Every frame the open chat thread handled all N messages: grouping flags
from two day keys each, a measuring layout of every body, then the
draw, which laid every body out a second time and ran the bubble, hover
and popup code, however few rows were on screen.
The thread now keeps a layout cache: grouping flags, each body's
wrapped size (keyed by message, so only new or re-wrapped bodies are
measured) and each row's height, with prefix offsets. A frame binary-
searches the visible range and submits those rows plus any failed send
(Retry stays reachable with Tab), the row being drag-selected and the
row whose context menu is open; one spacer stands in for each skipped
run, and scrolling to the newest message works as before.
- Rows are rebuilt when the chat store changes or when the wrap width,
fonts, font size, DPI scale, rasterizer density or compact mode
change. Fonts are keyed by FontId, so a font reload at the same size
(the colour-emoji toggle) re-measures. A rebuild is O(N), about
0.5-1 ms at 3000 messages.
- Grouping flags are recomputed on a data change and once a minute,
together with util::refreshTimezone(), so a system timezone change
reaches chat timestamps within a minute.
Rows above the visible range are now one spacer of their summed
heights, so the visible rows no longer move by a pixel each time a row
above them crosses the top of the app window. Debug builds log once if
a cached wrap width or row height ever disagrees with the live layout.
Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>
