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perf(rect_clip): skip segments beyond one edge, don't load large polygons twice #978

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perf(rect_clip): skip segments beyond one edge, don't load large polygons twice #978

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9 changes: 8 additions & 1 deletion src/geom.cpp
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Original file line number Diff line number Diff line change
Expand Up @@ -762,6 +762,11 @@ struct RectClipper {
bool inside(const Point &p) const {
return p.x() >= x0 && p.x() <= x1 && p.y() >= y0 && p.y() <= y1;
}
// Both end points beyond the same edge: the segment can't reach the box
bool beyondOneEdge(const Point &a, const Point &b) const {
return (a.x() < x0 && b.x() < x0) || (a.x() > x1 && b.x() > x1) ||
(a.y() < y0 && b.y() < y0) || (a.y() > y1 && b.y() > y1);
}
bool strictlyInside(const Point &p) const {
return p.x() > x0 && p.x() < x1 && p.y() > y0 && p.y() < y1;
}
Expand Down Expand Up @@ -888,7 +893,9 @@ RingClip clipRing(const RectClipper &rc, const Ring &ring, std::vector<RectChain
const Point &b = ring[(start + k + 1) % n];
double t0, t1;
Point pa, pb;
const bool hit = rc.clipSegment(a, b, t0, t1, pa, pb) && t1 > t0;
// Most segments of a large polygon lie far from a small tile's box: reject
// those with four comparisons before the clip computation
const bool hit = !rc.beyondOneEdge(a, b) && rc.clipSegment(a, b, t0, t1, pa, pb) && t1 > t0;
if (!hit || (building && t0 > 0)) {
if (building && !finish()) return RingClip::Fail;
if (!hit) continue;
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12 changes: 9 additions & 3 deletions src/tile_data.cpp
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Original file line number Diff line number Diff line change
Expand Up @@ -385,7 +385,13 @@ Geometry TileDataSource::buildWayGeometry(OutputGeometryType const geomType,
}

MultiPolygon mp;
if (cachedClip == nullptr)
// rect_clip below needs the input as it was before fast_clip. For a large valid
// polygon, keep it rather than load it from the store again for every tile.
std::size_t inputPoints = 0;
if (cachedClip == nullptr && inputKnownValid)
for (auto const &p : uncached) inputPoints += geom::num_points(p);
const bool keepUncached = inputPoints > 1000;
if (cachedClip == nullptr && !keepUncached)
mp = std::move(uncached);
else
geom::assign(mp, input);
Expand All @@ -405,9 +411,9 @@ Geometry TileDataSource::buildWayGeometry(OutputGeometryType const geomType,
// instead, which is much cheaper than the is_valid/intersection/repair
// path below; rect_clip bails out on anything it can't handle.
MultiPolygon original;
if (cachedClip == nullptr) populateMultiPolygon(original, objectID);
if (cachedClip == nullptr && !keepUncached) populateMultiPolygon(original, objectID);
MultiPolygon clipped;
if (rect_clip(cachedClip == nullptr ? original : input, box, clipped) &&
if (rect_clip(cachedClip == nullptr && !keepUncached ? original : input, box, clipped) &&
(multiPolygonDefinitelyValid(clipped) || geom::is_valid(clipped))) {
multiPolygonClipCache.add(bbox, objectID, clipped, true);
return clipped;
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