Look up shared nodes once per vertex instead of once per tile

With --no-simplification-of-shared-nodes, simplify_lines() used to offset
every vertex of every feature to world coordinates and check it against
the Bloom filter and the global sorted list of shared nodes, in every
tile at every zoom level.

Whether a vertex is a shared node depends only on its world coordinates,
so now it is found once, after the list of shared nodes has been made
and before the geometry is sorted, by a parallel pass over each reader's
geometry that marks each vertex in place, in the upper bits of its
serialized operation byte. Decoding puts that state into a new field of
draw (which still fits in 16 bytes), and it is carried through clipping,
the copies across the antimeridian at z0, and the geometry written for
the next zoom level. Polygon cleaning of coalesced features restores the
state of any output vertex with the same coordinates as an input vertex.

Vertices whose state is still unknown, because they were created by
clipping or polygon cleaning or came back from a prefilter, are still
looked up in the global list when they are simplified, so the output is
unchanged.

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_01P2nBqZisxNQfmEmon3vE9v

tile.cpp

@@ -476,7 +476,7 @@ static void rewrite(serial_feature const &osf, int z, int nextzoom, int maxzoom,
 
 		drawvec geom2;
 		for (auto const &g : osf.geometry) {
-			geom2.emplace_back(g.op, SHIFT_RIGHT(g.x + sx), SHIFT_RIGHT(g.y + sy));
+			geom2.emplace_back(g.op, SHIFT_RIGHT(g.x + sx), SHIFT_RIGHT(g.y + sy), g.node);
 		}
 
 		for (xo = bbox2[0]; xo <= bbox2[2]; xo++) {
@@ -631,7 +631,9 @@ static double simplify_feature(serial_feature *p, drawvec const &shared_nodes, n
 					// unioned exactly
 					//
 					// don't try to scale up because these are still world coordinates
+					drawvec before = geom;
 					coalesce_polygon(geom, false);
+					restore_node_states(before, geom);
 				}
 
 				// continues to simplify to line_detail even if we have extra detail
@@ -979,13 +981,13 @@ static bool clip_to_tile(serial_feature &sf, int z, long long buffer) {
 
 			if (sf.bbox[0] <= (1LL << 32) * buffer / 256) {
 				for (size_t i = 0; i < n; i++) {
-					sf.geometry.push_back(draw(sf.geometry[i].op, sf.geometry[i].x + (1LL << 32), sf.geometry[i].y));
+					sf.geometry.push_back(draw(sf.geometry[i].op, sf.geometry[i].x + (1LL << 32), sf.geometry[i].y, sf.geometry[i].node));
 				}
 			}
 
 			if (sf.bbox[2] >= (1LL << 32) - ((1LL << 32) * buffer / 256)) {
 				for (size_t i = 0; i < n; i++) {
-					sf.geometry.push_back(draw(sf.geometry[i].op, sf.geometry[i].x - (1LL << 32), sf.geometry[i].y));
+					sf.geometry.push_back(draw(sf.geometry[i].op, sf.geometry[i].x - (1LL << 32), sf.geometry[i].y, sf.geometry[i].node));
 				}
 			}
 
@@ -2295,6 +2297,7 @@ long long write_tile(decompressor *geoms, std::atomic<long long> *geompos_in, ch
 
 								// don't scale up because this is still world coordinates
 								coalesce_polygon(to_clean, false);
+								restore_node_states(features[simplified_geometry_through]->geometry, to_clean);
 								features[simplified_geometry_through]->geometry = std::move(to_clean);
 							}
 						}