JS canvas标签动态绘制图型

时间：2023-03-08 20:17:10
JS canvas标签动态绘制图型

使用canvas标签动态绘制图型，当点击鼠标时，以鼠标点击的坐标作为图形中心点。当点击数为偶数时画三角形，当点击数为奇数时画五角星

<!DOCTYPE HTML>

<html>

<head>

    <meta http-equiv="Content-Type" content="text/html; charset=utf-8">

    <title></title>

    <style type="text/css"></style>

    <script type="text/javascript">

        var g=0;

        function getStyles(obj) {

            return document.defaultView.getComputedStyle(obj);

        }

        function getCanvasPos(canvas,e)  {  //获取鼠标在canvas上的坐标

            var rect = canvas.getBoundingClientRect();

            var leftB = parseInt(getStyles(canvas).borderLeftWidth);//获取的是样式，需要转换为数值

            var topB = parseInt(getStyles(canvas).borderTopWidth);

            return {

                 x: (e.clientX - rect.left) - leftB,

                 y: (e.clientY - rect.top) - topB

               };

        }

        function drawStar(context, r, R, x, y) {   // 画五角星

            context.beginPath();

            for(var i=0;i<5;i++){

                context.lineTo(Math.cos((18+i*75)/180*Math.PI)*R+x,-Math.sin((18+i*75)/180*Math.PI)*R+y);

                context.lineTo(Math.cos((54+i*75)/180*Math.PI)*r+x,-Math.sin((54+i*75)/180*Math.PI)*r+y);

            }

            context.closePath();

            context.stroke();

            context.fill();

        }

        function drawsan(context,r,x,y){  // 画三角形

            context.beginPath();

            context.moveTo(x,y-r);

            context.lineTo(Math.cos( 320/180*Math.PI )*r+x,Math.sin(40/180*Math.PI )*r+y);

            context.lineTo(Math.cos( 210/180*Math.PI )*r+x,Math.sin(40/180*Math.PI )*r+y);

            context.closePath();

            context.stroke();

            context.fill();

        }

           function draw(e) {

            g++;

            var mycanvas=document.getElementById('mycanvas');

            var context=mycanvas.getContext('2d');

            context.clearRect(0,0,mycanvas.width,mycanvas.height);

            context.strokeStyle="powderblue";

            context.fillStyle="powderblue";

            if(g%2==0){

                drawsan(context, 30, getCanvasPos(mycanvas,e).x, getCanvasPos(mycanvas,e).y);

            }

            else{

                drawStar(context,25,50,getCanvasPos(mycanvas,e).x,getCanvasPos(mycanvas,e).y);

            }

        }

    </script>

</head>

<body>

    <div onmousedown="draw(event)">

        <canvas width="600px" height="400px" style="border: 1px solid black;" id="mycanvas"></canvas>

    </div>

</body>

</html>

相关文章