Canvas作图

2018-06-24 01:30:28来源：未知阅读 ()

　　前几天项目GIS部分一个功能模块需要一个控制仪表盘，虽然之前看过canvas作图，但是没怎么具体用过。今天就这个功能模块研究了下canvas。

什么是 Canvas？

　　canvas 元素用于在网页上绘制图形。<canvas> 元素本身并没有绘制能力（它仅仅是图形的容器），必须使用脚本来完成实际的绘图任务，通常是用JavaScript在网页上绘制图像。canvas所在画布是一个矩形区域，我们可以控制画布的每一像素。canvas 拥有多种绘制路径、矩形、圆形、字符以及添加图像的方法。一句话说完，功能很强大，需要研究的东西很多！

创建 Canvas 元素

　　在 HTML5 页面添加 canvas 元素。规定元素的 id、和宽高：

<body>
　　<canvas id="canvas" width="400" height="400"></canvas>
</body>

　　Canvas 对象表示一个 HTML 画布元素 - <canvas>。它没有自己的行为，但是定义了一个很多API 支持脚本化客户端绘图操作。

Canvas 对象的属性

　　height 属性

　　　　画布的高度。和一幅图像一样，这个属性可以指定为一个整数像素值或者是窗口高度的百分比。当这个值改变的时候，在该画布上已经完成的任何绘图都会擦除掉。默认值是 300。

　　width 属性

　　　　画布的宽度。和一幅图像一样，这个属性可以指定为一个整数像素值或者是窗口宽度的百分比。当这个值改变的时候，在该画布上已经完成的任何绘图都会擦除掉。默认值是 300。

具体的实验代码如下，效果可直接执行代码测试：所有的注释都写在了代码里面，故不另行做注释

<!DOCTYPE html>
<html>
<head>
    <meta http-equiv="content-type" content="text/html; charset=utf-8"/>
    <style type="text/css">
        canvas {
            border: 1px solid red;
            background-color: #fff;
            cursor: pointer;
        }

        input {
            position: absolute;
            font-size: 20px;
            color: #f8b500;
            top: 18%;
            left: 9%;
            width: 100px;
            height: 30px;
            line-height: 28px;
            text-align: center;
        }
    </style>
</head>
<body>
<body>
<canvas id="canvas" width="400" height="400"></canvas>
<input id="canvasText" value="">
<script>
    var canvasDrawing = {
        /**绘图对象初始化
         * 参数：type 初始化类型。arc：圆弧形；bar ：柱状图
         */
        init: function (type) {
            this.canvas = document.getElementById("canvas");    //获取用于canvas作图的对象
            this.canvasEnv = this.canvas.getContext("2d");    //getContext()返回一个用于在画布上绘图的环境。当前唯一的合法参数值是 "2d"，它指定了二维绘图。
            this.pathr = 120;  //滑动路径半径
            if(type === "arc"){
                this.event();       //事件绑定初始化
                this.canvasDrawing.prototype = this; //canvasDrawing方法继承父元素内方法
                this.ex = new this.canvasDrawing(type, 200, 200, 120);  //初始化创建实例，默认画弧形图
            }else {
                this.arr=[60, 90, 150, 130, 170, 190, 125, 175, 155, 165, 155, 145];
                this.ex = new this.canvasDrawing(type, 70, 280, 330, 280);  //初始化创建实例，根据type类型canvas作图；此处为柱状图
            }
        },
        /**事件绑定
         */
        event: function () {
            this.canvas.addEventListener("mousedown", this.onMouseDown.bind(this), false);
            this.canvas.addEventListener("mousemove", this.onMouseMove.bind(this), false);
            this.canvas.addEventListener("mouseup", this.onMouseUp.bind(this), false);
        },
        /**绘制图形
         * 参数：type绘图类型；x,y圆心位置；r内圆弧半径；j可变圆弧结束位置,bgc圆弧颜色
         */
        canvasDrawing: function (type, x, y, r, j, bgc) {
            if (type === "arc") {
                this.canvasEnv.clearRect(0, 0, 400, 400);
                this.x = x;
                this.y = y;
                this.r = r;
                this.j = j || 0.85 * Math.PI;

                this.canvasEnv.beginPath();
                this.canvasEnv.lineWidth = 3;
                this.canvasEnv.arc(this.x, this.y, this.r + 15, Math.PI * 0.85, Math.PI * 0.15, false); // 绘制外层单弧线
                this.canvasEnv.strokeStyle = '#f8b500';
                this.canvasEnv.stroke();

                this.canvasEnv.beginPath();
                this.canvasEnv.arc(this.x, this.y, this.r, Math.PI * 0.85, this.j, false); // 可变条状圆弧
                this.innerText = ((((this.j / Math.PI) - 0.85) * 100) / 1.3).toFixed(0);
                this.innerText = (this.innerText === "-0") ? (0) : (this.innerText);
                document.getElementById("canvasText").value = this.innerText;
                this.canvasEnv.strokeStyle = (bgc == undefined) ? (this.colorChoose(this.innerText)) : (bgc);
                this.canvasEnv.lineCap = "butt";
                this.canvasEnv.lineWidth = 20;
                this.canvasEnv.stroke();
            } else {        //绘制柱状图
                this.sX = x;
                this.sY = y;
                this.eX = r;
                this.eY = j;
                this.canvasEnv.beginPath();
                this.canvasEnv.moveTo(this.sX, this.sY);
                this.canvasEnv.lineTo(this.eX, this.eY);
                this.canvasEnv.stroke();
                for (var i = 0; i < 12; i++) {
                    var width = 10;
                    var height = this.arr[i];
                    var X = 85 + i * 20;
                    var Y = 280 - height;
                    this.canvasEnv.beginPath();
                    this.canvasEnv.fillStyle = "#900b09";
                    this.canvasEnv.rect(X, Y, width, height);   //rect()：创建矩形
                    this.canvasEnv.fill();
                    this.canvasEnv.closePath()
                }
            }
        },
        /**确定按下鼠标位置
         */
        onMouseDown: function (event) {
            var X = this.getX(event);   //获取鼠标左键按下所在的X坐标
            var Y = this.getY(event);   //获取鼠标左键按下所在的Y坐标
            var minX = this.ex.x - 2 * this.ex.r, msXX = this.ex.x + 2 * this.ex.r;     //鼠标按下横向区间
            var minY = this.ex.y - 2 * this.ex.r, msXY = this.ex.y + 2 * this.ex.r;     //鼠标按下纵向区间
            if ((minX < X && X < msXX) && (minY < Y && Y < msXY)) {   //判断鼠标是否在可允许区间
                this.ex.isDown = true;
            } else {
                this.ex.isDown = false;
            }
        },
        /**鼠标释放
         */
        onMouseUp: function () {
            this.ex.isDown = false
        },
        /**鼠标移动
         */
        onMouseMove: function (event) {
            if (this.ex.isDown) {
                var coordinate = {
                    "x": this.getX(event),
                    "y": this.getY(event)
                };
                var quadrantDoordinate = this.coordTransform(coordinate);
                if (this.check(quadrantDoordinate.x, quadrantDoordinate.y)) {
                    var co = this.getMoveto(quadrantDoordinate.x, quadrantDoordinate.y);
                    if (co == null) return;
                    this.ex.canvasDrawing("arc", this.ex.x, this.ex.y, this.ex.r, co.z);
                }
            }
        },
        /**canvas内坐标转换为圆形图内坐标
         */
        coordTransform: function (coordinates) {
            var target = new Object();      //象限按照数学顺时针划分
            if (coordinates.x > this.ex.x && coordinates.y > this.ex.y) {           //第一象限
                target.x = -(this.ex.x - coordinates.x);
                target.y = this.ex.y - coordinates.y;
            } else if (coordinates.x > this.ex.x && coordinates.y < this.ex.y) {      //第二象限
                target.x = -(this.ex.x - coordinates.x);
                target.y = this.ex.y - coordinates.y;
            } else if (coordinates.x < this.ex.x && coordinates.y < this.ex.y) {       //第三象限
                target.x = -(this.ex.x - coordinates.x);
                target.y = this.ex.y - coordinates.y;
            } else if (coordinates.x < this.ex.x && coordinates.y > this.ex.y) {       //第四象限
                target.x = -(this.ex.x - coordinates.x);
                target.y = this.ex.y - coordinates.y;
            }
            return target;
        },
        /**限制鼠标可拖动范围
         */
        check: function (x, y) {
            var xx = x * x;
            var yy = y * y;
            var minArea = (this.ex.x - this.ex.r) * (this.ex.x - this.ex.r);    //可滑动最小区域
            var msXArea = (this.ex.x - this.ex.r / 4) * (this.ex.x - this.ex.r / 4);  //可滑动最大区域
            if (xx + yy > minArea && xx + yy < msXArea) {
                return true;
            } else {
                return false;
            }
        },
        getMoveto: function (x, y) {
            if (!this.ex.isDown) {
                return null;
            }
            var temp = new Object();
            temp.o = Math.atan(y / x); //鼠标移动点圆形角
            temp.x = this.pathr * Math.cos(temp.o);
            temp.y = this.pathr * Math.sin(temp.o);
            if (y < -60) { //坐标点处理；这里判断没处理好，坐标判定有些问题，鼠标滑动到-60上下，容易将最下面一段圆弧也画出来
                return null;
            }
            if (x > 0) {  //弧度值计算
                temp.z = -Math.atan(temp.y / temp.x) + Math.PI * 2;
            } else {
                temp.z = -Math.atan(temp.y / temp.x) + Math.PI;
            }
            if (temp.z > 6.77) {  //条状圆弧最大值(右下角位置)
                temp.z = 6.77;
                temp.x = this.pathr * Math.cos(Math.PI * 2.05);
                temp.y = -this.pathr * Math.sin(Math.PI * 2.05);
            } else if (temp.z < 2.67) { //条状圆弧最小值(左下角位置)
                temp.z = 2.67;
                temp.x = -this.pathr * Math.cos(Math.PI * 0.85);
                temp.y = -this.pathr * Math.sin(Math.PI * 0.85);
            }
            return temp;
        },
        /**获取鼠标在canvas内坐标x
         */
        getX: function (event) {
            return event.clientX - this.canvas.getBoundingClientRect().left;
        },
        /**获取鼠标在canvas内坐标y
         */
        getY: function (event) {
            return event.clientY - this.canvas.getBoundingClientRect().top;
        },
        /**根据数值进行颜色的变换
         */
        colorChoose: function (val) {
            var color = null;
            var marginLeftSet = document.getElementById("canvasText");
            if (val > 90) {
                color = "#FFD800";
            } else if (val > 75) {
                color = "#BF9900";
            } else if (val > 60) {
                color = "#997C00";
            } else if (val > 45) {
                color = "#725B00";
            } else if (val > 30) {
                color = "#4C3B00";
            } else if (val > 15) {
                color = "#261D00";
            } else {
                color = "#000000";
            }
            if (val == 100) {
                marginLeftSet.style.marginLeft = "-10px";
            } else if (val < 10) {
                marginLeftSet.style.marginLeft = "-30px";
            } else {
                marginLeftSet.style.marginLeft = "-20px";
            }
            return color;
        }
    };
    canvasDrawing.init("arc");
    /**给文本框绑定事件；同时回车更改圆弧形状
     */
    document.getElementById("canvasText").addEventListener("keydown", function (event) {
        var keyCode = window.event ? event.keyCode : event.which;
        var value = document.getElementById("canvasText").value;
        if (keyCode == 13 && (value != undefined && value != null)) {
            if (parseInt(value) <= 0) {
                value = 0;
            } else if (parseInt(value) >= 100) {
                value = 100;
            }
            canvasDrawing.canvasDrawing("arc", 200, 200, 120, ((1.3 * parseInt(value)) / 100 + 0.85) * Math.PI, canvasDrawing.colorChoose(value));
        }
    }, false);
</script>
</body>
</html>