Avoid clipping if the input and output tiles are the same

clip.cpp

@@ -931,6 +931,7 @@ std::string overzoom(mvt_tile tile, int oz, int ox, int oy, int nz, int nx, int
 
 			long long tilesize = 1LL << (32 - oz);	// source tile size in world coordinates
 			draw ring_closure(0, 0, 0);
+			bool sametile = (nz == ox && nx == ox && ny == oy);
 
 			for (auto const &g : feature.geometry) {
 				if (g.op == mvt_closepath) {
@@ -956,6 +957,7 @@ std::string overzoom(mvt_tile tile, int oz, int ox, int oy, int nz, int nx, int
 				g.y -= ny * outtilesize;
 			}
 
+			if (!sametile) {
 				// Clip to output tile
 
 				long long xmin = LLONG_MAX;
@@ -983,16 +985,22 @@ std::string overzoom(mvt_tile tile, int oz, int ox, int oy, int nz, int nx, int
 				} else if (t == VT_POINT) {
 					geom = clip_point(geom, nz, buffer);
 				}
+			}
 
 			// Scale to output tile extent
 
 			to_tile_scale(geom, nz, det);
 
+			if (!sametile) {
 				// Clean geometries
 
 				geom = remove_noop(geom, t, 0);
 				if (t == VT_POLYGON) {
 					geom = clean_or_clip_poly(geom, 0, 0, false, false);
+				}
+			}
+
+			if (t == VT_POLYGON) {
 				geom = close_poly(geom);
 			}