Use middle_point placement for marker POINT placement on lines

REFS #1604, #1350, #1607 and #1625

deps/agg/include/agg_conv_adaptor_vcgen.h

@@ -29,6 +29,7 @@ namespace agg
 
         void rewind(unsigned) {}
         unsigned vertex(double*, double*) { return path_cmd_stop; }
+        unsigned type() const { return 0; }
     };
 
 
@@ -64,6 +65,7 @@ namespace agg
         }
 
         unsigned vertex(double* x, double* y);
+        unsigned type() const { return m_source->type(); }
 
     private:
         // Prohibit copying

deps/agg/include/agg_conv_adaptor_vpgen.h

@@ -33,6 +33,7 @@ namespace agg
 
         void rewind(unsigned path_id);
         unsigned vertex(double* x, double* y);
+        unsigned type() const { return m_source->type(); }
 
     private:
         conv_adaptor_vpgen(const conv_adaptor_vpgen<VertexSource, VPGen>&);

deps/agg/include/agg_conv_clip_polygon.h

@@ -51,6 +51,7 @@ namespace agg
         double y1() const { return base_type::vpgen().y1(); }
         double x2() const { return base_type::vpgen().x2(); }
         double y2() const { return base_type::vpgen().y2(); }
+        unsigned type() const { return base_type::type(); }
 
     private:
         conv_clip_polygon(const conv_clip_polygon<VertexSource>&);

deps/agg/include/agg_conv_clip_polyline.h

@@ -51,6 +51,7 @@ namespace agg
         double y1() const { return base_type::vpgen().y1(); }
         double x2() const { return base_type::vpgen().x2(); }
         double y2() const { return base_type::vpgen().y2(); }
+        unsigned type() const { return base_type::type(); }
 
     private:
         conv_clip_polyline(const conv_clip_polyline<VertexSource>&);

deps/agg/include/agg_conv_smooth_poly1.h

@@ -42,6 +42,7 @@ namespace agg
 
         void   smooth_value(double v) { base_type::generator().smooth_value(v); }
         double smooth_value() const { return base_type::generator().smooth_value(); }
+        unsigned type() const { return base_type::type(); }
 
     private:
         conv_smooth_poly1(const conv_smooth_poly1<VertexSource>&);
@@ -64,6 +65,7 @@ namespace agg
 
         void   smooth_value(double v) { m_smooth.generator().smooth_value(v); }
         double smooth_value() const { return m_smooth.generator().smooth_value(); }
+        unsigned type() const { return m_smooth.type(); }
 
     private:
         conv_smooth_poly1_curve(const conv_smooth_poly1_curve<VertexSource>&);

include/mapnik/ctrans.hpp

@@ -81,6 +81,11 @@ struct MAPNIK_DECL coord_transform
         geom_.rewind(pos);
     }
 
+    unsigned type() const
+    {
+      return static_cast<unsigned>(geom_.type());
+    }
+
     Geometry const& geom() const
     {
         return geom_;

include/mapnik/marker_helpers.hpp

@@ -91,7 +91,12 @@ struct vector_markers_rasterizer_dispatch
         {
             double x = 0;
             double y = 0;
-            if (placement_method == MARKER_INTERIOR_PLACEMENT)
+            if (path.type() == LineString)
+            {
+                if (!label::middle_point(path, x, y))
+                    return;
+            }
+            else if (placement_method == MARKER_INTERIOR_PLACEMENT)
             {
                 if (!label::interior_position(path, x, y))
                     return;
@@ -187,7 +192,12 @@ struct raster_markers_rasterizer_dispatch
         {
             double x = 0;
             double y = 0;
-            if (placement_method == MARKER_INTERIOR_PLACEMENT)
+            if (path.type() == LineString)
+            {
+                if (!label::middle_point(path, x, y))
+                    return;
+            }
+            else if (placement_method == MARKER_INTERIOR_PLACEMENT)
             {
                 if (!label::interior_position(path, x, y))
                     return;