canvas怎么在html5 中使用
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这期内容当中小编将会给大家带来有关canvas怎么在html5 中使用，文章内容丰富且以专业的角度为大家分析和叙述，阅读完这篇文章希望大家可以有所收获。
<!DOCTYPE HTML><html><head> <meta charset="UTF-8"> <title>HTML5示例</title> <style type="text/css"> #container{border:1px solid #ccc;width:800px;height:600px;position:relative;} canvas{position:absolute;top:0px;left:0px;z-index:1;} </style></head><body> <select id="tools"> <option value="pen">铅笔</option> <option value="line">直线</option> <option value="rect">矩形</option> <option value="circle">圆形</option> <option value="ellipse">椭圆</option> </select> <div id="container"> <canvas id="canvas" width="800" height="600"></canvas> <canvas id="canvas_temp" width="800" height="600"></canvas> </div> <script type="text/javascript"> var canvas = document.getElementById('canvas'); var context = canvas.getContext('2d'); var _canvas = document.getElementById('canvas_temp'); var _context = _canvas.getContext('2d'); var tools= document.getElementById('tools'); tools.onchange = function (e){ tool[this.value](); }; var tool = { pen:function (){ this.reset(); _canvas.onmousedown=function (e){ _context.moveTo(e.layerX,e.layerY); _canvas.onmousemove=function (e){ _context.lineTo(e.layerX,e.layerY); _context.stroke(); }; _canvas.onmouseup=function (e){ _canvas.onmousemove=null; _canvas.onmouseup=null; tool.updata(); }; }; }, line:function (){ this.reset(); _canvas.onmousedown=function (e){ var _e = e; _canvas.onmousemove=function (e){ _context.clearRect(0,0,canvas.width,canvas.height); _context.beginPath(); _context.moveTo(_e.layerX,_e.layerY); _context.lineTo(e.layerX,e.layerY); _context.stroke(); _context.closePath(); }; _canvas.onmouseup=function (e){ _canvas.onmousemove=null; _canvas.onmouseup=null; tool.updata(); }; } }, rect:function (){ this.reset(); _canvas.onmousedown=function (e){ var _e = e; _context.strokeStyle="#000"; _canvas.onmousemove=function (e){ _context.clearRect(0,0,canvas.width,canvas.height); _context.strokeRect(_e.layerX,_e.layerY,e.layerX-_e.layerX,e.layerY-_e.layerY); }; _canvas.onmouseup=function (e){ _canvas.onmousemove=null; _canvas.onmouseup=null; tool.updata(); }; } }, circle:function (){ this.reset(); _canvas.onmousedown=function (e){ var _e = e; _canvas.onmousemove=function (e){ _context.clearRect(0,0,canvas.width,canvas.height); _context.beginPath(); _context.arc(_e.layerX,_e.layerY,e.layerX-_e.layerX,0,Math.PI*2,true); _context.stroke(); _context.closePath(); }; _canvas.onmouseup=function (e){ _canvas.onmousemove=null; _canvas.onmouseup=null; tool.updata(); }; } }, ellipse:function (){ this.reset(); _canvas.onmousedown=function (e){ var _e = e; _canvas.onmousemove=function (e){ var st=0; _context.clearRect(0,0,canvas.width,canvas.height); _context.beginPath(); _context.moveTo(_e.layerX+(e.layerX-_e.layerX)*Math.cos(st), _e.layerY+(e.layerX-_e.layerX)*Math.sin(st)); st+=1/180*Math.PI; for(var i=0;i<360;i++){ _context.lineTo(_e.layerX+(e.layerX-_e.layerX)*Math.cos(st),_e.layerY+(e.layerY-_e.layerY)*Math.sin(st)); st+=1/180*Math.PI; } _context.stroke(); _context.closePath(); }; _canvas.onmouseup=function (e){ _canvas.onmousemove=null; _canvas.onmouseup=null; tool.updata(); }; } }, reset:function (){ _canvas.onmousedown=null; _canvas.onmouseup=null; _canvas.onmousemove=null; }, updata:function (){ context.drawImage(_canvas, 0, 0); _context.clearRect(0, 0, canvas.width, canvas.height); } }; tool['pen'](); </script></body></html>上述就是小编为大家分享的canvas怎么在html5 中使用了，如果刚好有类似的疑惑，不妨参照上述分析进行理解。如果想知道更多相关知识，欢迎关注编程网行业资讯频道。
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