Indexed export (GIF, PNG-8, BMP, TIFF) finds each pixel's nearest
palette entry with a linear scan, and the k-means refinement in median
cut does the same once per cell per pass. With the 256-entry palettes
this code produces, that is 256 distance evaluations per query.
PaletteIndex is an exact nearest-neighbour kd-tree over the palette,
balanced at the widest weighted axis, with tight channel bounds in every
subtree so branch-and-bound can skip whole boxes. Small palettes (12 or
fewer entries) keep the scan, which is cheaper than tree traversal.
Results match the linear scan exactly, including ties: an equal-distance
entry with a smaller index still wins. The bound uses the same weighted
squared f32 form as dist() rather than a transformed space, so rounding
cannot change which entry is chosen.
Three tests: randomized parity against the original scan across palette
sizes spanning the cutoff, three weight vectors, duplicate colours and
fractional query points; explicit tie-breaking cases; and an opt-in
benchmark comparing 100k queries at both, behind -- --ignored.
objects_at() found Select Behind targets by running hit_test_skipping()
in a loop, skipping everything found so far. Each round is a full tree
traversal, so a stack of n overlapping paths costs O(n^2) hit tests
before the loop finds no further object.
The fast path walks each editable top-level layer once. Every selectable
object's subtree is visited only until its first hit, and a HashSet
records found ids so subtrees already covered by an earlier hit are not
searched again. Sublayers recurse the same way, so a stack of n paths
costs one traversal total.
The original traversal stays in charge where Select Behind semantics
differ from the plain front-to-back order: isolation (scope), and Edit
Contents, which exposes objects nested inside a top-level group. Non-
layer roots in malformed files also fall back. objects_at_repeated()
keeps the old loop for those cases.
Three tests: a 256-path stack asserts front-to-back order and
completeness; a mixed document (sublayer, groups, clipping group,
outline and path-only options) asserts the one-pass result equals the
repeated-traversal result; an envelope in Edit Contents asserts the
fallback preserves the original order.
Export::class() deduplicated declaration blocks with
classes.iter().position(), an O(n) scan per style, making exports with
many distinct styles (e.g. large palettes) quadratic overall. Track the
1-based class number per declaration in a HashMap alongside the
first-use-ordered Vec, so each lookup is O(1) while output stays
byte-identical.
Also adds a regression test covering 256 distinct declarations with
recurrence of early styles, for both InternalCss and StyleEntities
styling.
Ayanprogrammer11