Add an option to extend zooms if still dropping, but with a limit (#131)

* Add an option to extend zooms if still dropping, but with a limit

* At least when to overzoom, even if not actually doing it yet

* Refactor to give tile-join access to overzoom()

* Didn't work, but *might* have worked

* OK, it did something now

* Ah, there's the bug!

* Hook up pmtiles and dirtiles as overzooming sources

* Add command line option to enable or disable overzooming

* Add (currently broken) test of overzooming in tile-join

* Slightly more abstraction for the tile-join readers

* Factor out duplicated code

* Move construction into a constructor

* More changing accessors to methods

* Reduce magic

* Start tracking a list of the tiles at maxzoom

* I think it worked?

* Add missing #include

* Fix sequence of overzoomed tiles (Y sorts backwards for TMS)

* Don't spend memory on overzooming when we aren't going to use it

* Diff rather than cmp, in the hope of figuring out this broken test

* Keep full coordinate precision if we might extend zooms

* Try a slightly different byte limit

* Make drop-densest more consistent across tile boundaries

* Also affects this test

* Does it behave any differently if it can extend forever?

* I think the discrepancy is a thread-safety problem here

* Revert "Does it behave any differently if it can extend forever?"

This reverts commit 0dff0a0acc.

* Lost this change to the test

* This time for sure!

* Revert "Also affects this test"

This reverts commit cd1f7c2e78.

* Revert "Make drop-densest more consistent across tile boundaries"

This reverts commit 563f7d2bc2.

* Revert "Try a slightly different byte limit"

This reverts commit 2e271213d6.

* Add some more explanatory comments

* Amend the join-test to detect my current bug

* Allow overzooming to complete the zoom if it ever starts

* Forgot to correct the test

* Update changelog and version

* Cleanups from code review

* Remove version number from fixture to fix test

clip.cpp

@@ -5,6 +5,8 @@
 #include <mapbox/geometry/snap_rounding.hpp>
 #include "geometry.hpp"
 #include "errors.hpp"
+#include "compression.hpp"
+#include "mvt.hpp"
 
 drawvec simple_clip_poly(drawvec &geom, long long minx, long long miny, long long maxx, long long maxy) {
 	drawvec out;
@@ -565,3 +567,127 @@ drawvec close_poly(drawvec &geom) {
 
 	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) {
+	mvt_tile tile, outtile;
+	bool was_compressed;
+
+	try {
+		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);
+	}
+
+	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
+
+			if (t == VT_LINE) {
+				geom = clip_lines(geom, nz, buffer);
+			} else if (t == VT_POLYGON) {
+				geom = simple_clip_poly(geom, nz, buffer);
+			} else if (t == VT_POINT) {
+				geom = clip_point(geom, nz, buffer);
+			}
+
+			// Scale to output tile extent
+
+			to_tile_scale(geom, nz, det);
+
+			// Clean geometries
+
+			geom = remove_noop(geom, t, 0);
+			if (t == VT_POLYGON) {
+				geom = clean_or_clip_poly(geom, 0, 0, false);
+				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 (outtile.layers.size() > 0) {
+		std::string pbf = outtile.encode();
+		std::string compressed;
+		compress(pbf, compressed, true);
+
+		return compressed;
+	} else {
+		return "";
+	}
+}