html5 canvas结构基础

<!DOCTYPE html PUBLIC "-//W3C//DTD XHTML 1.0 Transitional//EN" "http://www.w3.org/TR/xhtml1/DTD/xhtml1-transitional.dtd">
<html xmlns="http://www.w3.org/1999/xhtml">
<head>
<meta http-equiv="Content-Type" content="text/html; charset=utf-8" />
<title>小白童鞋的canvas之基本配置篇</title>
<script src="js/modernizr.js"></script>
</head>
 
<body>
<script type="text/javascript">
window.addEventListener('load',eventWindowLoaded,false);
function eventWindowLoaded(){
    canvasApp();
}
function canvasSupport(){
    return Modernizr.canvas;
}
function canvasApp(){
    if(!canvasSupport()){
        return;
    }else{
        var theCanvas = document.getElementById('canvas')
        var context = theCanvas.getContext("2d")
 
    }
    drawScreen();
        function drawScreen(){
      context.fillStyle="#ff0000";
      context.fillRect(0,0,400,400);
      context.fillStyle="#000000";
      context.font="20px _sans";
      context.textBaseline="top";
      context.fillText("如有疑问加QQ：1035417613;小白童鞋",0,0);
        }
}
 
 
</script>
<canvas id="canvas" width="500" height="500">
你的浏览器无法使用canvas
如有疑问加QQ：1035417613;小白童鞋；你的支持是我最大的快乐！！
</canvas>
</body>
</html>

https://files.cnblogs.com/files/LoveOrHate/canvas1-1.rar（DEMO下载）

window.addEventListener('load',eventWindowLoaded,false);

脚本执行的过程中需要第一个监听load对象

在html页面加载结束时发生

事件load

事件处理器函数eventWindowLoaded

1	`theCanvas.getContext("2d"）获取2d上下文`

modernizr.js是个不错的东西可以检测支持情况<br>我是在这里下的（吐槽一下链接有点长）<br

>modernizr.com/download/#-fontface-backgroundsize-borderimage-borderradius-boxshadow-flexbox-hsla-multiplebgs-opacity-rgba-textshadow-cssanimations-csscolumns-generatedcontent-cssgradients-cssreflections-csstransforms-csstransforms3d-csstransitions-applicationcache-canvas-canvastext-draganddrop-hashchange-history-audio-video-indexeddb-input-inputtypes-localstorage-postmessage-sessionstorage-websockets-websqldatabase-webworkers-geolocation-inlinesvg-smil-svg-svgclippaths-touch-webgl-shiv-cssclasses-addtest-prefixed-teststyles-testprop-testallprops-hasevent-prefixes-domprefixes-load