dlib C++ Library - polygon.h

    // Copyright (C) 2022  Davis E. King (davis@dlib.net), Adrià Arrufat
    // License: Boost Software License   See LICENSE.txt for the full license.
    #ifndef DLIB_POLYGOn_
    #define DLIB_POLYGOn_

    #include "polygon_abstract.h"
    #include "rectangle.h"
    #include "vector.h"

    namespace dlib
    {
        class polygon
        {
        public:
            using size_type = std::vector<point>::size_type;

            polygon(std::vector<point> points) : points(std::move(points)) {}

            size_type size() const { return points.size(); }

            point& operator[](const size_type idx) { return points[idx]; }
            const point& operator[](const size_type idx) const { return points[idx]; }
            const point& at(const size_type idx) const { return points.at(idx); }

            std::vector<point>::iterator begin() { return points.begin(); }
            std::vector<point>::iterator end() { return points.end(); }
            const std::vector<point>::const_iterator begin() const { return points.begin(); }
            const std::vector<point>::const_iterator end() const { return points.end(); }

            rectangle get_rect() const
            {
                rectangle rect;
                for (const auto& p : points)
                    rect += p;
                return rect;
            }

            double area() const { return polygon_area(points); }

            template <typename alloc>
            void get_left_and_right_bounds (
                const long top,
                const long bottom,
                std::vector<double, alloc>& left_boundary,
                std::vector<double, alloc>& right_boundary
            ) const
            {
                using std::min;
                using std::max;

                left_boundary.assign(bottom-top+1, std::numeric_limits<double>::infinity());
                right_boundary.assign(bottom-top+1, -std::numeric_limits<double>::infinity());

                // trace out the points along the edge of the polynomial and record them
                for (unsigned long i = 0; i < points.size(); ++i)
                {
                    const point p1 = points[i];
                    const point p2 = points[(i+1)%points.size()];

                    if (p1.y() == p2.y())
                    {
                        if (top <= p1.y() && p1.y() <= bottom)
                        {
                            const long y = p1.y() - top;
                            const double xmin = min(p1.x(), p2.x());
                            const double xmax = min(p1.x(), p2.x());
                            left_boundary[y]  = min(left_boundary[y], xmin);
                            right_boundary[y] = max(right_boundary[y], xmax);
                        }
                    }
                    else
                    {
                        // Here we trace out the line from p1 to p2 and record where it hits.

                        // x = m*y + b
                        const double m = (p2.x() - p1.x())/(double)(p2.y()-p1.y());
                        const double b = p1.x() - m*p1.y(); // because: x1 = m*y1 + b

                        const long ymin = max(top,min(p1.y(), p2.y()));
                        const long ymax = min(bottom,max(p1.y(), p2.y()));
                        for (long y = ymin; y <= ymax; ++y)
                        {
                            const double x = m*y + b;
                            const unsigned long idx = y-top;
                            left_boundary[idx]  = min(left_boundary[idx], x);
                            right_boundary[idx] = max(right_boundary[idx], x);
                        }
                    }
                }
            }

        private:
            std::vector<point> points;
        };
    }

    #endif  // polygon_h_INCLUDED