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[Bug Fix] Improve scrolling speed when dragging items #3216

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[Bug Fix] Improve scrolling speed when dragging items #3216

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31 changes: 17 additions & 14 deletions src/utils.ts
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Original file line number Diff line number Diff line change
Expand Up @@ -590,28 +590,31 @@ export class Utils {
const elRect = el.getBoundingClientRect();
const scrollRect = scrollEl.getBoundingClientRect();
const innerHeightOrClientHeight = (window.innerHeight || document.documentElement.clientHeight);
const prevScroll = scrollEl.scrollTop;

// Calculate how far element extends past viewport edges
const offsetDiffDown = elRect.bottom - Math.min(scrollRect.bottom, innerHeightOrClientHeight);
const offsetDiffUp = elRect.top - Math.max(scrollRect.top, 0);
const prevScroll = scrollEl.scrollTop;

// Cap the maximum scroll speed per update
const maxScrollPerUpdate = 10;
let scrollAmount = 0;

if (offsetDiffUp < 0 && distance < 0) {
// scroll up
if (el.offsetHeight > scrollRect.height) {
scrollEl.scrollTop += distance;
} else {
scrollEl.scrollTop += Math.abs(offsetDiffUp) > Math.abs(distance) ? distance : offsetDiffUp;
}
// Element is above viewport, scroll up
// Limit scroll speed to maxScrollPerUpdate
scrollAmount = Math.max(offsetDiffUp, -maxScrollPerUpdate);
} else if (offsetDiffDown > 0 && distance > 0) {
// scroll down
if (el.offsetHeight > scrollRect.height) {
scrollEl.scrollTop += distance;
} else {
scrollEl.scrollTop += offsetDiffDown > distance ? distance : offsetDiffDown;
}
// Element is below viewport, scroll down
// Limit scroll speed to maxScrollPerUpdate
scrollAmount = Math.min(offsetDiffDown, maxScrollPerUpdate);
}

position.top += scrollEl.scrollTop - prevScroll;
// Apply scroll
if (scrollAmount !== 0) {
scrollEl.scrollTop += scrollAmount;
position.top += scrollEl.scrollTop - prevScroll;
}
}

/**
Expand Down