add 'interior' placement option to text_symbolizr - patch from Toby Collet - closes #709

bindings/python/mapnik_text_symbolizer.cpp

@@ -165,6 +165,7 @@ void export_text_symbolizer()
         .value("LINE_PLACEMENT",LINE_PLACEMENT)
         .value("POINT_PLACEMENT",POINT_PLACEMENT)
         .value("VERTEX_PLACEMENT",VERTEX_PLACEMENT)
+        .value("INTERIOR_PLACEMENT",INTERIOR_PLACEMENT)
         ;
     enumeration_<vertical_alignment_e>("vertical_alignment")
         .value("TOP",TOP)

include/mapnik/geometry.hpp

@@ -105,6 +105,75 @@ public:
         }
         return result;
     }
+
+    void label_interior_position(double *x, double *y) const
+    {
+        // start with the default label position
+        label_position(x,y);
+        unsigned size = cont_.size();
+        // if we are not a polygon, or the default is within the polygon we are done
+        if (size < 3 || hit_test(*x,*y,0))
+            return;
+
+        // otherwise we find a horizontal line across the polygon and then return the
+        // center of the widest intersection between the polygon and the line.
+
+        std::vector<double> intersections; // only need to store the X as we know the y
+
+        double x0, y0;
+        rewind(0);
+        unsigned command = vertex(&x0, &y0);
+        double x1,y1;
+        while (SEG_END != (command=vertex(&x1, &y1)))
+        {
+            if (command != SEG_MOVETO)
+            {
+                // if the segments overlap
+                if (y0==y1)
+                {
+                    if (y0==*y)
+                    {
+                        double xi = (x0+x1)/2.0;
+                        intersections.push_back(xi);
+                    }
+                }
+                // if the path segment crosses the bisector
+                else if ((y0 <= *y && y1 >= *y) ||
+                        (y0 >= *y && y1 <= *y))
+                {
+                    // then calculate the intersection
+                    double xi = x0;
+                    if (x0 != x1)
+                    {
+                        double m = (y1-y0)/(x1-x0);
+                        double c = y0 - m*x0;
+                        xi = (*y-c)/m;
+                    }
+
+                    intersections.push_back(xi);
+                }
+            }
+            x0 = x1;
+            y0 = y1;
+        }
+        // no intersections we just return the default
+        if (intersections.empty())
+            return;
+        x0=intersections[0];
+        double max_width = 0;
+        for (unsigned ii = 1; ii < intersections.size(); ++ii)
+        {
+            double x1=intersections[ii];
+            double xc=(x0+x1)/2.0;
+            double width = fabs(x1-x0);
+            if (width > max_width && hit_test(xc,*y,0))
+            {
+                *x=xc;
+                max_width = width;
+            }
+        }
+    }
+
     void label_position(double *x, double *y) const
     {
         unsigned size = cont_.size();

include/mapnik/text_symbolizer.hpp

@@ -45,6 +45,7 @@ enum label_placement_enum {
     POINT_PLACEMENT,
     LINE_PLACEMENT,
     VERTEX_PLACEMENT,
+    INTERIOR_PLACEMENT,
     label_placement_enum_MAX
 };
 

src/agg/process_shield_symbolizer.cpp

@@ -121,7 +121,7 @@ void  agg_renderer<T>::process(shield_symbolizer const& sym,
                     path_type path(t_,geom,prj_trans);
 
                     label_placement_enum how_placed = sym.get_label_placement();
-                    if (how_placed == POINT_PLACEMENT || how_placed == VERTEX_PLACEMENT)
+                    if (how_placed == POINT_PLACEMENT || how_placed == VERTEX_PLACEMENT || how_placed == INTERIOR_PLACEMENT)
                     {
                         // for every vertex, try and place a shield/text
                         geom.rewind(0);
@@ -138,6 +138,8 @@ void  agg_renderer<T>::process(shield_symbolizer const& sym,
 
                             if( how_placed == VERTEX_PLACEMENT )
                                 geom.vertex(&label_x,&label_y);  // by vertex
+                            else if( how_placed == INTERIOR_PLACEMENT )
+                                geom.label_interior_position(&label_x,&label_y);
                             else
                                 geom.label_position(&label_x, &label_y);  // by middle of line or by point
                             prj_trans.backward(label_x,label_y, z);

src/agg/process_text_symbolizer.cpp

@@ -95,10 +95,14 @@ void agg_renderer<T>::process(text_symbolizer const& sym,
                 {           
                     placement text_placement(info,sym,scale_factor_);
                     text_placement.avoid_edges = sym.get_avoid_edges();
-                    if (sym.get_label_placement() == POINT_PLACEMENT)
+                    if (sym.get_label_placement() == POINT_PLACEMENT ||
+                            sym.get_label_placement() == INTERIOR_PLACEMENT)
                     {
                         double label_x, label_y, z=0.0;
-                        geom.label_position(&label_x, &label_y);
+                        if (sym.get_label_placement() == POINT_PLACEMENT)
+                            geom.label_position(&label_x, &label_y);
+                        else
+                            geom.label_interior_position(&label_x, &label_y);
                         prj_trans.backward(label_x,label_y, z);
                         t_.forward(&label_x,&label_y);
 

src/cairo_renderer.cpp

@@ -1141,7 +1141,7 @@ void cairo_renderer_base::process(shield_symbolizer const& sym,
                     path_type path(t_, geom, prj_trans);
 
                     label_placement_enum how_placed = sym.get_label_placement();
-                    if (how_placed == POINT_PLACEMENT || how_placed == VERTEX_PLACEMENT)
+                    if (how_placed == POINT_PLACEMENT || how_placed == VERTEX_PLACEMENT || how_placed == INTERIOR_PLACEMENT)
                     {
                         // for every vertex, try and place a shield/text
                         geom.rewind(0);
@@ -1158,6 +1158,8 @@ void cairo_renderer_base::process(shield_symbolizer const& sym,
 
                             if( how_placed == VERTEX_PLACEMENT )
                                 geom.vertex(&label_x,&label_y);  // by vertex
+                            else if( how_placed == INTERIOR_PLACEMENT )
+                                geom.label_interior_position(&label_x,&label_y);
                             else
                                 geom.label_position(&label_x, &label_y);  // by middle of line or by point
                             prj_trans.backward(label_x,label_y, z);
@@ -1550,11 +1552,14 @@ void cairo_renderer_base::process(text_symbolizer const& sym,
                     path_type path(t_, geom, prj_trans);
                     placement text_placement(info, sym, 1.0);
 
-                    if (sym.get_label_placement() == POINT_PLACEMENT)
+                    if (sym.get_label_placement() == POINT_PLACEMENT ||
+                            sym.get_label_placement() == INTERIOR_PLACEMENT)
                     {
-                        double label_x, label_y, z = 0.0;
+                        double label_x, label_y, z=0.0;
-
+                        if (sym.get_label_placement() == POINT_PLACEMENT)
-                        geom.label_position(&label_x, &label_y);
+                            geom.label_position(&label_x, &label_y);
+                        else
+                            geom.label_interior_position(&label_x, &label_y);
                         prj_trans.backward(label_x, label_y, z);
                         t_.forward(&label_x, &label_y);
 

src/text_symbolizer.cpp

@@ -34,6 +34,7 @@ static const char * label_placement_strings[] = {
     "point",
     "line",
     "vertex",
+    "interior",
     ""
 };