tile
 				return out; 
 			}
 
-			try {
-				MultiPolygon out;
-				geom::intersection(mp, clippingPolygon, out);
-				return out;
-			} catch (geom::overlay_invalid_input_exception &err) {
-				std::cout << "Couldn't clip polygon (self-intersection)" << std::endl;
-				return MultiPolygon(); // blank
+			MultiPolygon out;
+			for(auto const &p: mp) {
+				Polygon newp;
+				newp.outer().reserve(p.outer.size());
+
+				geom::append(newp.outer(), p.outer[0]);
+				for(std::size_t i = 1; i < p.outer.size(); ++i) {
+					std::size_t next_i = (i + 1) % p.outer.size();
+
+					bool keep_point = 
+						geom::within(newp.outer().back(), bbox.clippingBox) || 
+					   	geom::within(p.outer[i], bbox.clippingBox) || 
+					   	geom::within(p.outer[next_i], bbox.clippingBox);
+
+					if(!keep_point) {
+						double det = 
+							(p.outer[i].x() - newp.outer().back().x()) * (p.outer[next_i].y() * newp.outer().back().y()) - 
+							(p.outer[next_i].x() - newp.outer().back().x()) * (p.outer[i].y() * newp.outer().back().y());
+
+						if(det < 0) { 
+							Linestring ls({ newp.outer().back(), p.outer[next_i] });
+							bool intersects = geom::intersects(ls, bbox.clippingBox);
+							for(auto const &inner: p.inners) {
+								intersects |= geom::intersects(ls, inner);
+							} 
+
+							if(!intersects) 
+								continue;
+						}
+					}
+
+					geom::append(newp.outer(), p.outer[i]);
+				}
+
+				newp.inners().reserve(p.inners.size());
+				for(auto const &inner: p.inners) {
+					if(geom::within(inner, newp.outer())) { 
+						newp.inners().resize(newp.inners().size() + 1);
+						boost::geometry::assign(newp.inners().back(), inner);
+					}
+				}
+
+				out.push_back(std::move(newp));
 			}
+
+			return out;
 		}
 
 		default: