Canvas作图

2018-02-10 13:07:20来源:cnblogs.com作者:西岭千秋雪人点击

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  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>

效果图如下:(中间显示值表示当前弧形占比。值为0~100)

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