如何在比例动画中保持图像中心的原点？

Question

我的情况与fiddle 类似，我有一个 CSS3 动画，可以缩放绝对定位在另一个元素中心的元素。但是，当动画发生时，它会偏离中心，如示例中相对于蓝色的红色方块所示。我如何居中？我已经围绕transform-origin 属性尝试了几种配置，但这并没有产生正确的结果。

@keyframes ripple_large {
	0% {transform:scale(1); }
	75% {transform:scale(3); opacity:0.4;}
	100% {transform:scale(4); opacity:0;}
}

.container {
  position: relative;
	display: inline-block;
  margin: 10vmax;
}

.cat {
  height: 20vmax;
}

.center-point {
  position: absolute;
  top: 50%;
  left: 50%;
  transform: translate(-50%, -50%);
  height: 10px;
  width: 10px;
  background: blue;
}

.to-animate {
  position: absolute;
  top: 50%;
  left: 50%;
  transform: translate(-50%, -50%);
  border: 1px solid red;
  height: 5vmax;
  width: 5vmax;
  transform-origin:center;
}

.one {
		animation: ripple_large 2s linear 0s infinite;
}

.two {
		animation: ripple_large 2s linear 1s infinite;
}

<div class='container'>
  <img src='http://www.catster.com/wp-content/uploads/2017/08/Pixiebob-cat.jpg' class='cat'>
  <div class='center-point'>
  </div>
  <div class='to-animate one'></div>
  <div class='to-animate two'></div>
</div>

Answer 1

问题是您正在覆盖translate 转换。

当您指定一个新的转换（动画中的那个）时，它会覆盖第一个转换。在您的情况下，您 正在删除修复 center 对齐的翻译。

您需要将它们添加到相同的 transform 属性中并注意顺序，因为它很重要 (Why does order of transforms matter? rotate/scale doesn't give the same result as scale/rotate)

@keyframes ripple_large {
  0% {
    transform: translate(-50%, -50%) scale(1);
  }
  75% {
    transform: translate(-50%, -50%) scale(3);
    opacity: 0.4;
  }
  100% {
    transform: translate(-50%, -50%) scale(4);
    opacity: 0;
  }
}

.container {
  position: relative;
  display: inline-block;
  margin: 10vmax;
}

.cat {
  height: 20vmax;
}

.center-point {
  position: absolute;
  top: 50%;
  left: 50%;
  transform: translate(-50%, -50%);
  height: 10px;
  width: 10px;
  background: blue;
  transform-origin: center;
}

.to-animate {
  position: absolute;
  top: 50%;
  left: 50%;
  transform: translate(-50%, -50%);
  border: 1px solid red;
  height: 5vmax;
  width: 5vmax;
}

.one {
  -webkit-animation: ripple_large 2s linear 0s infinite;
  animation: ripple_large 2s linear 0s infinite;
}

.two {
  -webkit-animation: ripple_large 2s linear 1s infinite;
  animation: ripple_large 2s linear 1s infinite;
}

<div class='container'>
  <img src='http://www.catster.com/wp-content/uploads/2017/08/Pixiebob-cat.jpg' class='cat'>
  <div class='center-point'>
  </div>
  <div class='to-animate one'></div>
  <div class='to-animate two'></div>
</div>

更新

正如评论的那样，最好使用其他方法而不是平移来使元素居中，以避免更改动画，因为这可以与其他元素一起使用。

例子：

@keyframes ripple_large {
  0% {
    transform: scale(1) ;
  }
  75% {
    transform:scale(3) ;
    opacity: 0.4;
  }
  100% {
    transform: scale(4) ;
    opacity: 0;
  }
}

.container {
  position: relative;
  display: inline-block;
  margin: 10vmax;
}

.cat {
  height: 20vmax;
}

.center-point {
  position: absolute;
  top: 50%;
  left: 50%;
  transform: translate(-50%, -50%);
  height: 10px;
  width: 10px;
  background: blue;
  transform-origin:center;
}

.to-animate {
  position: absolute;
  top: 0;
  left: 0;
  bottom:0;
  right:0;
  margin:auto;
  border: 1px solid red;
  height: 5vmax;
  width: 5vmax;
}

.one {
  animation: ripple_large 2s linear 0s infinite;
}

.two {
  animation: ripple_large 2s linear 1s infinite;
}

<div class='container'>
  <img src='http://www.catster.com/wp-content/uploads/2017/08/Pixiebob-cat.jpg' class='cat'>
  <div class='center-point'>
  </div>
  <div class='to-animate one'></div>
  <div class='to-animate two'></div>
</div>