分段式滚动
在三幅作品之间滚动,松手后停靠到其中一节。
在画框内上下滚动,观察作品停靠的位置。
使用场景
分章节浏览作品。例如让读者一次看清一幅作品,再继续滚到下一幅。
行为定义
局部纵向滚动在章节边缘停靠,状态栏显示最接近的一节。到达两端后可以继续滚动正文。
实现要点
用 CSS Scroll Snap 定义停靠点。原生监听滚动位置,GSAP 用 ScrollTrigger 读取同一容器的进度,两版都按最近停靠点更新章节。
原生 HTML / CSS / JS
完整示例,可另存为 HTML 直接打开。
打开示例查看源码
<!doctype html>
<html lang="zh-CN">
<head>
<meta charset="utf-8">
<meta name="viewport" content="width=device-width, initial-scale=1">
<title>分段式滚动 · 原生示例</title>
<script>
if (new URLSearchParams(location.search).get('theme') === 'dark') {
document.documentElement.dataset.theme = 'dark';
}
</script>
<style>
:root {
color-scheme: light;
--page: #fbfaf7;
--surface: #fff;
--surface-2: #edf3f6;
--text: #222c36;
--text-2: #434f5d;
--text-3: #5c6875;
--line-hi: #b8c4cd;
--line-strong: #82939f;
--accent: #b8412c;
--accent-text: #963324;
}
:root[data-theme="dark"] {
color-scheme: dark;
--page: #19222d;
--surface: #222e3c;
--surface-2: #2b3c4d;
--text: #f6f5f1;
--text-2: #d8dce1;
--text-3: #b4becc;
--line-hi: #576575;
--line-strong: #8396a8;
--accent: #ff9d7c;
--accent-text: #ff9d7c;
}
* { box-sizing: border-box; }
body { margin: 0; background: var(--page); color: var(--text); font: 16px/1.5 system-ui, sans-serif; }
main { max-width: 48rem; margin-inline: auto; padding: clamp(1rem, 4vw, 2rem); }
h1 { margin: 0 0 1rem; font-size: clamp(1.5rem, 4vw, 2rem); }
.scroll-context { min-height: 60vh; color: var(--text-2); }
.section-snap {
--snap-height: clamp(11.5rem, 42vw, 23rem);
max-inline-size: 54rem;
margin-inline: auto;
color: var(--text);
}
.section-snap-hint {
margin-block: 0 .75rem;
color: var(--text-2);
font-size: .9375rem;
line-height: 1.55;
}
.section-snap-viewport {
position: relative;
block-size: var(--snap-height);
overflow-y: auto;
scroll-snap-type: y mandatory;
scrollbar-width: thin;
scrollbar-color: var(--line-strong) var(--surface-2);
border-radius: 12px;
background: var(--surface-2);
}
.section-snap-viewport:focus-visible,
.section-snap-buttons button:focus-visible {
outline: 2px solid var(--accent);
outline-offset: 3px;
}
.section-snap-chapters {
margin: 0;
padding: 0;
list-style: none;
}
.section-snap-chapter {
position: relative;
block-size: var(--snap-height);
scroll-snap-align: start;
}
.section-snap-chapter svg {
display: block;
inline-size: 100%;
block-size: 100%;
}
.section-snap-label {
position: absolute;
inset-inline-start: .75rem;
inset-block-end: .75rem;
padding: .35rem .65rem;
border: 1px solid var(--line-hi);
border-radius: 6px;
background: var(--surface);
color: var(--text);
font-size: .8125rem;
font-variant-numeric: tabular-nums;
line-height: 1.2;
}
.section-snap-controls {
display: flex;
flex-wrap: wrap;
align-items: center;
justify-content: space-between;
gap: .5rem .75rem;
margin-block-start: .75rem;
padding: .6rem .75rem;
border-radius: 12px;
background: var(--surface-2);
}
.section-snap-controls[hidden] { display: none; }
.section-snap-status {
margin: 0;
color: var(--text);
font-size: .875rem;
font-variant-numeric: tabular-nums;
}
.section-snap-buttons {
display: flex;
flex-wrap: wrap;
gap: .5rem;
}
.section-snap-buttons button {
min-block-size: 44px;
padding-inline: .75rem;
border: 1px solid var(--line-strong);
border-radius: 10px;
background: var(--surface);
color: var(--text);
font: inherit;
font-size: .875rem;
cursor: pointer;
}
.section-snap-buttons button:not([aria-disabled="true"]):hover {
border-color: var(--accent);
color: var(--accent-text);
}
.section-snap-buttons button[aria-disabled="true"] {
border-color: var(--line-hi);
background: transparent;
color: var(--text-3);
cursor: default;
}
</style>
<style>.demo-guide {
display: flex;
align-items: center;
justify-content: space-between;
gap: .5rem .9rem;
min-inline-size: 0;
margin-block: 0 .75rem;
padding-block-end: .5rem;
border-block-end: 1px solid var(--line-hi, #b8c4cd);
color: var(--text-2, #434f5d);
font-size: .8125rem;
line-height: 1.5;
}
.trigger-stage > .demo-guide {
margin: .35rem clamp(.85rem, 2.2vw, 1.4rem) 0;
}
.demo-guide [data-guide-caption] { margin: 0; }
.demo-guide > button[data-guide-replay] {
flex: none;
min-block-size: 44px;
margin: 0;
padding: .35rem .65rem;
border: 1px solid var(--line-strong, #82939f);
border-radius: 7px;
background: var(--surface, #fff);
color: var(--text, #222c36);
font: inherit;
font-weight: 550;
cursor: pointer;
}
.demo-guide > button[data-guide-replay]:hover { border-color: var(--accent-text, #963324); }
.demo-guide > button[data-guide-replay]:focus-visible { outline: 2px solid var(--accent-text, #963324); outline-offset: 2px; }
.demo-guide-cursor {
position: fixed;
z-index: 20;
inset: 0 auto auto 0;
inline-size: 20px;
block-size: 24px;
pointer-events: none;
}
.demo-guide-cursor svg { display: block; inline-size: 100%; block-size: 100%; }
.demo-guide-cursor::before {
position: absolute;
inset: -7px auto auto -7px;
inline-size: 18px;
block-size: 18px;
border: 2px solid var(--accent-text, #963324);
border-radius: 50%;
content: '';
opacity: 0;
}
.demo-guide-cursor[data-press]::before { opacity: 1; }
@media (prefers-reduced-motion: reduce) { .demo-guide-cursor { display: none; } }
</style>
</head>
<body>
<main>
<h1>分段式滚动</h1>
<section class="section-snap" data-section-snap aria-label="分段式滚动演示">
<p class="section-snap-hint" id="section-snap-hint">在画框内上下滚动,观察作品停靠的位置。</p>
<div class="section-snap-viewport" id="section-snap-viewport" data-snap-viewport tabindex="0" role="region" aria-label="三节作品展" aria-describedby="section-snap-hint">
<ol class="section-snap-chapters">
<li class="section-snap-chapter" data-snap-chapter data-caption="弧面">
<svg viewBox="0 0 760 430" preserveAspectRatio="xMidYMid slice" aria-hidden="true" focusable="false"><path fill="#e8f3fa" d="M0 0h760v430H0z"/>
<circle cx="380" cy="114" r="44" fill="#ef784d"/>
<path fill="none" stroke="#39688b" stroke-width="21" d="M257 343v-96a123 123 0 0 1 246 0v96M303 343v-96a77 77 0 0 1 154 0v96"/>
<path fill="#628ca8" d="M365 247h30v96h-30z"/></svg>
<span class="section-snap-label">01 · 弧面</span>
</li>
<li class="section-snap-chapter" data-snap-chapter data-caption="折面">
<svg viewBox="0 0 760 430" preserveAspectRatio="xMidYMid slice" aria-hidden="true" focusable="false"><path fill="#fffdf8" d="M0 0h760v430H0z"/>
<path fill="#628ca8" d="m384 83 151 103-15 151-138-86-142 86-10-151z"/>
<path fill="#e5a38a" d="m384 83-2 168-142 86-10-151z"/>
<path fill="#f7c98b" d="m384 83 151 103-153 65-152-65z"/></svg>
<span class="section-snap-label">02 · 折面</span>
</li>
<li class="section-snap-chapter" data-snap-chapter data-caption="切面">
<svg viewBox="0 0 760 430" preserveAspectRatio="xMidYMid slice" aria-hidden="true" focusable="false"><path fill="#adcfdf" d="M0 0h760v430H0z"/>
<circle cx="380" cy="215" r="128" fill="#39688b"/>
<path fill="#ef784d" d="M380 87a128 128 0 0 1 0 256z"/>
<ellipse cx="380" cy="215" rx="194" ry="54" transform="rotate(-22 380 215)" fill="none" stroke="#fffdf8" stroke-width="13"/></svg>
<span class="section-snap-label">03 · 切面</span>
</li>
</ol>
</div>
<div class="section-snap-controls" data-snap-controls hidden>
<p class="section-snap-status" data-snap-status role="status"></p>
<div class="section-snap-buttons" role="group" aria-label="章节导航">
<button type="button" data-snap-prev aria-controls="section-snap-viewport">上一节</button>
<button type="button" data-snap-next aria-controls="section-snap-viewport">下一节</button>
</div>
</div>
</section>
<p class="scroll-context">滚到画框的首节或末节后,可沿同一方向继续滚动页面。</p>
</main>
<script>
/**
* @param {Element} root
* @param {(viewport: Element, sync: () => void, measure: () => void) => void} [connectScrollTrigger]
*/
function bindSectionSnap(root, connectScrollTrigger) {
const viewport = root.querySelector('[data-snap-viewport]');
const chapters = [...root.querySelectorAll('[data-snap-chapter]')];
const status = root.querySelector('[data-snap-status]');
const controls = root.querySelector('[data-snap-controls]');
const previous = root.querySelector('[data-snap-prev]');
const next = root.querySelector('[data-snap-next]');
if (!viewport || !chapters.length || !status || !controls || !previous || !next) return;
const reducedMotion = matchMedia('(prefers-reduced-motion: reduce)');
let stops = [];
let active = -1;
function syncChapter() {
const top = viewport.scrollTop;
const closest = stops.reduce((nearest, stop, index) => (
Math.abs(stop - top) < Math.abs(stops[nearest] - top) ? index : nearest
), 0);
if (closest === active) return;
chapters[active]?.removeAttribute('aria-current');
active = closest;
chapters[active].setAttribute('aria-current', 'step');
status.textContent = `第 ${active + 1} / ${chapters.length} 节 · ${chapters[active].dataset.caption}`;
previous.setAttribute('aria-disabled', String(active === 0));
next.setAttribute('aria-disabled', String(active === chapters.length - 1));
}
function measure() {
stops = chapters.map((chapter) => chapter.offsetTop);
syncChapter();
}
function goTo(offset) {
const top = stops[active + offset];
if (top === undefined) return;
viewport.scrollTo({ top, behavior: reducedMotion.matches ? 'instant' : 'smooth' });
}
previous.addEventListener('click', () => goTo(-1));
next.addEventListener('click', () => goTo(1));
root.addEventListener('formtempo:guide-reset', () => {
viewport.scrollTo({ top: stops[0], behavior: 'instant' });
syncChapter();
});
root.addEventListener('formtempo:guide-cancel', () => {
viewport.scrollTo({ top: viewport.scrollTop, behavior: 'instant' });
});
window.addEventListener('pageshow', measure);
const resize = new ResizeObserver(measure);
resize.observe(viewport);
measure();
controls.hidden = false;
if (connectScrollTrigger) {
connectScrollTrigger(viewport, syncChapter, measure);
} else {
let frame = 0;
viewport.addEventListener('scroll', () => {
if (frame) return;
frame = requestAnimationFrame(() => {
frame = 0;
syncChapter();
});
}, { passive: true });
}
}
const stage = document.querySelector('[data-section-snap]');
bindSectionSnap(stage);
</script>
<script>
(() => {
/** @param {number} duration @param {AbortSignal} signal @param {(progress: number) => void} [render] */
function guideBeat(duration, signal, render) {
if (signal.aborted) return Promise.resolve();
if (duration === 0) {
render?.(1);
return Promise.resolve();
}
return new Promise((resolve) => {
let timer = 0;
let frame = 0;
const done = () => {
clearTimeout(timer);
cancelAnimationFrame(frame);
signal.removeEventListener('abort', done);
resolve(undefined);
};
signal.addEventListener('abort', done, { once: true });
if (!render) {
timer = window.setTimeout(done, duration);
return;
}
const start = performance.now();
const tick = (now) => {
const progress = Math.min(1, (now - start) / duration);
render(progress);
if (progress === 1) done();
else if (!signal.aborted) frame = requestAnimationFrame(tick);
};
frame = requestAnimationFrame(tick);
});
}
/** @param {HTMLElement} root @param {import('./demo-guide-cases').DemoGuide} guide */
function bindDemoGuide(root, guide) {
const view = root.querySelector(guide.view);
if (!view || root.dataset.guideState || guide.steps.some(({ target }) => !root.querySelector(target))) return;
const dock = guide.dock ? root.querySelector(guide.dock) : null;
const bar = document.createElement('div');
bar.className = 'demo-guide';
bar.innerHTML = '<p data-guide-caption></p><button type="button" data-guide-replay>重播导览</button>';
const caption = bar.querySelector('[data-guide-caption]');
const replay = bar.querySelector('button');
const heading = root === document.body ? root.querySelector('h1') : null;
if (dock) dock.prepend(bar);
else if (heading) heading.after(bar);
else root.prepend(bar);
const cursor = document.createElement('div');
cursor.className = 'demo-guide-cursor';
cursor.setAttribute('aria-hidden', 'true');
cursor.hidden = true;
cursor.innerHTML = '<svg viewBox="0 0 20 24" focusable="false"><path d="M2 2v17l4.8-4.5L10 21l3.2-1.6-3.2-6.2 6.6-.7L2 2Z" fill="#222c36" stroke="#fff" stroke-width="1.5" stroke-linejoin="round"/></svg>';
document.body.append(cursor);
const reduced = matchMedia('(prefers-reduced-motion: reduce)');
const threshold = .5;
const idleCaption = '导览在画面进入视口后播放一次。';
const reducedCaption = '可重播关键状态,或直接操作。';
const reset = guide.reset ? (root.matches(guide.reset) ? root : root.querySelector(guide.reset)) : null;
const releaseTarget = guide.release ? root.querySelector(guide.release) : null;
let autoPending = !reduced.matches;
let inView = false;
let playbackScroll = window.scrollY;
/** @type {AbortController | undefined} */
let run;
/** @type {[number, number] | undefined} */
let cursorPosition;
root.dataset.guideState = 'idle';
caption.textContent = reduced.matches ? reducedCaption : idleCaption;
function hideCursor() {
cursor.hidden = true;
delete cursor.dataset.press;
cursorPosition = undefined;
}
/** @param {PointerEvent} [pointer] */
function stop(pointer) {
autoPending = false;
if (!run) return;
run.abort();
run = undefined;
hideCursor();
if (releaseTarget) {
// A real pointer inside the target keeps its hover when the guide yields.
if (pointer) sendPointer(releaseTarget, 'pointerenter', [pointer.clientX, pointer.clientY]);
else sendPointer(releaseTarget, 'pointerleave', [0, 0]);
}
reset?.dispatchEvent(new Event('formtempo:guide-cancel'));
root.dataset.guideState = 'interrupted';
caption.textContent = '导览已停止,可以继续手动操作。';
}
/** @param {[number, number]} position */
function moveCursor(position) {
cursor.hidden = false;
cursor.style.transform = `translate3d(${position[0]}px, ${position[1]}px, 0)`;
cursorPosition = position;
}
/** @param {Element} target @param {readonly [number, number]} point */
function location(target, [x, y]) {
const rect = target.getBoundingClientRect();
return /** @type {[number, number]} */ ([rect.left + rect.width * x, rect.top + rect.height * y]);
}
/** @param {Element} target @param {string} type @param {readonly [number, number]} position */
function sendPointer(target, type, [clientX, clientY]) {
target.dispatchEvent(new PointerEvent(type, { pointerType: 'mouse', clientX, clientY }));
}
/** @param {HTMLInputElement} slider @param {number} value */
function setProgress(slider, value) {
const next = Math.round(value);
if (slider.valueAsNumber === next) return;
slider.value = String(next);
slider.dispatchEvent(new Event('input', { bubbles: true }));
}
/** @param {number} value */
function showReducedProgress(value) {
const options = Array.from(root.querySelectorAll('button[data-driven-step], button[data-scale-step], button[data-progress-step], button[data-progress]'));
const percent = (button) => button.hasAttribute('data-progress')
? Number(button.getAttribute('data-progress')) * 100
: Number(button.getAttribute('data-driven-step') ?? button.getAttribute('data-scale-step') ?? button.getAttribute('data-progress-step'));
options.sort((a, b) => Math.abs(percent(a) - value) - Math.abs(percent(b) - value));
if (options[0] instanceof HTMLButtonElement) options[0].click();
}
/** @param {import('./demo-guide-cases').DemoGuide['steps'][number]} step @param {AbortSignal} signal */
async function playStep(step, signal) {
const target = root.querySelector(step.target);
if (!target) return;
caption.textContent = step.text;
const { action, value = 0, point = [.5, .5] } = step;
if (action === 'progress' && target instanceof HTMLInputElement) {
if (reduced.matches) {
showReducedProgress(value);
} else {
const from = target.valueAsNumber;
await guideBeat(step.duration ?? 0, signal, (progress) => {
const current = from + (value - from) * progress;
setProgress(target, current);
moveCursor(location(target, [.04 + .92 * current / 100, .65]));
});
}
} else {
if (!reduced.matches) {
const to = location(target, point);
const [x, y] = point;
const entry = x < .25 ? [-.08, y] : x > .75 ? [1.08, y] : [x, y < .5 ? -.08 : 1.08];
const from = action === 'enter' ? location(target, /** @type {[number, number]} */ (entry))
: cursorPosition ?? [to[0] + 26, to[1] + 19];
const duration = action === 'leave' ? 200 : 340;
await guideBeat(duration, signal, (progress) => {
const t = 1 - (1 - progress) ** 3;
const end = location(target, point);
const position = /** @type {[number, number]} */ ([
from[0] + (end[0] - from[0]) * t,
from[1] + (end[1] - from[1]) * t,
]);
moveCursor(position);
if (action === 'move') sendPointer(target, 'pointermove', position);
});
}
if (signal.aborted) return;
if (action === 'click' && target instanceof HTMLElement) {
if (!reduced.matches) {
cursor.dataset.press = '';
await guideBeat(125, signal);
if (signal.aborted) return;
}
target.click();
delete cursor.dataset.press;
} else if (action === 'enter' || action === 'leave') {
sendPointer(target, `pointer${action}`, location(target, point));
}
}
await guideBeat(reduced.matches ? 600 : step.hold ?? 500, signal);
}
function bringViewIntoFrame() {
const rect = view.getBoundingClientRect();
const visibleHeight = Math.min(rect.bottom, window.innerHeight) - Math.max(rect.top, 0);
if (visibleHeight < rect.height * threshold) view.scrollIntoView({ block: 'center', behavior: 'instant' });
}
async function start(replaying = false) {
stop();
const controller = new AbortController();
const { signal } = controller;
run = controller;
root.dataset.guideState = 'playing';
if (guide.ready) {
caption.textContent = '正在等待视频就绪…';
const deadline = performance.now() + 4000;
while (!signal.aborted && !root.querySelector(guide.ready) && performance.now() < deadline &&
!root.querySelector('[data-video-state="error"]')) {
await guideBeat(90, signal);
}
if (signal.aborted) return;
if (!root.querySelector(guide.ready)) {
run = undefined;
root.dataset.guideState = 'unavailable';
caption.textContent = '视频暂未就绪,可以查看关键帧或重播。';
return;
}
}
reset?.dispatchEvent(new Event('formtempo:guide-reset'));
if (replaying) bringViewIntoFrame();
playbackScroll = window.scrollY;
const steps = (reduced.matches && guide.reducedSteps) || guide.steps;
for (const step of steps) {
if (signal.aborted) return;
await playStep(step, signal);
}
if (signal.aborted) return;
run = undefined;
hideCursor();
root.dataset.guideState = 'complete';
caption.textContent = '导览结束,可以继续手动操作。';
}
function tryAutoplay() {
if (autoPending && inView && !document.hidden) void start();
}
if (typeof IntersectionObserver === 'function') {
const observer = new IntersectionObserver(([entry]) => {
inView = entry.intersectionRatio >= threshold;
if (!entry.isIntersecting && run) stop();
tryAutoplay();
}, { threshold: [0, threshold] });
observer.observe(view);
}
replay.addEventListener('click', () => {
bringViewIntoFrame();
void start(true);
});
const takeOver = (event) => {
if (!event.isTrusted || replay.contains(event.target)) return;
if (!run) {
if (event.type === 'wheel' || !(event.target instanceof Element)) return;
if (!event.target.closest('button, input') && !view.contains(event.target)) return;
}
const pointer = event instanceof PointerEvent && event.pointerType === 'mouse' && releaseTarget?.contains(event.target)
? event : undefined;
stop(pointer);
};
for (const event of ['pointerdown', 'keydown', 'focusin', 'input', 'click', 'wheel']) {
root.addEventListener(event, takeOver, { capture: true, passive: true });
}
if (guide.steps.some(({ action }) => action === 'enter' || action === 'move')) {
view.addEventListener('pointermove', takeOver, { capture: true, passive: true });
}
if (guide.pageScrollInput) {
window.addEventListener('scroll', () => {
if (run && window.scrollY !== playbackScroll) stop();
}, { passive: true });
}
document.addEventListener('visibilitychange', () => {
if (document.hidden && run) stop();
else tryAutoplay();
});
reduced.addEventListener('change', () => {
if (!reduced.matches) return;
const wasIdle = root.dataset.guideState === 'idle';
stop();
if (wasIdle) caption.textContent = reducedCaption;
});
}
bindDemoGuide(document.body, {"view":"[data-snap-viewport]","reset":"[data-section-snap]","steps":[{"target":"[data-snap-next]","action":"click","text":"向下浏览,画面停靠在第二节。","hold":650},{"target":"[data-snap-next]","action":"click","text":"继续向下,停靠在第三节。","hold":650},{"target":"[data-snap-prev]","action":"click","text":"反向浏览,回到上一节的停靠点。","hold":650}]});
})();
</script>
</body>
</html>GSAP 3.15.0
完整示例,从 CDN 加载指定版本。
打开示例查看源码
<!doctype html>
<html lang="zh-CN">
<head>
<meta charset="utf-8">
<meta name="viewport" content="width=device-width, initial-scale=1">
<title>分段式滚动 · GSAP示例</title>
<script>
if (new URLSearchParams(location.search).get('theme') === 'dark') {
document.documentElement.dataset.theme = 'dark';
}
</script>
<style>
:root {
color-scheme: light;
--page: #fbfaf7;
--surface: #fff;
--surface-2: #edf3f6;
--text: #222c36;
--text-2: #434f5d;
--text-3: #5c6875;
--line-hi: #b8c4cd;
--line-strong: #82939f;
--accent: #b8412c;
--accent-text: #963324;
}
:root[data-theme="dark"] {
color-scheme: dark;
--page: #19222d;
--surface: #222e3c;
--surface-2: #2b3c4d;
--text: #f6f5f1;
--text-2: #d8dce1;
--text-3: #b4becc;
--line-hi: #576575;
--line-strong: #8396a8;
--accent: #ff9d7c;
--accent-text: #ff9d7c;
}
* { box-sizing: border-box; }
body { margin: 0; background: var(--page); color: var(--text); font: 16px/1.5 system-ui, sans-serif; }
main { max-width: 48rem; margin-inline: auto; padding: clamp(1rem, 4vw, 2rem); }
h1 { margin: 0 0 1rem; font-size: clamp(1.5rem, 4vw, 2rem); }
.scroll-context { min-height: 60vh; color: var(--text-2); }
.section-snap {
--snap-height: clamp(11.5rem, 42vw, 23rem);
max-inline-size: 54rem;
margin-inline: auto;
color: var(--text);
}
.section-snap-hint {
margin-block: 0 .75rem;
color: var(--text-2);
font-size: .9375rem;
line-height: 1.55;
}
.section-snap-viewport {
position: relative;
block-size: var(--snap-height);
overflow-y: auto;
scroll-snap-type: y mandatory;
scrollbar-width: thin;
scrollbar-color: var(--line-strong) var(--surface-2);
border-radius: 12px;
background: var(--surface-2);
}
.section-snap-viewport:focus-visible,
.section-snap-buttons button:focus-visible {
outline: 2px solid var(--accent);
outline-offset: 3px;
}
.section-snap-chapters {
margin: 0;
padding: 0;
list-style: none;
}
.section-snap-chapter {
position: relative;
block-size: var(--snap-height);
scroll-snap-align: start;
}
.section-snap-chapter svg {
display: block;
inline-size: 100%;
block-size: 100%;
}
.section-snap-label {
position: absolute;
inset-inline-start: .75rem;
inset-block-end: .75rem;
padding: .35rem .65rem;
border: 1px solid var(--line-hi);
border-radius: 6px;
background: var(--surface);
color: var(--text);
font-size: .8125rem;
font-variant-numeric: tabular-nums;
line-height: 1.2;
}
.section-snap-controls {
display: flex;
flex-wrap: wrap;
align-items: center;
justify-content: space-between;
gap: .5rem .75rem;
margin-block-start: .75rem;
padding: .6rem .75rem;
border-radius: 12px;
background: var(--surface-2);
}
.section-snap-controls[hidden] { display: none; }
.section-snap-status {
margin: 0;
color: var(--text);
font-size: .875rem;
font-variant-numeric: tabular-nums;
}
.section-snap-buttons {
display: flex;
flex-wrap: wrap;
gap: .5rem;
}
.section-snap-buttons button {
min-block-size: 44px;
padding-inline: .75rem;
border: 1px solid var(--line-strong);
border-radius: 10px;
background: var(--surface);
color: var(--text);
font: inherit;
font-size: .875rem;
cursor: pointer;
}
.section-snap-buttons button:not([aria-disabled="true"]):hover {
border-color: var(--accent);
color: var(--accent-text);
}
.section-snap-buttons button[aria-disabled="true"] {
border-color: var(--line-hi);
background: transparent;
color: var(--text-3);
cursor: default;
}
</style>
<style>.demo-guide {
display: flex;
align-items: center;
justify-content: space-between;
gap: .5rem .9rem;
min-inline-size: 0;
margin-block: 0 .75rem;
padding-block-end: .5rem;
border-block-end: 1px solid var(--line-hi, #b8c4cd);
color: var(--text-2, #434f5d);
font-size: .8125rem;
line-height: 1.5;
}
.trigger-stage > .demo-guide {
margin: .35rem clamp(.85rem, 2.2vw, 1.4rem) 0;
}
.demo-guide [data-guide-caption] { margin: 0; }
.demo-guide > button[data-guide-replay] {
flex: none;
min-block-size: 44px;
margin: 0;
padding: .35rem .65rem;
border: 1px solid var(--line-strong, #82939f);
border-radius: 7px;
background: var(--surface, #fff);
color: var(--text, #222c36);
font: inherit;
font-weight: 550;
cursor: pointer;
}
.demo-guide > button[data-guide-replay]:hover { border-color: var(--accent-text, #963324); }
.demo-guide > button[data-guide-replay]:focus-visible { outline: 2px solid var(--accent-text, #963324); outline-offset: 2px; }
.demo-guide-cursor {
position: fixed;
z-index: 20;
inset: 0 auto auto 0;
inline-size: 20px;
block-size: 24px;
pointer-events: none;
}
.demo-guide-cursor svg { display: block; inline-size: 100%; block-size: 100%; }
.demo-guide-cursor::before {
position: absolute;
inset: -7px auto auto -7px;
inline-size: 18px;
block-size: 18px;
border: 2px solid var(--accent-text, #963324);
border-radius: 50%;
content: '';
opacity: 0;
}
.demo-guide-cursor[data-press]::before { opacity: 1; }
@media (prefers-reduced-motion: reduce) { .demo-guide-cursor { display: none; } }
</style>
</head>
<body>
<main>
<h1>分段式滚动</h1>
<section class="section-snap" data-section-snap aria-label="分段式滚动演示">
<p class="section-snap-hint" id="section-snap-hint">在画框内上下滚动,观察作品停靠的位置。</p>
<div class="section-snap-viewport" id="section-snap-viewport" data-snap-viewport tabindex="0" role="region" aria-label="三节作品展" aria-describedby="section-snap-hint">
<ol class="section-snap-chapters">
<li class="section-snap-chapter" data-snap-chapter data-caption="弧面">
<svg viewBox="0 0 760 430" preserveAspectRatio="xMidYMid slice" aria-hidden="true" focusable="false"><path fill="#e8f3fa" d="M0 0h760v430H0z"/>
<circle cx="380" cy="114" r="44" fill="#ef784d"/>
<path fill="none" stroke="#39688b" stroke-width="21" d="M257 343v-96a123 123 0 0 1 246 0v96M303 343v-96a77 77 0 0 1 154 0v96"/>
<path fill="#628ca8" d="M365 247h30v96h-30z"/></svg>
<span class="section-snap-label">01 · 弧面</span>
</li>
<li class="section-snap-chapter" data-snap-chapter data-caption="折面">
<svg viewBox="0 0 760 430" preserveAspectRatio="xMidYMid slice" aria-hidden="true" focusable="false"><path fill="#fffdf8" d="M0 0h760v430H0z"/>
<path fill="#628ca8" d="m384 83 151 103-15 151-138-86-142 86-10-151z"/>
<path fill="#e5a38a" d="m384 83-2 168-142 86-10-151z"/>
<path fill="#f7c98b" d="m384 83 151 103-153 65-152-65z"/></svg>
<span class="section-snap-label">02 · 折面</span>
</li>
<li class="section-snap-chapter" data-snap-chapter data-caption="切面">
<svg viewBox="0 0 760 430" preserveAspectRatio="xMidYMid slice" aria-hidden="true" focusable="false"><path fill="#adcfdf" d="M0 0h760v430H0z"/>
<circle cx="380" cy="215" r="128" fill="#39688b"/>
<path fill="#ef784d" d="M380 87a128 128 0 0 1 0 256z"/>
<ellipse cx="380" cy="215" rx="194" ry="54" transform="rotate(-22 380 215)" fill="none" stroke="#fffdf8" stroke-width="13"/></svg>
<span class="section-snap-label">03 · 切面</span>
</li>
</ol>
</div>
<div class="section-snap-controls" data-snap-controls hidden>
<p class="section-snap-status" data-snap-status role="status"></p>
<div class="section-snap-buttons" role="group" aria-label="章节导航">
<button type="button" data-snap-prev aria-controls="section-snap-viewport">上一节</button>
<button type="button" data-snap-next aria-controls="section-snap-viewport">下一节</button>
</div>
</div>
</section>
<p data-snap-fallback role="status" hidden>GSAP 未加载,当前使用原生章节定位。</p>
<p class="scroll-context">滚到画框的首节或末节后,可沿同一方向继续滚动页面。</p>
</main>
<script src="https://cdn.jsdelivr.net/npm/gsap@3.15.0/dist/gsap.min.js"></script>
<script src="https://cdn.jsdelivr.net/npm/gsap@3.15.0/dist/ScrollTrigger.min.js"></script>
<script>
/**
* @param {Element} root
* @param {(viewport: Element, sync: () => void, measure: () => void) => void} [connectScrollTrigger]
*/
function bindSectionSnap(root, connectScrollTrigger) {
const viewport = root.querySelector('[data-snap-viewport]');
const chapters = [...root.querySelectorAll('[data-snap-chapter]')];
const status = root.querySelector('[data-snap-status]');
const controls = root.querySelector('[data-snap-controls]');
const previous = root.querySelector('[data-snap-prev]');
const next = root.querySelector('[data-snap-next]');
if (!viewport || !chapters.length || !status || !controls || !previous || !next) return;
const reducedMotion = matchMedia('(prefers-reduced-motion: reduce)');
let stops = [];
let active = -1;
function syncChapter() {
const top = viewport.scrollTop;
const closest = stops.reduce((nearest, stop, index) => (
Math.abs(stop - top) < Math.abs(stops[nearest] - top) ? index : nearest
), 0);
if (closest === active) return;
chapters[active]?.removeAttribute('aria-current');
active = closest;
chapters[active].setAttribute('aria-current', 'step');
status.textContent = `第 ${active + 1} / ${chapters.length} 节 · ${chapters[active].dataset.caption}`;
previous.setAttribute('aria-disabled', String(active === 0));
next.setAttribute('aria-disabled', String(active === chapters.length - 1));
}
function measure() {
stops = chapters.map((chapter) => chapter.offsetTop);
syncChapter();
}
function goTo(offset) {
const top = stops[active + offset];
if (top === undefined) return;
viewport.scrollTo({ top, behavior: reducedMotion.matches ? 'instant' : 'smooth' });
}
previous.addEventListener('click', () => goTo(-1));
next.addEventListener('click', () => goTo(1));
root.addEventListener('formtempo:guide-reset', () => {
viewport.scrollTo({ top: stops[0], behavior: 'instant' });
syncChapter();
});
root.addEventListener('formtempo:guide-cancel', () => {
viewport.scrollTo({ top: viewport.scrollTop, behavior: 'instant' });
});
window.addEventListener('pageshow', measure);
const resize = new ResizeObserver(measure);
resize.observe(viewport);
measure();
controls.hidden = false;
if (connectScrollTrigger) {
connectScrollTrigger(viewport, syncChapter, measure);
} else {
let frame = 0;
viewport.addEventListener('scroll', () => {
if (frame) return;
frame = requestAnimationFrame(() => {
frame = 0;
syncChapter();
});
}, { passive: true });
}
}
const stage = document.querySelector('[data-section-snap]');
if (window.gsap && window.ScrollTrigger) {
gsap.registerPlugin(ScrollTrigger);
bindSectionSnap(stage, (viewport, sync, measure) => {
ScrollTrigger.create({
scroller: viewport,
start: 0,
end: () => viewport.scrollHeight - viewport.clientHeight,
onUpdate: sync,
onRefresh: measure,
});
});
} else {
document.querySelector('[data-snap-fallback]').hidden = false;
bindSectionSnap(stage);
}
</script>
<script>
(() => {
/** @param {number} duration @param {AbortSignal} signal @param {(progress: number) => void} [render] */
function guideBeat(duration, signal, render) {
if (signal.aborted) return Promise.resolve();
if (duration === 0) {
render?.(1);
return Promise.resolve();
}
return new Promise((resolve) => {
let timer = 0;
let frame = 0;
const done = () => {
clearTimeout(timer);
cancelAnimationFrame(frame);
signal.removeEventListener('abort', done);
resolve(undefined);
};
signal.addEventListener('abort', done, { once: true });
if (!render) {
timer = window.setTimeout(done, duration);
return;
}
const start = performance.now();
const tick = (now) => {
const progress = Math.min(1, (now - start) / duration);
render(progress);
if (progress === 1) done();
else if (!signal.aborted) frame = requestAnimationFrame(tick);
};
frame = requestAnimationFrame(tick);
});
}
/** @param {HTMLElement} root @param {import('./demo-guide-cases').DemoGuide} guide */
function bindDemoGuide(root, guide) {
const view = root.querySelector(guide.view);
if (!view || root.dataset.guideState || guide.steps.some(({ target }) => !root.querySelector(target))) return;
const dock = guide.dock ? root.querySelector(guide.dock) : null;
const bar = document.createElement('div');
bar.className = 'demo-guide';
bar.innerHTML = '<p data-guide-caption></p><button type="button" data-guide-replay>重播导览</button>';
const caption = bar.querySelector('[data-guide-caption]');
const replay = bar.querySelector('button');
const heading = root === document.body ? root.querySelector('h1') : null;
if (dock) dock.prepend(bar);
else if (heading) heading.after(bar);
else root.prepend(bar);
const cursor = document.createElement('div');
cursor.className = 'demo-guide-cursor';
cursor.setAttribute('aria-hidden', 'true');
cursor.hidden = true;
cursor.innerHTML = '<svg viewBox="0 0 20 24" focusable="false"><path d="M2 2v17l4.8-4.5L10 21l3.2-1.6-3.2-6.2 6.6-.7L2 2Z" fill="#222c36" stroke="#fff" stroke-width="1.5" stroke-linejoin="round"/></svg>';
document.body.append(cursor);
const reduced = matchMedia('(prefers-reduced-motion: reduce)');
const threshold = .5;
const idleCaption = '导览在画面进入视口后播放一次。';
const reducedCaption = '可重播关键状态,或直接操作。';
const reset = guide.reset ? (root.matches(guide.reset) ? root : root.querySelector(guide.reset)) : null;
const releaseTarget = guide.release ? root.querySelector(guide.release) : null;
let autoPending = !reduced.matches;
let inView = false;
let playbackScroll = window.scrollY;
/** @type {AbortController | undefined} */
let run;
/** @type {[number, number] | undefined} */
let cursorPosition;
root.dataset.guideState = 'idle';
caption.textContent = reduced.matches ? reducedCaption : idleCaption;
function hideCursor() {
cursor.hidden = true;
delete cursor.dataset.press;
cursorPosition = undefined;
}
/** @param {PointerEvent} [pointer] */
function stop(pointer) {
autoPending = false;
if (!run) return;
run.abort();
run = undefined;
hideCursor();
if (releaseTarget) {
// A real pointer inside the target keeps its hover when the guide yields.
if (pointer) sendPointer(releaseTarget, 'pointerenter', [pointer.clientX, pointer.clientY]);
else sendPointer(releaseTarget, 'pointerleave', [0, 0]);
}
reset?.dispatchEvent(new Event('formtempo:guide-cancel'));
root.dataset.guideState = 'interrupted';
caption.textContent = '导览已停止,可以继续手动操作。';
}
/** @param {[number, number]} position */
function moveCursor(position) {
cursor.hidden = false;
cursor.style.transform = `translate3d(${position[0]}px, ${position[1]}px, 0)`;
cursorPosition = position;
}
/** @param {Element} target @param {readonly [number, number]} point */
function location(target, [x, y]) {
const rect = target.getBoundingClientRect();
return /** @type {[number, number]} */ ([rect.left + rect.width * x, rect.top + rect.height * y]);
}
/** @param {Element} target @param {string} type @param {readonly [number, number]} position */
function sendPointer(target, type, [clientX, clientY]) {
target.dispatchEvent(new PointerEvent(type, { pointerType: 'mouse', clientX, clientY }));
}
/** @param {HTMLInputElement} slider @param {number} value */
function setProgress(slider, value) {
const next = Math.round(value);
if (slider.valueAsNumber === next) return;
slider.value = String(next);
slider.dispatchEvent(new Event('input', { bubbles: true }));
}
/** @param {number} value */
function showReducedProgress(value) {
const options = Array.from(root.querySelectorAll('button[data-driven-step], button[data-scale-step], button[data-progress-step], button[data-progress]'));
const percent = (button) => button.hasAttribute('data-progress')
? Number(button.getAttribute('data-progress')) * 100
: Number(button.getAttribute('data-driven-step') ?? button.getAttribute('data-scale-step') ?? button.getAttribute('data-progress-step'));
options.sort((a, b) => Math.abs(percent(a) - value) - Math.abs(percent(b) - value));
if (options[0] instanceof HTMLButtonElement) options[0].click();
}
/** @param {import('./demo-guide-cases').DemoGuide['steps'][number]} step @param {AbortSignal} signal */
async function playStep(step, signal) {
const target = root.querySelector(step.target);
if (!target) return;
caption.textContent = step.text;
const { action, value = 0, point = [.5, .5] } = step;
if (action === 'progress' && target instanceof HTMLInputElement) {
if (reduced.matches) {
showReducedProgress(value);
} else {
const from = target.valueAsNumber;
await guideBeat(step.duration ?? 0, signal, (progress) => {
const current = from + (value - from) * progress;
setProgress(target, current);
moveCursor(location(target, [.04 + .92 * current / 100, .65]));
});
}
} else {
if (!reduced.matches) {
const to = location(target, point);
const [x, y] = point;
const entry = x < .25 ? [-.08, y] : x > .75 ? [1.08, y] : [x, y < .5 ? -.08 : 1.08];
const from = action === 'enter' ? location(target, /** @type {[number, number]} */ (entry))
: cursorPosition ?? [to[0] + 26, to[1] + 19];
const duration = action === 'leave' ? 200 : 340;
await guideBeat(duration, signal, (progress) => {
const t = 1 - (1 - progress) ** 3;
const end = location(target, point);
const position = /** @type {[number, number]} */ ([
from[0] + (end[0] - from[0]) * t,
from[1] + (end[1] - from[1]) * t,
]);
moveCursor(position);
if (action === 'move') sendPointer(target, 'pointermove', position);
});
}
if (signal.aborted) return;
if (action === 'click' && target instanceof HTMLElement) {
if (!reduced.matches) {
cursor.dataset.press = '';
await guideBeat(125, signal);
if (signal.aborted) return;
}
target.click();
delete cursor.dataset.press;
} else if (action === 'enter' || action === 'leave') {
sendPointer(target, `pointer${action}`, location(target, point));
}
}
await guideBeat(reduced.matches ? 600 : step.hold ?? 500, signal);
}
function bringViewIntoFrame() {
const rect = view.getBoundingClientRect();
const visibleHeight = Math.min(rect.bottom, window.innerHeight) - Math.max(rect.top, 0);
if (visibleHeight < rect.height * threshold) view.scrollIntoView({ block: 'center', behavior: 'instant' });
}
async function start(replaying = false) {
stop();
const controller = new AbortController();
const { signal } = controller;
run = controller;
root.dataset.guideState = 'playing';
if (guide.ready) {
caption.textContent = '正在等待视频就绪…';
const deadline = performance.now() + 4000;
while (!signal.aborted && !root.querySelector(guide.ready) && performance.now() < deadline &&
!root.querySelector('[data-video-state="error"]')) {
await guideBeat(90, signal);
}
if (signal.aborted) return;
if (!root.querySelector(guide.ready)) {
run = undefined;
root.dataset.guideState = 'unavailable';
caption.textContent = '视频暂未就绪,可以查看关键帧或重播。';
return;
}
}
reset?.dispatchEvent(new Event('formtempo:guide-reset'));
if (replaying) bringViewIntoFrame();
playbackScroll = window.scrollY;
const steps = (reduced.matches && guide.reducedSteps) || guide.steps;
for (const step of steps) {
if (signal.aborted) return;
await playStep(step, signal);
}
if (signal.aborted) return;
run = undefined;
hideCursor();
root.dataset.guideState = 'complete';
caption.textContent = '导览结束,可以继续手动操作。';
}
function tryAutoplay() {
if (autoPending && inView && !document.hidden) void start();
}
if (typeof IntersectionObserver === 'function') {
const observer = new IntersectionObserver(([entry]) => {
inView = entry.intersectionRatio >= threshold;
if (!entry.isIntersecting && run) stop();
tryAutoplay();
}, { threshold: [0, threshold] });
observer.observe(view);
}
replay.addEventListener('click', () => {
bringViewIntoFrame();
void start(true);
});
const takeOver = (event) => {
if (!event.isTrusted || replay.contains(event.target)) return;
if (!run) {
if (event.type === 'wheel' || !(event.target instanceof Element)) return;
if (!event.target.closest('button, input') && !view.contains(event.target)) return;
}
const pointer = event instanceof PointerEvent && event.pointerType === 'mouse' && releaseTarget?.contains(event.target)
? event : undefined;
stop(pointer);
};
for (const event of ['pointerdown', 'keydown', 'focusin', 'input', 'click', 'wheel']) {
root.addEventListener(event, takeOver, { capture: true, passive: true });
}
if (guide.steps.some(({ action }) => action === 'enter' || action === 'move')) {
view.addEventListener('pointermove', takeOver, { capture: true, passive: true });
}
if (guide.pageScrollInput) {
window.addEventListener('scroll', () => {
if (run && window.scrollY !== playbackScroll) stop();
}, { passive: true });
}
document.addEventListener('visibilitychange', () => {
if (document.hidden && run) stop();
else tryAutoplay();
});
reduced.addEventListener('change', () => {
if (!reduced.matches) return;
const wasIdle = root.dataset.guideState === 'idle';
stop();
if (wasIdle) caption.textContent = reducedCaption;
});
}
bindDemoGuide(document.body, {"view":"[data-snap-viewport]","reset":"[data-section-snap]","steps":[{"target":"[data-snap-next]","action":"click","text":"向下浏览,画面停靠在第二节。","hold":650},{"target":"[data-snap-next]","action":"click","text":"继续向下,停靠在第三节。","hold":650},{"target":"[data-snap-prev]","action":"click","text":"反向浏览,回到上一节的停靠点。","hold":650}]});
})();
</script>
</body>
</html>