Html5中canvas的一些使用

   最近在研究HTML5，发现其中的canvas用途很广。不但可以绘制图形，还可以制作图片线性渐变，而且还能渲染文字做成特效。觉得挺有趣，于是把学习的内容记录起来了。

     1.绘制圆形图

  Html代码：   
                  
                      

   js代码：     var canvas = document.getElementById("roundness");
                    var context = canvas.getContext("2d");
                    context.strokeStyle = "aqua";//圆形的颜色
                    context.lineWidth = "2";
                    context.beginPath();
                   context.arc(100,100,40,0,2*Math.PI);  //40此值设置圆形的大小

                   context.stroke();

效果如下图：

 2.绘制五角星

 Html代码： 
                             
                      

 js代码：      var canvas = document.getElementById("canvasFive");
                    var context = canvas.getContext("2d");
                    context.beginPath();
                    //设置是个顶点的坐标，根据顶点制定路径
                    for (var i = 0; i < 5; i++) {
                   context.lineTo(Math.cos((18+i*72)/180*Math.PI)*50+200,
                         -Math.sin((18+i*72)/180*Math.PI)*50+200);
                  context.lineTo(Math.cos((54+i*72)/180*Math.PI)*20+200,
                         -Math.sin((54+i*72)/180*Math.PI)*20+200);
                   }
             context.closePath();
             //设置边框样式以及填充颜色
            context.lineWidth="3";
            context.fillStyle = "red";
            context.strokeStyle = "wheat";
            context.fill();
            context.stroke();

 效果如下图：

3.绘制矩形

Html代码： 
                          
                   

js代码：     

                 var canvas = document.getElementById("canvasFour");
                 var context = canvas.getContext("2d");

               context.rect(10,10,150,150);
               context.lineWidth = 2;
              context.fillStyle = "cyan"; //设置填充颜色
               context.strokeStyle = "#F5270B";  //边框颜色
              context.fill();
               context.stroke();

效果如下图：

4.制作图片颜色线性渐变

  Html代码：    
               
                         

   js代码：        var canvas = document.getElementById("line");
                        var context = canvas.getContext("2d");
                        var grd = context.createLinearGradient( 50 , 250, 500 , 800 );
                       grd.addColorStop(0,"white");   //设置颜色
                       grd.addColorStop(0.25,"blue");  //设置颜色
                       grd.addColorStop(0.5,"yellow"); //设置颜色
                       grd.addColorStop(0.75,"purple"); //设置颜色
                       grd.addColorStop(1,"black");
                       context.fillStyle = grd;
                      context.fillRect(50,250,500,800);      

效果如下图：

 5.画一条直线，长度可选。

 Html代码： 
                        
                    

  js代码：

                 var canvas = document.getElementById("canvas");
                 var context = canvas.getContext("2d");
                 context.beginPath();
                 context.moveTo(100,100);
                context.lineTo(600,100);

                context.lineWidth = 2;
                context.strokeStyle = "#F5270B";
                context.stroke();

效果如下图：