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base repository: scverse/spatialdata-plot
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compare: perf/datashader-vectorize-polygon-scale
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Commits on Jun 22, 2026

  1. perf(shapes): vectorize datashader polygon scaling 

    The datashader path scaled polygons with a per-geometry affinity.scale loop
(_geometry[is_polygon].apply(lambda g: affinity.scale(...))) — a pure-Python
loop that dominates large polygon renders (measured ~60% of a 100k-polygon
render; the prototype's 33s at 1M is almost entirely this loop).

Replace with _scale_geometries: scale every coordinate about each geometry's
bounding-box centre (affinity.scale's default origin) in one vectorized pass
via shapely.get_coordinates/set_coordinates. Byte-identical to affinity.scale
including asymmetric shapes, multipolygons and holes (verified main-vs-branch,
diff_px=0); ~12x polygons / ~6.5x multipolygons -> ~2x+ end-to-end at 100k,
growing with n. Only fires for scale != 1.0.

The affine transform loop is left as-is (vectorizing it is ~0.9x: shapely
coordinate (de)serialization dominates, not the Python callback).
    @timtreis
    timtreis committed Jun 22, 2026
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