tippecanoe/clip.cpp

#include <stdlib.h>
#include <mapbox/geometry/point.hpp>
#include <mapbox/geometry/multi_polygon.hpp>
#include <mapbox/geometry/wagyu/wagyu.hpp>
#include <limits.h>
#include "geometry.hpp"
#include "errors.hpp"
#include "compression.hpp"
#include "mvt.hpp"
#include "polygon.hpp"

static std::vector<std::pair<double, double>> clip_poly1(std::vector<std::pair<double, double>> &geom,
							 long long minx, long long miny, long long maxx, long long maxy,
							 long long ax, long long ay, long long bx, long long by, drawvec &edge_nodes,
							 bool prevent_simplify_shared_nodes);

drawvec simple_clip_poly(drawvec &geom, long long minx, long long miny, long long maxx, long long maxy,
			 long long ax, long long ay, long long bx, long long by, drawvec &edge_nodes, bool prevent_simplify_shared_nodes) {
	drawvec out;
	if (prevent_simplify_shared_nodes) {
		geom = remove_noop(geom, VT_POLYGON, 0);
	}

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

			std::vector<std::pair<double, double>> tmp;
			for (size_t k = i; k < j; k++) {
				double x = geom[k].x;
				double y = geom[k].y;
				tmp.emplace_back(x, y);
			}
			tmp = clip_poly1(tmp, minx, miny, maxx, maxy, ax, ay, bx, by, edge_nodes, prevent_simplify_shared_nodes);
			if (tmp.size() > 0) {
				if (tmp[0].first != tmp[tmp.size() - 1].first || tmp[0].second != tmp[tmp.size() - 1].second) {
					fprintf(stderr, "Internal error: Polygon ring not closed\n");
					exit(EXIT_FAILURE);
				}
			}
			for (size_t k = 0; k < tmp.size(); k++) {
				if (k == 0) {
					out.push_back(draw(VT_MOVETO, std::round(tmp[k].first), std::round(tmp[k].second)));
				} else {
					out.push_back(draw(VT_LINETO, std::round(tmp[k].first), std::round(tmp[k].second)));
				}
			}

			i = j - 1;
		} else {
			fprintf(stderr, "Unexpected operation in polygon %d\n", (int) geom[i].op);
			exit(EXIT_IMPOSSIBLE);
		}
	}

	return out;
}

drawvec simple_clip_poly(drawvec &geom, long long minx, long long miny, long long maxx, long long maxy, bool prevent_simplify_shared_nodes) {
	drawvec dv;
	return simple_clip_poly(geom, minx, miny, maxx, maxy, minx, miny, maxx, maxy, dv, prevent_simplify_shared_nodes);
}

drawvec simple_clip_poly(drawvec &geom, int z, int buffer, drawvec &edge_nodes, bool prevent_simplify_shared_nodes) {
	long long area = 1LL << (32 - z);
	long long clip_buffer = buffer * area / 256;

	return simple_clip_poly(geom, -clip_buffer, -clip_buffer, area + clip_buffer, area + clip_buffer,
				0, 0, area, area, edge_nodes, prevent_simplify_shared_nodes);
}

drawvec clip_point(drawvec &geom, int z, long long buffer) {
	long long min = 0;
	long long area = 1LL << (32 - z);

	min -= buffer * area / 256;
	area += buffer * area / 256;

	return clip_point(geom, min, min, area, area);
}

drawvec clip_point(drawvec &geom, long long minx, long long miny, long long maxx, long long maxy) {
	drawvec out;

	for (size_t i = 0; i < geom.size(); i++) {
		if (geom[i].x >= minx && geom[i].y >= miny && geom[i].x <= maxx && geom[i].y <= maxy) {
			out.push_back(geom[i]);
		}
	}

	return out;
}

drawvec clip_lines(drawvec &geom, int z, long long buffer) {
	long long min = 0;
	long long area = 1LL << (32 - z);
	min -= buffer * area / 256;
	area += buffer * area / 256;

	return clip_lines(geom, min, min, area, area);
}

drawvec clip_lines(drawvec &geom, long long minx, long long miny, long long maxx, long long maxy) {
	drawvec out;

	for (size_t i = 0; i < geom.size(); i++) {
		if (i > 0 && (geom[i - 1].op == VT_MOVETO || geom[i - 1].op == VT_LINETO) && geom[i].op == VT_LINETO) {
			long long x1 = geom[i - 1].x;
			long long y1 = geom[i - 1].y;

			long long x2 = geom[i - 0].x;
			long long y2 = geom[i - 0].y;

			int c = clip(&x1, &y1, &x2, &y2, minx, miny, maxx, maxy);

			if (c > 1) {  // clipped
				out.push_back(draw(VT_MOVETO, x1, y1));
				out.push_back(draw(VT_LINETO, x2, y2));
				out.push_back(draw(VT_MOVETO, geom[i].x, geom[i].y));
			} else if (c == 1) {  // unchanged
				out.push_back(geom[i]);
			} else {  // clipped away entirely
				out.push_back(draw(VT_MOVETO, geom[i].x, geom[i].y));
			}
		} else {
			out.push_back(geom[i]);
		}
	}

	return out;
}

#define INSIDE 0
#define LEFT 1
#define RIGHT 2
#define BOTTOM 4
#define TOP 8

static int computeOutCode(long long x, long long y, long long xmin, long long ymin, long long xmax, long long ymax) {
	int code = INSIDE;

	if (x < xmin) {
		code |= LEFT;
	} else if (x > xmax) {
		code |= RIGHT;
	}

	if (y < ymin) {
		code |= BOTTOM;
	} else if (y > ymax) {
		code |= TOP;
	}

	return code;
}

int clip(long long *x0, long long *y0, long long *x1, long long *y1, long long xmin, long long ymin, long long xmax, long long ymax) {
	int outcode0 = computeOutCode(*x0, *y0, xmin, ymin, xmax, ymax);
	int outcode1 = computeOutCode(*x1, *y1, xmin, ymin, xmax, ymax);
	int accept = 0;
	int changed = 0;

	while (1) {
		if (!(outcode0 | outcode1)) {  // Bitwise OR is 0. Trivially accept and get out of loop
			accept = 1;
			break;
		} else if (outcode0 & outcode1) {  // Bitwise AND is not 0. Trivially reject and get out of loop
			break;
		} else {
			// failed both tests, so calculate the line segment to clip
			// from an outside point to an intersection with clip edge
			long long x = *x0, y = *y0;

			// At least one endpoint is outside the clip rectangle; pick it.
			int outcodeOut = outcode0 ? outcode0 : outcode1;

			// XXX truncating division

			// Now find the intersection point;
			// use formulas y = y0 + slope * (x - x0), x = x0 + (1 / slope) * (y - y0)
			if (outcodeOut & TOP) {	 // point is above the clip rectangle
				x = *x0 + (*x1 - *x0) * (ymax - *y0) / (*y1 - *y0);
				y = ymax;
			} else if (outcodeOut & BOTTOM) {  // point is below the clip rectangle
				x = *x0 + (*x1 - *x0) * (ymin - *y0) / (*y1 - *y0);
				y = ymin;
			} else if (outcodeOut & RIGHT) {  // point is to the right of clip rectangle
				y = *y0 + (*y1 - *y0) * (xmax - *x0) / (*x1 - *x0);
				x = xmax;
			} else if (outcodeOut & LEFT) {	 // point is to the left of clip rectangle
				y = *y0 + (*y1 - *y0) * (xmin - *x0) / (*x1 - *x0);
				x = xmin;
			}

			// Now we move outside point to intersection point to clip
			// and get ready for next pass.
			if (outcodeOut == outcode0) {
				*x0 = x;
				*y0 = y;
				outcode0 = computeOutCode(*x0, *y0, xmin, ymin, xmax, ymax);
				changed = 1;
			} else {
				*x1 = x;
				*y1 = y;
				outcode1 = computeOutCode(*x1, *y1, xmin, ymin, xmax, ymax);
				changed = 1;
			}
		}
	}

	if (accept == 0) {
		return 0;
	} else {
		return changed + 1;
	}
}

static void decode_clipped(mapbox::geometry::multi_polygon<long long> &t, drawvec &out, double scale) {
	out.clear();

	for (size_t i = 0; i < t.size(); i++) {
		for (size_t j = 0; j < t[i].size(); j++) {
			drawvec ring;

			for (size_t k = 0; k < t[i][j].size(); k++) {
				ring.push_back(draw((k == 0) ? VT_MOVETO : VT_LINETO, std::round(t[i][j][k].x / scale), std::round(t[i][j][k].y / scale)));
			}

			if (ring.size() > 0 && ring[ring.size() - 1] != ring[0]) {
				fprintf(stderr, "Had to close ring\n");
				ring.push_back(draw(VT_LINETO, ring[0].x, ring[0].y));
			}

			double area = get_area(ring, 0, ring.size());

			if ((j == 0 && area < 0) || (j != 0 && area > 0)) {
				fprintf(stderr, "Ring area has wrong sign: %f for %zu\n", area, j);
				exit(EXIT_IMPOSSIBLE);
			}

			for (size_t k = 0; k < ring.size(); k++) {
				out.push_back(ring[k]);
			}
		}
	}
}

drawvec clean_or_clip_poly(drawvec &geom, int z, int buffer, bool clip, bool try_scaling) {
	geom = remove_noop(geom, VT_POLYGON, 0);
	mapbox::geometry::multi_polygon<long long> result;

	double scale = 16.0;
	if (!try_scaling) {
		scale = 1.0;
	}

	bool again = true;
	while (again) {
		mapbox::geometry::wagyu::wagyu<long long> wagyu;
		again = false;

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

				if (j >= i + 4) {
					mapbox::geometry::linear_ring<long long> lr;

					for (size_t k = i; k < j; k++) {
						lr.push_back(mapbox::geometry::point<long long>(geom[k].x * scale, geom[k].y * scale));
					}

					if (lr.size() >= 3) {
						wagyu.add_ring(lr);
					}
				}

				i = j - 1;
			}
		}

		if (clip) {
			long long area = 0xFFFFFFFF;
			if (z != 0) {
				area = 1LL << (32 - z);
			}
			long long clip_buffer = buffer * area / 256;

			mapbox::geometry::linear_ring<long long> lr;

			lr.push_back(mapbox::geometry::point<long long>(scale * -clip_buffer, scale * -clip_buffer));
			lr.push_back(mapbox::geometry::point<long long>(scale * -clip_buffer, scale * (area + clip_buffer)));
			lr.push_back(mapbox::geometry::point<long long>(scale * (area + clip_buffer), scale * (area + clip_buffer)));
			lr.push_back(mapbox::geometry::point<long long>(scale * (area + clip_buffer), scale * -clip_buffer));
			lr.push_back(mapbox::geometry::point<long long>(scale * -clip_buffer, scale * -clip_buffer));

			wagyu.add_ring(lr, mapbox::geometry::wagyu::polygon_type_clip);
		}

		try {
			result.clear();
			wagyu.execute(mapbox::geometry::wagyu::clip_type_union, result, mapbox::geometry::wagyu::fill_type_positive, mapbox::geometry::wagyu::fill_type_positive);
		} catch (std::runtime_error &e) {
			FILE *f = fopen("/tmp/wagyu.log", "w");
			fprintf(f, "%s\n", e.what());
			fprintf(stderr, "%s\n", e.what());
			fprintf(f, "[");

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

					if (j >= i + 4) {
						mapbox::geometry::linear_ring<long long> lr;

						if (i != 0) {
							fprintf(f, ",");
						}
						fprintf(f, "[");

						for (size_t k = i; k < j; k++) {
							lr.push_back(mapbox::geometry::point<long long>(geom[k].x, geom[k].y));
							if (k != i) {
								fprintf(f, ",");
							}
							fprintf(f, "[%lld,%lld]", (long long) geom[k].x, (long long) geom[k].y);
						}

						fprintf(f, "]");

						if (lr.size() >= 3) {
						}
					}

					i = j - 1;
				}
			}

			fprintf(f, "]");
			fprintf(f, "\n\n\n\n\n");

			fclose(f);
			fprintf(stderr, "Internal error: Polygon cleaning failed. Log in /tmp/wagyu.log\n");
			exit(EXIT_IMPOSSIBLE);
		}

		if (scale != 1) {
			for (auto const &outer : result) {
				for (auto const &ring : outer) {
					for (auto const &p : ring) {
						if (p.x / scale != std::round(p.x / scale) ||
						    p.y / scale != std::round(p.y / scale)) {
							scale = 1;
							again = true;
							break;
						}
					}
				}
			}
		}
	}

	drawvec ret;
	decode_clipped(result, ret, scale);
	return ret;
}

void to_tile_scale(drawvec &geom, int z, int detail) {
	if (32 - detail - z < 0) {
		for (size_t i = 0; i < geom.size(); i++) {
			geom[i].x = std::round((double) geom[i].x * (1LL << (-(32 - detail - z))));
			geom[i].y = std::round((double) geom[i].y * (1LL << (-(32 - detail - z))));
		}
	} else {
		for (size_t i = 0; i < geom.size(); i++) {
			geom[i].x = std::round((double) geom[i].x / (1LL << (32 - detail - z)));
			geom[i].y = std::round((double) geom[i].y / (1LL << (32 - detail - z)));
		}
	}
}

drawvec from_tile_scale(drawvec const &geom, int z, int detail) {
	drawvec out;
	for (size_t i = 0; i < geom.size(); i++) {
		draw d = geom[i];
		d.x *= (1LL << (32 - detail - z));
		d.y *= (1LL << (32 - detail - z));
		out.push_back(d);
	}
	return out;
}

drawvec remove_noop(drawvec geom, int type, int shift) {
	// first pass: remove empty linetos

	long long ox = 0, oy = 0;
	drawvec out;

	for (size_t i = 0; i < geom.size(); i++) {
		long long nx = std::round((double) geom[i].x / (1LL << shift));
		long long ny = std::round((double) geom[i].y / (1LL << shift));

		if (geom[i].op == VT_LINETO && nx == ox && ny == oy) {
			continue;
		}

		if (geom[i].op == VT_CLOSEPATH) {
			out.push_back(geom[i]);
		} else { /* moveto or lineto */
			out.push_back(geom[i]);
			ox = nx;
			oy = ny;
		}
	}

	// second pass: remove unused movetos

	if (type != VT_POINT) {
		geom = out;
		out.resize(0);

		for (size_t i = 0; i < geom.size(); i++) {
			if (geom[i].op == VT_MOVETO) {
				if (i + 1 >= geom.size()) {
					// followed by end-of-geometry: not needed
					continue;
				}

				if (geom[i + 1].op == VT_MOVETO) {
					// followed by another moveto: not needed
					continue;
				}

				if (geom[i + 1].op == VT_CLOSEPATH) {
					// followed by closepath: not possible
					fprintf(stderr, "Shouldn't happen\n");
					i++;  // also remove unused closepath
					continue;
				}
			}

			out.push_back(geom[i]);
		}
	}

	// second pass: remove empty movetos

	if (type == VT_LINE) {
		geom = out;
		out.resize(0);

		for (size_t i = 0; i < geom.size(); i++) {
			if (i > 1 && geom[i].op == VT_MOVETO) {
				if (geom[i - 1].op == VT_LINETO &&
				    std::round((double) geom[i - 1].x / (1LL << shift)) == std::round((double) geom[i].x / (1LL << shift)) &&
				    std::round((double) geom[i - 1].y / (1LL << shift)) == std::round((double) geom[i].y / (1LL << shift))) {
					continue;
				}
			}

			out.push_back(geom[i]);
		}
	}

	return out;
}

double get_area_scaled(const drawvec &geom, size_t i, size_t j) {
	const double max_exact_double = (double) ((1LL << 53) - 1);

	// keep scaling the geometry down until we can calculate its area without overflow
	for (long long scale = 2; scale < (1LL << 30); scale *= 2) {
		long long bx = geom[i].x;
		long long by = geom[i].y;
		bool again = false;

		// https://en.wikipedia.org/wiki/Shoelace_formula
		double area = 0;
		for (size_t k = i; k < j; k++) {
			area += (double) ((geom[k].x - bx) / scale) * (double) ((geom[i + ((k - i + 1) % (j - i))].y - by) / scale);
			if (std::fabs(area) >= max_exact_double) {
				again = true;
				break;
			}
			area -= (double) ((geom[k].y - by) / scale) * (double) ((geom[i + ((k - i + 1) % (j - i))].x - bx) / scale);
			if (std::fabs(area) >= max_exact_double) {
				again = true;
				break;
			}
		}

		if (again) {
			continue;
		} else {
			area /= 2;
			return area * scale * scale;
		}
	}

	fprintf(stderr, "get_area_scaled: can't happen\n");
	exit(EXIT_IMPOSSIBLE);
}

double get_area(const drawvec &geom, size_t i, size_t j) {
	const double max_exact_double = (double) ((1LL << 53) - 1);

	// Coordinates in `geom` are 40-bit integers, so there is no good way
	// to multiply them without possible precision loss. Since they probably
	// do not use the full precision, shift them nearer to the origin so
	// their product is more likely to be exactly representable as a double.
	//
	// (In practice they are actually 34-bit integers: 32 bits for the
	// Mercator world plane, plus another two bits so features can stick
	// off either the left or right side. But that is still too many bits
	// for the product to fit either in a 64-bit long long or in a
	// double where the largest exact integer is 2^53.)
	//
	// If the intermediate calculation still exceeds 2^53, start trying to
	// recalculate the area by scaling down the geometry. This will not
	// produce as precise an area, but it will still be close, and the
	// sign will be correct, which is more important, since the sign
	// determines the winding order of the rings. We can then use that
	// sign with this generally more precise area calculation.

	long long bx = geom[i].x;
	long long by = geom[i].y;

	// https://en.wikipedia.org/wiki/Shoelace_formula
	double area = 0;
	bool overflow = false;
	for (size_t k = i; k < j; k++) {
		area += (double) (geom[k].x - bx) * (double) (geom[i + ((k - i + 1) % (j - i))].y - by);
		if (std::fabs(area) >= max_exact_double) {
			overflow = true;
		}
		area -= (double) (geom[k].y - by) * (double) (geom[i + ((k - i + 1) % (j - i))].x - bx);
		if (std::fabs(area) >= max_exact_double) {
			overflow = true;
		}
	}
	area /= 2;

	if (overflow) {
		double scaled_area = get_area_scaled(geom, i, j);
		if ((area < 0 && scaled_area > 0) || (area > 0 && scaled_area < 0)) {
			area = -area;
		}
	}

	return area;
}

double get_mp_area(drawvec &geom) {
	double ret = 0;

	for (size_t i = 0; i < geom.size(); i++) {
		if (geom[i].op == VT_MOVETO) {
			size_t j;

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

			ret += get_area(geom, i, j);
			i = j - 1;
		}
	}

	return ret;
}

drawvec close_poly(drawvec &geom) {
	drawvec out;

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

			if (j - 1 > i) {
				if (geom[j - 1].x != geom[i].x || geom[j - 1].y != geom[i].y) {
					fprintf(stderr, "Internal error: polygon not closed\n");
				}
			}

			for (size_t n = i; n < j - 1; n++) {
				out.push_back(geom[n]);
			}
			out.push_back(draw(VT_CLOSEPATH, 0, 0));

			i = j - 1;
		}
	}

	return out;
}

static bool inside(std::pair<double, double> d, int edge, long long minx, long long miny, long long maxx, long long maxy) {
	switch (edge) {
	case 0:	 // top
		return d.second > miny;

	case 1:	 // right
		return d.first < maxx;

	case 2:	 // bottom
		return d.second < maxy;

	case 3:	 // left
		return d.first > minx;
	}

	fprintf(stderr, "internal error inside\n");
	exit(EXIT_FAILURE);
}

static std::pair<double, double> intersect(std::pair<double, double> a, std::pair<double, double> b, int edge, long long minx, long long miny, long long maxx, long long maxy) {
	switch (edge) {
	case 0:	 // top
		return std::pair<double, double>((a.first + (double) (b.first - a.first) * (miny - a.second) / (b.second - a.second)), miny);

	case 1:	 // right
		return std::pair<double, double>(maxx, (a.second + (double) (b.second - a.second) * (maxx - a.first) / (b.first - a.first)));

	case 2:	 // bottom
		return std::pair<double, double>((a.first + (double) (b.first - a.first) * (maxy - a.second) / (b.second - a.second)), maxy);

	case 3:	 // left
		return std::pair<double, double>(minx, (a.second + (double) (b.second - a.second) * (minx - a.first) / (b.first - a.first)));
	}

	fprintf(stderr, "internal error intersecting\n");
	exit(EXIT_FAILURE);
}

// http://en.wikipedia.org/wiki/Sutherland%E2%80%93Hodgman_algorithm
static std::vector<std::pair<double, double>> clip_poly1(std::vector<std::pair<double, double>> &geom,
							 long long minx, long long miny, long long maxx, long long maxy,
							 long long ax, long long ay, long long bx, long long by, drawvec &edge_nodes,
							 bool prevent_simplify_shared_nodes) {
	std::vector<std::pair<double, double>> out = geom;

	for (int edge = 0; edge < 4; edge++) {
		if (out.size() > 0) {
			std::vector<std::pair<double, double>> in = out;
			out.resize(0);

			std::pair<double, double> S = in[in.size() - 1];

			for (size_t e = 0; e < in.size(); e++) {
				std::pair<double, double> E = in[e];

				if (!inside(S, edge, minx, miny, maxx, maxy)) {
					// was outside the buffer

					if (!inside(E, edge, minx, miny, maxx, maxy)) {
						// still outside the buffer
					} else if (!inside(E, edge, ax, ay, bx, by)) {
						// outside the tile but inside the buffer
						out.push_back(intersect(S, E, edge, minx, miny, maxx, maxy));  // on buffer edge
						out.push_back(E);
					} else {
						out.push_back(intersect(S, E, edge, minx, miny, maxx, maxy));  // on buffer edge
						if (prevent_simplify_shared_nodes) {
							out.push_back(intersect(S, E, edge, ax, ay, bx, by));  // on tile boundary
							edge_nodes.push_back(draw(VT_MOVETO, std::round(out.back().first), std::round(out.back().second)));
						}
						out.push_back(E);
					}
				} else if (!inside(S, edge, ax, ay, bx, by)) {
					// was inside the buffer but outside the tile edge

					if (!inside(E, edge, minx, miny, maxx, maxy)) {
						// now outside the buffer
						out.push_back(intersect(S, E, edge, minx, miny, maxx, maxy));  // on buffer edge
					} else if (!inside(E, edge, ax, ay, bx, by)) {
						// still outside the tile edge but inside the buffer
						out.push_back(E);
					} else {
						// now inside the tile
						if (prevent_simplify_shared_nodes) {
							out.push_back(intersect(S, E, edge, ax, ay, bx, by));  // on tile boundary
							edge_nodes.push_back(draw(VT_MOVETO, std::round(out.back().first), std::round(out.back().second)));
						}
						out.push_back(E);
					}
				} else {
					// was inside the tile

					if (!inside(E, edge, minx, miny, maxx, maxy)) {
						// now outside the buffer
						if (prevent_simplify_shared_nodes) {
							out.push_back(intersect(S, E, edge, ax, ay, bx, by));  // on tile boundary
							edge_nodes.push_back(draw(VT_MOVETO, std::round(out.back().first), std::round(out.back().second)));
						}
						out.push_back(intersect(S, E, edge, minx, miny, maxx, maxy));  // on buffer edge
					} else if (!inside(E, edge, ax, ay, bx, by)) {
						// now inside the buffer but outside the tile edge
						if (prevent_simplify_shared_nodes) {
							out.push_back(intersect(S, E, edge, ax, ay, bx, by));  // on tile boundary
							edge_nodes.push_back(draw(VT_MOVETO, std::round(out.back().first), std::round(out.back().second)));
						}
						out.push_back(E);
					} else {
						// still inside the tile
						out.push_back(E);
					}
				}

				S = E;
			}
		}
	}

	if (out.size() > 0) {
		// If the polygon begins and ends outside the edge,
		// the starting and ending points will be left as the
		// places where it intersects the edge. Need to add
		// another point to close the loop.

		if (out[0].first != out[out.size() - 1].first || out[0].second != out[out.size() - 1].second) {
			out.push_back(out[0]);
		}

		if (out.size() < 3) {
			// fprintf(stderr, "Polygon degenerated to a line segment\n");
			out.clear();
			return out;
		}
	}

	return out;
}

std::string overzoom(std::string s, int oz, int ox, int oy, int nz, int nx, int ny,
		     int detail, int buffer, std::set<std::string> const &keep, bool do_compress,
		     std::vector<std::pair<unsigned, unsigned>> *next_overzoomed_tiles) {
	mvt_tile tile;

	try {
		bool was_compressed;
		if (!tile.decode(s, was_compressed)) {
			fprintf(stderr, "Couldn't parse tile %d/%u/%u\n", oz, ox, oy);
			exit(EXIT_MVT);
		}
	} catch (std::exception const &e) {
		fprintf(stderr, "PBF decoding error in tile %d/%u/%u\n", oz, ox, oy);
		exit(EXIT_PROTOBUF);
	}

	return overzoom(tile, oz, ox, oy, nz, nx, ny, detail, buffer, keep, do_compress, next_overzoomed_tiles);
}

std::string overzoom(mvt_tile tile, int oz, int ox, int oy, int nz, int nx, int ny,
		     int detail, int buffer, std::set<std::string> const &keep, bool do_compress,
		     std::vector<std::pair<unsigned, unsigned>> *next_overzoomed_tiles) {
	mvt_tile outtile;

	for (auto const &layer : tile.layers) {
		mvt_layer outlayer = mvt_layer();

		int det = detail;
		if (det <= 0) {
			det = std::round(log(layer.extent) / log(2));
		}

		outlayer.name = layer.name;
		outlayer.version = layer.version;
		outlayer.extent = 1LL << det;

		for (auto const &feature : layer.features) {
			mvt_feature outfeature;
			drawvec geom;
			int t = feature.type;

			// Convert feature geometry to world coordinates

			long long tilesize = 1LL << (32 - oz);	// source tile size in world coordinates
			draw ring_closure(0, 0, 0);

			for (auto const &g : feature.geometry) {
				if (g.op == mvt_closepath) {
					geom.push_back(ring_closure);
				} else {
					geom.emplace_back(g.op,
							  g.x * tilesize / layer.extent + ox * tilesize,
							  g.y * tilesize / layer.extent + oy * tilesize);

					if (g.op == mvt_moveto) {
						ring_closure = geom.back();
						ring_closure.op = mvt_lineto;
					}
				}
			}

			// Now offset from world coordinates to output tile coordinates,
			// but retain world scale, because that is what tippecanoe clipping expects

			long long outtilesize = 1LL << (32 - nz);  // destination tile size in world coordinates
			for (auto &g : geom) {
				g.x -= nx * outtilesize;
				g.y -= ny * outtilesize;
			}

			// Clip to output tile

			long long xmin = LLONG_MAX;
			long long ymin = LLONG_MAX;
			long long xmax = LLONG_MIN;
			long long ymax = LLONG_MIN;

			for (auto const &g : geom) {
				xmin = std::min(xmin, g.x);
				ymin = std::min(ymin, g.y);
				xmax = std::max(xmax, g.x);
				ymax = std::max(ymax, g.y);
			}

			long long b = outtilesize * buffer / 256;
			if (xmax < -b || ymax < -b || xmin > outtilesize + b || ymin > outtilesize + b) {
				continue;
			}

			if (t == VT_LINE) {
				geom = clip_lines(geom, nz, buffer);
			} else if (t == VT_POLYGON) {
				drawvec dv;
				geom = simple_clip_poly(geom, nz, buffer, dv, false);
			} else if (t == VT_POINT) {
				geom = clip_point(geom, nz, buffer);
			}

			// Scale to output tile extent

			if (t == VT_POLYGON) {
				geom = scale_polygon(geom, nz, det);
			} else {
				to_tile_scale(geom, nz, det);
			}

			// Clean geometries

			geom = remove_noop(geom, t, 0);
			if (t == VT_POLYGON) {
				geom = clean_polygon(geom, 1LL << det);
				geom = close_poly(geom);
			}

			// Add geometry to output feature

			outfeature.type = t;
			for (auto const &g : geom) {
				outfeature.geometry.emplace_back(g.op, g.x, g.y);
			}

			// ID and attributes, if it didn't get clipped away

			if (outfeature.geometry.size() > 0) {
				if (feature.has_id) {
					outfeature.has_id = true;
					outfeature.id = feature.id;
				}

				for (size_t i = 0; i + 1 < feature.tags.size(); i += 2) {
					if (keep.size() == 0 || keep.find(layer.keys[feature.tags[i]]) != keep.end()) {
						outlayer.tag(outfeature, layer.keys[feature.tags[i]], layer.values[feature.tags[i + 1]]);
					}
				}

				outlayer.features.push_back(outfeature);
			}
		}

		if (outlayer.features.size() > 0) {
			outtile.layers.push_back(outlayer);
		}
	}

	if (next_overzoomed_tiles != NULL) {
		// will any child tiles have features in them?
		// find out recursively from the tile we just made.
		//
		// (yes, we should keep them instead of remaking them
		// later, but that first requires figuring out where to
		// keep them.)

		if (outtile.layers.size() > 0) {
			for (size_t x = 0; x < 2; x++) {
				for (size_t y = 0; y < 2; y++) {
					std::string child = overzoom(outtile, nz, nx, ny,
								     nz + 1, nx * 2 + x, ny * 2 + y,
								     detail, buffer, keep, false, NULL);
					if (child.size() > 0) {
						next_overzoomed_tiles->emplace_back(nx * 2 + x, ny * 2 + y);
					}
				}
			}
		}
	}

	if (outtile.layers.size() > 0) {
		std::string pbf = outtile.encode();

		std::string compressed;
		if (do_compress) {
			compress(pbf, compressed, true);
		} else {
			compressed = pbf;
		}

		return compressed;
	} else {
		return "";
	}
}

/* pnpoly:
Copyright (c) 1970-2003, Wm. Randolph Franklin

Permission is hereby granted, free of charge, to any person obtaining a copy of this software and associated documentation files (the "Software"), to deal in the Software without restriction, including without limitation the rights to use, copy, modify, merge, publish, distribute, sublicense, and/or sell copies of the Software, and to permit persons to whom the Software is furnished to do so, subject to the following conditions:

Redistributions of source code must retain the above copyright notice, this list of conditions and the following disclaimers.
Redistributions in binary form must reproduce the above copyright notice in the documentation and/or other materials provided with the distribution.
The name of W. Randolph Franklin may not be used to endorse or promote products derived from this Software without specific prior written permission.
THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY, FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM, OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE SOFTWARE.
*/

int pnpoly(const drawvec &vert, size_t start, size_t nvert, long long testx, long long testy) {
	size_t i, j;
	bool c = false;
	for (i = 0, j = nvert - 1; i < nvert; j = i++) {
		if (((vert[i + start].y > testy) != (vert[j + start].y > testy)) &&
		    (testx < (vert[j + start].x - vert[i + start].x) * (testy - vert[i + start].y) / (double) (vert[j + start].y - vert[i + start].y) + vert[i + start].x))
			c = !c;
	}
	return c;
}