Iris's report was that expanding a tool card holding a long,
horizontally-scrolling edit lags on her phone. The cause is not text
layout: shaping and rasterising a 51,200-glyph block is 20ms, and the
frame that drew it took 1.37 seconds.
A widget redrawn in place frees every primitive it owned and writes
fresh ones. Freeing compacts each layer's draw order with swap_remove,
so ~N primitives are renumbered, and finding the handle to renumber was
a linear scan of everything that widget drew -- O(N^2) in the widget's
own primitive count. A paragraph never notices; one text widget holding
a whole old_string and new_string is every glyph in the card.
The arena now records, per slot, where that slot's handle sits in its
owner's ActiveData::primitives, written at the one place a handle is
taken (Painter::own), and apply_free indexes straight to it.
50,000 glyphs, redrawn: before 636ms after 2.4ms
per glyph: before 12.7us after 0.043us, flat in N
benches/message_list.rs gains scenario (g) for it, reporting per-glyph
because flat is the pass condition and a total hides it. That file had
also stopped running entirely: scenarios (a) and (e) built a LazySpan
with no mask around it, which the span now asserts against, so the
benchmark panicked on its second line. Fixed here too.
Also, on Iris's instruction: the copied report no longer inlines a tail
of the app log. Dev Updater's Runtime tab reads the same ring through
devlog's provider, so it was the same lines twice; the diagnostics pane
still names the provider's authority to read them from.
iris
1318e149f5