将Div保存为JPG保存，但某些内容为空/空白

Question

我有一个小应用程序(下面是所有代码(，它应该将c0复制到其他画布并允许打印；后者是目前唯一不起作用的部分。我的意思是，它保存了一个图像，但当我在电脑上打开它时，转移的画布会显示为空白。

为什么？提前谢谢。

var canvas = [],
image;
var mainCanvas;
mainCanvas = new fabric.Canvas('c0');
for (i = 1; i <= 3; i++) {
canvas[i] = new fabric.StaticCanvas('sc' + i);
}
function addText() {
var text = new fabric.IText('Type here...', {
fontSize: 27,
top: 10,
left: 10,
});
mainCanvas.add(text);
}
var rect = new fabric.Rect({
fill: '#ff0000',
width: 100,
height: 100,
id: 1
});
var circle = new fabric.Circle({
fill: '#ffff00',
radius: 50,
left: 150,
top: 150,
originX: 'center',
originY: 'center',
id: 2
});
mainCanvas.on('object:added', onModified);
mainCanvas.on('object:modified', onModified);
mainCanvas.on('object:scaling', onModified);
mainCanvas.on('object:moving', onModified);
mainCanvas.add(rect, circle);
function onModified(option) {
var ob = option.target;
var index = mainCanvas.getObjects().indexOf(ob);
ob.clone(function(obj) {
for (i = 1; i <= 3; i++) {
canvas[i].insertAt(obj, index, true);
}
});
};
$('#update').click(function() {
updateCanvas();
});
function updateCanvas() {
var json = JSON.stringify(mainCanvas);
for (i = 1; i <= 3; i++) {
canvas[i].loadFromJSON(json);
}
}
// Toggling Images
function replaceImage(imgUrl) {
if (!isImageLoaded) return; //return if initial image not loaded
image.setSrc(imgUrl, function() {
mainCanvas.renderAll();
updateCanvas();
});
}
// Default (Blank)
fabric.Image.fromURL('https://i.imgur.com/SamdNdX.png', function(img) {
isImageLoaded = true;
image = img.set({
selectable: false,
evented: false,
});
mainCanvas.add(image);
mainCanvas.sendToBack(image);
updateCanvas();
});
$('#save').click(function() {
html2canvas($('#imagesave'), {
onrendered: function(canvas) {
var a = document.createElement('a');
// toDataURL defaults to png, so we need to request a jpeg, then convert for file download.
a.href = canvas.toDataURL("image/jpeg").replace("image/jpeg", "image/octet-stream");
a.download = 'myfile.jpg';
a.click();
}
});
});

html * {
margin: 0px;
padding: 0px;
}
body {
margin: 0px;
padding: 0px;
}
canvas {
margin: 0px;
display: block;
padding: 0;
}
td,
tr {
margin: 0;
padding: 0;
border: 0;
outline: 0;
vertical-align: baseline;
}
#imagesave {
background-color: white;
height: 637.5px;
width: 825px;
padding-left: 75px;
border: 1px solid black;
}

<script src="https://ajax.googleapis.com/ajax/libs/jquery/2.1.1/jquery.min.js"></script>
<script src="https://cdnjs.cloudflare.com/ajax/libs/html2canvas/0.4.1/html2canvas.js"></script>
<script src="https://cdnjs.cloudflare.com/ajax/libs/fabric.js/1.7.22/fabric.js"></script>
<button onclick="addText();" class="dropdown-item">Add Text</button><button id="save">Save</button>
<button onclick="replaceImage('https://i.imgur.com/SamdNdX.png')">Blank</button>
<button onclick="replaceImage('https://i.imgur.com/TIINd6E.png')">Hands Pic</button>
<div id="imagesave">
<table>
<tr>
<td>
<canvas id="c0" width="187.5" height="636"></canvas>
</td>
<td>
<canvas id="sc1" width="187.5" height="636"></canvas>
</td>
<td>
<canvas id="sc2" width="187.5" height="636"></canvas>
</td>
<td>
<canvas id="sc3" width="187.5" height="636"></canvas>
</td>
</tr>
</table>
</div>

Answer 1

你的织物画布被你在上面画的图像污染了html2canvas因此不会绘制这些，因为它们也会污染生成的画布。

由于您的图像带有正确的标头，因此解决方案是使用crossOrigin标志请求它们。

你可以在最初的织物中同时做到这两件事。图像调用

fabric.Image.fromURL( url, callback, { crossOrigin: true } )

并且在replaceImage功能中

image.setSrc( imgUrl, callback, { crossOrigin: true } );

var canvas = [],
image;
var mainCanvas;
mainCanvas = new fabric.Canvas('c0');
for (i = 1; i <= 3; i++) {
canvas[i] = new fabric.StaticCanvas('sc' + i);
}
function addText() {
var text = new fabric.IText('Type here...', {
fontSize: 27,
top: 10,
left: 10,
});
mainCanvas.add(text);
}
var rect = new fabric.Rect({
fill: '#ff0000',
width: 100,
height: 100,
id: 1
});
var circle = new fabric.Circle({
fill: '#ffff00',
radius: 50,
left: 150,
top: 150,
originX: 'center',
originY: 'center',
id: 2
});
mainCanvas.on('object:added', onModified);
mainCanvas.on('object:modified', onModified);
mainCanvas.on('object:scaling', onModified);
mainCanvas.on('object:moving', onModified);
mainCanvas.add(rect, circle);
function onModified(option) {
var ob = option.target;
var index = mainCanvas.getObjects().indexOf(ob);
ob.clone(function(obj) {
for (i = 1; i <= 3; i++) {
canvas[i].insertAt(obj, index, true);
}
});
};
$('#update').click(function() {
updateCanvas();
});
function updateCanvas() {
var json = JSON.stringify(mainCanvas);
for (i = 1; i <= 3; i++) {
canvas[i].loadFromJSON(json);
}
}
// Toggling Images
function replaceImage(imgUrl) {
if (!isImageLoaded) return; //return if initial image not loaded
image.setSrc(imgUrl, function() {
mainCanvas.renderAll();
updateCanvas();
},{ crossOrigin: 'anonymous' } );
}
// Default (Blank)
fabric.Image.fromURL('https://i.imgur.com/SamdNdX.png', function(img) {
isImageLoaded = true;
image = img.set({
selectable: false,
evented: false,
});
mainCanvas.add(image);
mainCanvas.sendToBack(image);
updateCanvas();
},{ crossOrigin: 'anonymous' });
$('#save').click(function() {
html2canvas($('#imagesave'), {
onrendered: function(canvas) {
var a = document.createElement('a');
// toDataURL defaults to png, so we need to request a jpeg, then convert for file download.
a.href = canvas.toDataURL("image/jpeg").replace("image/jpeg", "image/octet-stream");
a.download = 'myfile.jpg';
a.click();
}
});
});

html * {
margin: 0px;
padding: 0px;
background: white;
}
body {
margin: 0px;
padding: 0px;
}
canvas {
margin: 0px;
display: block;
padding: 0;
}
td,
tr {
margin: 0;
padding: 0;
border: 0;
outline: 0;
vertical-align: baseline;
}
#imagesave {
background-color: white;
height: 637.5px;
width: 825px;
padding-left: 75px;
border: 1px solid black;
}

<script src="https://ajax.googleapis.com/ajax/libs/jquery/2.1.1/jquery.min.js"></script>
<script src="https://cdnjs.cloudflare.com/ajax/libs/html2canvas/0.4.1/html2canvas.js"></script>
<script src="https://cdnjs.cloudflare.com/ajax/libs/fabric.js/1.7.22/fabric.js"></script>
<button onclick="addText();" class="dropdown-item">Add Text</button><button id="save">Save</button>
<button onclick="replaceImage('https://i.imgur.com/SamdNdX.png')">Blank</button>
<button onclick="replaceImage('https://i.imgur.com/TIINd6E.png')">Hands Pic</button>
<div id="imagesave">
<table>
<tr>
<td>
<canvas id="c0" width="187.5" height="636"></canvas>
</td>
<td>
<canvas id="sc1" width="187.5" height="636"></canvas>
</td>
<td>
<canvas id="sc2" width="187.5" height="636"></canvas>
</td>
<td>
<canvas id="sc3" width="187.5" height="636"></canvas>
</td>
</tr>
</table>
</div>

还要注意的是，你的html2canvas版本已经过时了，你可能想使用一个最新版本，其中已经修复了很多错误(但不是这个问题(。