perf(shapes): vectorize datashader polygon scaling#740
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Re-lands #738 (accidentally merged then reverted in #739), with the code-review cleanups applied: the helper lives in _geometry.py next to its matplotlib-Path twin _scale_path_around_centroid (module-level shapely import, no local one). The datashader path scaled polygons with a per-geometry affinity.scale loop — a pure-Python loop that dominates large polygon renders (~60% of a 100k-polygon render). _scale_geometries scales every coordinate about each geometry's bounding-box centre (affinity.scale's default origin) in one vectorized get_coordinates/set_coordinates pass. Byte-identical to affinity.scale incl. asymmetric shapes, multipolygons and holes (verified main-vs-branch diff_px=0; unit test at 1e-9); ~12x polygons / ~6.5x multipolygons. Only fires for scale != 1.0.
Codecov Report✅ All modified and coverable lines are covered by tests. Additional details and impacted files@@ Coverage Diff @@
## main #740 +/- ##
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+ Coverage 79.29% 79.33% +0.03%
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Files 17 17
Lines 4599 4603 +4
Branches 1030 1030
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+ Hits 3647 3652 +5
Misses 602 602
+ Partials 350 349 -1
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Vectorize datashader polygon/multipolygon scaling: the old per-geometry
affinity.scaleloop is pure Python and dominates large renders (~60% of a 100k-polygon render)._scale_geometriesscales all coordinates about each geometry's bounding-box centre (affinity.scale's default origin) in oneget_coordinates/set_coordinatespass. Only fires forscale != 1.0.Byte-identical to
affinity.scale(asymmetric shapes, multipolygons, holes; main-vs-branch render diff_px=0). Trades peak memory for speed (scale=0.6):Re-land of #738 (reverted in #739); helper lives in
_geometry.pynext to_scale_path_around_centroid.