<div style="height: 50vh;"></div>

<section class="panel red">
  <p><span class="line line-1"></span>When this panel's top edge reaches 100px from the top of the viewport, the ScrollTrigger will start (<code>start: "top 100px"</code>), then end when its bottom is 100px from the bottom of the viewport (<code>end: "bottom bottom-=100px"</code>). Callbacks are logged to the right, and progress below: <br><span class="red-progress">progress: 0</span></p>
</section>

<div style="height: 100vh;"></div>

.orange {
  background-color: #e77614;
  background-image: radial-gradient(circle at 46% 40%, rgba(228, 228, 228,0.06) 0%, rgba(228, 228, 228,0.06) 13%,transparent 13%, transparent 100%),radial-gradient(circle at 11% 41%, rgba(198, 198, 198,0.06) 0%, rgba(198, 198, 198,0.06) 19%,transparent 19%, transparent 100%),radial-gradient(circle at 52% 23%, rgba(14, 14, 14,0.06) 0%, rgba(14, 14, 14,0.06) 69%,transparent 69%, transparent 100%),radial-gradient(circle at 13% 85%, rgba(148, 148, 148,0.06) 0%, rgba(148, 148, 148,0.06) 44%,transparent 44%, transparent 100%),radial-gradient(circle at 57% 74%, rgba(232, 232, 232,0.06) 0%, rgba(232, 232, 232,0.06) 21%,transparent 21%, transparent 100%),radial-gradient(circle at 59% 54%, rgba(39, 39, 39,0.06) 0%, rgba(39, 39, 39,0.06) 49%,transparent 49%, transparent 100%),radial-gradient(circle at 98% 38%, rgba(157, 157, 157,0.06) 0%, rgba(157, 157, 157,0.06) 24%,transparent 24%, transparent 100%),radial-gradient(circle at 8% 6%, rgba(60, 60, 60,0.06) 0%, rgba(60, 60, 60,0.06) 12%,transparent 12%, transparent 100%),linear-gradient(90deg, #ff7600, #ff7600);
}

.red {
  background-color: #c82736;
  background-image: radial-gradient(circle at 19% 90%, rgba(190, 190, 190,0.04) 0%, rgba(190, 190, 190,0.04) 17%,transparent 17%, transparent 100%),radial-gradient(circle at 73% 2%, rgba(78, 78, 78,0.04) 0%, rgba(78, 78, 78,0.04) 94%,transparent 94%, transparent 100%),radial-gradient(circle at 45% 2%, rgba(18, 18, 18,0.04) 0%, rgba(18, 18, 18,0.04) 55%,transparent 55%, transparent 100%),radial-gradient(circle at 76% 60%, rgba(110, 110, 110,0.04) 0%, rgba(110, 110, 110,0.04) 34%,transparent 34%, transparent 100%),radial-gradient(circle at 68% 56%, rgba(246, 246, 246,0.04) 0%, rgba(246, 246, 246,0.04) 16%,transparent 16%, transparent 100%),radial-gradient(circle at 71% 42%, rgba(156, 156, 156,0.04) 0%, rgba(156, 156, 156,0.04) 47%,transparent 47%, transparent 100%),radial-gradient(circle at 46% 82%, rgba(247, 247, 247,0.04) 0%, rgba(247, 247, 247,0.04) 39%,transparent 39%, transparent 100%),radial-gradient(circle at 50% 47%, rgba(209, 209, 209,0.04) 0%, rgba(209, 209, 209,0.04) 45%,transparent 45%, transparent 100%),linear-gradient(90deg, #e53949,#cc2232);
}
.panel.align-top {
  align-items: flex-start;
}
.purple {
  background-color: #8d3dae;
  background-image: radial-gradient(circle at 47% 14%, rgba(205, 205, 205,0.04) 0%, rgba(205, 205, 205,0.04) 43%,transparent 43%, transparent 100%),radial-gradient(circle at 35% 12%, rgba(215, 215, 215,0.04) 0%, rgba(215, 215, 215,0.04) 4%,transparent 4%, transparent 100%),radial-gradient(circle at 1% 35%, rgba(24, 24, 24,0.04) 0%, rgba(24, 24, 24,0.04) 37%,transparent 37%, transparent 100%),radial-gradient(circle at 21% 1%, rgba(0, 0, 0,0.04) 0%, rgba(0, 0, 0,0.04) 26%,transparent 26%, transparent 100%),radial-gradient(circle at 23% 82%, rgba(249, 249, 249,0.04) 0%, rgba(249, 249, 249,0.04) 60%,transparent 60%, transparent 100%),radial-gradient(circle at 11% 54%, rgba(251, 251, 251,0.04) 0%, rgba(251, 251, 251,0.04) 23%,transparent 23%, transparent 100%),radial-gradient(circle at 69% 68%, rgba(234, 234, 234,0.04) 0%, rgba(234, 234, 234,0.04) 10%,transparent 10%, transparent 100%),linear-gradient(90deg, #8d3dae,#8d3dae);
}
.line {
  width: 100%;
  max-width: 800px;
  height: 8px;
  margin: 0 0 10px 0;
  position: relative;
  display: inline-block;
  background-color: rgba(255,255,255,1);
}

.red .red-progress {
  //color: white;
  font-weight: 400;
  font-size: 1.3em;
  padding-top: 14px;
  display: inline-block;
}

    gsap.registerPlugin(ScrollTrigger);

    const animation = gsap.from(".line-1", {
      scaleX: 0,
      transformOrigin: "left center",
      ease: "none"
    });
    const logRed = (text, e) => {
      console.log(text, e);
    }
    ScrollTrigger.create({
      trigger: ".red",
      start: "top 100px",
      end: "bottom bottom-=100px",
      // 滚动条刻度100px开始, 滚动条-100px的位置结束
      markers: true,
      scrub: true,
      animation: animation,
      onEnter: () => logRed("越过start这根线"),
      onLeave: () => logRed("越过end这根线"),
      onEnterBack: () => logRed("返回越过end这根线"),
      onLeaveBack: () => logRed("返回越过start这根线"),
      onRefresh: (e) => logRed("默认执行两次", e),
      // onUpdate: self => redProgress.innerText = "progress: " + self.progress.toFixed(3)
      onUpdate: (self) => {
        // 更新的值
               document.querySelector('.red-progress').textContent='progress: '+self.progress.toFixed(3)
        console.log(self.progress.toFixed(3));
      }
    });