41 lines
1.3 KiB
TypeScript
41 lines
1.3 KiB
TypeScript
function clampInt(n: number, min: number, max: number): number {
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if (!Number.isFinite(n)) return min;
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return Math.min(max, Math.max(min, Math.floor(n)));
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}
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function hashStringToInt32(input: string): number {
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// 简单可复现 hash：用于把 seed 映射为偏移量（不用于安全场景）
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let h = 0;
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for (let i = 0; i < input.length; i += 1) {
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// eslint-disable-next-line no-bitwise
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h = (h * 31 + input.charCodeAt(i)) | 0;
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}
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return h;
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}
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/**
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* 生成 t ∈ [0,1]，用于 Color(t)=lerp(top,bottom,t)
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*
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* 说明：
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* - Home 没有 scroll，用“切换文案 step_index”模拟连续流动
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* - 采用往返波形，避免从 1 回到 0 的突跳
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*/
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export function computeTFromStep(args: {
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stepIndex: number;
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segments?: number; // N，默认 12
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seed?: string; // 允许用 seed 做初始相位偏移（同一次冷启动内稳定）
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}): number {
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const N = clampInt(args.segments ?? 12, 3, 60);
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const stepIndex = clampInt(args.stepIndex, 0, 1_000_000_000);
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const period = 2 * (N - 1);
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const seed = String(args.seed ?? '');
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const offset = seed ? Math.abs(hashStringToInt32(seed)) % period : 0;
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const phase = (stepIndex + offset) % period;
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const up = phase <= (N - 1);
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const pos = up ? phase : period - phase;
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return pos / (N - 1);
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}
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