我写了一个canvas js程序,但是如果我在ubuntu 13.04 chromium中使用DOM元素它不起作用(它在firefox 23.0中很好)。这是代码:
<body>
<canvas id="map" width="600" height="600"></canvas>
<img id="photo" src="jiuwo.jpg" style="display:none;">
<img id="frame" src="frame.png" style="display:none;">
</body>
<script type="text/javascript">
function drawGallary(){
var canvas = document.getElementById('map');
if(canvas.getContext){
var ctx = canvas.getContext('2d');
var img1 = document.getElementById('photo');
var img2 = document.getElementById('frame');
ctx.drawImage(img1, 300, 300, 100, 100, 20, 21, 100, 100); // block of image
ctx.drawImage(img2, 0, 0);
}
}
</script>
我发现如果我把drawImage放到onload函数中,它运行良好:
function drawGallary2(){
var canvas = document.getElementById('map');
if(canvas.getContext){
var ctx = canvas.getContext('2d');
var img1 = new Image();
img1.src = "jiuwo.jpg";
img1.onload = function(){
ctx.drawImage(img1, 300, 300, 100, 100, 20, 21, 100, 100);
}
var img2 = document.getElementById('frame');
img2.onload = function(){
ctx.drawImage(img2, 0, 0);
}
}
}
如果使用DOM元素作为图像源,是否需要onload?感谢。
答案 0 :(得分:2)
确保您使用window.onload为页面充分加载时间。
通过这种方式,您的图像可以在画布上完全绘制。
// wait until the page is fully loaded
window.onload = function() {
function drawGallary(){
var canvas = document.getElementById('map');
if(canvas.getContext){
var ctx = canvas.getContext('2d');
var img1 = document.getElementById('photo');
var img2 = document.getElementById('frame');
ctx.drawImage(img1, 300, 300, 100, 100, 20, 21, 100, 100);
ctx.drawImage(img2, 0, 0);
}
}
} // end window.onload