javascript - 使用drawImage时“可能无法导出受污染的 Canvas ”

Question

当尝试将图像绘制到 Canvas 上，然后将 Canvas 保存到图像时，出现以下错误:

Uncaught SecurityError: Failed to execute 'toDataURL' on 'HTMLCanvasElement': Tainted canvases may not be exported

var picture = new Image();
picture.src = "https://upload.wikimedia.org/wikipedia/commons/thumb/8/85/Smiley.svg/800px-Smiley.svg.png";
var canvas = document.getElementById("background");
var context = canvas.getContext("2d");
function generate(){
	var ctx = document.createElement("canvas").getContext("2d");
		ctx.canvas.width = canvas.width;
		ctx.canvas.height = canvas.height;
	ctx.fillStyle = "red";	
	ctx.rect (0, 0, 40, 40);
	ctx.fill();

	ctx.drawImage(picture,0,0);
	
	image = new Image();
	image.setAttribute('crossOrigin', 'anonymous');
	image.src = ctx.canvas.toDataURL("image/png");		
}
function draw(){
	context.clearRect(0, 0, canvas.width, canvas.height);
	context.drawImage(image, 0,0,100,100,0,0,100,100);	
}
function play(){
  generate();
  setInterval(function(){draw();}, 0.0333);
}

window.onload = function(){
	if(picture.complete)play();
	else picture.onload = play;	
}

<canvas id="background" width=500 height=500></canvas>

我知道这与在 Canvas 上绘制图像有关，因为当删除该行后，一切都正常，您可以看到红色框:

var picture = new Image();
picture.src = "https://upload.wikimedia.org/wikipedia/commons/thumb/8/85/Smiley.svg/800px-Smiley.svg.png";
var canvas = document.getElementById("background");
var context = canvas.getContext("2d");
function generate(){
	var ctx = document.createElement("canvas").getContext("2d");
		ctx.canvas.width = canvas.width;
		ctx.canvas.height = canvas.height;
	ctx.fillStyle = "red";	
	ctx.rect (0, 0, 40, 40);
	ctx.fill();
	
	image = new Image();
	image.setAttribute('crossOrigin', 'anonymous');
	image.src = ctx.canvas.toDataURL("image/png");		
}
function draw(){
	context.clearRect(0, 0, canvas.width, canvas.height);
	context.drawImage(image, 0,0,100,100,0,0,100,100);	
}
function play(){
  generate();
  setInterval(function(){draw();}, 0.0333);
}

window.onload = function(){
	if(picture.complete)play();
	else picture.onload = play;	
}

<canvas id="background" width=500 height=500></canvas>

所以是drawImage导致了失败。

我读过其他问题，解决方案是“只需添加 image.setAttribute('crossOrigin', 'anonymous'); ”(我已经这样做了)或将它们放在同一目录中(我通过将这两个文件放在桌面上尝试了这一点)，但似乎都没有帮我解决一下。

有解决办法或替代方法吗？我想做的就是将多个图像绘制到一张图像上。 (红框只是为了展示。)

Answer 1

I tried this by placing both files on desktop

没有。您需要一个 Web 服务器并在 http://(或 https://)中打开文件，以便将它们视为同一来源。当您在 file:// 中打开文件时，即使您从同一目录提供它们，它们也不会被视为同源。