Interior: cover the case of empty polygon or exterior ring

include/mapnik/geometry/interior.hpp

@@ -24,11 +24,14 @@
 #define MAPNIK_GEOMETRY_INTERIOR_HPP
 
 #include <mapnik/geometry.hpp>
+#include <mapnik/config.hpp> // for MAPNIK_DECL
 
 namespace mapnik { namespace geometry {
 
 template <class T>
-point<T> interior(polygon<T> const& polygon, double scale_factor);
+MAPNIK_DECL bool interior(polygon<T> const& polygon,
+                          double scale_factor,
+                          point<T> & pt);
 
 } }
 

include/mapnik/markers_placements/interior.hpp

@@ -62,8 +62,14 @@ public:
         {
             geometry::polygon_vertex_processor<double> vertex_processor;
             vertex_processor.add_path(this->locator_);
-            geometry::point<double> placement = geometry::interior(vertex_processor.polygon_,
-                                                                   this->params_.scale_factor);
+            geometry::point<double> placement;
+            if (!geometry::interior(vertex_processor.polygon_,
+                                   this->params_.scale_factor,
+                                   placement))
+            {
+                this->done_ = true;
+                return false;
+            }
 
             x = placement.x;
             y = placement.y;

include/mapnik/renderer_common/process_point_symbolizer.hpp

@@ -80,7 +80,7 @@ void render_point_symbolizer(point_symbolizer const &sym,
         else if (type == mapnik::geometry::geometry_types::Polygon)
         {
             auto const& poly = mapnik::util::get<geometry::polygon<double> >(geometry);
-            pt = geometry::interior(poly, common.scale_factor_);
+            if (!geometry::interior(poly, common.scale_factor_, pt)) return;
         }
         else
         {

src/geometry/interior.cpp

@@ -30,6 +30,11 @@
 #include <iostream>
 #include <queue>
 
+#pragma GCC diagnostic push
+#include <mapnik/warning_ignore.hpp>
+#include <boost/optional.hpp>
+#pragma GCC diagnostic pop
+
 namespace mapnik { namespace geometry {
 
 // Interior algorithm is realized as a modification of Polylabel algorithm
@@ -148,8 +153,13 @@ struct cell
 };
 
 template <class T>
-point<T> polylabel(const polygon<T>& polygon, T precision = 1)
+boost::optional<point<T>> polylabel(polygon<T> const& polygon, T precision = 1)
 {
+    if (polygon.exterior_ring.empty())
+    {
+        return boost::none;
+    }
+
     // find the bounding box of the outer ring
     const box2d<T> bbox = envelope(polygon.exterior_ring);
     const point<T> size { bbox.width(), bbox.height() };
@@ -167,14 +177,14 @@ point<T> polylabel(const polygon<T>& polygon, T precision = 1)
 
     if (cell_size == 0)
     {
-        return { bbox.minx(), bbox.miny() };
+        return point<T>{ bbox.minx(), bbox.miny() };
     }
 
     point<T> centroid;
     if (!mapnik::geometry::centroid(polygon, centroid))
     {
         auto center = bbox.center();
-        return { center.x, center.y };
+        return point<T>{ center.x, center.y };
     }
 
     fitness_functor<T> fitness_func(centroid, size);
@@ -220,15 +230,21 @@ point<T> polylabel(const polygon<T>& polygon, T precision = 1)
 } // namespace detail
 
 template <class T>
-point<T> interior(polygon<T> const& polygon, double scale_factor)
+bool interior(polygon<T> const& polygon, double scale_factor, point<T> & pt)
 {
     // This precision has been chosen to work well in the map (viewport) coordinates.
     double precision = 10.0 * scale_factor;
-    return detail::polylabel(polygon, precision);
+    if (boost::optional<point<T>> opt = detail::polylabel(polygon, precision))
+    {
+        pt = *opt;
+        return true;
+    }
+
+    return false;
 }
 
 template
-point<double> interior(polygon<double> const& polygon, double scale_factor);
+bool interior(polygon<double> const& polygon, double scale_factor, point<double> & pt);
 
 } }
 

src/text/symbolizer_helpers.cpp

@@ -300,8 +300,11 @@ void base_symbolizer_helper::initialize_points() const
                 using transform_group_type = geometry::strategy_group<proj_strategy, view_strategy>;
                 transform_group_type transform_group(ps, vs);
                 geometry::polygon<double> tranformed_poly(geometry::transform<double>(poly, transform_group));
-                geometry::point<double> pt = geometry::interior(tranformed_poly, scale_factor_);
+                geometry::point<double> pt;
+                if (geometry::interior(tranformed_poly, scale_factor_, pt))
+                {
                     points_.emplace_back(pt.x, pt.y);
+                }
                 continue;
             }
             else

test/unit/geometry/interior.cpp

@@ -0,0 +1,31 @@
+#include "catch.hpp"
+
+#include <mapnik/geometry/interior.hpp>
+
+TEST_CASE("polygon interior") {
+
+SECTION("empty polygon") {
+
+    mapnik::geometry::polygon<double> poly;
+    mapnik::geometry::point<double> pt;
+
+    CHECK(!mapnik::geometry::interior(poly, 1.0, pt));
+}
+
+SECTION("interior of a square") {
+
+    mapnik::geometry::polygon<double> poly;
+    poly.exterior_ring.emplace_back(-1, -1);
+    poly.exterior_ring.emplace_back( 1, -1);
+    poly.exterior_ring.emplace_back( 1,  1);
+    poly.exterior_ring.emplace_back(-1,  1);
+    poly.exterior_ring.emplace_back(-1, -1);
+
+    mapnik::geometry::point<double> pt{ -3, -3 };
+
+    CHECK(mapnik::geometry::interior(poly, 1.0, pt));
+    CHECK(pt.x == Approx(0));
+    CHECK(pt.y == Approx(0));
+}
+
+}