From 6943276357bed2b7c5e2919d6e9f80d7f226ee4b Mon Sep 17 00:00:00 2001
From: geoneutrino <geoneutrino@users.noreply.github.com>
Date: Wed, 2 Sep 2026 17:07:41 +0200
Subject: [PATCH] Avoid redundant work when writing features

Two pre-existing redundancies in the tile write path, neither of which
changes what is written:

- writeMultiLinestring() called scaleLatpLon() twice for every point,
  once to count the distinct points and once to emit them. Scale each
  point once into a reused buffer instead.
- The multipoint vector was allocated per point feature. Reuse a
  thread_local buffer, as scaledMultiPolygon already does.

Verified byte-identical to the parent commit on a Bangladesh extract
(93930 tiles, 25544140 features). The comparison has to run with
--threads 1: with several threads tilemaker's own output varies by a
feature or two between runs of the same binary, because
addObjectToSmallIndex() falls back to a per-thread pending list under
lock contention.
---
 src/tile_worker.cpp | 14 +++++++++++---
 1 file changed, 11 insertions(+), 3 deletions(-)

diff --git a/src/tile_worker.cpp b/src/tile_worker.cpp
index 30d09ebe..222b626c 100644
--- a/src/tile_worker.cpp
+++ b/src/tile_worker.cpp
@@ -12,6 +12,9 @@ extern bool verbose;
 
 thread_local bool enabledUserSignal = false;
 thread_local MultiPolygon scaledMultiPolygon;
+// Reused scratch buffers, so writing a feature does not allocate per feature.
+thread_local std::vector<std::pair<int, int>> scaledLinestring;
+thread_local std::vector<std::pair<int, int>> multipointBuffer;
 typedef std::vector<OutputObjectID>::const_iterator OutputObjectsConstIt;
 typedef std::pair<OutputObjectsConstIt, OutputObjectsConstIt> OutputObjectsConstItPair;
 
@@ -138,9 +141,14 @@ void writeMultiLinestring(
 
 		// vtzero dislikes linesegments that have zero-length segments,
 		// e.g. where p(x) == p(x + 1). So filter those out.
+		// Both passes below need the same tile coordinates, so scale each point
+		// once into a reused buffer rather than calling scaleLatpLon() twice.
+		scaledLinestring.clear();
+		scaledLinestring.reserve(ls.size());
 		int points = 0;
 		for (const Point& p : ls) {
 			pair<int,int> xy = bbox.scaleLatpLon(p.get<1>(), p.get<0>());
+			scaledLinestring.push_back(xy);
 			if (points == 0 || xy != lastXy) {
 				points++;
 				lastXy = xy;
@@ -154,8 +162,7 @@ void writeMultiLinestring(
 		hadLine = true;
 		fbuilder.add_linestring(points);
 		bool firstPoint = true;
-		for (const Point& p : ls) {
-			pair<int,int> xy = bbox.scaleLatpLon(p.get<1>(), p.get<0>());
+		for (const pair<int,int>& xy : scaledLinestring) {
 			if (firstPoint || xy != lastXy) {
 				// vtzero doesn't like linesegments with zero-length segments,
 				// so filter those out
@@ -324,7 +331,8 @@ void ProcessObjects(
 			// The very first point; below we check if there are more compatible points
 			// so that we can write a multipoint instead of many point features
 
-			std::vector<std::pair<int, int>> multipoint;
+			multipointBuffer.clear();
+			std::vector<std::pair<int, int>>& multipoint = multipointBuffer;
 			const int tile_extent = bbox.hires ? 8192 : 4096;
 			const int margin = 256; // Just in case something happens near the edges.