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Only set programmatic scroll if room scroll will move

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This commit is contained in:
Jon Staab 2026-09-21 10:56:28 -07:00
parent 2b26c033f6
commit 3f57607780
1 changed files with 8 additions and 11 deletions
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19
src/app/components/RoomChat.svelte
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@ -245,25 +245,22 @@
const topOf = (target: HTMLElement) =>
target.getBoundingClientRect().top - element!.getBoundingClientRect().top
// Messages loading in below the pinned row are inserted at the scroll origin, which pushes
// everything else away from it. The browser has no reason to compensate for that, so put the
// row back where it was. scrollBy is in visual terms, so this reads the same way either way up.
//
// A row the scroll clamped at the origin is the exception: it is pinned to the live end of the
// loaded window, and once the forward walk reaches the present that is the live end of the
// conversation, where an arriving message belongs on screen. Settling there while the origin is
// still within reach of the row leaves a jump deep into history — clamped the same way with
// nothing newer loaded yet — where it landed.
// Messages arriving at the origin push the pinned row away, and the browser does not compensate.
const keepPinned = (caughtUp: boolean) => {
const target = pinned && element?.querySelector(`[data-event="${pinned.id}"]`)
if (target instanceof HTMLElement && pinned) {
const origin = Math.abs(element!.scrollTop)
// A pin clamped at the origin belongs at the live end once the forward walk catches up.
if (pinned.clamped && caughtUp && topOf(target) > origin) {
release()
isProgrammaticScroll = true
element!.scrollTo({top: 0})
// Only a scroll event clears the flag, so claiming one that never fires discards the next.
if (origin >= 1) {
isProgrammaticScroll = true
element!.scrollTo({top: 0})
}
} else {
const drift = topOf(target) - pinned.top