知识库

html
<!DOCTYPE html>
<html lang="en">
<head>
  <meta charset="UTF-8">
  <meta http-equiv="X-UA-Compatible" content="IE=edge">
  <meta name="viewport" content="width=device-width, initial-scale=1.0">
  <title>Document</title>
  <style>
    html, 
    body {
      width: 100vw;
      height: 100vh;
      display: flex;
      flex-direction: column;
      justify-content: center;
      align-items: center;
    }
  </style>
</head>
<body>
  <img src="./imgs/save-restore.png" alt="">
  <canvas id="canvas"></canvas>

  <script>
    const canvas = document.getElementById('canvas')
    const context = canvas.getContext('2d')

    canvas.style.backgroundColor = '#ddd'

    context.fillStyle = 'red'
    context.font = '32px Arial'
    context.fillText('Hello Canvas', 0, 50)

    // 将当前状态放入栈中，保存 canvas 全部状态，保存到栈中的绘制状态由下面四部分组成：
    // 1.当前的变换矩阵。
    // 2.当前的剪切区域。
    // 3.当前的虚线列表。
    // 4.以下属性当前的值： strokeStyle, fillStyle, globalAlpha, lineWidth, lineCap, 
    // lineJoin, miterLimit, lineDashOffset, shadowOffsetX, shadowOffsetY, 
    // shadowBlur, shadowColor, globalCompositeOperation, font, textAlign, 
    // textBaseline, direction, imageSmoothingEnabled。
    context.save()
    context.fillStyle = 'green'

    setTimeout(() => {
      context.restore()
      console.log(context.fillStyle) // -> #ff0000
    }, 3000);
  </script>
</body>
</html>