-------------------------------------------------- From: "Michael Marcin" <mike.marcin@gmail.com> Sent: Tuesday, September 23, 2008 1:37 PM Newsgroups: gmane.comp.lib.boost.devel To: <boost@lists.boost.org> Subject: Re: generative geometry algorithms library idea
Brandon Kohn wrote:
Hi all,
I've been doing some work for the past few weeks on a generative/generic 2D geometry library (leaving open the possibility for 3D in the future). The idea is for all the algorithms to be generative taking coordinate, point, segment, polyline/gon types as template parameters (or deducing where presented as nested typedefs) and specialized traits types for accessing type traits and methods ( things like access_traits<point_type>::get_x( point ) .). So far the library has allowed me to work with the same algorithms in native floating type and exact types like gmp's mpq_class. It's just a first rough draft of ideas, and I would really like some input from the community to see if I'm on the right track for something that boost would be interested in having. I'll post a copy of the lib in the va ult. It's header only (with a small testbed with trivial testing and a visual studio 2008 solution/project). I hope there should not be too many issues compiling these tests/headers under ot her platforms.
I'll put it in the vault as generative_geometry_algorithms.zip
Thanks for any constructive input.
Apologies I haven't looked at your library yet but is it likely that the algorithms will be usable with eigen2* data types? Eigen2 seems to be the best open source small vector/matrix library right now for performance. At least that I can find.
Thanks,
-- Michael Marcin
HI Michael, I wouldn't see any reason why it wouldn't. The basic rationale for representation of primitives is that their numeric traits, dimension etc are embedded in a point_traits<> specialization. Access functions are specified in a separate traits specialization. There are a couple of ways you can use the code: (apologies if the format doesn't come out right... this is my first time posting code) For example, say you have a vector type for your point: (eigen seems to use: VectorXf ) BOOST_DEFINE_USER_POINT_TRAITS( VectorXf, float, 2 );//note the 2 is dimension. template <> struct cartesian_access_traits< VectorXf > { typedef VectorXf point_type; typedef boost::numeric::geometry::point_traits< VectorXf
::coordinate_type coordinate_type; typedef boost::numeric::geometry::point_traits< VectorXf>::dimension_type dimension_type;
static inline coordinate_type get_x( const point_type& p ) { return p[0]; } static inline coordinate_type get_y( const point_type& p ) { return p[1]; } //Note, the template requirement here is due to some experimentation I'm doing on how to deal with different dimensions and the //construct member functions specification both 2 and higher dimensions. //I wanted to make use the enable_if/disable_if based on the point_traits<>::dimension_type and to do that, you have to be in a template member function //(at least in visual studio) template <typename Point> static inline point_type construct( const coordinate_type& x, const coordinate_type& y ) { point_type p(dimenstion_type::value); p[0] = x; p[1] = y; return p; } }; BOOST_DEFINE_SEGMENT_TRAITS( VectorXf, segment< VectorXf > ); BOOST_DEFINE_SEGMENT_ACCESS_TRAITS( segment< VectorXf > ); Here is a specialization I did for the GMP rational type using the point template provided with my code: typedef point<mpq_class, 2> point_rational_2d; BOOST_DEFINE_POINT_TRAITS( point_rational_2d ); BOOST_DEFINE_CARTESIAN_ACCESS_TRAITS( point_rational_2d ); BOOST_DEFINE_SEGMENT_TRAITS( point_rational_2d, segment< point_rational_2d
); BOOST_DEFINE_SEGMENT_ACCESS_TRAITS( segment< point_rational_2d > );
You can then use the points as-is in the algorithms: For example: BOOST_AUTO_TEST_CASE( TestIntersections ) { using namespace boost::numeric::geometry; typedef cartesian_access_traits< VectorFx > point_access; VectorFx p1 = point_access::construct< VectorFx >( 0., 0. ); //I agree... it's annoying to have the point type specified here as a template parameter. VectorFx p2 = point_access::construct< VectorFx >( 1., 1. ); VectorFx p3 = point_access::construct< VectorFx >( 1., 0. ); VectorFx p4 = point_access::construct< VectorFx >( 0., 1. ); segment< VectorFx > seg1( p1, p2 ); segment< VectorFx > seg2( p3, p4 ); VectorFx xPoints[2]; intersection_type iType = intersect( seg1, seg2, xPoints, fraction_tolerance_comparison_policy<float>(1e-5) ); std::cout << iType << " at point: " << point_access::get_x( Points[0] ) << ", " << point_access::get_y( xPoints[0] ) << std::endl; } This is still very much a work in progress, but please do have a look and see what you think. I'd like to hear suggestions about the design or how I might improve things. Cheers, Brandon