Iris's phone: typing newlines into the composer with the keyboard up
dropped the caret flush against the bar's bottom edge, eating the 12dp
padding, and closing the keyboard fixed it.
`Scroll::draw` offers its child last frame's content length on purpose,
so an ordinary scroll tick is an O(1) move rather than a redraw. The
comment claimed the lag self-corrects on the next frame; nothing asked
for that frame. A keystroke dirties the field, that frame draws it in a
box one line short of its text, and the tree is clean afterwards -- so
the stale placement is the last one drawn. The composer's text is
centred in its box, so one line short hung half a line past each end and
put the caret's line box a whole padding low. Closing the keyboard
rewrote the bar's inset, dirtied it, and forced the missing redraw.
`Scroll::draw` now calls `Painter::draw_again` when what it measured
differs from what it offered, and a frame that leaves anything dirty asks
for another frame on both backends -- `draw_again` sets its mark during
the update, after the input path's own check has run, so nothing asked
before this (which applied to `List::clamp_to_content` too).
Verified at layer 1 (the new test fails on the old code with the caret
exactly on the bar's edge) and on the emulator: the caret's bottom moved
from 1535 -- the bar's own bottom edge -- to 1509, 26px inside a 31px
padding, the remainder being parley's line box overhanging its line
height. `phone.rs` grew `--typed TEXT`, which enters text over frames
rather than preloading it; only that reproduces this.
Co-Authored-By: Claude Opus 5 <noreply@anthropic.com>
irisandClaude Opus 5
ba57086361