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Avoid redundant work when writing features #931

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14 changes: 11 additions & 3 deletions src/tile_worker.cpp
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Original file line number Diff line number Diff line change
Expand Up @@ -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;

Expand Down Expand Up @@ -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;
Expand All @@ -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
Expand Down Expand Up @@ -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.

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