The index arithmetic in `Sub::spliced`, `Sub::resize` and `KeptPath::update`
uses `checked_sub` and `checked_add` instead of plain subtraction. When the
segments or runs kept for a subpath do not fit its anchors before the edit,
`resize` returns `None` without changing anything, and `update` writes the
subpath's elements again from the new anchors and measures it whole, as it
does for a subpath of fewer than two anchors. A compound path whose kept
members do not pair with the new ones returns false, and the renderer makes
the path again whole.
When anchors of a kept path (a path or compound path of 1,024 anchors or
more) are added or deleted, or a subpath is closed or opened, the next
frame writes again only the path elements from the first anchor that
changed to the last, and the closing segment and ClosePath when an end
anchor changed or the subpath was closed or opened. The elements after
the change move with it. Before, such an edit made the whole path again
and measured it whole.
- The runs of segments now carry their own ends. The runs that held the
segments written become one run, split into runs of 128 when it grows
past 256, and only those runs are measured again, with the miter tips
of the run of the segment with length before each span. When a
subpath is closed or opened and the stroke reaches farther from one
than from the other, all of that subpath's tips are measured again.
- On a subpath that is open before and after the edit, the handle before
the first anchor and the one after the last are not compared, so
Delete Anchor Point, which clears them, writes again only the segments
around the anchor deleted.
- A subpath that has fewer than two anchors before or after the edit is
written again whole. A compound path member that gains or loses
subpaths is made again. When members are added or removed, those
members and every member between the first and the last of them are
made again, and the members before and after them stay.
- An edit that adds or deletes anchors in, closes or opens more than 16
subpaths makes the whole path again, as before.
- An edit that leaves every anchor as it was, such as a new stroke,
leaves the kept path as it is.
The pixels and the cull bounds are the same as with a path made again.
Docs: docs/target-app-parity.md.
The renderer keeps the path of a path or compound path of 1,024 anchors
or more by object id, with the bounds of its segments and of its miter
spikes in runs of 128 segments. When anchors move and the subpaths and
anchor counts stay the same, the next frame rewrites only the path
elements of the segments that start or end at a moved anchor, and
measures again only the runs that hold them and the runs of the
segments with length before them. Other edits make the path again as
before. The pixels and the cull bounds are the same.
- StrokeLayer::bounds_on is unchanged. The miter tip of one joint
(miter_tip) and the stroke box with given tips (bounds_with_tips) are
new functions beside it, and Appearance::stroked_bounds_by takes the
box of each shaped stroke, so the cull bounds of a kept path use the
kept tips.
- geom::bez::has_length is the predicate reach.rs used for segments
that draw, made public.
Docs: docs/target-app-parity.md.
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