html - 如何在 CSS "roller coaster"动画中曲线一条线？

Question

我正在尝试使用 CSS 创建过山车风格的动画。

我想知道如何在循环阶段 flex “过山车”。

我正在寻找一个全 CSS 解决方案，但如果需要一点 JavaScript，我可以接受。

到目前为止我的代码:

#container {
  width: 200px;
  height: 300px;
  margin-top: 50px;
  position: relative;
  animation: 10s infinite loop;
  animation-timing-function: linear;
}

#coaster {
  width: 100px;
  height: 10px;
  background: lightblue;
  position: absolute;
  bottom: 0;
  left: 1px;
  right: 1px;
  margin: 0 auto;
}

@keyframes loop {
  from {
    margin-left: -200px;
  }
  30% {
    margin-left: calc(50% - 75px);
    transform: rotate(0deg);
  }
  60% {
    margin-left: calc(50% - 125px);
    transform: rotate(-360deg);
  }
  to {
    transform: rotate(-360deg);
    margin-left: 100%;
  }
}

<div id="container">
  <div id="coaster"></div>
</div>

Answer 1

你可以考虑border-radius .这是您可以改进的基本示例

.box {
  height:100px;
  margin-top:50px;
  border:10px solid transparent;
  border-bottom:10px solid red;
  width:100px;
  animation:
    loop   5s infinite alternate linear,
    radius 5s infinite alternate linear;
}
@keyframes loop{
  0% {
    transform:translateX(0);
  }
  40% {
    transform:translateX(100px) rotate(0deg);
  }
  60% {
    transform:translateX(100px) rotate(-360deg); 
  }
  100% {
    transform:translateX(200px) rotate(-360deg);
  }
}
@keyframes radius{
   0%,28% {
     border-radius:0%
   }
   35%,38% {
     border-bottom-right-radius:50%;
     border-bottom-left-radius:0%;
   }
   45%,55% {
     border-radius:50%
   }
   62%,65% {
     border-bottom-right-radius:0%;
     border-bottom-left-radius:50%;
   }
   70%,100% {
     border-radius:0%
   }
}

<div class="box"></div>

另一个疯狂的想法，您可以在透明 flex 路径后面为矩形设置动画:

.box {
  height: 165px;
  width: 315px;
  position: relative;
  border-radius: 0 100px 100px 0;
  animation: hide 3s infinite linear alternate;
  overflow:hidden;
}

.box:after {
  content: "";
  display:block;
  height: 100%;
  background: white padding-box;
  border-radius: inherit;
  border: 15px solid transparent;
  border-left:0;
  box-sizing: border-box;
}

.alt {
  margin-top: -165px;
  transform: scaleX(-1);
  transform-origin: 170px 0;
  animation-direction: alternate-reverse;
}

.box:before {
  content: "";
  position: absolute;
  z-index: -1;
  width: 90px;
  height: 90px;
  background: blue;
  bottom: -40px;
  animation: loop 3s infinite linear alternate;
  transform-origin: 50% -20px;
}

.alt:before {
  animation-direction: alternate-reverse;
}

@keyframes loop {
  15% {
    transform: translateX(180px) rotate(0deg);
  }
  40% {
    transform: translateX(180px) rotate(-180deg);
  }
  50%,100% {
    transform: translateX(125px) rotate(-180deg);
  }
}

@keyframes hide {
  0%,50% {
    visibility: visible;
  }
  50.2%,100% {
    visibility: hidden;
  }
}

<div class="box"></div>

<div class="box alt"></div>

代码较少且透明的优化版本(为此将考虑 mask )

.box {
  height: 165px;
  width: 315px;
  position: relative;
  border-radius: 0 100px 100px 0;
  animation: hide 3s infinite linear alternate;
  overflow:hidden;
  -webkit-mask:
    linear-gradient(#fff,#fff) top left   /235px 15px,
    linear-gradient(#fff,#fff) bottom left/235px 15px,
    radial-gradient(farthest-side at left,transparent calc(100% - 15px),#fff 0) right/100px 100%;
   -webkit-mask-repeat:no-repeat;
   mask:
    linear-gradient(#fff,#fff) top    left/235px 15px,
    linear-gradient(#fff,#fff) bottom left/235px 15px,
    radial-gradient(farthest-side at left,transparent calc(100% - 15px),#fff 0) right/100px 100%;
   mask-repeat:no-repeat;  
}
.alt {
  margin-top: -165px;
  transform: scaleX(-1);
  transform-origin: 170px 0;
  animation-direction: alternate-reverse;
}

.box:before {
  content: "";
  position: absolute;
  width: 90px;
  height: 90px;
  background: blue;
  bottom: -40px;
  animation: loop 3s infinite linear alternate;
  transform-origin: 50% -20px;
}

.alt:before {
  animation-direction: alternate-reverse;
}

@keyframes loop {
  15% {
    transform: translateX(180px) rotate(0deg);
  }
  40% {
    transform: translateX(180px) rotate(-180deg);
  }
  50%,100% {
    transform: translateX(125px) rotate(-180deg);
  }
}

@keyframes hide {
  0%,50% {
    visibility: visible;
  }
  50.2%,100% {
    visibility: hidden;
  }
}

body {
  background:linear-gradient(to right,yellow,gray);
}

<div class="box"></div>

<div class="box alt"></div>

另一个具有较少像素值和 CSS 变量的版本，您可以在其中轻松调整所有内容。

在整页上运行代码段并享受所有杯垫的乐趣!

.box {
  --w:400px; /* Total width of the coaster */
  --h:180px; /* Height of the coaster */
  --b:90px;  /* width of the small bar */
  --t:15px;  /* height of the small bar */
  --c:blue;  /* Color of the small bar */
  
  width:var(--w);
  height:var(--h);
}

.box > div {
  height: 100%;
  position:relative;
  width: calc(50% + var(--h)/2 + var(--b)/2);
  border-radius: 0 1000px 1000px 0;
  animation: hide 3s infinite linear alternate;
  -webkit-mask:
    linear-gradient(#fff,#fff) top left   /calc(100% - var(--h)/2) var(--t),
    linear-gradient(#fff,#fff) bottom left/calc(100% - var(--h)/2) var(--t),
    radial-gradient(farthest-side at left,transparent calc(100% - var(--t)),#fff 0) right/calc(var(--h)/2) 100%;
   -webkit-mask-repeat:no-repeat; 
   mask:
    linear-gradient(#fff,#fff) top left   /calc(100% - var(--h)/2) var(--t),
    linear-gradient(#fff,#fff) bottom left/calc(100% - var(--h)/2) var(--t),
    radial-gradient(farthest-side at left,transparent calc(100% - var(--t)),#fff 0) right/calc(var(--h)/2) 100%;
   mask-repeat:no-repeat;
}
.box > div:last-child {
  margin-top:calc(-1*var(--h));
  margin-left:auto;
  transform: scaleX(-1);
  animation-direction: alternate-reverse;
}

.box > div:before {
  content: "";
  position: absolute;
  width: var(--b);
  height: 50%;
  background: var(--c);
  bottom: -25%;
  animation: loop 3s infinite linear alternate;
  transform-origin: 50% -50%;
}

.box > div:last-child:before {
  animation-direction: alternate-reverse;
}

@keyframes loop {
  15% {
    transform: translateX(calc(var(--w)/2)) rotate(0deg);
  }
  40% {
    transform: translateX(calc(var(--w)/2)) rotate(-180deg);
  }
  50%,100% {
    transform: translateX(calc(var(--w)/2 - var(--b)/2)) rotate(-180deg);
  }
}

@keyframes hide {
  50% {
    visibility: visible;
  }
  50.1%,100% {
    visibility: hidden;
  }
}

body {
  background:linear-gradient(to right,yellow,gray);
}

<div class="box">
<div></div><div></div>
</div>

<div class="box" style="--w:500px;--h:80px;--b:50px;--c:red;--t:5px">
<div></div><div></div>
</div>

<div class="box" style="--w:90vw;--h:200px;--b:100px;--c:purple;--t:20px">
<div></div><div></div>
</div>

为了理解这个技巧，让我们移除蒙版并用简单的渐变替换它并移除隐藏动画:

.box {
  --w:400px; /* Total width of the coaster */
  --h:180px; /* Height of the coaster */
  --b:90px;  /* width of the small bar */
  --t:15px;  /* height of the small bar */
  --c:blue;  /* Color of the small bar */
  
  width:var(--w);
  height:var(--h);
}

.box > div {
  height: 100%;
  position:relative;
  width: calc(50% + var(--h)/2 + var(--b)/2);
  border-radius: 0 1000px 1000px 0;
  /*animation: hide 3s infinite linear alternate;*/
  background:
    linear-gradient(red,red) top left   /calc(100% - var(--h)/2) var(--t),
    linear-gradient(green,green) bottom left/calc(100% - var(--h)/2) var(--t),
    radial-gradient(farthest-side at left,transparent calc(100% - var(--t)),black 0) right/calc(var(--h)/2) 100%;
  background-repeat:no-repeat; 
}
.box > div:last-child {
  margin-top:calc(-1*var(--h));
  margin-left:auto;
  transform: scaleX(-1);
  animation-direction: alternate-reverse;
}

.box > div:before {
  content: "";
  position: absolute;
  width: var(--b);
  height: 50%;
  background: var(--c);
  bottom: -25%;
  animation: loop 3s infinite linear alternate;
  transform-origin: 50% -50%;
}

.box > div:last-child:before {
  animation-direction: alternate-reverse;
  background:purple;
}

@keyframes loop {
  15% {
    transform: translateX(calc(var(--w)/2)) rotate(0deg);
  }
  40% {
    transform: translateX(calc(var(--w)/2)) rotate(-180deg);
  }
  50%,100% {
    transform: translateX(calc(var(--w)/2 - var(--b)/2)) rotate(-180deg);
  }
}

@keyframes hide {
  0%,50% {
    visibility: visible;
  }
  50.2%,100% {
    visibility: hidden;
  }
}

body {
  background:linear-gradient(to right,yellow,gray);
}

<div class="box">
<div></div><div></div>
</div>

渐变创建的路径是我们的蒙版，我们只会看到那部分。然后我们让我们的矩形跟随路径，诀窍是有两个对称元素来创建循环效果。隐藏动画将允许我们只看到其中一个，而完美的重叠将创建一个连续的动画。

这是一个版本，以防您想要一个过山车的圆圈

.box {
  --w:400px; /* Total width of the coaster */
  --h:180px; /* Height of the coaster */
  --b:90px;  /* width of the small bar */
  --t:15px;  /* height of the small bar */
  --c:blue;  /* Color of the small bar */
  
  width:var(--w);
  height:var(--h);
}

.box > div {
  height: 100%;
  position:relative;
  width: calc(50% + var(--h)/2);
  border-radius: 0 1000px 1000px 0;
  animation: hide 3s infinite linear alternate;
  -webkit-mask:
    radial-gradient(farthest-side at bottom right,transparent calc(100% - var(--t)),#fff 0 100%,transparent 100%) top 0 right calc(var(--h)/2)/calc(var(--h)/2) 50%,
    linear-gradient(#fff,#fff) bottom left/calc(100% - var(--h)/2) var(--t),
    radial-gradient(farthest-side at left,transparent calc(100% - var(--t)),#fff 0) right/calc(var(--h)/2) 100%;
   -webkit-mask-repeat:no-repeat; 
   mask:
    radial-gradient(farthest-side at bottom right,transparent calc(100% - var(--t)),#fff 0 100%,transparent 100%) top 0 right calc(var(--h)/2)/calc(var(--h)/2) 50%,
    linear-gradient(#fff,#fff) bottom left/calc(100% - var(--h)/2) var(--t),
    radial-gradient(farthest-side at left,transparent calc(100% - var(--t)),#fff 0) right/calc(var(--h)/2) 100%;
   mask-repeat:no-repeat;
}
.box > div:last-child {
  margin-top:calc(-1*var(--h));
  margin-left:auto;
  transform: scaleX(-1);
  animation-direction: alternate-reverse;
}

.box > div:before {
  content: "";
  position: absolute;
  width: var(--b);
  height: 50%;
  background: var(--c);
  bottom: -25%;
  animation: loop 3s infinite linear alternate;
  transform-origin: 50% -50%;
}

.box > div:last-child:before {
  animation-direction: alternate-reverse;
}

@keyframes loop {
  15% {
    transform: translateX(calc(var(--w)/2 - var(--b)/2)) rotate(0deg);
  }
  50%,100% {
    transform: translateX(calc(var(--w)/2 - var(--b)/2)) rotate(-180deg);
  }
}

@keyframes hide {
  50% {
    visibility: visible;
  }
  50.1%,100% {
    visibility: hidden;
  }
}

body {
  background:linear-gradient(to right,yellow,gray);
}

<div class="box">
<div></div><div></div>
</div>

<div class="box" style="--w:500px;--h:80px;--b:50px;--c:red;--t:5px">
<div></div><div></div>
</div>

<div class="box" style="--w:90vw;--h:200px;--b:100px;--c:purple;--t:20px">
<div></div><div></div>
</div>