`lerp_inv` returns `Option`. Inverting a lerp over a range of zero
length has no one answer, and `div_or`'s fallback picked one: the start
of the range. Measured, that is not a wrong number so much as a
plausible one -- taking a part out of a box fixed at the top of the
window hands back exactly what went in, and out of a box fixed at the
middle hands back the parent's own `rel` of 0.5 as if it were the
child's fraction. Either way the caller cannot tell that nothing was
recovered, which is the defect; the previous commit's claim that it
"returns a rel of 0" is right only for the first case.
`UiScalar::outside` and `UiSpan::outside` follow it to `Option`, and
`Remap` is the answer at the region level: `new` says whether a drawing
in one box can be put in another and `apply` then cannot fail, so
`try_reuse` asks once for a whole subtree and `reusable` goes back to
reporting only what the widget claims. That replaces the predicate the
last commit put in `reusable`, which stated the same rule in a second
place.
`DivOr` existed only for the fallback and is gone, along with
`UiRegion::outside` and `UiVec2::outside`, which had no callers once
`Remap` owned the operation. `UiRegion::axis` took `&mut self` to
return a shared reference; `Remap::new` needs it on a shared one.
This does not redraw less. `Remap::new` refuses exactly what the
predicate refused; what it buys is one statement of the rule and a
remap that cannot half-apply. Counted on a resize, with the old
wipe-everything for comparison:
20 padded rows, 101 widgets 101 draws -> 0
the `tabs` example 73 draws -> 0
the `text` example 49 draws -> 48
So the saving is whole where a resize does not change any widget's
size, and nil in `text`, where both paragraphs rewrap to a different
height and the relayout that forces reaches the root. The last commit's
message oversold that case.
Checked: fmt, clippy and 35 tests. `tabs` (with the image replay),
`view` and `minimal` still byte-identical to `upstream/main`, `text`
unchanged, and the live sway resize round trip still matches a cold
start at each size.
iris-ai
53e61289f5