我有一个代码，它从 (x,y) 坐标拖动一条线到新鼠标 (x,y) 坐标。这在桌面浏览器中工作正常，但由于某种原因它在移动浏览器中不起作用。我添加了触摸事件监听器，但我想坐标是如何变得不正确的。这是我的代码:

   function getMouse(e) {
     var element = canvas, offsetX = 0, offsetY = 0;
     if (element.offsetParent) {
       do {
         offsetX += element.offsetLeft;
         offsetY += element.offsetTop;
       } while ((element = element.offsetParent));
     }

     mx = (e.pageX - offsetX) - LINE_WIDTH;
     my =( e.pageY - offsetY )- LINE_WIDTH;
   }
   function mouseDown(e){
     getMouse(e);
     clear(fctx);
     var l = lines.length;
     for (var i = l-1; i >= 0; i--) {
       draw(fctx,lines[i]);
       var imageData = fctx.getImageData(mx, my, 1, 1);
       if (imageData.data[3] > 0) {
         selectedObject = lines[i];
         isDrag = true;
         canvas.onmousemove = drag;
         clear(fctx);
       }
     }
   }
   function mouseUp(){
     isDrag = false;
   }
   canvas.onmousedown = mouseDown;
   canvas.onmouseup = mouseUp;
   canvas.addEventListener('touchstart', mouseDown, false);
   canvas.addEventListener('touchend', mouseUp, false);

最佳答案

从触摸事件生成鼠标事件

好的，在这里看到这个问题有一段时间了，没有人提出答案，我会给出一个答案。

与鼠标事件不同的触摸事件涉及与 UI 的许多接触点。为了适应这种情况，触摸事件提供了一组接触点。由于鼠标不能同时在两个地方，两种交互方式真的应该分开处理，以获得最佳的用户体验。 OP，因为您没有询问检测设备是触摸驱动还是鼠标驱动，我已将其留给另一个人询问。

处理两者

鼠标和触摸事件可以共存。在没有一个或另一个的设备上添加鼠标或触摸事件的监听器不是问题。缺少的输入接口(interface)根本不会生成任何事件。这使得为​​您的页面实现透明解决方案变得容易。

这归结为您喜欢哪个接口(interface)，并在其硬件不可用时模拟该接口(interface)。在这种情况下，我将从创建的任何触摸事件中模拟鼠标。

以编程方式创建事件。

该代码使用 MouseEvent 对象来创建和调度事件。它使用简单，事件与真实的鼠标事件无法区分。有关 MouseEvents 的详细说明，请转到 MDN MouseEvent

最基本的。

创建鼠标点击事件并将其分派(dispatch)到文档

  var event = new MouseEvent( "click", {'view': window, 'bubbles': true,'cancelable': true});
  document.dispatchEvent(event);

  document.getElementById("someButton").dispatchEvent(event);

  document.getElementById("someButton").addEventListener(function(event){
        // your code
  ));

function touchEventHandler(event){
    if (event.touches.length > 1){  // Ignor multi touch events
        return;
    }
}

touch = event.changedTouches[0]; // get the position information
if(type === "touchmove"){        
    mouseEventType = "mousemove";   // get the name of the mouse event
                                    // this touch will emulate   
}else
if(type === "touchstart"){  
    mouseEventType = "mousedown";     // mouse event to create
}else
if(type === "touchend"){ 
    mouseEventType = "mouseup";     // ignore mouse up if click only
}

var mouseEvent = new MouseEvent( // create event
    mouseEventType,   // type of event
    {
        'view': event.target.ownerDocument.defaultView,
        'bubbles': true,
        'cancelable': true,
        'screenX':touch.screenX,  // get the touch coords 
        'screenY':touch.screenY,  // and add them to the 
        'clientX':touch.clientX,  // mouse event
        'clientY':touch.clientY,
});
// send it to the same target as the touch event contact point.
touch.target.dispatchEvent(mouseEvent);

//                                _______               _     
//                               |__   __|             | |    
//    _ __ ___   ___  _   _ ___  ___| | ___  _   _  ___| |__  
//   | '_ ` _ \ / _ \| | | / __|/ _ \ |/ _ \| | | |/ __| '_ \ 
//   | | | | | | (_) | |_| \__ \  __/ | (_) | |_| | (__| | | |
//   |_| |_| |_|\___/ \__,_|___/\___|_|\___/ \__,_|\___|_| |_|
//                                                            
//    
// Demonstration of a simple mouse emulation API using touch events.

// Using touch to simulate a mouse.
// Keeping it clean with touchMouse the only pubic reference.
// See Usage instructions at bottom.
var touchMouse = (function(){
    "use strict";
    var timeStart, touchStart, mouseTouch, listeningElement, hypot;


    mouseTouch = {};  // the public object 
    // public properties.
    mouseTouch.clickRadius = 3; // if touch start and end within 3 pixels then may be a click
    mouseTouch.clickTime = 200; // if touch start and end in under this time in ms then may be a click
    mouseTouch.generateClick = true; // if true simulates onClick event
                                     // if false only generate mousedown, mousemove, and mouseup
    mouseTouch.clickOnly = false; // if true on generate click events
    mouseTouch.status = "Started."; // just for debugging



    // ES6 new math function
    // not sure the extent of support for Math.hypot so hav simple poly fill
    if(typeof Math.hypot === 'function'){
        hypot = Math.hypot;
    }else{
        hypot = function(x,y){  // Untested 
            return Math.sqrt(Math.pow(x,2)+Math.pow(y,2));
        };
    }
    // Use the new API and MouseEvent object
    function triggerMouseEvemt(type,fromTouch,fromEvent){
      var mouseEvent = new MouseEvent(
          type, 
          {
              'view': fromEvent.target.ownerDocument.defaultView,
              'bubbles': true,
              'cancelable': true,
                'screenX':fromTouch.screenX,
                'screenY':fromTouch.screenY,
                'clientX':fromTouch.clientX,
                'clientY':fromTouch.clientY,
                'offsetX':fromTouch.clientX, // this is for old Chrome 
                'offsetY':fromTouch.clientY,
                'ctrlKey':fromEvent.ctrlKey,
                'altKey':fromEvent.altKey,
                'shiftKey':fromEvent.shiftKey,
                'metaKey':fromEvent.metaKey,
                'button':0,
                'buttons':1,
          });
        // to do.
        // dispatch returns cancelled you will have to 
        // add code here if needed
        fromTouch.target.dispatchEvent(mouseEvent);
    }

    // touch listener. Listens to Touch start, move and end.
    // dispatches mouse events as needed. Also sends a click event
    // if click falls within supplied thresholds and conditions
    function emulateMouse(event) {

        var type, time, touch, isClick, mouseEventType, x, y, dx, dy, dist;
        event.preventDefault();  // stop any default happenings interfering
        type = event.type ;  // the type.

        // ignore multi touch input
        if (event.touches.length > 1){
            if(touchStart !== undefined){ // don't leave the mouse down
                triggerMouseEvent("mouseup",event.changedTouches[0],event);
            }
            touchStart = undefined;
            return;
        }
        mouseEventType = "";
        isClick = false;  // default no click
        // check for each event type I have the most numorus move event first, Good practice to always think about the efficancy for conditional coding.
        if(type === "touchmove" && !mouseTouch.clickOnly){        // touchMove
            touch = event.changedTouches[0];
            mouseEventType = "mousemove";      // not much to do just move the mouse
        }else
        if(type === "touchstart"){  
            touch = touchStart = event.changedTouches[0]; // save the touch start for dist check
            timeStart = event.timeStamp; // save the start time
            mouseEventType = !mouseTouch.clickOnly?"mousedown":"";     // mouse event to create
        }else
        if(type === "touchend"){  // end check time and distance
            touch =  event.changedTouches[0];
            mouseEventType = !mouseTouch.clickOnly?"mouseup":"";     // ignore mouse up if click only
            // if click generator active
            if(touchStart !== undefined && mouseTouch.generateClick){
                time = event.timeStamp - timeStart;  // how long since touch start
                // if time is right
                if(time < mouseTouch.clickTime){
                    // get the distance from the start touch
                    dx = touchStart.clientX-touch.clientX;
                    dy = touchStart.clientY-touch.clientY;
                    dist = hypot(dx,dy);
                    if(dist < mouseTouch.clickRadius){
                        isClick = true;
                    }
                }
            }
        }
        // send mouse basic events if any
        if(mouseEventType !== ""){
            // send the event
            triggerMouseEvent(mouseEventType,touch,event);
        }
        // if a click also generates a mouse click event
        if(isClick){
            // generate mouse click
            triggerMouseEvent("click",touch,event);
        }
    }

    // remove events
    function removeTouchEvents(){
        listeningElement.removeEventListener("touchstart", emulateMouse);
        listeningElement.removeEventListener("touchend", emulateMouse);
        listeningElement.removeEventListener("touchmove", emulateMouse);
        listeningElement = undefined;  

    }

    // start  adds listeners and makes it all happen.
    // element is optional and will default to document.
    // or will Listen to element.
    function startTouchEvents(element){
        if(listeningElement !== undefined){ // untested
            // throws to stop cut and past useage of this example code.
            // Overwriting the listeningElement can result in a memory leak.
            // You can remove this condition block and it will work
            // BUT IT IS NOT RECOGMENDED

            throw new ReferanceError("touchMouse says!!!! API limits functionality to one element.");
        }
        if(element === undefined){
            element = document;
        }
        listeningElement = element;
        listeningElement.addEventListener("touchstart", emulateMouse);
        listeningElement.addEventListener("touchend", emulateMouse);
        listeningElement.addEventListener("touchmove", emulateMouse);
    }

    // add the start event to public object.
    mouseTouch.start = startTouchEvents;
    // stops event listeners and remove them from the DOM 
    mouseTouch.stop = removeTouchEvents;

    return mouseTouch;

})(); 











// How to use

touchMouse.start(); // done using defaults will emulate mouse on the entier page 

// For one element and only clicks
// HTML
<input value="touch click me" id="touchButton" type="button"></input>
// Script
var el = document.getElementById("touchButton");
if(el !== null){
    touchMouse.clickOnly = true;
    touchMouse.start(el);
}

// For drawing on a canvas
<canvas id="touchCanvas"></canvas> 
// script
var el = document.getElementById("touchButton");
if(el !== null){
    touchMouse.generateClick = false; // no mouse clicks please
    touchMouse.start(el);
}

// For switching elements call stop then call start on the new element
// warning touchMouse retained a reference to the element you
// pass it with start. Dereferencing touchMouse will not delete it.
// Once you have called start you must call stop in order to delete it.

// API
//---------------------------------------------------------------
// To dereference call the stop method if you have called start . Then dereference touchMouse
// Example
touchMouse.stop();
touchMouse = undefined;


// Methods.
//---------------------------------------------------------------
// touchMouse.start(element); // element optional. Element is the element to attach listeners to.
                              // Calling start a second time without calling stop will
                              // throw a reference error. This is to stop memory leaks.
                              // YOU Have been warned...

// touchMouse.stop();          // removes listeners and dereferences any DOM objects held
//---------------------------------------------------------------
// Properties
// mouseTouch.clickRadius = 3; // Number. Default 3. If touch start and end within 3 pixels then may be a click
// mouseTouch.clickTime = 200; // Number. Default 200. If touch start and end in under this time in ms then may be a click
// mouseTouch.generateClick;   // Boolean. Default true. If true simulates onClick event
//                                    // if false only generate mousedown, mousemove, and mouseup
// mouseTouch.clickOnly;      // Boolean.  Default false. If true only generate click events Default false
// mouseTouch.status;         // String. Just for debugging kinda pointless really. 

关于javascript - Canvas 在移动网络上获得触摸位置，我们在Stack Overflow上找到一个类似的问题： https://stackoverflow.com/questions/33951943/