simplify scale_denominator interface

CHANGELOG.md

@@ -8,6 +8,8 @@ For a complete change history, see the git log.
 
 ## Future
 
+- Changed scale_denominator C++ interface to take scale as first argument rather than map.
+
 - Added support for `background-image` in cairo_renderer (#1724)
 
 - Added Layer `buffer-size` that can be used to override Map `buffer-size` to avoid

bindings/python/mapnik_python.cpp

@@ -329,7 +329,7 @@ void render_to_file3(const mapnik::Map& map,
 
 double scale_denominator(mapnik::Map const &map, bool geographic)
 {
-    return mapnik::scale_denominator(map, geographic);
+    return mapnik::scale_denominator(map.scale(), geographic);
 }
 
 // http://docs.python.org/c-api/exceptions.html#standard-exceptions
@@ -691,6 +691,7 @@ BOOST_PYTHON_MODULE(_mapnik)
 #endif
 
     def("scale_denominator", &scale_denominator,
+        (arg("map"),arg("is_geographic")),
         "\n"
         "Return the Map Scale Denominator.\n"
         "Also available as Map.scale_denominator()\n"

include/mapnik/feature_style_processor_impl.hpp

@@ -157,7 +157,7 @@ void feature_style_processor<Processor>::apply()
     try
     {
         projection proj(m_.srs(),true);
-        double scale_denom = mapnik::scale_denominator(m_,proj.is_geographic());
+        double scale_denom = mapnik::scale_denominator(m_.scale(),proj.is_geographic());
         scale_denom *= scale_factor_;
 
         BOOST_FOREACH ( layer const& lyr, m_.layers() )
@@ -191,7 +191,7 @@ void feature_style_processor<Processor>::apply(mapnik::layer const& lyr, std::se
     try
     {
         projection proj(m_.srs(),true);
-        double scale_denom = mapnik::scale_denominator(m_,proj.is_geographic());
+        double scale_denom = mapnik::scale_denominator(m_.scale(),proj.is_geographic());
         scale_denom *= scale_factor_;
 
         if (lyr.visible(scale_denom))

include/mapnik/scale_denominator.hpp

@@ -29,7 +29,7 @@
 namespace mapnik {
 
 class Map;
-MAPNIK_DECL double scale_denominator(Map const& map, bool geographic);
+MAPNIK_DECL double scale_denominator(double map_scale, bool geographic);
 }
 
 #endif // MAPNIK_SCALE_DENOMINATOR_HPP

src/map.cpp

@@ -530,7 +530,7 @@ double Map::scale() const
 double Map::scale_denominator() const
 {
     projection map_proj(srs_);
-    return mapnik::scale_denominator( *this, map_proj.is_geographic());
+    return mapnik::scale_denominator( scale(), map_proj.is_geographic());
 }
 
 CoordTransform Map::view_transform() const

src/scale_denominator.cpp

@@ -22,19 +22,18 @@
 
 // mapnik
 #include <mapnik/scale_denominator.hpp>
-#include <mapnik/map.hpp>
+#include <mapnik/global.hpp>
 
 // stl
 #include <cmath>
 
 namespace mapnik {
 
-static const double pi = 3.14159265359;
+static const double meters_per_degree = 6378137 * 2 * M_PI / 360;
-static const double meters_per_degree = 6378137 * 2 * pi/ 360;
 
-double scale_denominator(Map const& map, bool geographic)
+double scale_denominator(double map_scale, bool geographic)
 {
-    double denom = map.scale() / 0.00028;
+    double denom = map_scale / 0.00028;
     if (geographic) denom *= meters_per_degree;
     return denom;
 }