boost::geometry svg_mapper, the polygon is not fully saved? - boost

Question

I have a simple example where a graph of polygon is created and saved to an svg file. However, the polygon is partially saved only. So how can I resize the graph?
#include <string>
#include <fstream>
#include <boost/geometry.hpp>
#include <boost/geometry/geometries/point_xy.hpp>
#include <boost/geometry/geometries/polygon.hpp>
#include <boost/geometry/geometries/adapted/c_array.hpp>
// Using the boost namespace
using namespace boost::geometry;
// Register the C array points for boost
BOOST_GEOMETRY_REGISTER_C_ARRAY_CS(cs::cartesian)
template <typename Geometry>
void create_svg(std::string const& file_path, Geometry const& geometry, std::string
const& style) {
using PointType = typename point_type<Geometry>::type;
std::ofstream svg_file(file_path.c_str());
svg_mapper<PointType> mapper(svg_file, 2000, 2000);
mapper.add(geometry);
mapper.map(geometry, style);
}
int main() {
model::polygon<model::d2::point_xy<double>, false> polygon;
double points[][2] = {{0., 0.}, {2., 1.}, {3., 3.}, {-0.5, 0.5}, {0., 0.}};
append(polygon, points);
std::string style{"fill-rule:nonzero;fill-opacity:0.5;fill:yellow;stroke:black;stroke-width:2;"};
create_svg("image.svg", polygon, style);
return 0;
}
The output is like:

Answer 1

It seems that somehow the scale factor/bounding box get miscalculated.
Using
bg::svg_mapper<PointType> mapper(svg_file, 400, 400);
works fine. If all coords get scaled at (larger than) integral grid, all is fine.
I tried to isolate any contibuting factor (integral coordinate type, clockwise orientation polygons, SameScale = true template argument for the svg_mapper) but it all seems unrelated. Ubsan did not flag anything. I would report this at the library. Meanwhile, try smaller SVG dimensions to "hide" the issue:
Live On Coliru
#include <fstream>
#include <iostream>
#include <boost/geometry.hpp>
#include <boost/geometry/geometries/point_xy.hpp>
#include <boost/geometry/geometries/polygon.hpp>
// Using the boost namespace
namespace bg = boost::geometry;
template <typename Geometry>
void create_svg(std::string const& file_path, Geometry const& geometry,
std::string const& style)
{
using PointType = typename bg::point_type<Geometry>::type;
std::ofstream svg_file(file_path);
bg::svg_mapper<PointType/*, true*/> mapper(svg_file, 400, 400);
mapper.add(geometry);
mapper.map(geometry, style);
}
template <typename T> void check(T& geo) {
for (std::string reason; !bg::is_valid(geo, reason); bg::correct(geo)) {
std::cout << "Correcting: " << reason << "\n";
}
}
int main()
{
bg::model::polygon<bg::model::d2::point_xy<double>> polygon{
{{0, 0}, {-.5, .5}, {3, 3}, {2, 1}, {0, 0}}};
check(polygon);
std::string style{"fill-rule:nonzero;fill-opacity:0.5;fill:yellow;stroke:"
"black;stroke-width:2;"};
create_svg("image.svg", polygon, style);
}
Rendering:
BREAKTHROUGH
I just noticed that for me Chrome renders the "weird" SVG as
I thought is was strange that is is rendered differently from your question.
I just thought to check with Inkscape, and lo and behold, it comes out "normal":
The x/y rulers seem to indicate correct scaling. So my best theory is that it's a browser-specific limitation that doesn't render "very large" SVG scales well?