Webworker OffscreenCanvas绘制常规图像

时间:2019-06-12 00:42:17

标签: javascript canvas web-worker

网络工作者可以通过XMLHttpRequest获取常规图像,对吗?工人如何将这些图像绘制到OffscreenCanvas?可能要使用XMLHttp.responseType = 'blob'

另一种方法是设置图像元素的src,然后将其传送给工作人员,但我的工作人员总是拒绝此类图像。

谢谢

1 个答案:

答案 0 :(得分:1)

ImageBitmap API用于此目的(以及其他目的)。

注意:此演示当前仅在Chrome上运行...

const offcanvas = canvas.transferControlToOffscreen();
const worker = new Worker(getWorkerURL());
worker.onmessage = e => console.log(e.data);
worker.postMessage(offcanvas, [offcanvas]);


function getWorkerURL() {
  return URL.createObjectURL(
    new Blob([
      worker_script.textContent
    ])
  );
}
<canvas id="canvas" height="450"></canvas>

<script id="worker_script" type="ws">
onmessage = async (evt) => {
  try {
    const canvas = evt.data;
    const ctx = canvas.getContext('2d');
    if(!ctx) {
      postMessage('unsupported browser');
      return;
    }
    const imgblob = await fetch('https://upload.wikimedia.org/wikipedia/commons/5/55/John_William_Waterhouse_A_Mermaid.jpg')
      .then(r => r.blob());
    const img = await createImageBitmap(imgblob);
    ctx.drawImage(img, 0,0, canvas.width, canvas.height);
 }
 catch(e) {
  postMessage('unsupported browser');
  throw e;
  }
};
</script>