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| 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 | 14x 1x 13x 13x 13x 13x 13x | export interface VirtualWindowInput {
itemCount: number;
rowHeight: number;
viewportHeight: number;
scrollTop: number;
overscan?: number;
}
export interface VirtualWindow {
startIndex: number;
endIndex: number;
offsetTop: number;
totalHeight: number;
visibleCount: number;
}
export function calculateVirtualWindow({
itemCount,
rowHeight,
viewportHeight,
scrollTop,
overscan = 6
}: VirtualWindowInput): VirtualWindow {
if (itemCount <= 0 || rowHeight <= 0 || viewportHeight <= 0) {
return {
startIndex: 0,
endIndex: 0,
offsetTop: 0,
totalHeight: Math.max(0, itemCount * rowHeight),
visibleCount: 0
};
}
const visibleRows = Math.ceil(viewportHeight / rowHeight);
const firstVisible = Math.floor(Math.max(0, scrollTop) / rowHeight);
const startIndex = Math.max(0, firstVisible - overscan);
const endIndex = Math.min(itemCount, firstVisible + visibleRows + overscan);
return {
startIndex,
endIndex,
offsetTop: startIndex * rowHeight,
totalHeight: itemCount * rowHeight,
visibleCount: Math.max(0, endIndex - startIndex)
};
}
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