69 lines
3.0 KiB
JavaScript
69 lines
3.0 KiB
JavaScript
'use strict';
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/**
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* 动态缩略图的档位配置。
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*
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* 每项是 [细节分辨率, 帧率, 编码质量]，作为搜索路径上的锚点：
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* - 细节分辨率决定画面保留多少细节（输出画布始终 400×400，小分辨率会被放大填满）；
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* - 帧率决定每秒采样多少帧，只改采样密度不改时间轴，每档的帧延迟会自动重算；
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* - 编码质量是 0–1 的 WebP 质量，APNG 是无损编码会忽略这一项。
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*
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* 数组顺序是从最高画质到最低画质的搜索方向。运行时会在相邻锚点之间插值成一条更密的
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* 路径，再按用户填写的目标体积在路径上二分定位，取命中位置附近若干档完整生成，
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* 所以锚点的疏密决定可搜索的粒度，锚点数量决定画廊里的候选数量。
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*/
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const ANIMATED_PRIORITIES = {
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// 分辨率优先：先把帧率压到底，再降分辨率。
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resolution: [
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[400, 18, 1.0], [400, 15, 0.8], [400, 12, 0.6], [400, 9, 0.4], [400, 6, 0.2],
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[200, 18, 1.0], [200, 15, 0.8], [200, 12, 0.6], [200, 9, 0.4], [200, 6, 0.2],
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],
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// 帧率优先：先把分辨率压到底，再降帧率。
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framerate: [
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[400, 18, 1.0], [400, 18, 0.5], [350, 15, 1.0], [350, 15, 0.5], [300, 9, 1.0],
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[300, 9, 0.5], [250, 6, 1.0], [250, 6, 0.5], [200, 9, 1.0], [200, 6, 0.5],
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],
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// 交替进行：分辨率和帧率交替下降。
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balanced: [
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[400, 15, 0.8], [400, 12, 0.6], [400, 9, 0.4], [400, 6, 0.2], [200, 15, 0.8],
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[200, 12, 0.6], [200, 9, 0.4], [200, 6, 0.2], [100, 3, 0.5], [100, 3, 0.1],
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],
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};
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const DEFAULT_PRIORITY = 'resolution';
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// 相邻锚点之间插多少个采样点。数值越大，越容易压在目标体积附近，但粗估阶段耗时略增。
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const PATH_STEPS_PER_SEGMENT = 6;
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function animatedProfiles(priority) {
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const plan = ANIMATED_PRIORITIES[priority] || ANIMATED_PRIORITIES[DEFAULT_PRIORITY];
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return plan.map(([size, fps, quality]) => ({ size, fps, quality }));
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}
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/**
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* 把锚点路径插值成更密的采样路径，供按目标体积二分定位使用。
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* 分辨率取整、帧率至少 1、质量保留两位小数；首尾锚点原样保留。
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*/
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function expandAnimatedPath(priority) {
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const anchors = ANIMATED_PRIORITIES[priority] || ANIMATED_PRIORITIES[DEFAULT_PRIORITY];
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const lerp = (from, to, t) => from + (to - from) * t;
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const path = [];
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for (let index = 0; index < anchors.length - 1; index++) {
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const [fromSize, fromFps, fromQuality] = anchors[index];
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const [toSize, toFps, toQuality] = anchors[index + 1];
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for (let step = 0; step < PATH_STEPS_PER_SEGMENT; step++) {
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const t = step / PATH_STEPS_PER_SEGMENT;
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path.push({
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size: Math.round(lerp(fromSize, toSize, t)),
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fps: Math.max(1, Math.round(lerp(fromFps, toFps, t))),
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quality: Math.round(lerp(fromQuality, toQuality, t) * 100) / 100,
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});
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}
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}
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const [size, fps, quality] = anchors[anchors.length - 1];
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path.push({ size, fps, quality });
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return path;
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}
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module.exports = { ANIMATED_PRIORITIES, DEFAULT_PRIORITY, PATH_STEPS_PER_SEGMENT, animatedProfiles, expandAnimatedPath };
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