Pointer Event Api-整合鼠标事件、触摸和触控笔事件

Pointer Events API 是Hmtl5的事件规范之一，它主要目的是用来将鼠标（Mouse）、触摸（touch)和触控笔（pen）三种事件整合为统一的API。

Pointer Event

Pointer指可以在屏幕上反馈一个指定坐标的输入设备。Pointer Event事件和Touch Event API对应的触摸事件类似，它继承扩展了Touch Event,因此拥有Touch Event的常用属性。Pointer属性如下图：

说明：

pointerId:代表每一个独立的Pointer。根据id，我们可以很轻松的实现多点触控应用。

width/height:Mouse Event在屏幕上只能覆盖一个点的位置，但是一个Pointer可能覆盖一个更大的区域。

isPrimary:当有多个Pointer被检测到的时候（比如多点触摸），对每一种类型的Pointer会存在一个Primary Poiter。只有Primary Poiter会产生与之对应的Mouse Event。

Pointer Event API核心事件：

Mouse events, pointer events和touch events 对照表

Pointer API 的好处

Poiter API 整合了鼠标、触摸和触控笔的输入，使得我们无需对各种类型的事件区分对待。

目前不论是web还是本地应用都被设计成跨终端（手机，平板，PC）应用，鼠标多数应用在桌面应用，触摸则出现在各种设备上。过去开发人员必须针对不同的输入设备写不同的代码，或者写一个polyfill 来封装不同的逻辑。Pointer Events 改变了这种状况。

Pointer API实例

使用canvas画布来展示追踪一个pointer移动轨迹:

<canvas id="mycanvas" width="400px" height="500px" style="border: 1px solid #000"></canvas>

<script type="text/javascript">

var DrawFigure = (function(){

    function DrawFigure(canvas,options) {

        var _this = this;

        this.canvas = canvas;

        this._ctx = this.canvas.getContext('2d');

        this.lastPt = null;

        if(options === void 0) {

            options = {};

        }

        this.options = options;

        this._handleMouseDown = function(event) {

            _this._mouseButtonDown = true;

        }

        this._handleMouseMove = function(event) {

            if(_this._mouseButtonDown) {

                var event = window.event || event;

                if(_this.lastPt !== null) {

                    _this._ctx.beginPath();

                    _this._ctx.moveTo(_this.lastPt.x,_this.lastPt.y);

                    _this._ctx.lineTo(event.pageX,event.pageY);

                    _this._ctx.strokeStyle = _this.options.strokeStyle || 'green';

                    _this._ctx.lineWidth = _this.options.lineWidth || 3;

                    _this._ctx.stroke();

                }

                _this.lastPt = {

                    x: event.pageX,

                    y: event.pageY

                }

            }

        }

        this._handleMouseUp = function(event) {

            _this._mouseButtonDown = false;

            _this.canvas.removeEventListener('pointermove',_this.__handleMouseMove,false);

            _this.canvas.removeEventListener('mousemove',_this.__handleMouseMove,false);

            _this.lastPt = null;

            console.log('移除事件');

        }

        DrawFigure.prototype.init = function() {

            this._mouseButtonDown = false;

            if(window.PointerEvent) {

                this.canvas.addEventListener('pointerdown',this._handleMouseDown,false);

                this.canvas.addEventListener('pointermove',this._handleMouseMove,false);

                this.canvas.addEventListener('pointerup',this._handleMouseUp,false);

            } else {

                this.canvas.addEventListener('mousedownn',this._handleMouseDown,false);

                this.canvas.addEventListener('mousemove',this._handleMouseMove,false);

                this.canvas.addEventListener('mouseup',this._handleMouseUp,false);

            }

        }

    }

    return DrawFigure;

}());

window.onload = function() {

    var canvas = document.getElementById('mycanvas');

    var drawFigure = new DrawFigure(canvas);

    drawFigure.init();

}

</script>

结果如图所示：

多点触控实例

首先初始一个多个颜色的数组，用来追踪不同的pointer。

var colours = ['red', 'green', 'blue', 'yellow','black'];

画线的时候通过pointer的id来取色。

 multitouchctx.strokeStyle = colours[id%5];

 multitouchctx.lineWidth = 3;

在这个demo中，我们要追踪每一个pointer，所以需要分别保存每一个pointer的相关坐标点。这里我们使用关联数组来存储数据，每个数据使用pointerId做key，我们使用一个Object对象作为关联数组，用如下方法添加数据：

// This will be our associative array

var multiLastPt=new Object();

...

// Get the id of the pointer associated with the event

var id = e.pointerId;

...

// Store coords

multiLastPt[id] = {x:e.pageX, y:e.pageY};

完整代码：

<!DOCTYPE html>

<html>

<head>

<title>test</title>

<meta charset="utf-8">

<meta name="viewport" content="width=device-width,initial-scale=1.0,minimum-scale=1.0,maximum-scale=1.0,user-scalable=no" />

<style>

    html,body{

        margin:0;

        padding:0;

        width: 100%;

        height: 100%;

        overflow: hidden;

    }

</style>

</head>

<body ontouchstart="return false;">

<canvas id="mycanvas"></canvas>

<script type="text/javascript">

var DrawFigure = (function(){

    function DrawFigure(canvas,options) {

        var _this = this;

        this.canvas = canvas;

        this.canvas.width = document.documentElement.clientWidth;

        this.canvas.height = document.documentElement.clientHeight;

        this._ctx = this.canvas.getContext('2d');

        this.lastPt = {};

        if(options === void 0) {

            options = {};

        }

        this.options = options;

        this.colours = ['red', 'green', 'blue', 'yellow', 'black']; // 初始一个多个颜色的数组，用来追踪不同的pointer

        this._handleMouseDown = function(event) {

            _this._mouseButtonDown = true;

        }

        this._handleMouseMove = function(event) {

            var id = event.pointerId;

            if(_this._mouseButtonDown) {

                var event = window.event || event;

                if(_this.lastPt[id]) {

                    _this._ctx.beginPath();

                    _this._ctx.moveTo(_this.lastPt[id].x,_this.lastPt[id].y);

                    _this._ctx.lineTo(event.pageX,event.pageY);

                    _this._ctx.strokeStyle = _this.colours[id%5]; // 画线的时候通过pointer的id来取色

                    _this._ctx.lineWidth = _this.options.lineWidth || 3;

                    _this._ctx.stroke();

                }

                _this.lastPt[id] = {

                    x: event.pageX,

                    y: event.pageY

                }

            }

        }

        this._handleMouseUp = function(event) {

            var id = event.pointerId;

            _this._mouseButtonDown = false;

            _this.canvas.removeEventListener('pointermove',_this.__handleMouseMove,false);

            _this.canvas.removeEventListener('mousemove',_this.__handleMouseMove,false);

             delete _this.lastPt[id];

        }

        DrawFigure.prototype.init = function() {

            this._mouseButtonDown = false;

            if(window.PointerEvent) {

                this.canvas.addEventListener('pointerdown',this._handleMouseDown,false);

                this.canvas.addEventListener('pointermove',this._handleMouseMove,false);

                this.canvas.addEventListener('pointerup',this._handleMouseUp,false);

            } else {

                this.canvas.addEventListener('mousedownn',this._handleMouseDown,false);

                this.canvas.addEventListener('mousemove',this._handleMouseMove,false);

                this.canvas.addEventListener('mouseup',this._handleMouseUp,false);

            }

        }

    }

    return DrawFigure;

}());

window.onload = function() {

    var canvas = document.getElementById('mycanvas');

    var drawFigure = new DrawFigure(canvas);

    drawFigure.init();

}

</script>

</body>

</html>

手机效果如图所示：

参考地址：