From d027ed67c7c26d5830c2c1b7df1568f3d76fd9df Mon Sep 17 00:00:00 2001
From: artemp <artem@mapnik.org>
Date: Wed, 27 Jan 2016 14:50:17 +0100
Subject: [PATCH] more `const` strictness, update to work with latest
 `mapbox::variant/visitor-no-copy` branch

---
 deps/mapbox/variant                           |  2 +-
 include/mapnik/geometry_reprojection_impl.hpp | 34 +++++++++----------
 include/mapnik/image_filter.hpp               | 16 ++++-----
 .../apply_vertex_converter.hpp                |  2 +-
 .../process_markers_symbolizer.hpp            |  6 ++--
 include/mapnik/transform_processor.hpp        | 14 ++++----
 include/mapnik/util/variant.hpp               | 25 +++++++-------
 include/mapnik/vertex_processor.hpp           | 20 +++++------
 src/agg/agg_renderer.cpp                      | 12 +++----
 src/agg/process_debug_symbolizer.cpp          | 10 +++---
 src/agg/process_line_pattern_symbolizer.cpp   |  8 ++---
 .../process_polygon_pattern_symbolizer.cpp    |  6 ++--
 src/cairo/cairo_renderer.cpp                  |  6 ++--
 src/image_compositing.cpp                     |  8 ++---
 src/image_copy.cpp                            |  8 ++---
 src/image_util.cpp                            |  2 +-
 src/marker_cache.cpp                          |  6 ++--
 src/warp.cpp                                  |  4 +--
 test/unit/geometry/geometry_equal.hpp         | 20 +++++------
 test/visual/runner.cpp                        | 11 +++---
 utils/svg2png/svg2png.cpp                     |  6 ++--
 21 files changed, 113 insertions(+), 113 deletions(-)

diff --git a/deps/mapbox/variant b/deps/mapbox/variant
index 9afd64060..f7b63cc15 160000
--- a/deps/mapbox/variant
+++ b/deps/mapbox/variant
@@ -1 +1 @@
-Subproject commit 9afd6406065440e02b6bf42db4633b815846db0d
+Subproject commit f7b63cc1501bf9d9f740e9a8957a25bc9be5f1ca
diff --git a/include/mapnik/geometry_reprojection_impl.hpp b/include/mapnik/geometry_reprojection_impl.hpp
index 867c0ba44..ff01bd451 100644
--- a/include/mapnik/geometry_reprojection_impl.hpp
+++ b/include/mapnik/geometry_reprojection_impl.hpp
@@ -178,12 +178,12 @@ struct geom_reproj_copy_visitor
         : proj_trans_(proj_trans),
           n_err_(n_err) {}
 
-    geometry<T> operator() (geometry_empty const&)
+    geometry<T> operator() (geometry_empty const&) const
     {
         return geometry_empty();
     }
 
-    geometry<T> operator() (point<T> const& p)
+    geometry<T> operator() (point<T> const& p) const
     {
         geometry<T> geom; // default empty
         unsigned int intial_err = n_err_;
@@ -193,7 +193,7 @@ struct geom_reproj_copy_visitor
         return geom;
     }
 
-    geometry<T> operator() (line_string<T> const& ls)
+    geometry<T> operator() (line_string<T> const& ls) const
     {
         geometry<T> geom; // default empty
         unsigned int intial_err = n_err_;
@@ -203,7 +203,7 @@ struct geom_reproj_copy_visitor
         return geom;
     }
 
-    geometry<T> operator() (polygon<T> const& poly)
+    geometry<T> operator() (polygon<T> const& poly) const
     {
         geometry<T> geom; // default empty
         polygon<T> new_poly = reproject_internal(poly, proj_trans_, n_err_);
@@ -212,7 +212,7 @@ struct geom_reproj_copy_visitor
         return geom;
     }
 
-    geometry<T> operator() (multi_point<T> const& mp)
+    geometry<T> operator() (multi_point<T> const& mp) const
     {
         geometry<T> geom; // default empty
         multi_point<T> new_mp = reproject_internal(mp, proj_trans_, n_err_);
@@ -221,7 +221,7 @@ struct geom_reproj_copy_visitor
         return geom;
     }
 
-    geometry<T> operator() (multi_line_string<T> const& mls)
+    geometry<T> operator() (multi_line_string<T> const& mls) const
     {
         geometry<T> geom; // default empty
         multi_line_string<T> new_mls = reproject_internal(mls, proj_trans_, n_err_);
@@ -230,7 +230,7 @@ struct geom_reproj_copy_visitor
         return geom;
     }
 
-    geometry<T> operator() (multi_polygon<T> const& mpoly)
+    geometry<T> operator() (multi_polygon<T> const& mpoly) const
     {
         geometry<T> geom; // default empty
         multi_polygon<T> new_mpoly = reproject_internal(mpoly, proj_trans_, n_err_);
@@ -239,7 +239,7 @@ struct geom_reproj_copy_visitor
         return geom;
     }
 
-    geometry<T> operator() (geometry_collection<T> const& c)
+    geometry<T> operator() (geometry_collection<T> const& c) const
     {
         geometry<T> geom; // default empty
         geometry_collection<T> new_c = reproject_internal(c, proj_trans_, n_err_);
@@ -284,15 +284,15 @@ struct geom_reproj_visitor {
         : proj_trans_(proj_trans) {}
 
     template <typename T>
-    bool operator() (geometry<T> & geom)
+    bool operator() (geometry<T> & geom) const
     {
         return mapnik::util::apply_visitor((*this), geom);
     }
 
-    bool operator() (geometry_empty &) { return true; }
+    bool operator() (geometry_empty &) const { return true; }
 
     template <typename T>
-    bool operator() (point<T> & p)
+    bool operator() (point<T> & p) const
     {
         if (!proj_trans_.forward(p))
         {
@@ -302,7 +302,7 @@ struct geom_reproj_visitor {
     }
 
     template <typename T>
-    bool operator() (line_string<T> & ls)
+    bool operator() (line_string<T> & ls) const
     {
         if (proj_trans_.forward(ls) > 0)
         {
@@ -312,7 +312,7 @@ struct geom_reproj_visitor {
     }
 
     template <typename T>
-    bool operator() (polygon<T> & poly)
+    bool operator() (polygon<T> & poly) const
     {
         if (proj_trans_.forward(poly.exterior_ring) > 0)
         {
@@ -330,13 +330,13 @@ struct geom_reproj_visitor {
     }
 
     template <typename T>
-    bool operator() (multi_point<T> & mp)
+    bool operator() (multi_point<T> & mp) const
     {
         return (*this) (static_cast<line_string<T> &>(mp));
     }
 
     template <typename T>
-    bool operator() (multi_line_string<T> & mls)
+    bool operator() (multi_line_string<T> & mls) const
     {
         for (auto & ls : mls)
         {
@@ -349,7 +349,7 @@ struct geom_reproj_visitor {
     }
 
     template <typename T>
-    bool operator() (multi_polygon<T> & mpoly)
+    bool operator() (multi_polygon<T> & mpoly) const
     {
         for (auto & poly : mpoly)
         {
@@ -362,7 +362,7 @@ struct geom_reproj_visitor {
     }
 
     template <typename T>
-    bool operator() (geometry_collection<T> & c)
+    bool operator() (geometry_collection<T> & c) const
     {
         for (auto & g : c)
         {
diff --git a/include/mapnik/image_filter.hpp b/include/mapnik/image_filter.hpp
index 62a3f3b5b..9b0b754cc 100644
--- a/include/mapnik/image_filter.hpp
+++ b/include/mapnik/image_filter.hpp
@@ -683,7 +683,7 @@ void color_blind_filter(Src & src, ColorBlindFilter const& op)
     using namespace boost::gil;
     rgba8_view_t src_view = rgba8_view(src);
     bool premultiplied = src.get_premultiplied();
-    
+
     for (std::ptrdiff_t y = 0; y < src_view.height(); ++y)
     {
         rgba8_view_t::x_iterator src_it = src_view.row_begin(static_cast<long>(y));
@@ -738,7 +738,7 @@ void color_blind_filter(Src & src, ColorBlindFilter const& op)
             X = deviate_x * Y / deviate_y;
             Z = (1.0 - (deviate_x + deviate_y)) * Y / deviate_y;
             // Neutral grey calculated from luminance (in D65)
-            double neutral_X = 0.312713 * Y / 0.329016; 
+            double neutral_X = 0.312713 * Y / 0.329016;
             double neutral_Z = 0.358271 * Y / 0.329016;
             // Difference between simulated color and neutral grey
             double diff_X = neutral_X - X;
@@ -761,12 +761,12 @@ void color_blind_filter(Src & src, ColorBlindFilter const& op)
             // Convert to RGB color space
             dr = X * 3.24071 + Y * -1.53726 + Z * -0.498571; // XYZ->RGB (sRGB:D65)
             dg = X * -0.969258 + Y * 1.87599 + Z * 0.0415557;
-            db = X * 0.0556352 + Y * -0.203996 + Z * 1.05707;            
+            db = X * 0.0556352 + Y * -0.203996 + Z * 1.05707;
             // Compensate simulated color towards a neutral fit in RGB space
             double fit_r = ((dr < 0.0 ? 0.0 : 1.0) - dr) / diff_r;
             double fit_g = ((dg < 0.0 ? 0.0 : 1.0) - dg) / diff_g;
             double fit_b = ((db < 0.0 ? 0.0 : 1.0) - db) / diff_b;
-            double adjust = std::max( (fit_r > 1.0 || fit_r < 0.0) ? 0.0 : fit_r, 
+            double adjust = std::max( (fit_r > 1.0 || fit_r < 0.0) ? 0.0 : fit_r,
                                       (fit_g > 1.0 || fit_g < 0.0) ? 0.0 : fit_g
                                     );
             adjust = std::max((fit_b > 1.0 || fit_b < 0.0) ? 0.0 : fit_b, adjust);
@@ -777,7 +777,7 @@ void color_blind_filter(Src & src, ColorBlindFilter const& op)
             // Apply gamma correction
             dr = std::pow(dr, 1.0 / 2.2);
             dg = std::pow(dg, 1.0 / 2.2);
-            db = std::pow(db, 1.0 / 2.2);            
+            db = std::pow(db, 1.0 / 2.2);
             // premultiply
             dr *= da;
             dg *= da;
@@ -917,7 +917,7 @@ struct filter_visitor
     : src_(src) {}
 
     template <typename T>
-    void operator () (T const& filter)
+    void operator () (T const& filter) const
     {
         apply_filter(src_, filter);
     }
@@ -931,9 +931,9 @@ struct filter_radius_visitor
     filter_radius_visitor(int & radius)
         : radius_(radius) {}
     template <typename T>
-    void operator () (T const& /*filter*/) {}
+    void operator () (T const& /*filter*/)  const {}
 
-    void operator () (agg_stack_blur const& op)
+    void operator () (agg_stack_blur const& op) const
     {
         if (static_cast<int>(op.rx) > radius_) radius_ = static_cast<int>(op.rx);
         if (static_cast<int>(op.ry) > radius_) radius_ = static_cast<int>(op.ry);
diff --git a/include/mapnik/renderer_common/apply_vertex_converter.hpp b/include/mapnik/renderer_common/apply_vertex_converter.hpp
index de239c95b..503dc4176 100644
--- a/include/mapnik/renderer_common/apply_vertex_converter.hpp
+++ b/include/mapnik/renderer_common/apply_vertex_converter.hpp
@@ -31,7 +31,7 @@ struct apply_vertex_converter
     apply_vertex_converter(VertexConverter & converter, Processor & proc)
         : converter_(converter), proc_(proc) {}
     template <typename Adapter>
-    void operator() (Adapter const& adapter) const
+    void operator() (Adapter const& adapter)
     {
         converter_.apply(adapter, proc_);
     }
diff --git a/include/mapnik/renderer_common/process_markers_symbolizer.hpp b/include/mapnik/renderer_common/process_markers_symbolizer.hpp
index 1009d2fcf..66a002dab 100644
--- a/include/mapnik/renderer_common/process_markers_symbolizer.hpp
+++ b/include/mapnik/renderer_common/process_markers_symbolizer.hpp
@@ -62,9 +62,9 @@ struct render_marker_symbolizer_visitor
           clip_box_(clip_box),
           renderer_context_(renderer_context) {}
 
-    void operator() (marker_null const&) {}
+    void operator() (marker_null const&) const {}
 
-    void operator() (marker_svg const& mark)
+    void operator() (marker_svg const& mark) const
     {
         using namespace mapnik::svg;
         bool clip = get<value_bool, keys::clip>(sym_, feature_, common_.vars_);
@@ -179,7 +179,7 @@ struct render_marker_symbolizer_visitor
         }
     }
 
-    void operator() (marker_rgba8 const& mark)
+    void operator() (marker_rgba8 const& mark) const
     {
         using namespace mapnik::svg;
         bool clip = get<value_bool, keys::clip>(sym_, feature_, common_.vars_);
diff --git a/include/mapnik/transform_processor.hpp b/include/mapnik/transform_processor.hpp
index bec6bff3b..2e4bfa3ed 100644
--- a/include/mapnik/transform_processor.hpp
+++ b/include/mapnik/transform_processor.hpp
@@ -111,11 +111,11 @@ struct transform_processor
               vars_(v),
               scale_factor_(scale_factor) {}
 
-        void operator() (identity_node const&)
+        void operator() (identity_node const&) const
         {
         }
 
-        void operator() (matrix_node const& node)
+        void operator() (matrix_node const& node) const
         {
             double a = eval(node.a_); // scale x;
             double b = eval(node.b_);
@@ -126,21 +126,21 @@ struct transform_processor
             transform_.multiply(agg::trans_affine(a, b, c, d, e, f));
         }
 
-        void operator() (translate_node const& node)
+        void operator() (translate_node const& node) const
         {
             double tx = eval(node.tx_) * scale_factor_;
             double ty = eval(node.ty_, 0.0) * scale_factor_;
             transform_.translate(tx, ty);
         }
 
-        void operator() (scale_node const& node)
+        void operator() (scale_node const& node) const
         {
             double sx = eval(node.sx_);
             double sy = eval(node.sy_, sx);
             transform_.scale(sx, sy);
         }
 
-        void operator() (rotate_node const& node)
+        void operator() (rotate_node const& node) const
         {
             double angle = deg2rad(eval(node.angle_));
             double cx = eval(node.cx_, 0.0);
@@ -150,7 +150,7 @@ struct transform_processor
             transform_.translate(cx, cy);
         }
 
-        void operator() (skewX_node const& node)
+        void operator() (skewX_node const& node) const
         {
             auto degrees = std::fmod(eval(node.angle_),90.0);
             if (degrees < -89.0) degrees = -89.0;
@@ -159,7 +159,7 @@ struct transform_processor
             transform_.multiply(agg::trans_affine_skewing(angle, 0.0));
         }
 
-        void operator() (skewY_node const& node)
+        void operator() (skewY_node const& node) const
         {
             auto degrees = std::fmod(eval(node.angle_),90.0);
             if (degrees < -89.0) degrees = -89.0;
diff --git a/include/mapnik/util/variant.hpp b/include/mapnik/util/variant.hpp
index 8473903e0..61832a0b7 100644
--- a/include/mapnik/util/variant.hpp
+++ b/include/mapnik/util/variant.hpp
@@ -46,30 +46,31 @@ public:
 
 // unary visitor interface
 // const
-template <typename V, typename F>
-auto VARIANT_INLINE static apply_visitor(F f, V const& v) -> decltype(V::visit(v, f))
+template <typename F, typename V>
+auto VARIANT_INLINE static apply_visitor(F && f, V const& v) -> decltype(V::visit(v, f))
 {
-    return V::visit(v, f);
+    return V::visit(v, std::forward<F>(f));
 }
 // non-const
-template <typename V, typename F>
-auto VARIANT_INLINE static apply_visitor(F f, V & v) -> decltype(V::visit(v, f))
+template <typename F, typename V>
+auto VARIANT_INLINE static apply_visitor(F && f, V & v) -> decltype(V::visit(v, f))
 {
-    return V::visit(v, f);
+    return V::visit(v, std::forward<F>(f));
 }
 
 // binary visitor interface
 // const
-template <typename V, typename F>
-auto VARIANT_INLINE static apply_visitor(F f, V const& v0, V const& v1) -> decltype(V::binary_visit(v0, v1, f))
+template <typename F, typename V>
+auto VARIANT_INLINE static apply_visitor(F && f, V const& v0, V const& v1) -> decltype(V::binary_visit(v0, v1, f))
 {
-    return V::binary_visit(v0, v1, f);
+    return V::binary_visit(v0, v1, std::forward<F>(f));
 }
+
 // non-const
-template <typename V, typename F>
-auto VARIANT_INLINE static apply_visitor(F f, V & v0, V & v1) -> decltype(V::binary_visit(v0, v1, f))
+template <typename F, typename V>
+auto VARIANT_INLINE static apply_visitor(F && f, V & v0, V & v1) -> decltype(V::binary_visit(v0, v1, f))
 {
-    return V::binary_visit(v0, v1, f);
+    return V::binary_visit(v0, v1, std::forward<F>(f));
 }
 
 // getter interface
diff --git a/include/mapnik/vertex_processor.hpp b/include/mapnik/vertex_processor.hpp
index a3b63c133..7cd2c40a4 100644
--- a/include/mapnik/vertex_processor.hpp
+++ b/include/mapnik/vertex_processor.hpp
@@ -35,38 +35,38 @@ struct vertex_processor
         : proc_(proc) {}
 
     template <typename Geometry>
-    void operator() (Geometry const& geom)
+    void operator() (Geometry const& geom) const
     {
         util::apply_visitor(*this, geom);
     }
-    void operator() (geometry_empty const&)
+    void operator() (geometry_empty const&) const
     {
         // no-op
     }
-    
+
     template <typename T1>
-    void operator() (point<T1> const& pt)
+    void operator() (point<T1> const& pt) const
     {
         point_vertex_adapter<T1> va(pt);
         proc_(va);
     }
 
     template <typename T1>
-    void operator() (line_string<T1> const& line)
+    void operator() (line_string<T1> const& line) const
     {
         line_string_vertex_adapter<T1> va(line);
         proc_(va);
     }
 
     template <typename T1>
-    void operator() (polygon<T1> const& poly)
+    void operator() (polygon<T1> const& poly) const
     {
         polygon_vertex_adapter<T1> va(poly);
         proc_(va);
     }
 
     template <typename T1>
-    void operator() (multi_point<T1> const& multi_pt)
+    void operator() (multi_point<T1> const& multi_pt) const
     {
         for (auto const& pt : multi_pt)
         {
@@ -76,7 +76,7 @@ struct vertex_processor
     }
 
     template <typename T1>
-    void operator() (multi_line_string<T1> const& multi_line)
+    void operator() (multi_line_string<T1> const& multi_line) const
     {
         for (auto const& line : multi_line)
         {
@@ -86,7 +86,7 @@ struct vertex_processor
     }
 
     template <typename T1>
-    void operator() (multi_polygon<T1> const& multi_poly)
+    void operator() (multi_polygon<T1> const& multi_poly) const
     {
         for ( auto const& poly : multi_poly)
         {
@@ -96,7 +96,7 @@ struct vertex_processor
     }
 
     template <typename T1>
-    void operator() (geometry_collection<T1> const& collection)
+    void operator() (geometry_collection<T1> const& collection) const
     {
         for (auto const& geom : collection)
         {
diff --git a/src/agg/agg_renderer.cpp b/src/agg/agg_renderer.cpp
index 74e3c935b..9fbcdca4b 100644
--- a/src/agg/agg_renderer.cpp
+++ b/src/agg/agg_renderer.cpp
@@ -121,11 +121,11 @@ struct setup_agg_bg_visitor
            mode_(mode),
            opacity_(opacity) {}
 
-    void operator() (marker_null const&) {}
+    void operator() (marker_null const&) const {}
 
-    void operator() (marker_svg const&) {}
+    void operator() (marker_svg const&) const {}
 
-    void operator() (marker_rgba8 const& marker)
+    void operator() (marker_rgba8 const& marker) const
     {
         mapnik::image_rgba8 const& bg_image = marker.get_data();
         std::size_t w = bg_image.width();
@@ -361,9 +361,9 @@ struct agg_render_marker_visitor
           opacity_(opacity),
           comp_op_(comp_op) {}
 
-    void operator() (marker_null const&) {}
+    void operator() (marker_null const&) const {}
 
-    void operator() (marker_svg const& marker)
+    void operator() (marker_svg const& marker) const
     {
         using color_type = agg::rgba8;
         using order_type = agg::order_rgba;
@@ -414,7 +414,7 @@ struct agg_render_marker_visitor
         svg_renderer.render(*ras_ptr_, sl, renb, mtx, opacity_, bbox);
     }
 
-    void operator() (marker_rgba8 const& marker)
+    void operator() (marker_rgba8 const& marker) const
     {
         using color_type = agg::rgba8;
         using order_type = agg::order_rgba;
diff --git a/src/agg/process_debug_symbolizer.cpp b/src/agg/process_debug_symbolizer.cpp
index c56add951..2016c456d 100644
--- a/src/agg/process_debug_symbolizer.cpp
+++ b/src/agg/process_debug_symbolizer.cpp
@@ -165,12 +165,12 @@ struct RingRenderer {
 };
 
 template <typename BufferType>
-struct render_ring_visitor {
-
+struct render_ring_visitor
+{
     render_ring_visitor(RingRenderer<BufferType> & renderer)
      : renderer_(renderer) {}
 
-    void operator()(mapnik::geometry::multi_polygon<double> const& geom)
+    void operator()(mapnik::geometry::multi_polygon<double> const& geom) const
     {
         for (auto const& poly : geom)
         {
@@ -178,7 +178,7 @@ struct render_ring_visitor {
         }
     }
 
-    void operator()(mapnik::geometry::polygon<double> const& geom)
+    void operator()(mapnik::geometry::polygon<double> const& geom) const
     {
         agg::rgba8 red(255,0,0,255);
         agg::rgba8 green(0,255,255,255);
@@ -199,7 +199,7 @@ struct render_ring_visitor {
     }
 
     template<typename GeomType>
-    void operator()(GeomType const&) {}
+    void operator()(GeomType const&) const {}
 
     RingRenderer<BufferType> & renderer_;
 };
diff --git a/src/agg/process_line_pattern_symbolizer.cpp b/src/agg/process_line_pattern_symbolizer.cpp
index 17ec5bbf0..f5045c5a3 100644
--- a/src/agg/process_line_pattern_symbolizer.cpp
+++ b/src/agg/process_line_pattern_symbolizer.cpp
@@ -71,9 +71,9 @@ struct agg_renderer_process_visitor_l
           feature_(feature),
           prj_trans_(prj_trans) {}
 
-    void operator() (marker_null const&) {}
+    void operator() (marker_null const&) const {}
 
-    void operator() (marker_svg const& marker)
+    void operator() (marker_svg const& marker) const
     {
         using color = agg::rgba8;
         using order = agg::order_rgba;
@@ -147,7 +147,7 @@ struct agg_renderer_process_visitor_l
         mapnik::util::apply_visitor(vertex_processor_type(apply),feature_.get_geometry());
     }
 
-    void operator() (marker_rgba8 const& marker)
+    void operator() (marker_rgba8 const& marker) const
     {
         using color = agg::rgba8;
         using order = agg::order_rgba;
@@ -214,7 +214,7 @@ struct agg_renderer_process_visitor_l
         using apply_vertex_converter_type = detail::apply_vertex_converter<vertex_converter_type, rasterizer_type>;
         using vertex_processor_type = geometry::vertex_processor<apply_vertex_converter_type>;
         apply_vertex_converter_type apply(converter, ras);
-        mapnik::util::apply_visitor(vertex_processor_type(apply),feature_.get_geometry());
+        mapnik::util::apply_visitor(vertex_processor_type(apply), feature_.get_geometry());
     }
 
   private:
diff --git a/src/agg/process_polygon_pattern_symbolizer.cpp b/src/agg/process_polygon_pattern_symbolizer.cpp
index fb00b2a00..8e340a9a8 100644
--- a/src/agg/process_polygon_pattern_symbolizer.cpp
+++ b/src/agg/process_polygon_pattern_symbolizer.cpp
@@ -75,9 +75,9 @@ struct agg_renderer_process_visitor_p
         feature_(feature),
         prj_trans_(prj_trans) {}
 
-    void operator() (marker_null const&) {}
+    void operator() (marker_null const&) const {}
 
-    void operator() (marker_svg const& marker)
+    void operator() (marker_svg const& marker) const
     {
         agg::trans_affine image_tr = agg::trans_affine_scaling(common_.scale_factor_);
         auto image_transform = get_optional<transform_type>(sym_, keys::image_transform);
@@ -180,7 +180,7 @@ struct agg_renderer_process_visitor_p
         agg::render_scanlines(*ras_ptr_, sl, rp);
     }
 
-    void operator() (marker_rgba8 const& marker)
+    void operator() (marker_rgba8 const& marker) const
     {
         using color = agg::rgba8;
         using order = agg::order_rgba;
diff --git a/src/cairo/cairo_renderer.cpp b/src/cairo/cairo_renderer.cpp
index 17723071c..83e1208b1 100644
--- a/src/cairo/cairo_renderer.cpp
+++ b/src/cairo/cairo_renderer.cpp
@@ -104,10 +104,10 @@ struct setup_marker_visitor
     setup_marker_visitor(cairo_context & context, renderer_common const& common)
         : context_(context), common_(common) {}
 
-    void operator() (marker_null const &) {}
-    void operator() (marker_svg const &) {}
+    void operator() (marker_null const &) const{}
+    void operator() (marker_svg const &) const {}
 
-    void operator() (marker_rgba8 const& marker)
+    void operator() (marker_rgba8 const& marker) const
     {
         mapnik::image_rgba8 const& bg_image = marker.get_data();
         std::size_t w = bg_image.width();
diff --git a/src/image_compositing.cpp b/src/image_compositing.cpp
index 12633cbc2..925f56e64 100644
--- a/src/image_compositing.cpp
+++ b/src/image_compositing.cpp
@@ -190,7 +190,7 @@ struct composite_visitor
           dy_(dy) {}
 
     template <typename T>
-    void operator() (T & dst);
+    void operator() (T & dst) const;
 
   private:
     image_any const& src_;
@@ -201,19 +201,19 @@ struct composite_visitor
 };
 
 template <typename T>
-void composite_visitor::operator() (T & dst)
+void composite_visitor::operator() (T & dst) const
 {
     throw std::runtime_error("Error: Composite with " + std::string(typeid(dst).name()) + " is not supported");
 }
 
 template <>
-void composite_visitor::operator()<image_rgba8> (image_rgba8 & dst)
+void composite_visitor::operator()<image_rgba8> (image_rgba8 & dst) const
 {
     composite(dst, util::get<image_rgba8>(src_), mode_, opacity_, dx_, dy_);
 }
 
 template <>
-void composite_visitor::operator()<image_gray32f> (image_gray32f & dst)
+void composite_visitor::operator()<image_gray32f> (image_gray32f & dst) const
 {
     composite(dst, util::get<image_gray32f>(src_), mode_, opacity_, dx_, dy_);
 }
diff --git a/src/image_copy.cpp b/src/image_copy.cpp
index 01225c25b..04fa75c32 100644
--- a/src/image_copy.cpp
+++ b/src/image_copy.cpp
@@ -37,7 +37,7 @@ struct visitor_image_copy
 {
     using dst_type = typename T0::pixel_type;
 
-    T0 operator() (image_null const&)
+    T0 operator() (image_null const&) const
     {
         throw std::runtime_error("Can not cast a null image");
     }
@@ -48,7 +48,7 @@ struct visitor_image_copy
     }
 
     template <typename T1>
-    T0 operator() (T1 const& src)
+    T0 operator() (T1 const& src) const
     {
         T0 dst(safe_cast<int>(src.width()), safe_cast<int>(src.height()), false);
         for (std::size_t y = 0; y < dst.height(); ++y)
@@ -75,7 +75,7 @@ struct visitor_image_copy_so
         throw std::runtime_error("Can not cast a null image");
     }
 
-    T0 operator() (T0 const& src)
+    T0 operator() (T0 const& src) const
     {
         if (offset_ == src.get_offset() && scaling_ == src.get_scaling())
         {
@@ -91,7 +91,7 @@ struct visitor_image_copy_so
     }
 
     template <typename T1>
-    T0 operator() (T1 const& src)
+    T0 operator() (T1 const& src) const
     {
         double src_offset = src.get_offset();
         double src_scaling = src.get_scaling();
diff --git a/src/image_util.cpp b/src/image_util.cpp
index fdbd80c9b..43c599166 100644
--- a/src/image_util.cpp
+++ b/src/image_util.cpp
@@ -2087,7 +2087,7 @@ struct visitor_view_to_stream
         : os_(os) {}
 
     template <typename T>
-    void operator() (T const& view)
+    void operator() (T const& view) const
     {
         for (std::size_t i=0;i<view.height();i++)
         {
diff --git a/src/marker_cache.cpp b/src/marker_cache.cpp
index 664121854..9e4062226 100644
--- a/src/marker_cache.cpp
+++ b/src/marker_cache.cpp
@@ -118,19 +118,19 @@ namespace detail
 
 struct visitor_create_marker
 {
-    marker operator() (image_rgba8 & data)
+    marker operator() (image_rgba8 & data) const
     {
         mapnik::premultiply_alpha(data);
         return mapnik::marker(mapnik::marker_rgba8(data));
     }
 
-    marker operator() (image_null &)
+    marker operator() (image_null &) const
     {
         throw std::runtime_error("Can not make marker from null image data type");
     }
 
     template <typename T>
-    marker operator() (T &)
+    marker operator() (T &) const
     {
         throw std::runtime_error("Can not make marker from this data type");
     }
diff --git a/src/warp.cpp b/src/warp.cpp
index b250d6e39..4a468a8b3 100644
--- a/src/warp.cpp
+++ b/src/warp.cpp
@@ -181,10 +181,10 @@ struct warp_image_visitor
           nodata_value_(nodata_value)
     {}
 
-    void operator() (image_null const&) {}
+    void operator() (image_null const&) const {}
 
     template <typename T>
-    void operator() (T const& source)
+    void operator() (T const& source) const
     {
         using image_type = T;
         //source and target image data types must match
diff --git a/test/unit/geometry/geometry_equal.hpp b/test/unit/geometry/geometry_equal.hpp
index cb4a30ddf..3907149ac 100644
--- a/test/unit/geometry/geometry_equal.hpp
+++ b/test/unit/geometry/geometry_equal.hpp
@@ -89,26 +89,26 @@ void assert_g_equal(geometry<T> const& g1, geometry<T> const& g2);
 struct geometry_equal_visitor
 {
     template <typename T1, typename T2>
-    void operator() (T1 const&, T2 const&)
+    void operator() (T1 const&, T2 const&) const
     {
         // comparing two different types!
         REQUIRE(false);
     }
 
-    void operator() (geometry_empty const&, geometry_empty const&)
+    void operator() (geometry_empty const&, geometry_empty const&) const
     {
         REQUIRE(true);
     }
 
     template <typename T>
-    void operator() (point<T> const& p1, point<T> const& p2)
+    void operator() (point<T> const& p1, point<T> const& p2) const
     {
         REQUIRE(p1.x == Approx(p2.x));
         REQUIRE(p1.y == Approx(p2.y));
     }
 
     template <typename T>
-    void operator() (line_string<T> const& ls1, line_string<T> const& ls2)
+    void operator() (line_string<T> const& ls1, line_string<T> const& ls2) const
     {
         if (ls1.size() != ls2.size())
         {
@@ -123,7 +123,7 @@ struct geometry_equal_visitor
     }
 
     template <typename T>
-    void operator() (polygon<T> const& p1, polygon<T> const& p2)
+    void operator() (polygon<T> const& p1, polygon<T> const& p2) const
     {
         (*this)(static_cast<line_string<T> const&>(p1.exterior_ring), static_cast<line_string<T> const&>(p2.exterior_ring));
 
@@ -139,13 +139,13 @@ struct geometry_equal_visitor
     }
 
     template <typename T>
-    void operator() (multi_point<T> const& mp1, multi_point<T> const& mp2)
+    void operator() (multi_point<T> const& mp1, multi_point<T> const& mp2) const
     {
         (*this)(static_cast<line_string<T> const&>(mp1), static_cast<line_string<T> const&>(mp2));
     }
 
     template <typename T>
-    void operator() (multi_line_string<T> const& mls1, multi_line_string<T> const& mls2)
+    void operator() (multi_line_string<T> const& mls1, multi_line_string<T> const& mls2) const
     {
         if (mls1.size() != mls2.size())
         {
@@ -159,7 +159,7 @@ struct geometry_equal_visitor
     }
 
     template <typename T>
-    void operator() (multi_polygon<T> const& mpoly1, multi_polygon<T> const& mpoly2)
+    void operator() (multi_polygon<T> const& mpoly1, multi_polygon<T> const& mpoly2) const
     {
         if (mpoly1.size() != mpoly2.size())
         {
@@ -173,7 +173,7 @@ struct geometry_equal_visitor
     }
 
     template <typename T>
-    void operator() (mapnik::util::recursive_wrapper<geometry_collection<T> > const& c1_, mapnik::util::recursive_wrapper<geometry_collection<T> > const& c2_)
+    void operator() (mapnik::util::recursive_wrapper<geometry_collection<T> > const& c1_, mapnik::util::recursive_wrapper<geometry_collection<T> > const& c2_) const
     {
         geometry_collection<T> const& c1 = static_cast<geometry_collection<T> const&>(c1_);
         geometry_collection<T> const& c2 = static_cast<geometry_collection<T> const&>(c2_);
@@ -189,7 +189,7 @@ struct geometry_equal_visitor
     }
 
     template <typename T>
-    void operator() (geometry_collection<T> const& c1, geometry_collection<T> const& c2)
+    void operator() (geometry_collection<T> const& c1, geometry_collection<T> const& c2) const
     {
         if (c1.size() != c2.size())
         {
diff --git a/test/visual/runner.cpp b/test/visual/runner.cpp
index 5ff923172..d0c7222fb 100644
--- a/test/visual/runner.cpp
+++ b/test/visual/runner.cpp
@@ -57,13 +57,13 @@ public:
     }
 
     template <typename T, typename std::enable_if<T::renderer_type::support_tiles>::type* = nullptr>
-    void operator()(T const & renderer)
+    void operator()(T const& renderer) const
     {
         test(renderer);
     }
 
     template <typename T, typename std::enable_if<!T::renderer_type::support_tiles>::type* = nullptr>
-    void operator()(T const & renderer)
+    void operator()(T const & renderer) const
     {
         if (tiles_.width == 1 && tiles_.height == 1)
         {
@@ -73,7 +73,7 @@ public:
 
 private:
     template <typename T>
-    void test(T const & renderer)
+    void test(T const & renderer) const
     {
         map_size size { map_.width(), map_.height() };
         std::chrono::high_resolution_clock::time_point start(std::chrono::high_resolution_clock::now());
@@ -96,7 +96,7 @@ private:
     }
 
     template <typename T, typename std::enable_if<T::renderer_type::support_tiles>::type* = nullptr>
-    typename T::image_type render(T const & renderer)
+    typename T::image_type render(T const& renderer) const
     {
         if (tiles_.width == 1 && tiles_.height == 1)
         {
@@ -109,7 +109,7 @@ private:
     }
 
     template <typename T, typename std::enable_if<!T::renderer_type::support_tiles>::type* = nullptr>
-    typename T::image_type render(T const & renderer)
+    typename T::image_type render(T const & renderer) const
     {
         return renderer.render(map_, scale_factor_);
     }
@@ -364,4 +364,3 @@ void runner::parse_map_sizes(std::string const & str, std::vector<map_size> & si
 }
 
 }
-
diff --git a/utils/svg2png/svg2png.cpp b/utils/svg2png/svg2png.cpp
index 2b5e79369..c7fe79735 100644
--- a/utils/svg2png/svg2png.cpp
+++ b/utils/svg2png/svg2png.cpp
@@ -56,7 +56,7 @@ struct main_marker_visitor
           verbose_(verbose),
           auto_open_(auto_open) {}
 
-    int operator() (mapnik::marker_svg const& marker)
+    int operator() (mapnik::marker_svg const& marker) const
     {
         using pixfmt = agg::pixfmt_rgba32_pre;
         using renderer_base = agg::renderer_base<pixfmt>;
@@ -122,14 +122,14 @@ struct main_marker_visitor
 
     // default
     template <typename T>
-    int operator() (T const&)
+    int operator() (T const&) const
     {
         std::clog << "svg2png error: '" << svg_name_ << "' is not a valid vector!\n";
         return -1;
     }
 
   private:
-    std::string const& svg_name_;
+    std::string svg_name_;
     bool verbose_;
     bool auto_open_;
 };