An id the importer writes into an element no longer matches a style sheet's
#id selector or a <use> link that no element matched before. The ids are
read from the decoded attribute values and text of the file, once.
An ellipse whose radius is smaller than the point tolerance at its coordinates, but at least two
f32 steps, now imports as the four-anchor ellipse instead of usvg's curves with rounded handles.
The import gives an element an id when it needs to find it again in
usvg's tree (links, symbol uses, events, data attributes, and now
circles and ellipses). A made-up id could repeat one the file already
had, such as vectorcraft-id-0, so a <use> or paint reference to that
element showed the other one. Made-up ids now skip every id in the file.
Circles and ellipses in a file whose style sheet has an [id selector get
no made-up id and keep usvg's curves, so the selector matches the same
elements as before.
The tolerance that compares the points usvg makes of a <circle> or
<ellipse> grew with the center's distance from the origin, so a circle
of radius 400 at x 40,000,000 fell back to eight anchors. The tolerance
is now a few f32 steps at the size of the coordinates, and the on-ellipse
check allows the same steps relative to the smaller radius.
usvg turns each <circle> and <ellipse> into arcs and then into a number
of cubics that depends on f32 rounding: an ellipse that export wrote as
<ellipse> could come back with eight anchors instead of the four it was
written from. The renderer flattens the two outlines differently, so a
round trip of a flat filled ellipse redrew 158 edge pixels by up to 43
levels, and prop_svg::plain_art_survives_visually failed on main.
Import now records the ids of <circle> and <ellipse> elements in the
prepass and rebuilds each as the ellipse VectorCraft draws: four smooth
anchors on the axes, starting at the right as SVG defines, with handles
KAPPA of the radii long, then transformed as before.
Tests: prop_svg::filled_ellipse_on_the_artboard_edge_survives_visually
(the failing case) and basic_shapes::circles_and_ellipses_import_as_the_ellipse_drawn
fail without the change.
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