fix: use grapheme cluster count instead of UTF-16 code units for animation resume index#9
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…ation resume index In `_resumeCharacterByCharacterTyping` and `_resumeCharacterByCharacterTypingFromOldText`, `_displayedText.length` returns the count of UTF-16 code units, but the value is used as an index into `Characters().toList()` which is indexed by grapheme clusters. For characters that occupy multiple UTF-16 code units (e.g. emoji like 👍 which is a surrogate pair), the index overshoots, causing the character immediately after the emoji to be skipped when the animation resumes after new text is appended. The fix replaces `_displayedText.length` with `_displayedText.characters.length` in these two methods so the index correctly counts grapheme clusters.
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Hey @hooshyar! Thanks for making this package! Let me know if you need more information about this change 🙏 |
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Thanks for the fix @WilliamRWalsh! Great catch on the grapheme cluster vs UTF-16 code unit issue. We've applied this fix directly to main (along with tests for emoji text). Since the changes are identical, I'm going to close this PR. Your contribution is credited in the commit. Appreciate it! 🎉 |
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Apr 12, 2026
- Add 7 custom builder parameters (imageBuilder, onLinkTap, codeBuilder, latexBuilder, sourceTagBuilder, highlightBuilder, linkBuilder) to StreamingTextMarkdown and all named constructors (closes #10) - Fix emoji character skipping: use grapheme cluster count instead of UTF-16 code units for animation resume index (closes PR #9) - Add tests for emoji text and custom builders - Rewrite CLAUDE.md for accuracy and conciseness Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>
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Summary
_resumeCharacterByCharacterTypingand_resumeCharacterByCharacterTypingFromOldText,_displayedText.lengthreturns UTF-16 code units, but is used as an index intoCharacters().toList()which is indexed by grapheme clusters. For emoji (e.g. 👍, which is 2 UTF-16 code units but 1 grapheme), the index overshoots, skipping the next character._displayedText.lengthwith_displayedText.characters.lengthin these two methods.Reproduction
"Great 👍 Keep going")Changes
Two lines in
lib/src/streaming/streaming_text.dart:_resumeCharacterByCharacterTyping_displayedText.length_displayedText.characters.length_resumeCharacterByCharacterTypingFromOldText_displayedText.length_displayedText.characters.length