Javascript 虚拟画布图像数据不工作
我对虚拟画布的概念很陌生,你知道为什么下面的代码不起作用吗Javascript 虚拟画布图像数据不工作,javascript,html,canvas,off-screen,Javascript,Html,Canvas,Off Screen,我对虚拟画布的概念很陌生,你知道为什么下面的代码不起作用吗 <script type="text/javascript"> $(document).ready(function () { var c1 = document.createElement('canvas'); var ctx1 = c1.getContext("2d"); var c2 = documen
<script type="text/javascript">
$(document).ready(function () {
var c1 = document.createElement('canvas');
var ctx1 = c1.getContext("2d");
var c2 = document.getElementById('Canvas2');
var ctx2 = c2.getContext("2d");
c1.width = c2.width;
c1.height = c2.height;
img1 = new Image();
img1.src = 'A1.png';
img1.onload = function () {
ctx1.drawImage(this, 0, 0);
};
imgdata = ctx1.getImageData(0, 0, c2.width, c2.height);
ctx2.putImageData(imgdata, 0, 0);
});
</script>
<canvas id="Canvas2" style="display:block;position:absolute;background-color:transparent;border:1px solid red;">
Your browser does not support the HTML5 canvas tag.
</canvas>
您还必须等待getImageData等,直到图像加载完毕,因此将图像加载后需要执行的所有操作都移动到onload处理程序中(或将其包装在从onload调用的函数中):
如果不这样做,则在调用getImageData时,图像可能不会加载并绘制到画布,这将导致一个空白字节数组。。将不得不等待接受此:-)谢谢
$(document).ready(function () {
var c1 = document.createElement('canvas');
var ctx1 = c1.getContext("2d");
var c2 = document.getElementById('Canvas2');
var ctx2 = c2.getContext("2d");
c1.width = c2.width;
c1.height = c2.height;
ctx1.fillRect(0, 20, 20, 20);
imgdata = ctx1.getImageData(0, 0, c2.width, c2.height);
ctx2.putImageData(imgdata, 0, 0);
});
img1.onload = function () {
ctx1.drawImage(this, 0, 0);
imgdata = ctx1.getImageData(0, 0, c2.width, c2.height);
ctx2.putImageData(imgdata, 0, 0);
};