How to draw arcs and circles with canvas-H5 Tutorial-php.cn

How to draw arcs and circles with canvas

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Release： 2018-03-14 09:47:29

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This time I will show you how to use canvas to draw arcs and circles, and what are the precautions for using canvas to draw arcs and circles. The following is a practical case. Let’s take a look.

The html file is as follows:

<!DOCTYPE html><html lang="en"><head>
    <meta charset="UTF-8"/>
    <title>Canvas绘制弧线和圆</title></head><body><style>
    #canvas{        border: 1px solid #aaa;        text-align: center;
    }</style><canvas id="canvas" width="800" height="800">
    当用户浏览器不支持Canvas,请更换浏览器重试！</canvas></body></html>

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To draw an arc or circle, you need to use the arc method. First, let us understand this method:
context.arc( x,y,r ,sAngle,eAngle,counterclockwise);
This method has 6 parameters:

x: x-axis coordinate of the center of the circle

y: y-axis coordinate of the center of the circle

r: Radius

sAngle: arc starting position

eAngle: arc ending position

counterclockwise: optional parameter, default is false, specifies whether it should be counterclockwise or clockwisedrawing. false = clockwise, true = counterclockwise.
First, let us start drawing an arc. The code is as follows:

var canvas=document.getElementById("canvas");var context=canvas.getContext("2d");
context.lineWidth=5;
context.strokeStyle="blue"context.arc(300,300,200,0,2*Math.PI);
context.stroke();//画一个空心弧线
 context.fillStyle="red"
 context.fill();//收尾直接相连为一个封闭图形，以红色填充该图形

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After drawing an arc, let us try to draw multiple arcs so that they become a circle. Directly enter the code:

window.onload= function () {        var canvas=document.getElementById("canvas");        if(canvas.getContext("2d")){            var context=canvas.getContext("2d");
            context.lineWidth=5;
            context.strokeStyle="red";          
            for(var i=0;i<10;i++){//绘制十个弧线，收尾封闭，没有填充色
                context.beginPath();
                context.arc(50+i*100,60,40,0,2*Math.PI*(i+1)/10);
                context.closePath();//使弧线封闭，形成一个闭合图形
                context.stroke();
            }            for(var i=0;i<10;i++){//绘制十个弧线，收尾不封闭，没有填充色
                context.beginPath();
                context.arc(50+i*100,180,40,0,2*Math.PI*(i+1)/10);
                context.stroke();
            }            for(var i=0;i<10;i++){//绘制十个弧线，收尾封闭且填充为默认色
                context.beginPath();
                context.arc(50+i*100,300,40,0,2*Math.PI*(i+1)/10,true);//逆时针绘制
                context.fill();
            }
        }else {
            alert("不支持canvas,请更换浏览器！")
        }
    };

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How to draw arcs and circles with canvas

I believe you have mastered the method after reading the case in this article. For more exciting information, please pay attention to other related articles on the php Chinese website!