双指旋转操作的核心

var initHeading = 0;
var rotation = 0;
var lastTime;

function setGesture(el) {
    var obj = {};
    var istouch = false;
    var start = [];
    el.addEventListener("touchstart", function (e) {
        if (e.touches.length >= 2) { //判断是否有两个点在屏幕上
            istouch = true;
            start = e.touches; //得到第一组两个点
            obj.gesturestart && obj.gesturestart.call(el); //执行gesturestart方法
        };
    }, false);
    document.addEventListener("touchmove", function (e) {
        e.preventDefault();
        if (e.touches.length >= 2 && istouch) {
            var now = e.touches; //得到第二组两个点
            var scale = getDistance(now[0], now[1]) / getDistance(start[0], start[1]); //得到缩放比例，getDistance是勾股定理的一个方法
            var rotation = getAngle(now[0], now[1]) - getAngle(start[0], start[1]); //得到旋转角度，getAngle是得到夹角的一个方法
            e.scale = scale.toFixed(2);
            e.rotation = rotation.toFixed(2);
            obj.gesturemove && obj.gesturemove.call(el, e); //执行gesturemove方法
        };
    }, false);
    document.addEventListener("touchend", function (e) {
        if (istouch) {
            istouch = false;
            obj.gestureend && obj.gestureend.call(el); //执行gestureend方法
        };
    }, false);
    return obj;
};

function getDistance(p1, p2) {
    var x = p2.pageX - p1.pageX,
        y = p2.pageY - p1.pageY;
    return Math.sqrt((x * x) + (y * y));
};

function getAngle(p1, p2) {
    var x = p1.pageX - p2.pageX,
        y = p1.pageY - p2.pageY;
    return Math.atan2(y, x) * 180 / Math.PI;
};

var box = document.querySelector("#map3d");
var boxGesture = setGesture(box); //得到一个对象

boxGesture.gesturestart = function () { //双指开始
    /*box.style.backgroundColor="yellow";*/
    initHeading = map25D._coreMap.map.position.heading;
};

boxGesture.gesturemove = function (e) { //双指移动
    rotation = parseInt(e.rotation);
    var time = new Date().getTime();
    var realRotation = changeAngle(rotation, time);
    if (realRotation) {
        //TODO 得到旋转角度后想实现的功能
        map25D._coreMap.map.position.setHeading(realRotation);
        map25D._coreMap.map.renderer.update();
    }
};

boxGesture.gestureend = function () { //双指结束

};

//通过时间判断解决叠加初始方向
var changeAngle = function (heading, newTime) {
    if ((newTime - lastTime) < 2) {
        return false;
    }
    lastTime = newTime;
    return (initHeading + heading)
}

标签：function,双指,obj,核心,旋转,start,p2,var,rotation
来源： https://www.cnblogs.com/ezhar/p/14746365.html