Stefan HallerandClaude Opus 4.8 585c7f126d Cache each line's wrapping so scrolling doesn't re-wrap the whole buffer ...

refreshViewLinesIfNeeded re-wrapped every line of the buffer whenever
the view was tainted. That's cheap for short content, but scrolling a
long diff calls it constantly: adjustDownwardScrollAmount queries
ViewLinesHeight on every scroll event, and each newly-read line taints
the view, so every notch re-wrapped the entire buffer. Wrapping measures
each cell's width (uniseg) and allocates per line, so once you'd scrolled
far enough down the diff, scrolling turned sluggish - the cost grew with
how much had been read. (A CPU profile of scrolling deep in a long diff
put 77% of the time in lineWrap, reached almost entirely via
ViewLinesHeight rather than draw.)

Cache each line's wrapped result on the lineType, keyed by the width it
was wrapped at, and only re-wrap lines that have actually changed since
the last refresh. A firstDirtyLine index, updated in the same three
places that set `tainted` (write, clearViewLines' callers, SetHighlight),
marks the lowest line that might have changed; lines below it with a
matching cached width reuse their cached wrapping. The cache lives on the
line, so it's freed with the line when the view's content is replaced
(e.g. selecting a different commit) - it doesn't accumulate across a
session.

The wrapping cost per scroll now scales with the number of lines just
read, not with the total size of the buffer, so scrolling stays smooth
no matter how far down you are.

Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>

2026-07-09 09:32:35 +02:00

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