[英]HTML5 Canvas Slideshow Using Javascript
I'm not sure exactly where my issue lies, I'm relatively new to both canvas and JavaScript so I'm sorry if this is very vague but I cannot get my slideshow canvas to function, let alone display an image. 我不确定我的问题到底在哪里,我对canvas和JavaScript还是比较陌生,所以如果这很模糊我很抱歉,但是我无法让幻灯片画布发挥作用,更不用说显示图像了。
<!DOCTYPE html>
<html>
<head>
<title>PhotoGenesis</title>
<LINK REL=StyleSheet HREF="homecss.css" TYPE="text/css" MEDIA=screen>
<script type="text/javascript" src="homescript.js"></script>
</head>
<body onLoad="javascript:preloader()">
<header>
<a href=http://localhost.com/home><img id=logo alt="PhotoGenesis" src="logo.png""/> </a>
<nav id=headernav>
<a href=http://localhost.com/home>home</a>
<a href=http://localhost.com/news>news</a>
<a href=http://localhost.com/photography>photography</a>
<a href=http://localhost.com/video>video</a>
<script type="text/javascript">
var lightbox="lightbox ("+"0"+")";
document.write("<a href=http://localhost.come/lighbox>" + lightbox + "</a>");
</script>
<a href=http://localhost.com/about>about</a>
<a href=http://localhost.com/contact>contact</a>
<a href=http://localhost.com/blog>blog</a>
</nav>
<span id=search></span>
<img id=miscone alt="Full Screen" src="miscone.png"/>
<img id=misctwo alt="Share" src="misctwo.png"/>
</header>
<main onLoad="javascript:canvasslider()">
<canvas id="defaultbackground" width=100%; height=100%;/>
</main>
<footer>
<nav id="footernav">
<a href=http://www.facebook.com><img id="fbnav" alt="Facebook" src="fbooknav.png"/></a>
<a href=http://www.twitter.com><img id="tnav" alt="Twitter" src="twitternav.png"/></a>
<a href=http://www.stumbleupon.com><img id="snav" alt="StumbleUpon" src="stumblenav.png"/></a>
</nav>
</footer>
</body>
</html>
<script language="JavaScript">
function preloader()
{
// counter
var i = 0;
// create object
imageObj = new Image();
// set image list
images = new Array();
images[0]="background1.png"
images[1]="background2.png"
images[2]="background3.png"
// start preloading
for(i=0; i<=images.length; i++)
{
var backstring ="background"+i+".png";
images[i].id=backstring;
imageObj.src=images[i];
}
}
function canvasslide()
{
function init()
{
defaultbackground = document.getElementById("defaultbackground");
ctx = defaultbackground.getContext("2d");
for(i=0; i<=images.length; i++){
var backstring ="background"+i+".png";
sprite = document.getElementById(backstring);
ctx.drawImage(sprite,0,0);}
}
}
</script>
sprite.onload = function() {
ctx.drawImage(sprite,0,0);
}
I'm pretty sure your image isn't loaded yet when you draw it on canvas. 我很确定当您在画布上绘制图像时,尚未加载该图像。 Try something like this, I'm not sure this is the right code because I didn't get every part of your code, but you have to use image.onload function before you draw it onto a canvas.
尝试这样的事情,我不确定这是正确的代码,因为我没有得到代码的每个部分,但是在将其绘制到画布上之前必须使用image.onload函数。
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