Fix janky scrolling in markdown preview with code blocks#287050
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mjbvz merged 4 commits intoMar 26, 2026
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Fixes microsoft#278930 This commit fixes the scroll synchronization issues between the markdown editor and preview when scrolling through code blocks: 1. **Code block line tracking**: Added endLine calculation for fenced code blocks by counting newlines, enabling accurate line-to-position mapping within multi-line code blocks. 2. **Padding-aware scrolling**: Implemented getContentBounds() to calculate scroll positions excluding padding, preventing jumps when scrolling through code blocks with padding. 3. **Scroll loop prevention**: Changed scroll disable flags from counters to timer-based booleans (50ms) to prevent infinite sync loops while maintaining smooth bidirectional synchronization. The fix ensures smooth scrolling through code blocks without jumping or stuttering in both directions (editor ↔ preview).
Contributor
Author
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@microsoft-github-policy-service agree |
Contributor
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can confirm it fixes the scroll resetting issue |
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I can also confirm that this fixes the issue. |
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When will it be merged if everything is ok? |
DonJayamanne
approved these changes
Mar 26, 2026
Yoyokrazy
approved these changes
Mar 26, 2026
This was referenced Apr 4, 2026
AshtonYoon
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Apr 4, 2026
Two regressions from the merge of microsoft#287050: 1. preview.ts: The merge retained `this.#isScrolling = false` inside the early-return guard of `scrollTo()`, which was intentionally removed in the original PR. This resets the timer-based flag on the very first forward-sync call, allowing subsequent editor scroll events to re-trigger forward sync while reverse sync is in progress, causing the editor to jump back up. 2. index.ts: The PR converted `onUpdateView` from a decrement-counter to a timer-based approach but left initialization and resize handlers still using `scrollDisabledCount += 1` without a corresponding timer reset. The old scroll handler decremented the counter naturally; the new handler only returns early. As a result, after page load `scrollDisabledCount` stays at 1 indefinitely, blocking all preview-to-editor sync until the user scrolls the editor once. Fixes: - Remove the erroneous `this.#isScrolling = false` from scrollTo() - Apply the same timer-reset pattern (200ms) to initialization and resize handlers so scrollDisabledCount is always auto-cleared Fixes microsoft#307762
mjbvz
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May 1, 2026
…l-sync-regressions markdown: fix scroll sync regressions introduced in #287050
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Fixes #278930
Summary
This PR fixes the scroll synchronization issues between the markdown editor and preview when scrolling through code blocks. Previously, scrolling through code blocks would cause noticeable jumps and stuttering due to:
Changes
1. Code block line tracking (
scroll-sync.ts)endLinecalculation for fenced code blocks by counting newlinesCodeLineElementto include optionalendLineproperty2. Padding-aware scrolling (
scroll-sync.ts)getContentBounds()function to calculate content area excluding padding3. Scroll loop prevention
index.ts): ChangedscrollDisabledCountto use timer-based reset (50ms)preview.ts): Changed_isScrollingfrom counter to timer-based boolean (50ms)Result
Smooth scrolling through code blocks without any jumping or stuttering in both directions.
As-Is
Screen.Recording.2026-01-12.at.10.24.48.AM.mov
To-Be
Screen.Recording.2026-01-12.at.10.25.48.AM.mov