24 lines
1.1 KiB
TypeScript
24 lines
1.1 KiB
TypeScript
export const VISIBLE_ROWS = 5
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export const CENTER_OFFSET = (VISIBLE_ROWS - 1) / 2 // 2
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/** Index de valeur logique (0..length-1) centré pour un scrollTop donné. */
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export function valueIndexFromScroll(scrollTop: number, itemHeight: number, length: number): number {
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const flat = Math.round(scrollTop / itemHeight) + CENTER_OFFSET
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return ((flat % length) + length) % length
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}
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/** scrollTop qui centre l'index donné dans la copie du milieu (buffer à 3 copies). */
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export function scrollTopForValueIndex(valueIndex: number, itemHeight: number, length: number): number {
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const flat = length + valueIndex - CENTER_OFFSET
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return flat * itemHeight
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}
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/** Recentre le scrollTop dans la copie du milieu [length, 2*length) si on a dérivé. */
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export function loopCorrection(scrollTop: number, itemHeight: number, length: number): number {
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const block = length * itemHeight
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const centeredFlat = Math.round(scrollTop / itemHeight) + CENTER_OFFSET
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if (centeredFlat < length) return scrollTop + block
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if (centeredFlat >= 2 * length) return scrollTop - block
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return scrollTop
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}
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