Question

我有3层画布，我为每个画布分别提供了一个id。

这就是我在做的事。

HTML

<div style="position:relative;">
    <canvas id="layer1" style="position: absolute; left: 0; top: 0; z-index: 0;">
    </canvas>
    <canvas id="layer2" style="position: absolute; left: 0; top: 0; z-index: 1;">
    </canvas>
    <canvas id="layer3" style="position: absolute; left: 0; top: 0; z-index: 1;">
    </canvas>
</div>

我可以在layer1上绘制图像

JS

var canvas = document.getElementById('layer1');
var context = canvas.getContext('2d');
context.canvas.width  = window.innerWidth;
context.canvas.height = window.innerHeight*0.7;
var imageObj = new Image();
var imageObj1 = new Image();

imageObj.onload = function() {
    context.drawImage(imageObj, 0, 0,context.canvas.width,context.canvas.height*0.9);
    context.drawImage(imageObj1, x1, y1,6,canvasHeight);    
};

imageObj1.src='vertical.png';
imageObj.src = 'horizontal.png';

如何在所有图层上绘制图像并创建单个canvas.toDataUrl？

Answer 1

要绘制所有三个“图层”，您必须为所有图层创建上下文

// references to layer1
var canvas1 = document.getElementById('layer1');
var context1 = canvas1.getContext('2d');

// references to layer2
var canvas2 = document.getElementById('layer2');
var context2 = canvas2.getContext('2d');

// references to layer3
var canvas3 = document.getElementById('layer3');
var context3 = canvas3.getContext('2d');

然后，在完成所有图层的绘制后，合并它们（此处合并到layer1上）：

// merge all layers onto layer1
context1.drawImage(canvas2,0,0);
context1.drawImage(canvas3,0,0);

最后将合并的画布保存到图像并将img src设置为该图像。

// save the merged drawings as an image
// and set the img element src to that merged image
var img=new Image();
img.onload=function(){
    document.getElementById("results").src=img.src;
}
img.src=canvas1.toDataURL();

这是代码和小提琴：http://jsfiddle.net/m1erickson/fhjwY/

<!doctype html>
<html>
<head>
<link rel="stylesheet" type="text/css" media="all" href="css/reset.css" /> <!-- reset css -->
<script type="text/javascript" src="http://code.jquery.com/jquery.min.js"></script>

<style>
    body{ background-color: ivory; }
    canvas{border:1px solid red;}
</style>

<script>
$(function(){

// references to layer1
var canvas1 = document.getElementById('layer1');
var context1 = canvas1.getContext('2d');

// references to layer2
var canvas2 = document.getElementById('layer2');
var context2 = canvas2.getContext('2d');

// references to layer3
var canvas3 = document.getElementById('layer3');
var context3 = canvas3.getContext('2d');

// draw stuff on the layers
context1.fillStyle="red";
context2.fillStyle="blue";
context3.fillStyle="green";

context1.fillRect(20,20,50,50);
context2.fillRect(50,50,50,50);
context3.fillRect(80,80,50,50);

// merge all layers onto layer1
context1.drawImage(canvas2,0,0);
context1.drawImage(canvas3,0,0);

// save the merged drawings as an image
// and set the img element src to that merged image
var img=new Image();
img.onload=function(){
    document.getElementById("results").src=img.src;
}
img.src=canvas1.toDataURL();



}); // end $(function(){});
</script>

</head>

<body>
    <p>Draw rects on 3 canvases</p>
    <p>Merge all drawings to 1st canvas</p>
    <p>Create an image from merged drawings</p>
    <p>Set the image element with that merged image</p>
    <canvas id="layer1" width=150 height=150></canvas>
    <canvas id="layer2" width=150 height=150></canvas><br>
    <canvas id="layer3" width=150 height=150></canvas>
    <img id="results" width=150 height=150>
</body>
</html>

在3层画布上绘制图像并保存

1 个答案: