boost::optional<std::string> linestring_bbox_clipping(mapnik::box2d<double> bbox,
std::string wkt_in)
{
using namespace mapnik;
agg::trans_affine tr;
projection src(MAPNIK_LONGLAT_PROJ);
projection dst(MAPNIK_LONGLAT_PROJ);
proj_transform prj_trans(src,dst);
line_symbolizer sym;
CoordTransform t(bbox.width(),bbox.height(), bbox);
boost::ptr_vector<mapnik::geometry_type> output_paths;
output_geometry_backend backend(output_paths, mapnik::LineString);
typedef boost::mpl::vector<clip_line_tag> conv_types;
vertex_converter<box2d<double>, output_geometry_backend, line_symbolizer,
CoordTransform, proj_transform, agg::trans_affine, conv_types>
converter(bbox, backend, sym, t, prj_trans, tr, 1.0);
converter.set<clip_line_tag>();
boost::ptr_vector<geometry_type> p;
if (!mapnik::from_wkt(wkt_in , p))
{
throw std::runtime_error("Failed to parse WKT");
}
BOOST_FOREACH( geometry_type & geom, p)
{
converter.apply(geom);
}
box2d<double> get_buffered_extent() const
{
double extra = 2.0 * scale() * buffer_size_;
box2d<double> ext(extent_);
double extra_width = extent_.width() + extra;
double extra_height = extent_.height() + extra;
if (extra_width < 0.0)
{
extra_width = 0.0;
}
if (extra_height < 0.0)
{
extra_height = 0.0;
}
ext.width(extra_width);
ext.height(extra_height);
return ext;
}