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fix: enable vertical touch scrolling in mobile diff view #694

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Merged
matt2e merged 1 commit into from
May 7, 2026
+42 −4
Merged

fix: enable vertical touch scrolling in mobile diff view #694

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37 changes: 33 additions & 4 deletions apps/staged/src/lib/features/diff/DiffModal.svelte
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Open in desktop
Original file line number Diff line number Diff line change
Expand Up @@ -301,6 +301,10 @@
let mobileDiffStartY = 0;
let mobileDiffStartDragX = 0;
let mobileDiffIsDragging = $state(false);
let mobileDiffIsScrolling = false;
let mobileDiffLastY = 0;
let diffViewerScrollApi: { scrollBy: (side: 'before' | 'after', deltaY: number) => void } | null =
$state(null);
let mobileDiffStyle = $derived(
`--mobile-diff-drag-x: ${mobileDiffDragX}px;` +
`--mobile-diff-rest-offset: ${MOBILE_DIFF_REST_OFFSET}px;` +
Expand Down Expand Up @@ -1010,6 +1014,7 @@
function resetMobileDiffDrag() {
mobileDiffPointerId = null;
mobileDiffIsDragging = false;
mobileDiffIsScrolling = false;
mobileDiffDragX = 0;
}

Expand All @@ -1030,20 +1035,43 @@
mobileDiffPointerId = event.pointerId;
mobileDiffStartX = event.clientX;
mobileDiffStartY = event.clientY;
mobileDiffLastY = event.clientY;
mobileDiffStartDragX = mobileDiffDragX;
mobileDiffIsDragging = false;
diffViewerContainerEl?.setPointerCapture(event.pointerId);
mobileDiffIsScrolling = false;
}

function handleMobileDiffPointerMove(event: PointerEvent) {
if (!isSmallDiffViewport || mobileDiffPointerId !== event.pointerId) return;

const deltaX = event.clientX - mobileDiffStartX;
const deltaY = event.clientY - mobileDiffStartY;

// Already in vertical scroll mode — translate touch delta to scroll
if (mobileDiffIsScrolling) {
event.preventDefault();
const moveDeltaY = event.clientY - mobileDiffLastY;
mobileDiffLastY = event.clientY;
diffViewerScrollApi?.scrollBy('after', -moveDeltaY);
return;
}

if (!mobileDiffIsDragging) {
const horizontalIntent = Math.abs(deltaX) > 8 && Math.abs(deltaX) > Math.abs(deltaY);
if (!horizontalIntent) return;
mobileDiffIsDragging = true;
// Determine gesture direction once past dead zone
if (Math.abs(deltaX) > 8 && Math.abs(deltaX) > Math.abs(deltaY)) {
// Horizontal intent — capture pointer and start drag
mobileDiffIsDragging = true;
diffViewerContainerEl?.setPointerCapture(event.pointerId);
} else if (Math.abs(deltaY) > 8 && Math.abs(deltaY) > Math.abs(deltaX)) {
// Vertical intent — start scroll mode
mobileDiffIsScrolling = true;
mobileDiffLastY = event.clientY;
event.preventDefault();
diffViewerScrollApi?.scrollBy('after', -deltaY);
Comment on lines +1069 to +1070
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@chatgpt-codex-connector chatgpt-codex-connector Bot May 7, 2026

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P2 Badge Preserve mobile scrolling for markdown preview

When a Markdown diff is toggled to preview mode on a small viewport, the preview panes scroll via native overflow-y: auto on .code-area.markdown-mode, not via scrollController. This vertical branch now calls preventDefault() and only updates diffViewerScrollApi.scrollBy('after', ...), so a touch swipe that enters this mode can suppress the native preview scroll while changing an off-screen code-mode scroll position instead. Gate this path out for markdown preview or expose an API that scrolls the active markdown container.

Useful? React with 👍 / 👎.

return;
} else {
return;
}
}

event.preventDefault();
Expand Down Expand Up @@ -1273,6 +1301,7 @@
onCommentCommit={readonly ? undefined : handleNewCommit}
onCommentGithub={readonly || !hasPr ? undefined : handleSendToGithub}
commentGithubState={readonly || !hasPr ? undefined : getCommentGithubState}
bind:scrollApi={diffViewerScrollApi}
/>
</div>

Expand Down
9 changes: 9 additions & 0 deletions packages/diff-viewer/src/lib/components/DiffViewer.svelte
View file
Open in desktop
Original file line number Diff line number Diff line change
Expand Up @@ -119,6 +119,9 @@
onCommentGithub?: (comment: Comment) => void;
/** Returns the GitHub button state for a given comment. */
commentGithubState?: (comment: Comment) => GithubButtonState;

/** Bindable API object exposing scroll control for external callers (e.g. mobile touch scroll). */
scrollApi?: { scrollBy: (side: 'before' | 'after', deltaY: number) => void } | null;
}

let {
Expand All @@ -142,6 +145,7 @@
onCommentCommit,
onCommentGithub,
commentGithubState,
scrollApi = $bindable(null),
}: Props = $props();

// ==========================================================================
Expand Down Expand Up @@ -359,6 +363,11 @@

const scrollController = createScrollController();

// Expose scroll API for external callers (e.g. mobile touch scroll in DiffModal)
scrollApi = {
scrollBy: (side, deltaY) => scrollController.scrollBy(side, deltaY),
};

// Update scroll controller with active alignments
$effect(() => {
const filePath = diff ? getFilePath(diff) : null;
Expand Down