A widget's region is now held in the coordinates of the slot it draws in
rather than the window's, and `Painter::place` is how a container asks for a
slot: it draws a child it decides the box of and may decide again. Everything
under that slot is a fraction of its box, so placing the child a second time
is one entry to write whether it moved or changed length. A child drawn any
other way has no slot and shares its nearest ancestor's.
That is what keeps the chain short. `chain_cost` measured depth as the cost
-- free to 8, +42.6% at 16 -- and a slot per widget put a transcript's glyphs
past that for nothing, since almost every slot was zero. `Span`, `Aligned`
and `Scroll` are the containers that re-place a child after drawing it, and
`tests/layout.rs` pins that four widgets between a span and a leaf leave the
leaf's chain one deep.
`UiRegion::stretch`, `UiRegion::stretchable` and `UiScalar::stretch` are
gone. Nothing is inverted any more: a box that changed length is written to
its slot, and the descendants recompose against it in the shader. That also
retires the case the guard existed for, where a fixed length has no fraction
to recover -- `tests/layout.rs` now stretches a 40-tall row on its other
axis, which `stretchable` refused outright.
What still walks the CPU is deciding who must draw again, which no chain can
answer: `mark_resized` descends from the widget whose box changed and marks
anything whose own box changed length and whose drawing reads it. A part of
a box with no relative extent on an axis is a fixed length, and composing
into it leaves none either, so the walk stops where a length did not change
-- an 80-wide child in a widened row is not redrawn though it says `Redraw`.
`Span`, `Pad`, `Stack`, `Offset`, `Aligned`, `SetSize` and `LayerOffset` say
`Scale`: each places in fractions and offsets of its own box and none reads
the box's pixel length. `Scroll` and `MaxSize` do read pixels and stay
`Redraw`.
45 tests pass, five of them new. Render verification comes after the CPU
side, per the owner.
Co-Authored-By: Claude Opus 5 <noreply@anthropic.com>
`Sized` shadowed the marker trait, so a `?Sized` bound in any crate that imports the prelude failed to resolve -- a compile error in someone else's code that nothing here would have caught. It was already biting inside iris: `default/mod.rs`, `widget/ptr.rs` and `widget/text/build.rs` all imported `std::marker::Sized` explicitly to get out from under it, which they no longer need.
`SetSize` rather than `FixedSize` because the size it sets need not be fixed -- `width(rest(2))` (a flex weight) and `width(rel(0.5))` (half the parent) build the same widget, and both are more common than `sized((100, 100))`. It also pairs with the `MaxSize` beside it in that module: one sets a length, the other caps it. The builders are unchanged.
`tests/prelude_bounds.rs` is a compile-level guard -- it fails to build if the prelude shadows `Sized` again, which I checked by reverting `src/` under it:
```
error[E0404]: expected trait, found struct `Sized`
--> tests/prelude_bounds.rs:8:22
|
8 | fn takes_unsized<T: ?Sized>(_: &T) {}
| ^^^^^ not a trait
```
The pad tab of the tabs example -- the one built out of `sized` and the flexible widths -- renders pixel-identical to before the rename.
---------
Co-authored-by: iris <2+iris@noreply.localhost>
Reviewed-on: iris/iris#14
Co-authored-by: AIris <4+iris-ai@noreply.localhost>
iris-ai
