Minimal tile decoder, only geometry for the moment

Makefile

@@ -1,6 +1,6 @@
 PREFIX=/usr/local
 
-all: tippecanoe enumerate
+all: tippecanoe enumerate decode
 
 install: tippecanoe
 	cp tippecanoe $(PREFIX)/bin/tippecanoe
@@ -16,6 +16,9 @@ tippecanoe: geojson.o jsonpull.o vector_tile.pb.o tile.o clip.o pool.o mbtiles.o
 enumerate: enumerate.o
 	gcc $(PG) -O3 -g -Wall -o $@ $^ -lsqlite3
 
+decode: decode.o vector_tile.pb.o
+	g++ $(PG) -O3 -g -Wall -o $@ $^ -lm -lz -lprotobuf-lite -lsqlite3
+
 libjsonpull.a: jsonpull.o
 	ar rc $@ $^
 	ranlib $@

decode.cc

@@ -0,0 +1,165 @@
+#include <stdio.h>
+#include <stdlib.h>
+#include <unistd.h>
+#include <sqlite3.h>
+#include <string>
+#include <zlib.h>
+#include <math.h>
+#include "vector_tile.pb.h"
+
+// https://github.com/mapbox/mapnik-vector-tile/blob/master/src/vector_tile_compression.hpp
+inline bool is_compressed(std::string const& data) {
+	return data.size() > 2 && (uint8_t)data[0] == 0x78 && (uint8_t)data[1] == 0x9C;
+}
+
+// https://github.com/mapbox/mapnik-vector-tile/blob/master/src/vector_tile_compression.hpp
+inline int decompress(std::string const& input, std::string & output) {
+	z_stream inflate_s;
+	inflate_s.zalloc = Z_NULL;
+	inflate_s.zfree = Z_NULL;
+	inflate_s.opaque = Z_NULL;
+	inflate_s.avail_in = 0;
+	inflate_s.next_in = Z_NULL;
+	inflateInit(&inflate_s);
+	inflate_s.next_in = (Bytef *)input.data();
+	inflate_s.avail_in = input.size();
+	size_t length = 0;
+	do {
+		output.resize(length + 2 * input.size());
+		inflate_s.avail_out = 2 * input.size();
+		inflate_s.next_out = (Bytef *)(output.data() + length);
+		int ret = inflate(&inflate_s, Z_FINISH);
+		if (ret != Z_STREAM_END && ret != Z_OK && ret != Z_BUF_ERROR) {
+			return 0;
+		}
+
+		length += (2 * input.size() - inflate_s.avail_out);
+	} while (inflate_s.avail_out == 0);
+	inflateEnd(&inflate_s);
+	output.resize(length);
+	return 1;
+}
+
+int dezig(unsigned n) {
+	return (n >> 1) ^ (-(n & 1));
+}
+
+// http://wiki.openstreetmap.org/wiki/Slippy_map_tilenames
+void tile2latlon(unsigned int x, unsigned int y, int zoom, double *lat, double *lon) {
+        unsigned long long n = 1LL << zoom;
+        *lon = 360.0 * x / n - 180.0;
+        double lat_rad = atan(sinh(M_PI * (1 - 2.0 * y / n)));
+        *lat = lat_rad * 180 / M_PI;
+}
+
+void handle(std::string message, int z, unsigned x, unsigned y) {
+	GOOGLE_PROTOBUF_VERIFY_VERSION;
+
+	// https://github.com/mapbox/mapnik-vector-tile/blob/master/examples/c%2B%2B/tileinfo.cpp
+	mapnik::vector::tile tile;
+
+	if (is_compressed(message)) {
+		std::string uncompressed;
+		decompress(message,uncompressed);
+		if (!tile.ParseFromString(uncompressed)) {
+			fprintf(stderr, "Couldn't decompress tile %d/%u/%u\n", z, x, y);
+			exit(EXIT_FAILURE);
+		}
+	} else if (!tile.ParseFromString(message)) {
+		fprintf(stderr, "Couldn't parse tile %d/%u/%u\n", z, x, y);
+		exit(EXIT_FAILURE);
+	}
+
+	for (int l = 0; l < tile.layers_size(); l++) {
+		mapnik::vector::tile_layer layer = tile.layers(l);
+		int extent = layer.extent();
+
+		for (int f = 0; f < layer.features_size(); f++) {
+			mapnik::vector::tile_feature feat = layer.features(f);
+			int px = 0, py = 0;
+
+			for (int g = 0; g < feat.geometry_size(); g++) {
+				uint32_t geom = feat.geometry(g);
+				uint32_t op = geom & 7;
+				uint32_t count = geom >> 3;
+
+				if (op == 1 || op == 2) {
+					if (op == 1) {
+						printf("\n");
+					}
+
+					for (unsigned k = 0; k < count; k++) {
+						px += dezig(feat.geometry(g + 1));
+						py += dezig(feat.geometry(g + 2));
+						g += 2;
+
+						long long scale = 1LL << (32 - z);
+						long long wx = scale * x + (scale / extent) * (px + .5);
+						long long wy = scale * y + (scale / extent) * (py + .5);
+
+						double lat, lon;
+						tile2latlon(wx, wy, 32, &lat, &lon);
+						printf("%f,%f ", lat, lon);
+					}
+				}
+			}
+		}
+	}
+}
+
+void decode(char *fname, int z, unsigned x, unsigned y) {
+	sqlite3 *db;
+
+	if (sqlite3_open(fname, &db) != SQLITE_OK) {
+		fprintf(stderr, "%s: %s\n", fname,  sqlite3_errmsg(db));
+		exit(EXIT_FAILURE);
+	}
+
+	const char *sql = "SELECT tile_data from tiles where zoom_level = ? and tile_column = ? and tile_row = ?;";
+	sqlite3_stmt *stmt;
+	if (sqlite3_prepare_v2(db, sql, -1, &stmt, NULL) != SQLITE_OK) {
+		fprintf(stderr, "%s: select failed: %s\n", fname, sqlite3_errmsg(db));
+		exit(EXIT_FAILURE);
+	}
+
+	sqlite3_bind_int(stmt, 1, z);
+	sqlite3_bind_int(stmt, 2, x);
+	sqlite3_bind_int(stmt, 3, (1LL << z) - 1 - y);
+
+	while (sqlite3_step(stmt) == SQLITE_ROW) {
+		int len = sqlite3_column_bytes(stmt, 0);
+		const char *s = (const char *) sqlite3_column_blob(stmt, 0);
+
+		handle(std::string(s, len), z, x, y);
+	}
+
+	sqlite3_finalize(stmt);
+
+        if (sqlite3_close(db) != SQLITE_OK) {
+                fprintf(stderr, "%s: could not close database: %s\n", fname, sqlite3_errmsg(db));
+                exit(EXIT_FAILURE);
+        }
+}
+
+void usage(char **argv) {
+	fprintf(stderr, "Usage: %s file.mbtiles zoom x y\n", argv[0]);
+	exit(EXIT_FAILURE);
+}
+
+int main(int argc, char **argv) {
+	extern int optind;
+	// extern char *optarg;
+	int i;
+
+	while ((i = getopt(argc, argv, "")) != -1) {
+		usage(argv);
+	}
+
+	if (argc != optind + 4) {
+		usage(argv);
+	}
+
+	decode(argv[optind], atoi(argv[optind + 1]), atoi(argv[optind + 2]), atoi(argv[optind + 3]));
+
+	return 0;
+}