Use closepath for each polygon ring to match the vector tile spec

decode.cc

@@ -295,6 +295,12 @@ void handle(std::string message, int z, unsigned x, unsigned y, int describe) {
 							}
 
 							printf("[ %f, %f ]", rings[i][j].lon, rings[i][j].lat);
+						} else {
+							if (j != 0) {
+								printf(", ");
+							}
+
+							printf("[ %f, %f ]", rings[i][0].lon, rings[i][0].lat);
 						}
 					}
 

geometry.cc

@@ -98,7 +98,6 @@ drawvec remove_noop(drawvec geom, int type, int shift) {
 		}
 
 		if (geom[i].op == VT_CLOSEPATH) {
-			fprintf(stderr, "Shouldn't happen\n");
 			out.push_back(geom[i]);
 		} else { /* moveto or lineto */
 			out.push_back(geom[i]);
@@ -310,6 +309,36 @@ drawvec clean_or_clip_poly(drawvec &geom, int z, int detail, int buffer, bool cl
 	return out;
 }
 
+drawvec close_poly(drawvec &geom) {
+	drawvec out;
+
+	for (unsigned i = 0; i < geom.size(); i++) {
+		if (geom[i].op == VT_MOVETO) {
+			unsigned 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 (unsigned n = i; n < j - 1; n++) {
+				out.push_back(geom[n]);
+			}
+			out.push_back(draw(VT_CLOSEPATH, 0, 0));
+
+			i = j - 1;
+		}
+	}
+
+	return out;
+}
+
 drawvec reduce_tiny_poly(drawvec &geom, int z, int detail, bool *reduced, double *accum_area) {
 	drawvec out;
 	long long pixel = (1 << (32 - detail - z)) * 2;

geometry.hh

@@ -21,6 +21,7 @@ void to_tile_scale(drawvec &geom, int z, int detail);
 drawvec remove_noop(drawvec geom, int type, int shift);
 drawvec clip_point(drawvec &geom, int z, int detail, long long buffer);
 drawvec clean_or_clip_poly(drawvec &geom, int z, int detail, int buffer, bool clip);
+drawvec close_poly(drawvec &geom);
 drawvec reduce_tiny_poly(drawvec &geom, int z, int detail, bool *reduced, double *accum_area);
 drawvec clip_lines(drawvec &geom, int z, int detail, long long buffer);
 int quick_check(long long *bbox, int z, int detail, long long buffer);

tile.cc

@@ -656,6 +656,7 @@ long long write_tile(char **geoms, char *metabase, char *stringpool, int z, unsi
 				// Scaling may have made the polygon degenerate.
 				// Give Clipper a chance to try to fix it.
 				geom = clean_or_clip_poly(geom, 0, 0, 0, false);
+				geom = close_poly(geom);
 			}
 
 			if (t == VT_POINT || to_feature(geom, NULL)) {