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import { useEffect, useRef } from "react";
interface UseEdgeAutoScrollParams {
isActive: boolean;
getMouseClientX: () => number;
rulerScrollRef: React.RefObject<HTMLDivElement>;
tracksScrollRef: React.RefObject<HTMLDivElement>;
contentWidth: number;
edgeThreshold?: number;
maxScrollSpeed?: number;
}
// Provides smooth edge auto-scrolling for horizontal timeline interactions.
export function useEdgeAutoScroll({
isActive,
getMouseClientX,
rulerScrollRef,
tracksScrollRef,
contentWidth,
edgeThreshold = 100,
maxScrollSpeed = 15,
}: UseEdgeAutoScrollParams): void {
const rafRef = useRef<number | null>(null);
useEffect(() => {
if (!isActive) {
if (rafRef.current) {
cancelAnimationFrame(rafRef.current);
rafRef.current = null;
}
return;
}
const step = () => {
const rulerViewport = rulerScrollRef.current;
const tracksViewport = tracksScrollRef.current;
if (!rulerViewport || !tracksViewport) {
rafRef.current = requestAnimationFrame(step);
return;
}
const viewportRect = rulerViewport.getBoundingClientRect();
const mouseX = getMouseClientX();
const mouseXRelative = mouseX - viewportRect.left;
const viewportWidth = rulerViewport.clientWidth;
const intrinsicContentWidth = rulerViewport.scrollWidth;
const effectiveContentWidth = Math.max(
contentWidth,
intrinsicContentWidth
);
const scrollMax = Math.max(0, effectiveContentWidth - viewportWidth);
let scrollSpeed = 0;
if (mouseXRelative < edgeThreshold && rulerViewport.scrollLeft > 0) {
const edgeDistance = Math.max(0, mouseXRelative);
const intensity = 1 - edgeDistance / edgeThreshold;
scrollSpeed = -maxScrollSpeed * intensity;
} else if (
mouseXRelative > viewportWidth - edgeThreshold &&
rulerViewport.scrollLeft < scrollMax
) {
const edgeDistance = Math.max(
0,
viewportWidth - edgeThreshold - mouseXRelative
);
const intensity = 1 - edgeDistance / edgeThreshold;
scrollSpeed = maxScrollSpeed * intensity;
}
if (scrollSpeed !== 0) {
const newScrollLeft = Math.max(
0,
Math.min(scrollMax, rulerViewport.scrollLeft + scrollSpeed)
);
rulerViewport.scrollLeft = newScrollLeft;
tracksViewport.scrollLeft = newScrollLeft;
}
rafRef.current = requestAnimationFrame(step);
};
rafRef.current = requestAnimationFrame(step);
return () => {
if (rafRef.current) {
cancelAnimationFrame(rafRef.current);
rafRef.current = null;
}
};
}, [
isActive,
getMouseClientX,
rulerScrollRef,
tracksScrollRef,
contentWidth,
edgeThreshold,
maxScrollSpeed,
]);
}
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