gistfile1.hpp

   struct coloriser 
   {
       explicit coloriser(mapnik::Color const& c)
           : c_(c) {}

        template <typename PixelType>      
       void operator() ( PixelType & p)
       {
    // use c to modify p
           p[0] = c_.red();
           p[1] = c_.green();
           p[2] = c_.blue();
       }
           mapnik::Color const& c_;
       };

   template <typename T>
   void agg_renderer<T>::process(point_symbolizer const& sym,
                              Feature const& feature,
                              proj_transform const& prj_trans)
   {
      double x;
      double y;
      double z=0;
      boost::shared_ptr<ImageData32> const& data = sym.get_image();
      if ( data )
      {
          ImageData32 target(int(floor(data->width() * sym.get_scale())),int(floor(data->height() * sym.get_scale())));
          scale_image<ImageData32>(target,*data);

          // creating a lightweight view from  rgba  
          boost::gil::rgba8_view_t view = interleaved_view(target.width(),target.height(),
              (boost::gil::rgba8_pixel_t*)target.getData(),
              target.width() * 4);

          mapnik::Color c(255,0,0);
          coloriser op(c);
          for_each_pixel(view,coloriser<ImageData32::pixel_type>(c));
     
         for (unsigned i=0;i<feature.num_geometries();++i)
         {
            geometry2d const& geom = feature.get_geometry(i);
            
            geom.label_position(&x,&y);
            prj_trans.backward(x,y,z);
            t_.forward(&x,&y);

            int w = target.width();
            int h = target.height();
            std::clog << "scale=" << sym.get_scale() << "w=" << w << "h=" << h << "\n";            
            int px=int(floor(x - 0.5 * w));
            int py=int(floor(y - 0.5 * h));
            Envelope<double> label_ext (floor(x - 0.5 * w),
                                        floor(y - 0.5 * h),
                                        ceil (x + 0.5 * w),
                                        ceil (y + 0.5 * h));
            if (sym.get_allow_overlap() || 
                detector_.has_placement(label_ext))
            {    
               pixmap_.set_rectangle_alpha2(target,px,py,sym.get_opacity());
               detector_.insert(label_ext);
            }
         }
      }
   }