使用canvas画图的步骤:
一:在body中定义画板<canvas></canvas>
二:在css中设置画板样式
三:在js中获取画板对象
四:利用画板对象画图(文本,线,圆,矩形,渐变)
1,画矩形
<head> <style type="text/css"> #juxing { with: 15rem; height: 5rem; border: 0.1rem solid blue; } </style> </head> <body> <canvas id="juxing">1矩形</canvas> <script type="text/javascript"> var ju=document.getElementById("juxing"); var jutx=ju.getContext("2d");//创建 context 对象：getContext("2d") 对象是内建的 HTML5 对象，拥有多种绘制路径、矩形、圆形、字符以及添加图像的方法。 jutx.fillStyle="#CCHH";//设置fillStyle属性可以是CSS颜色，渐变，或图案。fillStyle 默认设置是#000000（黑色）。 jutx.fillRect(50,30,100,50);//fillRect(x,y,width,height) 方法定义了矩形当前的填充方式。 </script> </body>
2,画
<head> <style type="text/css"> #myCanvas { with: 15rem; height: 5rem; border: 0.1rem solid blue; } </style> </head> <body> <canvas id="myCanvas">2圆</canvas> <script> var c=document.getElementById("myCanvas"); var ctx=c.getContext("2d"); ctx.beginPath(); ctx.arc(95,50,40,0,2*Math.PI);//arc(x,y,r,start,stop) ctx.stroke(); </script> </body>
3,画线条
<head> <style type="text/css"> #line{ with: 15rem; height: 5rem; border: 0.1rem solid blue; } </style> </head> <body> <canvas id="line">3线条</canvas> <script type="text/javascript"> var line=document.getElementById("line"); var linetx=line.getContext("2d"); linetx.moveTo(0,0);//moveTo(x,y) 定义线条开始坐标 linetx.lineTo(400,200);//lineTo(x,y) 定义线条结束坐标 linetx.stroke();//定义开始坐标(0,0), 和结束坐标 (400,200). 然后使用 stroke() 方法来绘制线条: </script> </body>
4,画线性渐变
<head> <style type="text/css"> #lineStr{ with: 15rem; height: 5rem; border: 0.1rem solid blue; } </style> </head> <body> <canvas id="lineStr">4线性渐变</canvas> <script type="text/javascript"> var linestr=document.getElementById("lineStr"); var linersTx=linestr.getContext("2d"); //Create gradient var gray=linersTx.createLinearGradient(0,0,200,10);//createLinearGradient(x,y,x1,y1) 创建线条渐变 gray.addColorStop(0,"red");//addColorStop()方法指定颜色停止,参数使用坐标来描述，可以是0至1. gray.addColorStop(1,"black"); // Fill with gradient linersTx.fillStyle=gray; linersTx.fillRect(10,10,200,100); </script> </body>
5,画景象/圆渐变
<head> <style type="text/css"> #radiaStr{ with: 15rem; height: 5rem; border: 0.1rem solid blue; } </style> </head> <body> <canvas id="radiaStr">5景象/圆渐变</canvas> <script type="text/javascript"> var c1=document.getElementById("radiaStr"); var ctx1=c1.getContext("2d"); // Create gradient var grd1=ctx1.createRadialGradient(75,50,5,90,60,100); grd1.addColorStop(0,"red"); grd1.addColorStop(1,"white"); // Fill with gradient ctx1.fillStyle=grd1; ctx1.fillRect(10,10,150,80); </script> </body>
6,显示图片
<head> <style type="text/css"> #imgc{ with: 15rem; height: 5rem; border: 0.1rem solid blue; } </style> </head> <body> <canvas id="imgc">6图片</canvas> <img src="../imags/jiazai.png" id="userimg"/> <script type="text/javascript"> var ic=document.getElementById("imgc"); var icT=ic.getContext("2d");//把一幅图像放置到画布上, 使用以下方法:drawImage(image,x,y) var img=document.getElementById("userimg"); icT.drawImage(img,30,20);//drawImage(image,x,y) </script> </body>
7,文本
<head> <style type="text/css"> #fontT{ with: 15rem; height: 5rem; border: 0.1rem solid blue; } </style> </head> <body> <canvas id="fontT">7文本</canvas> <script type="text/javascript"> var cF=document.getElementById("fontT"); var cFT=cF.getContext("2d"); cFT.font="5rem Arial";//font 定义字体ctx.font="30px Arial"; cFT.fillText("Natalie",30,100);//fillText(text,x,y) - 在 canvas 上绘制实心的文本 cFT.strokeText("Natalie",20,80);//strokeText(text,x,y) - 在 canvas 上绘制空心的文本 </script> </body>