【发布时间】：2018-04-09 14:38:25
【问题描述】：
在 Chrome 中，当尝试从远程 url 测试画布绘图图像时，我在 jsfiddle 上收到以下错误。
错误：无法在“HTMLCanvasElement”上执行“toDataURL”：可能无法导出受污染的画布。
在 S3 存储桶上，我有以下 CORS 策略，允许跨资源共享：
<?xml version="1.0" encoding="UTF-8"?>
<CORSConfiguration xmlns="http://s3.amazonaws.com/doc/2006-03-01/">
<CORSRule>
<AllowedOrigin>*</AllowedOrigin>
<AllowedMethod>GET</AllowedMethod>
</CORSRule>
</CORSConfiguration>
如果我使用 jsfiddle 作为原点卷曲图像，我得到：
curl -H 'Origin: https://fiddle.jshell.net' -I 'https://i.ezr.io/products3/472_ARDSCR.jpg?h=45&w=165&fit=scale'
HTTP/1.1 200 OK
Cache-Control: public,max-age=31536000
Last-Modified: Wed, 07 Feb 2018 23:42:47 GMT
Server: imgix-fe
Content-Length: 6371
Accept-Ranges: bytes
Date: Fri, 16 Mar 2018 17:10:20 GMT
Age: 3173253
Connection: keep-alive
Content-Type: image/jpeg
Access-Control-Allow-Origin: *
X-Content-Type-Options: nosniff
X-Served-By: cache-lax8630-LAX, cache-sea1027-SEA
X-Cache: HIT, HIT
var Rack = {
init: function(params) {
Rack.conf = params;
Rack.bindEvents();
},
bindEvents: function() {
Rack.conf.scaleDown.addEventListener("click", function() {
Rack.clearCanvas();
Rack.conf.scaleW = Rack.round(Rack.conf.scaleW - .1, 1);
Rack.conf.scaleY = Rack.round(Rack.conf.scaleY - .1, 1);
if (Rack.conf.scaleW > 0 && Rack.conf.scaleY > 0) {
Rack.build();
}
});
Rack.conf.resetScale.addEventListener("click", function() {
Rack.clearCanvas();
Rack.conf.scaleW = 1;
Rack.conf.scaleY = 1;
Rack.build(true);
});
Rack.getRackJSON();
Rack.setNumImages();
Rack.build();
},
getRackJSON: function() { // will send ajax call based on item being added to the rack, will return json rack
Rack.conf.rack = {
"awards": [{
"src": "https://i.ezr.io/products3/472_ARDSCR.jpg?h=45&w=165&fit=scale",
"name": "Army Distinguished Service Cross",
"sku": "472_ARDSCR",
"x": 0,
"y": 0,
"width": 165,
"height": 45,
"attachments": [{
"src": "https://i.ezr.io/products3/913NP.png?h=20",
"name": "Bronze Oak Leaf",
"sku": "913NP",
"x": 73,
"y": 13,
"width": 20,
"height": 20
}]
},
{
"src": "https://i.ezr.io/products3/470_ARDDR.jpg?h=45&w=165&fit=scale",
"name": "Department of Defense Distinguished Service",
"sku": "470_ARDDR",
"x": 165,
"y": 0,
"width": 165,
"height": 45
}
]
};
},
setNumImages() {
for (var i = 0; i < Rack.conf.rack.awards.length; i++) {
var award = Rack.conf.rack.awards[i];
++Rack.conf.numImages;
if (award.hasOwnProperty('attachments')) {
Rack.conf.numImages += award.attachments.length;
}
}
},
loadImages: function(callback) {
var numImagesLoaded = 0;
for (var i = 0; i < Rack.conf.rack.awards.length; i++) {
var award = Rack.conf.rack.awards[i];
Rack.conf.images[award.sku] = new Image();
Rack.conf.images[award.sku].onload = function() {
if (++numImagesLoaded >= Rack.conf.numImages) {
callback();
}
}
Rack.conf.images[award.sku].src = award.src;
if (award.hasOwnProperty('attachments')) {
for (var j = 0; j < award.attachments.length; j++) {
var attachment = award.attachments[j];
Rack.conf.images[attachment.sku] = new Image();
Rack.conf.images[attachment.sku].crossOrigin = 'anonymous';
Rack.conf.images[attachment.sku].onload = function() {
if (++numImagesLoaded >= Rack.conf.numImages) {
callback();
}
}
Rack.conf.images[attachment.sku].src = attachment.src;
}
}
}
},
build: function(reset) {
if (Rack.conf.outputType === 'jpg') {
Rack.conf.ctx.fillStyle = "#ffffff";
Rack.conf.ctx.fillRect(0, 0, Rack.conf.c.width, Rack.conf.c.height);
}
reset === true ? Rack.conf.ctx.setTransform(1, 0, 0, 1, 0, 0) : Rack.conf.ctx.scale(Rack.conf.scaleW, Rack.conf.scaleY);
Rack.loadImages(function() {
for (var i = 0; i < Rack.conf.rack.awards.length; i++) {
var award = Rack.conf.rack.awards[i];
Rack.conf.ctx.drawImage(Rack.conf.images[award.sku], award.x, award.y, award.width, award.height);
if (award.hasOwnProperty('attachments')) {
for (var j = 0; j < award.attachments.length; j++) {
var attachment = award.attachments[j];
Rack.conf.ctx.drawImage(Rack.conf.images[attachment.sku], attachment.x, attachment.y, attachment.width, attachment.height);
}
}
}
});
Rack.conf.imageData = Rack.conf.c.toDataURL((Rack.conf.outputType === 'jpg' ? 'image/jpeg' : null), (Rack.conf.outputType === 'jpg' ? 1.0 : null));
},
clearCanvas: function() {
Rack.conf.ctx.clearRect(0, 0, Rack.conf.c.width, Rack.conf.c.height);
},
round: function(number, precision) {
var factor = Math.pow(10, precision);
var tempNumber = number * factor;
var roundedTempNumber = Math.round(tempNumber);
return roundedTempNumber / factor;
}
};
Rack.init({
c: document.getElementById("myCanvas"),
ctx: document.getElementById("myCanvas").getContext("2d"),
outputType: 'png',
scaleDown: document.getElementById('scale-down'),
resetScale: document.getElementById('reset-scale'),
images: {},
numImages: 0,
awards: null,
imageData: null,
scaleW: 1,
scaleY: 1,
rack: null
});<canvas id="myCanvas" width="330" height="45">Your browser does not support the HTML5 canvas tag.</canvas>
<div>
<button id="scale-down" style="cursor:pointer;">
Scale Down
</button>
<button id="reset-scale" style="cursor:pointer;">
Reset
</button>
</div>【问题讨论】：
-
它是图像托管服务器，通过在响应中添加适当的 CORS 标头来允许跨域。如果服务器的响应中不存在此内容，则您无法访问图像中包含的像素数据。
-
Access-Control-Allow-Origin: * 正在返回，所以应该没有 CORS 问题。
-
问题已解决：缺少 Rack.conf.images[award.sku].crossOrigin = 'anonymous';
-
这两个 url 可能解释了你需要那个。 github.com/locomotivecms/engine/issues/1152 和 stackoverflow.com/questions/20027839/…
标签： cors html5-canvas jsfiddle