我该如何计算图像的口宽和高度

Question

我想基于“宽度”和“高度”参数显示图像。如何计算图像的比例？例如30/45，我需要根据用户选择更改宽度和高度。有公式吗？

我的代码

.wall {
  background-image: url(living-room-2.jpg);
  background-size: cover;
  background-position: center center;
  background-repeat: no-repeat;
  height: 100%;
  display: flex;
  justify-content: end;
  /*transform: rotateY(40deg);*/
}
div.photo {
  position: relative;
  -webkit-transform: perspective(1000px) rotateY(30deg);
  transform: perspective(1000px) rotateY(00deg);
  margin: 50px 10px;
  background-size: cover;
background-image:url('http://placekitten.com/g/600/200');
  width: 500px;
  height: 300px;
  background-origin: border-box;
  border-left: 5px solid rgba(0, 0, 0, 0.5);
}
div.photo:before,
div.photo:after {
  content: "";
  position: absolute;
  top: 0;
  width: 0;
  height: 100%;
  box-sizing: border-box;
  background: transparent;
  /*border-top: 4px solid white;*/
  /*border-bottom: 4px solid white;*/
  /*border-left: 10px solid white;*/
  /*border-right: 6px solid rgba(0, 0, 0, 0.5);*/
}
@media only screen and (max-width: 600px) {

  div.photo {
    transform: perspective(1000px) rotateY(10deg);
    height: 150px;
    width: 150px;

  }
}

而且我想通过用户选择来计算宽度和高度。

Answer 1

不确定我是否理解您的要求，但是您可以根据宽度计算高度。看看这一点，看看在select中更改值时会发生什么：

const onChange = e => {
  const preview = document.querySelector('.preview')
  const previewHeight = `${parseFloat(e.target.value) * 100}%`;
  preview.style = `padding-bottom: ${previewHeight};`;
}

document.querySelector('select').addEventListener('change', onChange)

.preview {
  width: 100%;
  height: 0;
  position: relative;
  padding-bottom: 66.6666%;
  background: url('http://placekitten.com/g/1200/400') center no-repeat;
  background-size: cover;
  margin-top: 1rem;
}

<div class="demo">
  <select>
    <option value="0.666">30/45</option>
    <option value="0.5">50/100</option>
    <option value="0.5625">9/16</option>
    <option value="0.1">1/10</option>
    <option value="2">2/1</option>    
  </select>
  <div class="preview"></div>
</div>