Copy the geometric binning code to serve as intersection-finding code

clip.cpp

@@ -1934,6 +1934,75 @@ mvt_tile assign_to_bins(mvt_tile &features,
 	return ret;
 }
 
+drawvec clip_lines(drawvec const &geom, drawvec const &region) {
+	std::vector<index_event> events;
+
+	if (region.size() == 0) {
+		return drawvec();
+	}
+
+	// Index region segments
+	for (size_t i = 1; i < region.size(); i++) {
+		if (region[i].op == VT_LINETO) {
+			long long xmin = std::min(region[i - 1].x, region[i].x);
+			long long ymin = std::min(region[i - 1].y, region[i].y);
+			long long xmax = std::max(region[i - 1].x, region[i].x);
+			long long ymax = std::max(region[i - 1].y, region[i].y);
+			unsigned long long start, end;
+
+			get_quadkey_bounds(xmin, ymin, xmax, ymax, &start, &end);
+			events.emplace_back(start, index_event::ENTER, i, 0, xmin, ymin, xmax, ymax);
+			events.emplace_back(end, index_event::EXIT, i, 0, xmin, ymin, xmax, ymax);
+		}
+	}
+
+	// Index linestring segments
+	for (size_t i = 1; i < geom.size(); i++) {
+		if (geom[i].op == VT_LINETO) {
+			long long xmin = std::min(geom[i - 1].x, geom[i].x);
+			long long ymin = std::min(geom[i - 1].y, geom[i].y);
+			long long xmax = std::max(geom[i - 1].x, geom[i].x);
+			long long ymax = std::max(geom[i - 1].y, geom[i].y);
+			unsigned long long start, end;
+
+			get_quadkey_bounds(xmin, ymin, xmax, ymax, &start, &end);
+			events.emplace_back(start, index_event::CHECK, i, 0, xmin, ymin, xmax, ymax);
+		}
+	}
+
+	std::sort(events.begin(), events.end());
+	std::set<active_bin> active;
+
+	for (auto &e : events) {
+		if (e.kind == index_event::ENTER) {
+			active_bin a(e.layer, e.feature);
+			a.xmin = e.xmin;
+			a.ymin = e.ymin;
+			a.xmax = e.xmax;
+			a.ymax = e.ymax;
+
+			active.insert(std::move(a));
+		} else if (e.kind == index_event::CHECK) {
+			for (auto const &a : active) {
+				if (bbox_intersects(e.xmin, e.ymin, e.xmax, e.ymax,
+						    a.xmin, a.ymin, a.xmax, a.ymax)) {
+					// compare
+				}
+			}
+		} else /* EXIT */ {
+			auto const &found = active.find({e.layer, e.feature});
+			if (found != active.end()) {
+				active.erase(found);
+			} else {
+				fprintf(stderr, "event mismatch: can't happen\n");
+				exit(EXIT_IMPOSSIBLE);
+			}
+		}
+	}
+
+	return drawvec();
+}
+
 std::string overzoom(std::vector<source_tile> const &tiles, int nz, int nx, int ny,
 		     int detail_or_unspecified, int buffer,
 		     std::set<std::string> const &keep,