制作带有 SVG 图像边框的交互式画布

Question

我在访问具有"不规则"边框设计的div 内部元素时遇到问题。

我的要求是在div的顶部有一个有2个可点击元素的边框。div 本身有一个画布来绘制任何东西。

问题是，如果我需要使边框可见，那么我必须使div 的 z 索引更低，这将不再允许在画布中绘制。如果我使div 的 z 索引更高，那么边框元素就会被切断。

我尝试过边框图像，但它 (1( 它使角呈方形，(2( 它不会使 2 个项目可点击。所以，我有一个包含边框和 2 个可点击元素的 SVG。

(function() {
  const canvas = document.getElementById('signature-pad');
  function resizeCanvas() {
    const ratio = Math.max(window.devicePixelRatio || 1, 1);
    canvas.width = canvas.offsetWidth * ratio;
    canvas.height = canvas.offsetHeight * ratio;
    canvas.getContext('2d').scale(ratio, ratio);
  }
  window.onresize = resizeCanvas;
  resizeCanvas();
  const signaturePad = new SignaturePad(canvas, {
    backgroundColor: 'red' // necessary for saving image as JPEG; can be removed is only saving as PNG or SVG
  });
})();

.container {
  height: 500px;
  width: 409px;
  display: flex;
  align-items: center;
  justify-content: center;
  position: relative;
}
img {
  position: absolute;
  top: 0;
  height: 100%;
  z-index: 1;
}
.container::before {
  display: block;
  content: " ";
  position: absolute;
  width: calc(100% - 3rem);
  height: calc(100% - 2rem);
  background-color: red;
  z-index: -1;
}
canvas {
  width: calc(100% - 3rem);
  height: calc(100% - 2rem);
  z-index: 1;
}

<script src="https://cdn.jsdelivr.net/npm/signature_pad@2.3.2/dist/signature_pad.min.js"></script>
<div class="container">
  <img src="https://i.imgur.com/yWMwxJQ.png">
  <canvas id="signature-pad" class="signature-pad" height="500px;" width="409px;"></canvas>
</div>

JSFiddle

Answer 1

只需首先设置您的 (更高的 z-index(及其pointer-events CSS 规则即可none ，这样，指针事件将穿过它并到达您的画布：

(function() {
  const canvas = document.getElementById('signature-pad');
  function resizeCanvas() {
    const ratio = Math.max(window.devicePixelRatio || 1, 1);
    canvas.width = canvas.offsetWidth * ratio;
    canvas.height = canvas.offsetHeight * ratio;
    canvas.getContext('2d').scale(ratio, ratio);
  }
  window.onresize = resizeCanvas;
  resizeCanvas();
  const signaturePad = new SignaturePad(canvas, {
    backgroundColor: 'red' // necessary for saving image as JPEG; can be removed is only saving as PNG or SVG
  });
})();

.container {
  height: 500px;
  width: 409px;
  display: flex;
  align-items: center;
  justify-content: center;
  position: relative;
}
img {
  position: absolute;
  top: 0;
  height: 100%;
  z-index: 1;
  /* disable all pointer-events so we can reach underneath layer */
  pointer-events: none;
}
.container::before {
  display: block;
  content: " ";
  position: absolute;
  width: calc(100% - 3rem);
  height: calc(100% - 2rem);
  background-color: red;
  z-index: -1;
}
canvas {
  width: calc(100% - 3rem);
  height: calc(100% - 2rem);
  z-index: 1;
}

<script src="https://cdn.jsdelivr.net/npm/signature_pad@2.3.2/dist/signature_pad.min.js"></script>
<div class="container">
  <canvas id="signature-pad" class="signature-pad" height="500px;" width="409px;"></canvas>
  <!-- make <img> on top -->
  <img src="https://i.imgur.com/yWMwxJQ.png">
</div>

Answer 2

使用 ::before 伪元素，您可以使用z-index: -1在 .container 内部创建一个块

应用background-image(或使用<img>前景，我选择了背景(来.item。

.container {
  height: 500px;
  width: 409px;
  display: flex;
  align-items: center;
  justify-content: center;
  position: relative;
}
.container::before {
  display: block;
  content: " ";
  position: absolute;
  width: calc(100% - 3rem);
  height: calc(100% - 2rem);
  background-color: red;
  z-index: -1;
  
}
.item {
  background-size: contain;
  background-repeat: no-repeat;
  height: 100%;
  width: 100%;
  display: flex;
  align-items: center;
  justify-content: center;
}

<div class="container">
  <div class="item" style="background-image:url('https://i.imgur.com/yWMwxJQ.png')">
    <div><button onclick="alert(1)">Hello</button></div>
  </div>
</div>