Every widget that reads its box in pixels was making `Moves` compose its
slot's chain again, a mean of 2.8 levels, about eight hundred times a frame.
A draw already descends past every one of those entries on its way in, so
`DrawInfo` carries what the slot composes to and `draw_at` steps it one box
further -- which is a select where it was a walk. `Moves::size_of` and
`compose` are left for `redraw`, which starts mid-tree with nothing above it
in flight.
Measured on the fixed-shape fixture, seed 1 depth 8, 500 frames of `many`,
medians of 25 runs, twenty-five work counters identical throughout:
| | instructions | cycles |
| --- | ---: | ---: |
| `d21a215`, before exact composition | 1,908M | 760M |
| `45a7176`, composing on the fine grid | 1,880M | 755M |
| this | **1,840M** | **735M** |
So exact composition ends up 3.6% fewer instructions and 3.3% fewer cycles
than the rounding-per-level walk it replaced, and the widening it needed was
paid for twice over by not doing the walk.
`Holds::through`'s allowance does not move: two half steps is where shrinker
seed 220 pins it, not where the arithmetic does. `Painter` still composes a
child's region into its own on the grid before asking for it in pixels, which
is the last narrow step in that path; taking it out needs the child's region
as its parent stated it, which `draw_inner` is not handed.
Checked: fmt, clippy, 83 suite tests, 17 core unit tests, the release oracle
at 100 seeds and at 1000 seeds of depth 6, all fifteen shrinker cases at 400
seeds of depth 5, and `tabs`, `view`, `minimal`, `text`, `random` and the tab
replay byte-identical at 1920x1200 against `45a7176`.
Co-Authored-By: Claude Opus 5 <noreply@anthropic.com>
iris-aiandClaude Opus 5
5f16617511