canvas画贝塞尔曲线(bezierCurveTo)

简单描述:页面上有四个点,鼠标拖动四个点的位置来改变贝塞尔曲线的形状,双击放置点位

效果图:
这里写图片描述

这里写图片描述

这里写图片描述

<!DOCTYPE html>
<html lang="en">
    <head>
        <meta charset="UTF-8">
        <title>Title</title>
        <style>
            html{overflow: hidden;}
            * {padding: 0;margin: 0;}
            #box {background-color: #000000;}
            .point {
                width: 20px;
                height: 20px;
                background-color: #fff;
                border-radius: 50%;
                position: absolute;
                left: 100px;
                top:200px;
                text-align: center;
                line-height: 20px;
            }
        </style>
    </head>
    <body>
        <canvas id="box"></canvas>

        <div class="point startPoint">b</div>
        <div class="point endPoint">e</div>
        <div class="point point1">1</div>
        <div class="point point2">2</div>
    <script src="js/max.js"></script>
    </body>
</html>
/**
 * Created by Administrator on 2017/8/11.
 * js/max.js
 */
(function () {
    var curEle = null;
    var startPointView = document.querySelector(".startPoint");
    var endPointPointView = document.querySelector(".endPoint");
    var point1View = document.querySelector(".point1");
    var point2View = document.querySelector(".point2");
    var context = null;
    function init() {
        var canvasEle = document.querySelector("#box");
        canvasEle.width = innerWidth;
        canvasEle.height = innerHeight;
        //实时监听网页大小
        window.onresize = function () {
            canvasEle.width = innerWidth;
            canvasEle.height = innerHeight;
        };
        context = canvasEle.getContext("2d");

        context.strokeStyle = "white";
        context.lineWidth = 10;
        //贝塞尔曲线简单用法
        context.beginPath();
        context.moveTo(300,300);
        context.bezierCurveTo(500,200,600,250,600,600);
        context.stroke();
        //循环获取四个点的数组
        for(var i=0;i<4;i++){
        addEvent([startPointView,endPointPointView,point1View,point2View][i]);
        }
        //鼠标双击移除鼠标滑动事件 放下拖动的点
        document.ondblclick = function () {
            document.removeEventListener("mousemove",move);
        };
    }
    //鼠标按下拖动
    function addEvent(ele) {
        ele.onmousedown = function () {
            curEle = this;
            document.addEventListener("mousemove",move);
        };
    }
    //获取拖动位置并绘制贝塞尔曲线
    function move(event) {
        curEle.style.left = event.pageX+"px";
        curEle.style.top = event.pageY+"px";
        context.clearRect(0,0,innerWidth,innerHeight);
        context.beginPath();
        context.moveTo(getLeft(startPointView),getTop(startPointView));
        context.bezierCurveTo(getLeft(point1View),getTop(point1View),getLeft(point2View),getTop(point2View),getLeft(endPointPointView),getTop(endPointPointView));
        context.stroke();
    }
    function getLeft(ele) {
        return parseInt(ele.style.left);
    }
    function getTop(ele) {
        return parseInt(ele.style.top);
    }
    init();
})();
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