我正在尝试创建一个屏幕外渲染画布的基本示例，但我在 js 中出错“无法读取上下文属性”。实际上我的想法是像我在https://yalantis.com/ 中看到的那样创建一个演示我想创建我的名字首字母。如果有更好的想法来实现这一点，请赐教。感谢这是我在实际实施之前的基本尝试:)
<!DOCTYPE html>
<html lang="en">
<head>
<meta charset="UTF-8">
<title>Off Screen Canvas</title>
<script>
function createOffscreenCanvas() {
var offScreenCanvas= document.createElement('canvas');
offScreenCanvas.width= '1360px';
offScreenCanvas.height= '400px';
var context= offScreenCanvas.getContext("2d");
context.fillRect(10,10,200,200);
}
function copyToOnScreen(offScreenCanvas) {
var onScreenContext=document.getElementById('onScreen').getContext('2d');
var offScreenContext=offScreenCanvas.getContext('2d');
var image=offScreenCanvas.getImageData(10,10,200,200);
onScreenContext.putImageData(image,0,0);
}
function main() {
copyToOnScreen(createOffscreenCanvas());
}
</script>
<style>
#onScreen {
width:1360px;
height: 400px;
}
</style>
</head>
<body onload="main()">
<canvas id="onScreen"></canvas>
</body>
</html>
您可以通过以下方式实现这一目标......
function createOffscreenCanvas() {
var offScreenCanvas = document.createElement('canvas');
offScreenCanvas.width = '1360';
offScreenCanvas.height = '400';
var context = offScreenCanvas.getContext("2d");
context.fillStyle = 'orange'; //set fill color
context.fillRect(10, 10, 200, 200);
return offScreenCanvas; //return canvas element
}
function copyToOnScreen(offScreenCanvas) {
var onScreenContext = document.getElementById('onScreen').getContext('2d');
onScreenContext.drawImage(offScreenCanvas, 0, 0);
}
function main() {
copyToOnScreen(createOffscreenCanvas());
}canvas {
border: 1px solid black;
}<body onload="main()">
<canvas id="onScreen" width="1360" height="400"></canvas>注意：永远不要使用 css 设置画布的宽度和高度。而是使用画布的原生宽度和高度属性。