perf: avoid quadratic hole-point iteration in offset generation & triangulation#2211
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ben-milanko wants to merge 2 commits into
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perf: avoid quadratic hole-point iteration in offset generation & triangulation#2211ben-milanko wants to merge 2 commits into
ben-milanko wants to merge 2 commits into
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Widget- and kernel-level CPU benchmarks for the polyline, polygon, and
marker layers, plus a direct getOffsetsXY benchmark. Lives in
benchmark/ (not test/) so it is opt-in and does not extend CI runtime:
flutter test benchmark/feature_layer_benchmark_test.dart
Numbers are JIT and only meaningful relative to each other (before vs
after a change on the same machine).
…angulation points.followedBy(holePoints.expand(...)) indexed with per-element elementAt() walks the lazy iterable from the start on every call, making OffsetHelper.getOffsetsXY and the Earcut coordinate flattening O(n^2) in the total point count - on every frame. Flatten into a fixed-length list instead. Benchmark (benchmark/feature_layer_benchmark_test.dart, JIT): getOffsetsXY, 500-point polygon + 10 holes x 200 points: 26,761 us/call -> 33 us/call (~800x)
This was referenced Jun 10, 2026
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While profiling flutter_map in a production app on low-powered hardware, I found that
OffsetHelper.getOffsetsXYand thePolygonLayerEarcut coordinate flattening index a lazily concatenated iterable (points.followedBy(holePoints.expand(...))) withelementAt(i). On a lazy iterable that walks from the start on every call, so both paths are O(n²) in the total point count — every frame for any polygon with holes.This PR flattens the points + hole points into a fixed-length list before the loops (and writes the Earcut input into a
Float64Listdirectly).Results
Measured with the benchmark harness added in the first commit (
flutter test benchmark/feature_layer_benchmark_test.dart, JIT, best-of-reps):getOffsetsXY, 500-point polygon + 10 holes × 200 pointsAll existing tests pass. No behavioural change intended — output offsets are identical.
The harness commit is shared with #2212 and #2213 (identical file content, so whichever PR merges first, it collapses out of the others' diffs). It lives in
benchmark/rather thantest/so it doesn't extend CI runtime; numbers are only meaningful relative to each other on the same machine.