Processing.js 无法在内部绘制 canvas

Question

如果我将 canvas1 移到 holderCanvas 之外，下面的代码可以正常工作。但是，我在这种安排中需要它，因为 holderCanvas 正在实现缩放和平移功能。

<html>
<head>
  <script src="processing.min.js"></script>
</head>
<body><h1>Processing.js</h1>
<h2>Simple processing.js via JavaScript</h2>
<p>Clock</p>

<canvas id="holderCanvas" width="200" height="200" style="opacity:0.1;background-color:red;">
  <canvas id="canvas1" width="200" height="200"></canvas>
</canvas>

<script id="script1" type="text/javascript">

// Simple way to attach js code to the canvas is by using a function
function sketchProc(processing) {
  // Override draw function, by default it will be called 60 times per second
  processing.draw = function() {
    // determine center and max clock arm length
    var centerX = processing.width / 2, centerY = processing.height / 2;
    var maxArmLength = Math.min(centerX, centerY);

    function drawArm(position, lengthScale, weight) {      
      processing.strokeWeight(weight);
      processing.line(centerX, centerY, 
        centerX + Math.sin(position * 2 * Math.PI) * lengthScale * maxArmLength,
        centerY - Math.cos(position * 2 * Math.PI) * lengthScale * maxArmLength);
    }

    // erase background
    processing.background(224);

    var now = new Date();

    // Moving hours arm by small increments
    var hoursPosition = (now.getHours() % 12 + now.getMinutes() / 60) / 12;
    drawArm(hoursPosition, 0.5, 5);

    // Moving minutes arm by small increments
    var minutesPosition = (now.getMinutes() + now.getSeconds() / 60) / 60;
    drawArm(minutesPosition, 0.80, 3);

    // Moving hour arm by second increments
    var secondsPosition = now.getSeconds() / 60;
    drawArm(secondsPosition, 0.90, 1);
  };

}

var canvas = document.getElementById("canvas1");
var p = new Processing(canvas, sketchProc);
</script>
</body>
</html>

我可以在外面画所有的画canvas。但是，为了维护模块化组件，我正在实施此设计。如果这是错误的方式，请解释。

Answer 1

<canvas>里面的内容是回退的，只有在浏览器不支持<canvas>的时候才显示。这就是 canvas1 不会显示在这里的原因。

Processing.js 无法在内部绘制 canvas

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processing.js