滚动故事

滚动时，各图层以不同的深度移动，天空的颜色也随之变化。

scrollInputuseAnimatedCSSinterpolate

正在准备示例…

JavaScript 已关闭。下面的代码就是完整的示例。

App.jsx

import { useRef } from 'react';
import { input, scrollInput, useAnimated, useAnimatedCSS } from '@kkwaenggwari/animated';
import './styles.css';

const chapters = ['Dawn', 'Climb', 'Summit'];

export default function App({ depth = 1 }) {
  const scroller = useRef(null);

  // 0 at the top of the scroller, 1 at the bottom.
  const progress = useAnimated(
    0,
    (value) => {
      input(scroller, scrollInput({ progressY: value }));
    },
    [],
  );

  const move = (distance) =>
    progress.interpolate({ inputRange: [0, 1], outputRange: ['0px', `${distance * depth}px`] });

  // A color is not a calc() expression, so it gets its own CSS value.
  const sky = useAnimatedCSS(
    progress.interpolate({
      inputRange: [0, 0.5, 1],
      outputRange: ['#5c7cff', '#8fb0ff', '#0b1440'],
    }),
  );

  return (
    <div className="stage">
      <div ref={scroller} className="scroller">
        <div className="scene" style={{ background: sky }}>
          <span className="sun" style={{ transform: `translateY(${move(-150)})` }} />
          <span className="hill far" style={{ transform: `translateY(${move(-50)})` }} />
          <span className="hill near" style={{ transform: `translateY(${move(-110)})` }} />
          {chapters.map((chapter, index) => {
            const at = index / (chapters.length - 1);
            const opacity = progress.interpolate({
              inputRange: [at - 0.3, at, at + 0.3],
              outputRange: [0, 1, 0],
              extrapolate: 'clamp',
            });
            return (
              <h3 key={chapter} style={{ opacity }}>
                {chapter}
              </h3>
            );
          })}
        </div>
        <div className="spacer" />
      </div>
      <p>Scroll inside the frame.</p>
    </div>
  );
}

styles.css

.stage {
  display: grid;
  gap: 12px;
  padding: 24px;
}

.scroller {
  height: 340px;
  border-radius: 20px;
  overflow-y: auto;
  overscroll-behavior: contain;
}

.scene {
  position: sticky;
  top: 0;
  height: 340px;
  overflow: hidden;
}

.sun {
  position: absolute;
  left: 58%;
  top: 150px;
  width: 110px;
  height: 110px;
  border-radius: 50%;
  background: #ffffff;
}

.hill {
  position: absolute;
  left: -10%;
  width: 120%;
  border-radius: 50% 50% 0 0;
}

.far {
  bottom: -180px;
  height: 320px;
  background: #4a6bff;
}

.near {
  bottom: -240px;
  left: -40%;
  height: 360px;
  background: #16181d;
}

.scene h3 {
  position: absolute;
  inset: 32px 28px auto;
  margin: 0;
  color: #fff;
  font-size: 34px;
}

.spacer {
  height: 1100px;
}

.stage p {
  margin: 0;
  color: #5b6070;
  font-size: 14px;
}

工作原理

scrollInput({ progressY }) 把滚动容器的进度（0 到 1）写入一个值。
每个图层都把这个值插值成自己的距离，所以视差效果完全由 calc() 实现。
天空颜色不是 calc() 表达式，所以 useAnimatedCSS 为它提供了专属变量。
章节标题在各自对应的进度区间内淡入淡出。

滚动故事

工作原理

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