tippecanoe/earcut.cpp

#include "geometry.hpp"
#include "mapbox/geometry/earcut.hpp"

using Coord = long long;
using N = size_t;
using Point = std::array<Coord, 2>;

drawvec fix_by_triangulation(drawvec const &dv, int z, int detail) {
	std::vector<std::vector<Point>> polygon;
	drawvec out;
	double scale = 1LL << (32 - z - detail);

	for (size_t i = 0; i < dv.size(); i++) {
		if (dv[i].op == VT_MOVETO) {
			size_t j;
			for (j = i + 1; j < dv.size(); j++) {
				if (dv[j].op != VT_LINETO) {
					break;
				}
			}

			std::vector<Point> ring;
			// j - 1 because earcut docs indicate that it doesn't expect
			// a duplicate last point in each ring
			for (size_t k = i; k < j - 1; k++) {
				Point p = {(long long) dv[k].x, (long long) dv[k].y};
				ring.push_back(p);
				out.push_back(dv[k]);
			}
			polygon.push_back(ring);

			i = j - 1;
		}
	}

	std::vector<N> indices = mapbox::earcut<N>(polygon);

	bool again = true;
	while (again) {
		again = false;
		for (size_t i = 0; i + 2 < indices.size(); i += 3) {
			for (size_t j = 0; j < 3; j++) {
				size_t v1 = i + j;
				size_t v2 = i + ((j + 1) % 3);

				if (std::llround(out[indices[v1]].x / scale) == std::llround(out[indices[v2]].x / scale) &&
				    std::llround(out[indices[v1]].y / scale) == std::llround(out[indices[v2]].y / scale)) {
					double ang = atan2(out[indices[v2]].y - out[indices[v1]].y, out[indices[v2]].x - out[indices[v1]].x);

					printf("at %zu/%zu: %zu and %zu: ", i, j, v1, v2);
					printf("z%d: was %f,%f to %f,%f ",
					       z,
					       out[indices[v1]].x / scale, out[indices[v1]].y / scale,
					       out[indices[v2]].x / scale, out[indices[v2]].y / scale);

					out[indices[v1]].x -= scale * cos(ang) * sqrt(2);
					out[indices[v1]].y -= scale * sin(ang) * sqrt(2);
					out[indices[v2]].x += scale * cos(ang) * sqrt(2);
					out[indices[v2]].y += scale * sin(ang) * sqrt(2);
					again = true;

					printf("now %f,%f to %f,%f\n",
					       out[indices[v1]].x / scale, out[indices[v1]].y / scale,
					       out[indices[v2]].x / scale, out[indices[v2]].y / scale);
				}
			}
		}
	}

	drawvec out2;
	for (size_t i = 0; i < out.size(); i++) {
		if (out[i].op == VT_MOVETO) {
			size_t j;
			for (j = i + 1; j < out.size(); j++) {
				if (out[j].op != VT_LINETO) {
					break;
				}
			}

			for (size_t k = i; k < j; k++) {
				out2.push_back(out[k]);
			}

			// re-close the ring
			out2.push_back(draw(VT_LINETO, out[i].x, out[i].y));
			i = j - 1;
		}
	}

	return out2;
}