Snap to the tile grid as each simplified point is chosen

geometry.cpp

@@ -832,7 +832,7 @@ static double square_distance_from_line(long long point_x, long long point_y, lo
 }
 
 // https://github.com/Project-OSRM/osrm-backend/blob/733d1384a40f/Algorithms/DouglasePeucker.cpp
-static void douglas_peucker(drawvec &geom, int start, int n, double e, size_t kept, size_t retain) {
+static void douglas_peucker(drawvec &geom, int start, int n, double e, size_t kept, size_t retain, double res) {
 	e = e * e;
 	std::stack<int> recursion_stack;
 
@@ -875,7 +875,10 @@ static void douglas_peucker(drawvec &geom, int start, int n, double e, size_t ke
 
 		if (max_distance >= 0) {
 			// mark idx as necessary
-			geom[start + farthest_element_index].necessary = 1;
+			size_t k = start + farthest_element_index;
+			geom[k].necessary = 1;
+			geom[k].x = res * std::round((double) geom[k].x / res);
+			geom[k].y = res * std::round((double) geom[k].y / res);
 			kept++;
 
 			if (1 < farthest_element_index - first) {
@@ -961,6 +964,13 @@ drawvec simplify_lines(drawvec &geom, int z, int detail, bool mark_tile_bounds,
 			geom[i].necessary = 1;
 			geom[j - 1].necessary = 1;
 
+			for (size_t k = i; k < j; k++) {
+				if (geom[k].necessary) {
+					geom[k].x = res * std::round((double) geom[k].x / res);
+					geom[k].y = res * std::round((double) geom[k].y / res);
+				}
+			}
+
 			// empirical mapping from douglas-peucker simplifications
 			// to visvalingam simplifications that yield similar
 			// output sizes
@@ -972,7 +982,7 @@ drawvec simplify_lines(drawvec &geom, int z, int detail, bool mark_tile_bounds,
 				if (additional[A_VISVALINGAM]) {
 					visvalingam(geom, i, j, scale, retain);
 				} else {
-					douglas_peucker(geom, i, j - i, res * simplification, 2, retain);
+					douglas_peucker(geom, i, j - i, res * simplification, 2, retain, res);
 				}
 			}
 			i = j - 1;

main.cpp

@@ -34,7 +34,7 @@
 #include <map>
 #include <cmath>
 
-#if  defined(__APPLE__) || defined(__FreeBSD__)
+#if defined(__APPLE__) || defined(__FreeBSD__)
 #include <sys/types.h>
 #include <sys/sysctl.h>
 #include <sys/param.h>
@@ -3521,7 +3521,7 @@ int main(int argc, char **argv) {
 
 	long long file_bbox[4] = {UINT_MAX, UINT_MAX, 0, 0};
 
-	long long file_bbox1[4] = {0xFFFFFFFF, 0xFFFFFFFF, 0, 0};  // standard -180 to 180 world plane
+	long long file_bbox1[4] = {0xFFFFFFFF, 0xFFFFFFFF, 0, 0};	      // standard -180 to 180 world plane
 	long long file_bbox2[4] = {0x1FFFFFFFF, 0xFFFFFFFF, 0x100000000, 0};  // 0 to 360 world plane
 
 	auto input_ret = read_input(sources, name ? name : out_mbtiles ? out_mbtiles

serial.hpp

@@ -88,7 +88,7 @@ struct reader {
 
 	long long file_bbox[4] = {0, 0, 0, 0};
 
-	long long file_bbox1[4] = {0xFFFFFFFF, 0xFFFFFFFF, 0, 0};  // standard -180 to 180 world plane
+	long long file_bbox1[4] = {0xFFFFFFFF, 0xFFFFFFFF, 0, 0};	      // standard -180 to 180 world plane
 	long long file_bbox2[4] = {0x1FFFFFFFF, 0xFFFFFFFF, 0x100000000, 0};  // 0 to 360 world plane
 
 	struct stat geomst {};

tile-join.cpp

@@ -1178,7 +1178,7 @@ int main(int argc, char **argv) {
 				std::string sa;
 				filearg = 1;
 				while (getline(read_file, sa)) {
-					char* c = const_cast<char*>(sa.c_str());
+					char *c = const_cast<char *>(sa.c_str());
 					reader *r = begin_reading(c);
 					struct reader **rr;
 					for (rr = &readers; *rr != NULL; rr = &((*rr)->next)) {
@@ -1191,7 +1191,6 @@ int main(int argc, char **argv) {
 				}
 				read_file.close();
 			}
-
 		}
 
 		case 'q':
@@ -1262,7 +1261,6 @@ int main(int argc, char **argv) {
 	std::string description;
 	std::string name;
 
-
 	if (filearg == 0) {
 		for (i = optind; i < argc; i++) {
 			reader *r = begin_reading(argv[i]);

tile.cpp

@@ -573,6 +573,7 @@ double simplify_partial(partial *p, drawvec &shared_nodes) {
 				}
 
 				// continues to simplify to line_detail even if we have extra detail
+				// should this change since we are now snapping as part of simplifying?
 				drawvec ngeom = simplify_lines(geom, z, line_detail, !(prevent[P_CLIPPING] || prevent[P_DUPLICATION]), p->simplification, t == VT_POLYGON ? 4 : 0, shared_nodes);
 
 				if (t != VT_POLYGON || ngeom.size() >= 3) {
@@ -2301,7 +2302,7 @@ long long write_tile(decompressor *geoms, std::atomic<long long> *geompos_in, ch
 				std::string layername = (*layer_unmaps)[p.segment][p.layer];
 				serial_val sv, sv2, sv3, sv4;
 				long long point_count = p.clustered + 1;
-				char abbrev[17]; // to_string(LLONG_MAX).length() / 1000 + 1;
+				char abbrev[17];  // to_string(LLONG_MAX).length() / 1000 + 1;
 
 				p.full_keys.push_back("clustered");
 				sv.type = mvt_bool;