Added the rounding_cast utility, and added a scale_rounding_strategy to support this new casting type. Added tests for it

include/mapnik/geometry_strategy.hpp

@@ -24,6 +24,7 @@
 #define MAPNIK_GEOMETRY_STRATEGY_HPP
 
 #include <mapnik/geometry_adapters.hpp>
+#include <mapnik/util/rounding_cast.hpp>
 
 namespace mapnik { 
 namespace geometry {
@@ -192,6 +193,57 @@ private:
     double offset_;
 };
 
+struct scale_rounding_strategy
+{
+    scale_rounding_strategy(double scale, double offset = 0)
+        : scale_(scale), offset_(offset) {}
+
+    template <typename P1, typename P2>
+    inline bool apply(P1 const & p1, P2 & p2) const
+    {
+        
+        using p2_type = typename boost::geometry::coordinate_type<P2>::type;
+        double x = (boost::geometry::get<0>(p1) * scale_) + offset_;
+        double y = (boost::geometry::get<1>(p1) * scale_) + offset_;
+        try {
+            boost::geometry::set<0>(p2, util::rounding_cast<p2_type>(x));
+        }
+        catch(boost::numeric::negative_overflow&)
+        {
+            boost::geometry::set<0>(p2, std::numeric_limits<p2_type>::min());
+        }
+        catch(boost::numeric::positive_overflow&) 
+        {
+            boost::geometry::set<0>(p2, std::numeric_limits<p2_type>::max());
+        }
+        try {
+            boost::geometry::set<1>(p2, util::rounding_cast<p2_type>(y));
+        }
+        catch(boost::numeric::negative_overflow&)
+        {
+            boost::geometry::set<1>(p2, std::numeric_limits<p2_type>::min());
+        }
+        catch(boost::numeric::positive_overflow&) 
+        {
+            boost::geometry::set<1>(p2, std::numeric_limits<p2_type>::max());
+        }
+        return true;
+    }
+    
+    template <typename P1, typename P2>
+    inline P2 execute(P1 const& p1, bool & status) const
+    {
+        P2 p2;
+        status = apply(p1, p2);
+        return p2;
+    }
+
+private:
+    double scale_;
+    double offset_;
+};
+
+
 } // end geometry ns
 } // end mapnik ns
 

include/mapnik/util/rounding_cast.hpp

@@ -0,0 +1,48 @@
+/*****************************************************************************
+ *
+ * This file is part of Mapnik (c++ mapping toolkit)
+ *
+ * Copyright (C) 2015 Artem Pavlenko
+ *
+ * This library is free software; you can redistribute it and/or
+ * modify it under the terms of the GNU Lesser General Public
+ * License as published by the Free Software Foundation; either
+ * version 2.1 of the License, or (at your option) any later version.
+ *
+ * This library is distributed in the hope that it will be useful,
+ * but WITHOUT ANY WARRANTY; without even the implied warranty of
+ * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
+ * Lesser General Public License for more details.
+ *
+ * You should have received a copy of the GNU Lesser General Public
+ * License along with this library; if not, write to the Free Software
+ * Foundation, Inc., 51 Franklin St, Fifth Floor, Boston, MA  02110-1301  USA
+ *
+ *****************************************************************************/
+
+#ifndef MAPNIK_UTIL_ROUNDING_CAST_HPP
+#define MAPNIK_UTIL_ROUNDING_CAST_HPP
+
+#include <boost/numeric/conversion/converter.hpp> 
+
+namespace mapnik { 
+namespace util {
+
+template<typename Target, typename Source> 
+inline 
+Target rounding_cast ( Source arg ) 
+{ 
+  typedef boost::numeric::conversion_traits<Target,Source> Traits ; 
+
+  typedef 
+boost::numeric::converter<Target,Source,Traits,boost::numeric::def_overflow_handler,boost::numeric::RoundEven<Source> 
+ > Converter ; 
+
+  return Converter::convert(arg); 
+} 
+
+} // end util ns
+} // end mapnik ns
+
+#endif //MAPNIK_UTIL_ROUNDING_CAST_HPP
+

test/unit/geometry/geometry_strategy_test.cpp

@@ -88,8 +88,8 @@ SECTION("proj and view strategy") {
     }
     {
         // Test with scaling as well. This would be like projection from 4326 to a vector tile.
-        mapnik::geometry::scale_strategy ss(16, 0.5);
+        mapnik::geometry::scale_rounding_strategy ss(16);
-        using sg_type = strategy_group<mapnik::proj_strategy, mapnik::view_strategy, mapnik::geometry::scale_strategy >;
+        using sg_type = strategy_group<mapnik::proj_strategy, mapnik::view_strategy, mapnik::geometry::scale_rounding_strategy >;
         sg_type sg(ps, vs, ss);
         geometry<double> p1(std::move(point<double>(-97.553098,35.523105)));
         point<std::int64_t> r1(938 , 1615);
@@ -112,6 +112,32 @@ SECTION("proj and view strategy") {
         //std::cout << p3.x << " , " << p3.y << std::endl;
         assert_g_equal(r1, p3);
     }
+    {
+        // Test with scaling + offset as well. This would be like projection from 4326 to a vector tile.
+        mapnik::geometry::scale_rounding_strategy ss(16, 20);
+        using sg_type = strategy_group<mapnik::proj_strategy, mapnik::view_strategy, mapnik::geometry::scale_rounding_strategy >;
+        sg_type sg(ps, vs, ss);
+        geometry<double> p1(std::move(point<double>(-97.553098,35.523105)));
+        point<std::int64_t> r1(958 , 1635);
+        geometry<std::int64_t> p2 = transform<std::int64_t>(p1, sg);
+        REQUIRE(p2.is<point<std::int64_t> >());
+        point<std::int64_t> p3 = mapnik::util::get<point<std::int64_t> >(p2);
+        //std::cout << p3.x << " , " << p3.y << std::endl;
+        assert_g_equal(r1, p3);
+    }
+    {
+        // Test the entire scaling plus offset in reverse process in reverse! This would be like converting a vector tile coordinate to 4326.
+        mapnik::geometry::scale_strategy ss(1.0/16.0, -20.0/16.0);
+        using sg_type = strategy_group_first<mapnik::geometry::scale_strategy, mapnik::unview_strategy, mapnik::proj_strategy >;
+        sg_type sg(ss, uvs, ps_rev);
+        geometry<std::int64_t> p1(std::move(point<std::int64_t>(958 , 1635)));
+        point<double> r1(-97.5586 , 35.5322);
+        geometry<double> p2 = transform<double>(p1, sg);
+        REQUIRE(p2.is<point<double> >());
+        point<double> p3 = mapnik::util::get<point<double> >(p2);
+        //std::cout << p3.x << " , " << p3.y << std::endl;
+        assert_g_equal(r1, p3);
+    }
 
 }