JS + Canvas画图Demo

直接上代码，复制粘贴就能用：

HTML代码：

<%@ page language="java" contentType="text/html; charset=UTF-8"
    pageEncoding="UTF-8"%>
<!DOCTYPE html>
<html>
<head>
<meta charset="UTF-8">
<title>Insert title here</title>
<script src="Public/jquery.min.js" type="text/javascript"></script>
<style type="text/css">
canvas {
    background:#ccc;
    display:block;
    margin:0 auto;
}
#controls {
    width:200px;
    height:100%;
    position:absolute;
    left:0;
    top:0;
    background:linear-gradient(to bottom,#000000,#b8b8b8);
    user-select:none;
}
#controls section {
    margin-top:10px;
    height:20px;
}
#controls .label {
    width:50%;
    height:20px;
    line-height:20px;
    text-align:center;
    color:#FFF;
    display:block;
    float:left;
}
#xing {
    float:right;
    width:50%;
    height:20px;
}
/*#shape {
    */
        /*50%;
    height:20px;
    display:block;
    */
        /*
}
*/
#controls .color {
    width:50%;
    height:auto;
    float:right;
}
#colors input {
    float:right;
    width:48%;
    height:20px;
    border:none;
}
#widths input {
    float:right;
    width:49%;
    height:20px;
    border:none;
}
#style {
    float:right;
    width:49%;
    height:20px;
    border:none;
}
input[type=button] {
    width:150px;
    height:30px;
    background:#C40000;
    color:#FFF;
    border-radius:5px;
    margin-top:10px;
    margin-left:10px;
    border:none;
    display:block;
}
</style>
</head>
<body>
    <canvas width="500" height="500"></canvas>
<div id="controls">
    <section id="shape">
        <label for="shape" class="label">选择形状 : </label>
        <select id="xing">
            <option value="rect">矩形</option>
            <option value="line">直线</option>
            <option value="circle">内切圆</option>
            <option value="circle1">外接圆</option>
            <option value="circle2">中心圆</option>
            <option value="poly">多边形</option>
            <option value="pen">铅笔</option>
            <option value="eraser">橡皮</option>
　　　　     <option value="arrow">箭头</option>
        </select>
    </section>
 
    <section id="colors">
        <label for="color" class="label">选择颜色 : </label>
        <input type="color" id="color">
    </section>
    <section id="widths">
        <label for="color" class="label">选择线宽 : </label>
        <input type="number" id="width" value="2" step="2" min="2" max="20">
    </section>
    <section id="styles">
        <label for="shape" class="label">选择方式 : </label>
        <select id="style">
            <option value="stroke">描边</option>
            <option value="fill">填充</option>
        </select>
    </section>
    <section id="sides">
        <label for="side" class="label">选择边数 : </label>
        <input type="number" id="side" value="3" min="3" max="20">
    </section>
    <input type="button" value="撤销" id="redo">
    <input type="button" value="保存" id="save">
    <input type="button" value="清空" id="qingkong">
</div>
</body>
</html>

JS代码：

var canvas = document.querySelector("canvas");
var cobj = canvas.getContext("2d");
var shape = document.querySelector("#xing");
var color = document.querySelector("#color");
var width = document.querySelector("#width");
var style = document.querySelector("#style");
var side = document.querySelector("#side");
var redo = document.querySelector("#redo");
var save = document.querySelector("#save");
var qingkong = document.querySelector("#qingkong");
console.log(side);
var data = [];
var s = "rect";
shape.onchange = function() {
    s = this.value;
};
var c = "#000";
color.onchange = function() {
    c = this.value;
};
var w = "2";
width.onchange = function() {
    w = this.value;
};
var st = "stroke";
style.onchange = function() {
    st = this.value;
};
var sd = "3";
side.onchange = function() {
    sd = this.value;
};

canvas.onmousedown = function(e) {
    var ox = e.offsetX;
    var oy = e.offsetY;
    var draw = new Draw(cobj, {
        color: c,
         w,
        style: st,
        side: sd
    });
    if (s == "pen") {
        cobj.beginPath();
        cobj.moveTo(ox, oy);
    }
    canvas.onmousemove = function(e) {
        var mx = e.offsetX;
        var my = e.offsetY;
        if (s != "eraser") {
            cobj.clearRect(0, 0, 500, 500);
            if (data.length != 0) {
                cobj.putImageData(data[data.length - 1], 0, 0, 0, 0, 500, 500); //将某个图像数据放置到画布指定的位置上  后面四个参数可省略
            }
        }
        // cobj.strokeRect(ox,oy,mx-ox,my-oy);
        // cobj.beginPath()
        draw[s](ox, oy, mx, my, sd);
    };
    document.onmouseup = function() {
        data.push(cobj.getImageData(0, 0, 500, 500)); //获取画布当中指定区域当中所有的图形数据
        canvas.onmousemove = null;
        document.onmouseup = null;
    }
};
redo.onclick = function() {
    if (data.length == 0) {
        alert("无效操作");
        return;
    }
    cobj.clearRect(0, 0, 500, 500);
    data.pop();
    if (data.length == 0) {
        return;
    }
    cobj.putImageData(data[data.length - 1], 0, 0, 0, 0, 500, 500);
};
save.onclick = function() {
    var r = canvas.toDataURL();
    location.assign(r)
};
qingkong.onclick = function() {
    cobj.clearRect(0, 0, 500, 500);
    data = [];
}
class Draw {
    constructor(cobj, option) {
        this.cobj = cobj;
        this.color = option.color;
        this.width = option.width;
        this.style = option.style;
    }
    init() { //初始化
        this.cobj.strokeStyle = this.color;
        this.cobj.fillStyle = this.color;
        this.cobj.lineWidth = this.width;
    }
    rect(ox, oy, mx, my) {
        this.init();
        this.cobj.beginPath();
        this.cobj.rect(ox, oy, mx - ox, my - oy);
        this.cobj[this.style]();
    }
    line(ox, oy, mx, my) {
        this.init();
        this.cobj.beginPath();
        this.cobj.moveTo(ox, oy);
        this.cobj.lineTo(mx, my);
        this.cobj.stroke();
    }
    circle(ox, oy, mx, my) { //内切圆
        this.init();
        this.cobj.beginPath();
        /* var r=Math.sqrt(Math.pow(mx-ox,2)+Math.pow(my-oy,2))/2;
        this.cobj.arc(ox+(mx-ox)/2,oy+(my-oy)/2,r,0,2*Math.PI);*/
        var r = Math.abs(mx - ox) > Math.abs(my - oy) ? Math.abs(my - oy) / 2 : Math.abs(mx - ox) / 2;
        this.cobj.arc(ox + (ox < mx ? r : -r), oy + (oy < my ? r : -r), r, 0, 2 * Math.PI);
        this.cobj[this.style]();
    }
    circle1(ox, oy, mx, my) { //外接圆
        this.init();
        this.cobj.beginPath();
        var r = Math.sqrt(Math.pow(mx - ox, 2) + Math.pow(my - oy, 2)) / 2;
        this.cobj.arc(ox + (mx - ox) / 2, oy + (my - oy) / 2, r, 0, 2 * Math.PI);
        this.cobj[this.style]();
    }
    circle2(ox, oy, mx, my) { //中心圆
        this.init();
        this.cobj.beginPath();
        var r = Math.sqrt(Math.pow(mx - ox, 2) + Math.pow(my - oy, 2));
        this.cobj.arc(ox, oy, r, 0, 2 * Math.PI);
        this.cobj[this.style]();
    }
    poly(ox, oy, mx, my, sd) {
        this.init();
        this.cobj.save();
        cobj.translate(ox, oy);
        this.cobj.rotate(Math.PI / 2);
        var angle = Math.PI / sd;
        var r = Math.sqrt(Math.pow(mx - ox, 2) + Math.pow(my - oy, 2));
        var x = Math.cos(angle) * r;
        var y = Math.sin(angle) * r;
        this.cobj.beginPath();
        this.cobj.moveTo(x, y);
        for (var i = 0; i < sd; i++) {
            this.cobj.lineTo(x, -y);
            this.cobj.rotate(-angle * 2)
        }
        this.cobj[this.style]();
        this.cobj.restore()
    }
    pen(ox, oy, mx, my) {
        this.init();
        this.cobj.lineTo(mx, my);
        this.cobj.stroke();
    }
    eraser(ox, oy, mx, my) {
        this.cobj.clearRect(mx, my, 10, 10);
    }
    arrow(ox, oy, mx, my){//箭头工具
    this.init();
    beginPoint.x = ox;
    beginPoint.y = oy;
    stopPoint.x = mx;
    stopPoint.y = my;
    Plot.arrowCoord(beginPoint, stopPoint);
    Plot.sideCoord();
    Plot.drawArrow();
    }  

}

var beginPoint = {};//画箭头需要的开始坐标
var stopPoint = {};//画箭头需要的结束坐标
var polygonVertex = [];//箭头多边形顶点的坐标
var CONST = {//箭头参数
        edgeLen: 50,
        angle: 25
    };    
    
    //封装的作图箭头工具对象
       var Plot = {
           angle: "",
     
           //在CONST中定义的edgeLen以及angle参数
           //短距离画箭头的时候会出现箭头头部过大，修改：
           dynArrowSize: function() {
               var x = stopPoint.x - beginPoint.x,
                   y = stopPoint.y - beginPoint.y,
                   length = Math.sqrt(Math.pow(x, 2) + Math.pow(y, 2));
               if (length < 250) {
                   CONST.edgeLen = CONST.edgeLen/2;
                   CONST.angle = CONST.angle/2;
               }
               else if(length<500){
                   CONST.edgeLen=CONST.edgeLen*length/500;
                   CONST.angle=CONST.angle*length/500;
               }
               // console.log(length);
           },
     
           //getRadian 返回以起点与X轴之间的夹角角度值
           getRadian: function(beginPoint, stopPoint) {
               Plot.angle = Math.atan2(stopPoint.y - beginPoint.y, stopPoint.x - beginPoint.x) / Math.PI * 180;
               //console.log(Plot.angle);
               paraDef(50,40);
               Plot.dynArrowSize();
           },
     
           ///获得箭头底边两个点
           arrowCoord: function(beginPoint, stopPoint) {
               polygonVertex[0] = beginPoint.x;
               polygonVertex[1] = beginPoint.y;
               polygonVertex[6] = stopPoint.x;
               polygonVertex[7] = stopPoint.y;
               Plot.getRadian(beginPoint, stopPoint);
               polygonVertex[8] = stopPoint.x - CONST.edgeLen * Math.cos(Math.PI / 180 * (Plot.angle + CONST.angle));
               polygonVertex[9] = stopPoint.y - CONST.edgeLen * Math.sin(Math.PI / 180 * (Plot.angle + CONST.angle));
               polygonVertex[4] = stopPoint.x - CONST.edgeLen * Math.cos(Math.PI / 180 * (Plot.angle - CONST.angle));
               polygonVertex[5] = stopPoint.y - CONST.edgeLen * Math.sin(Math.PI / 180 * (Plot.angle - CONST.angle));
           },
     
           //获取另两个底边侧面点
           sideCoord: function() {
               var midpoint = {};
               // midpoint.x = polygonVertex[6] - (CONST.edgeLen * Math.cos(Plot.angle * Math.PI / 180));
               // midpoint.y = polygonVertex[7] - (CONST.edgeLen * Math.sin(Plot.angle * Math.PI / 180));
               midpoint.x=(polygonVertex[4]+polygonVertex[8])/2;
               midpoint.y=(polygonVertex[5]+polygonVertex[9])/2;
               polygonVertex[2] = (polygonVertex[4] + midpoint.x) / 2;
               polygonVertex[3] = (polygonVertex[5] + midpoint.y) / 2;
               polygonVertex[10] = (polygonVertex[8] + midpoint.x) / 2;
               polygonVertex[11] = (polygonVertex[9] + midpoint.y) / 2;
           },
     
           //画箭头
           drawArrow: function() {
               cobj.beginPath();
               cobj.moveTo(polygonVertex[0], polygonVertex[1]);
               cobj.lineTo(polygonVertex[2], polygonVertex[3]);
               cobj.lineTo(polygonVertex[4], polygonVertex[5]);
               cobj.lineTo(polygonVertex[6], polygonVertex[7]);
               cobj.lineTo(polygonVertex[8], polygonVertex[9]);
               cobj.lineTo(polygonVertex[10], polygonVertex[11]);
               // cobj.lineTo(polygonVertex[0], polygonVertex[1]);
               cobj.closePath();
               cobj.fill();
           }
       };    
       
       //自定义参数
       function paraDef(edgeLen, angle) {
           CONST.edgeLen = edgeLen;
           CONST.angle = angle;
       }

效果图：

 原文链接：http://www.jq22.com/webqd1418

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原文地址：https://www.cnblogs.com/qiantao/p/11958740.html