Cap rendering and editing of extremely long lines - #607
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A single very long line (e.g. a minified blob or a Unity YAML asset with an inline binary payload serialized as hex) froze the UI thread as it scrolled into view: TextMate tokenized and colorized the whole line, and TextFormatter shaped every character. - VisualLine shapes only the first LENGTH_LIMIT characters and collapses the remainder into a short "..." marker (a FormattedTextElement, the same mechanism used for collapsed fold regions). Document offsets are unchanged, so caret, selection and highlighting keep working. - TextMateColoringTransformer skips tokenizing/colorizing lines past LENGTH_LIMIT. - New LongLineEditProtection disallows edits inside the collapsed tail, and TextArea routes CanInsert/GetDeletableSegments through it so callers cannot insert into or delete the hidden region (deleting the delimiter would merge the next line into the hidden text). Co-authored-by: Daniel Penalba <daniel.penalba@unity3d.com>
danipen
self-requested a review
August 7, 2026 11:17
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Problem
A single very long line — e.g. a minified blob, or a Unity YAML asset with an inline binary payload serialized as hex — freezes the UI thread as it scrolls into view. Two full-line passes run synchronously: TextMate tokenizes and colorizes the whole line, and
TextFormattershapes every character.Change
VisualLineshapes only the firstLENGTH_LIMITcharacters and collapses the remainder into a short...marker via aFormattedTextElement— the same mechanism already used for collapsed fold regions. Document offsets are unchanged, so caret, selection and highlighting keep working.TextMateColoringTransformerskips tokenizing/colorizing lines pastLENGTH_LIMIT.LongLineEditProtectiondisallows edits inside the collapsed tail;TextArearoutesCanInsert/GetDeletableSegmentsthrough it so callers cannot insert into or delete the hidden region (deleting the line delimiter would otherwise merge the next line into the hidden text).This builds on the existing
VisualLine.LENGTH_LIMIT(3000) short-circuit, which previously still added a single full-lengthVisualLineTextfor over-limit lines.Builds cleanly against
net8.0andnet10.0.