canvas初学半动态画太极图

xwloveyu 2022-01-02 原文

可直接复制粘贴运行

<!DOCTYPE html>
<html xmlns="http://www.w3.org/1999/xhtml">
<head>
    <meta http-equiv="Content-Type" content="text/html; charset=utf-8" />
    <title>canvas</title>
</head>
<body>
    <canvas width="1000" height="1000" id="mycvs">当前浏览器不支持此控件，请更换或更新浏览器</canvas>
    <script type="text/javascript">
        var a = document.getElementById("mycvs");
        var can = a.getContext("2d");
        var beginx = -(1 / 2 * Math.PI);//起始值
        var r = 150;
        var sidex = 1 * (Math.PI / 180);//增加值
        var endx = beginx + 2 * Math.PI;//结束值
        var bendx = beginx + 2 * Math.PI;
        var aendx = beginx + Math.PI;
        var tmx = beginx;//当前值
        var t = 0;
        var rends = function () { 
            if (tmx + sidex >= endx) {
                tmx = beginx;
                t = t + 1;
                endx = endx - Math.PI;
                if (t == 2) {//填充颜色并退出
                    can.save();     
                    arcs(300, 300, r, beginx, aendx, true, "black");
                    arcs(300, 225, 75, beginx, aendx,null,"black");
                    arcs(300, 375, 75, beginx, aendx, true,"white");
                    arcs(300, 375, 20, beginx, bendx, null, "black");
                    arcs(300, 225, 20, beginx, bendx, null, "white");
                    return;
                }
            } else {
                tmx += sidex;
            }
            can.clearRect(0, 0, 1000, 1000);//用clearRect()函数使图像更加清晰 也造成一笔结束后上一笔清除了
            can.lineWidth = 5;
            if (t == 0)
            {            
            can.beginPath();
            can.arc(300, 300, r, beginx, tmx);            
            can.stroke();
            } else if (t == 1) {                
                can.beginPath();
                can.arc(300, 300, r, beginx, bendx);//所以在这里我又重新画了一遍外圆
        
                can.arc(300, 225, 75, beginx, tmx);
                can.arc(300, 375, 75, beginx, tmx, true);                          
                can.stroke();              
            }
            requestAnimationFrame(rends);//这个是动画控制
                
        };

        function arcs(x,y,r,begin,end,f,color) {//圆心(x,y),半径r，起始值begin，结束值end，方向f，填充颜色color
            can.beginPath();
            can.fillStyle = color;
            can.arc(x, y, r, begin, end,f);
            can.fill();
            can.stroke();
        }
        rends();
   </script>
</body>
</html>

这个代码有点冗余，初学者请多多指教谢谢。