CODEWITHSUNDEEP
javascript
Ben Shelock
Ben Shelock

Reputation: 20993

Find mouse position relative to element

I want to make a little painting app using canvas. So I need to find the mouse's position on the canvas.

Upvotes: 408

Views: 503175

Answers (30)

VS Shankar
VS Shankar

Reputation: 1

Possible approach:

  • The mousemove event is attached to the myElement element.
  • When the mouse moves within that element, a listener function (e.g. handleMouseMove) is called.
  • Inside that listener function, myElement.getBoundingClientRect() can used to get the element's position relative to the viewport.
  • Then, the event.clientX and event.clientY properties of the event object are used to calculate the mouse position relative to the element by subtracting the element's top-left coordinates.
  • Finally, the mouse position relative to the element can be used (e.g. logged to the console).

Upvotes: 0

anytimecoder
anytimecoder

Reputation: 7704

As I didn't find a jQuery-free answer that I could copy/paste, here's the solution I used:

document.getElementById('clickme').onclick = function(e) {
      // e = Mouse click event.
      var rect = e.target.getBoundingClientRect();
      var x = e.clientX - rect.left; //x position within the element.
      var y = e.clientY - rect.top;  //y position within the element.
      console.log("Left? : " + x + " ; Top? : " + y + ".");
    }
#clickme {
  margin-top: 20px;
  margin-left: 100px;
  border: 1px solid black;
  cursor: pointer;
}
<div id="clickme">Click Me -<br>
(this box has margin-left: 100px; margin-top: 20px;)</div>

JSFiddle of full example

Upvotes: 677

semi
semi

Reputation: 1

As I didnt find a solution that would help you get it if you append it into a parents element where you have a e.g. selection.

This is what I did:

let positions = {
  x: event.pageX,
  y: event.pageY - event.currentTarget.getBoundingClientRect().top + event.currentTarget.offsetTop
}

Upvotes: 0

Fei Sun
Fei Sun

Reputation: 518

Use this method to get mouse position quickly:

Object.defineProperty(MouseEvent.prototype, "mouseX", {
   get() {
      return this.clientX - this.currentTarget.getBoundingClientRect().left;
   }
});
Object.defineProperty(MouseEvent.prototype, "mouseY", {
   get() {
      return this.clientY - this.currentTarget.getBoundingClientRect().top;
   }
});

example:

document.body.onmousemove=function(e){console.log(e.mouseX,e.mouseY)}

Upvotes: 3

LindaQ
LindaQ

Reputation: 1079

The following calculates the mouse position relation to the canvas element:

const example = document.getElementById('example');

example.onmousemove = function(e) { 
    const x = e.pageX - e.currentTarget.offsetLeft; 
    const y = e.pageY - e.currentTarget.offsetTop; 
}

Upvotes: 88

Kohill Yang
Kohill Yang

Reputation: 141

If you want to get the layerX and layerY related to one element, maybe you could try：

let bbox_rect = document.getElementById("dom-ID").getBoundingClientRect()
let layerX = e.clientX-bbox_rect.left
let layerY = e.clientY-bbox_rect.top

Upvotes: 11

thomas
thomas

Reputation: 915

You can simply use jQuery’s event.pageX and event.pageY with the method offset() of jQuery to get the position of the mouse relative to an element.

  $(document).ready(function() {
    $("#myDiv").mousemove(function(event){            
      var X = event.pageX - $(this).offset().left;
      var Y = event.pageY - $(this).offset().top;
      $(".cordn").text("(" + X + "," + Y + ")");
    });
  });

You can see an example here: How to find mouse position relative to element

Upvotes: 1

ahwelp
ahwelp

Reputation: 87

I had to get the cursor position inside a very wide div with scrollbar. The objective was to drag elements to any position of the div.

To get the mouse position on a far away position deep in the scrolling.

$('.canvas').on('mousemove', function(e){
    $(dragElement).parent().css('top', e.currentTarget.scrollTop + e.originalEvent.clientY );
    $(dragElement).parent().css('left', e.currentTarget.scrollLeft + e.originalEvent.clientX )
});

Upvotes: 0

Emanuele Pavanello
Emanuele Pavanello

Reputation: 873

Based on @Patrick Boos solution but fixing potential problem with intermediate scrollbars.

export function getRelativeCoordinates(event: MouseEvent, referenceElement: HTMLElement) {
  const position = {
    x: event.pageX,
    y: event.pageY,
  };

  const offset = {
    left: referenceElement.offsetLeft,
    top: referenceElement.offsetTop,
  };

  let reference = referenceElement.offsetParent as HTMLElement;

  while (reference) {
    offset.left += reference.offsetLeft;
    offset.top += reference.offsetTop;
    reference = reference.offsetParent as HTMLElement;
  }

  const scrolls = {
    left: 0,
    top: 0,
  };

  reference = event.target as HTMLElement;
  while (reference) {
    scrolls.left += reference.scrollLeft;
    scrolls.top += reference.scrollTop;
    reference = reference.parentElement as HTMLElement;
  }

  return {
    x: position.x + scrolls.left - offset.left,
    y: position.y + scrolls.top - offset.top,
  };
}

Upvotes: 0

sparkyspider
sparkyspider

Reputation: 13529

For people using JQuery:

Sometimes, when you have nested elements, one of them with the event attached to it, it can be confusing to understand what your browser sees as the parent. Here, you can specify which parent.

You take the mouse position, and then subtract it from the parent element's offset position.

var x = evt.pageX - $('#element').offset().left;
var y = evt.pageY - $('#element').offset().top;

If you're trying to get the mouse position on a page inside a scrolling pane:

var x = (evt.pageX - $('#element').offset().left) + self.frame.scrollLeft();
var y = (evt.pageY - $('#element').offset().top) + self.frame.scrollTop();

Or the position relative to the page:

var x = (evt.pageX - $('#element').offset().left) + $(window).scrollLeft();
var y = (evt.pageY - $('#element').offset().top) + $(window).scrollTop();

Note the following performance optimisation:

var offset = $('#element').offset();
// Then refer to 
var x = evt.pageX - offset.left;

In this way, JQuery does not have to look up #element for each line.

Update

There is a newer, JavaScript-only version in an answer by @anytimecoder -- see also browser support for getBoundingClientRect().

Upvotes: 208

Artem Bochkarev
Artem Bochkarev

Reputation: 1360


const findMousePositionRelativeToElement = (e) => {
    const xClick = e.clientX - e.currentTarget.offsetLeft;
    const yClick = e.clientY - e.currentTarget.offsetTop;
    console.log(`x: ${xClick}`);
    console.log(`y: ${yClick}`);

    // or
    const rect = e.currentTarget.getBoundingClientRect();
    const xClick2 = e.clientX - rect.left;
    const yClick2 = e.clientY - rect.top;
    console.log(`x2: ${xClick2}`);
    console.log(`y2: ${yClick2}`);
}

Upvotes: 4

Brieuc Caillot
Brieuc Caillot

Reputation: 92

You can use getBoudingClientRect() of the relative parent.

document.addEventListener("mousemove", (e) => {
  let xCoord = e.clientX - e.target.getBoundingClientRect().left + e.offsetX
  let yCoord = e.clientY - e.target.getBoundingClientRect().top + e.offsetY
  console.log("xCoord", xCoord, "yCoord", yCoord)
})

Upvotes: 2

Fabian von Ellerts
Fabian von Ellerts

Reputation: 5211

I tried all these solutions and due to my special setup with a matrix transformed container (panzoom library) none worked. This returns the correct value, even if zoomed and paned:

mouseevent(e) {
 const x = e.offsetX,
       y = e.offsetY
}

But only if there are no child elements in the way. This can be circumvented by making them 'invisible' to the event, using CSS:

.child {
   pointer-events: none;
}

Upvotes: 46

MbPCM
MbPCM

Reputation: 497

function myFunction(e) {
    var x =  e.clientX - e.currentTarget.offsetLeft ; 
    var y = e.clientY - e.currentTarget.offsetTop ;
}

this works ok!

Upvotes: 1

David W. Keith
David W. Keith

Reputation: 2254

A good write up of the difficulty of this problem can be found here: http://www.quirksmode.org/js/events_properties.html#position

Using the technique that is described there you can find the mouses position in the document. Then you just check to see if it is inside the bounding box of your element, which you can find by calling element.getBoundingClientRect() which will return an object with the following properties: { bottom, height, left, right, top, width }. From there it is trivial to figure out if the even happened inside your element or not.

Upvotes: 22

Mouloud85
Mouloud85

Reputation: 4234

There is no answer in pure javascript that returns relative coordinates when the reference element is nested inside others which can be with absolute positioning. Here is a solution to this scenario: 

function getRelativeCoordinates (event, referenceElement) {

  const position = {
    x: event.pageX,
    y: event.pageY
  };

  const offset = {
    left: referenceElement.offsetLeft,
    top: referenceElement.offsetTop
  };

  let reference = referenceElement.offsetParent;

  while(reference){
    offset.left += reference.offsetLeft;
    offset.top += reference.offsetTop;
    reference = reference.offsetParent;
  }

  return { 
    x: position.x - offset.left,
    y: position.y - offset.top,
  }; 

}

Upvotes: 48

Athinodoros Sgouromallis
Athinodoros Sgouromallis

Reputation: 185

I implemented an other solution that I think is very simple so I thought I'd share with you guys.

So, the problem for me was that the dragged div would jump to 0,0 for the mouse cursor. So I needed to capture the mouses position on the div to adjust the divs new position.

I read the divs PageX and PageY and set the top and left of the according to that and then to get the values to adjust the coordinates to keep the cursor in the initial position in the div I use a onDragStart listener and store the e.nativeEvent.layerX and e.nativeEvent.layerY that only in the initial trigger gives you the mouses position within the draggable div.

Example code : 

 onDrag={(e) => {
          let newCoords;
          newCoords = { x: e.pageX - this.state.correctionX, y: e.pageY - this.state.correctionY };
          this.props.onDrag(newCoords, e, item.id);
        }}
        onDragStart={
          (e) => {
            this.setState({
              correctionX: e.nativeEvent.layerX,
              correctionY: e.nativeEvent.layerY,
            });
          }

I hope this will help someone that went through the same problems I went through :)

Upvotes: 1

Shmoo
Shmoo

Reputation: 1

Here is what I got.

    $(".some-class").click(function(e) {

    var posx = 0;
    var posy = 0;

    posx = e.pageX;
    posy = e.pageY;

    alert(posx);
    alert(posy);
});

Upvotes: -2

John T.
John T.

Reputation: 491

For those of you developing regular websites or PWAs (Progressive Web Apps) for mobile devices and/or laptops/monitors with touch screens, then you have landed here because you might be used to mouse events and are new to the sometimes painful experience of Touch events... yay!

There are just 3 rules:

  1. Do as little as possible during mousemove or touchmove events.
  2. Do as much as possible during mousedown or touchstart events.
  3. Cancel propagation and prevent defaults for touch events to prevent mouse events from also firing on hybrid devices.

Needless to say, things are more complicated with touch events because there can be more than one and they're more flexible (complicated) than mouse events. I'm only going to cover a single touch here. Yes, I'm being lazy, but it's the most common type of touch, so there.

var posTop;
var posLeft;
function handleMouseDown(evt) {
  var e = evt || window.event; // Because Firefox, etc.
  posTop = e.target.offsetTop;
  posLeft = e.target.offsetLeft;
  e.target.style.background = "red";
  // The statement above would be better handled by CSS
  // but it's just an example of a generic visible indicator.
}
function handleMouseMove(evt) {
  var e = evt || window.event;
  var x = e.offsetX; // Wonderfully
  var y = e.offsetY; // Simple!
  e.target.innerHTML = "Mouse: " + x + ", " + y;
  if (posTop)
    e.target.innerHTML += "<br>" + (x + posLeft) + ", " + (y + posTop);
}
function handleMouseOut(evt) {
  var e = evt || window.event;
  e.target.innerHTML = "";
}
function handleMouseUp(evt) {
  var e = evt || window.event;
  e.target.style.background = "yellow";
}
function handleTouchStart(evt) {
  var e = evt || window.event;
  var rect = e.target.getBoundingClientRect();
  posTop = rect.top;
  posLeft = rect.left;
  e.target.style.background = "green";
  e.preventDefault(); // Unnecessary if using Vue.js
  e.stopPropagation(); // Same deal here
}
function handleTouchMove(evt) {
  var e = evt || window.event;
  var pageX = e.touches[0].clientX; // Touches are page-relative
  var pageY = e.touches[0].clientY; // not target-relative
  var x = pageX - posLeft;
  var y = pageY - posTop;
  e.target.innerHTML = "Touch: " + x + ", " + y;
  e.target.innerHTML += "<br>" + pageX + ", " + pageY;
  e.preventDefault();
  e.stopPropagation();
}
function handleTouchEnd(evt) {
  var e = evt || window.event;
  e.target.style.background = "yellow";
  // Yes, I'm being lazy and doing the same as mouseout here
  // but obviously you could do something different if needed.
  e.preventDefault();
  e.stopPropagation();
}
div {
  background: yellow;
  height: 100px;
  left: 50px;
  position: absolute;
  top: 80px;
  user-select: none; /* Disable text selection */
  -ms-user-select: none;
  width: 100px;
}
<div 
  onmousedown="handleMouseDown()" 
  onmousemove="handleMouseMove()"
  onmouseout="handleMouseOut()"
  onmouseup="handleMouseUp()" 
  ontouchstart="handleTouchStart()" 
  ontouchmove="handleTouchMove()" 
  ontouchend="handleTouchEnd()">
</div>
Move over box for coordinates relative to top left of box.<br>
Hold mouse down or touch to change color.<br>
Drag to turn on coordinates relative to top left of page.

Prefer using Vue.js? I do! Then your HTML would look like this:

<div @mousedown="handleMouseDown"
     @mousemove="handleMouseMove"
     @mouseup="handleMouseUp"
     @touchstart.stop.prevent="handleTouchStart"
     @touchmove.stop.prevent="handleTouchMove"
     @touchend.stop.prevent="handleTouchEnd">

Upvotes: 7

John
John

Reputation: 11429

I came across this question, but in order to make it work for my case (using dragover on a DOM-element (not being canvas in my case)), I found that you only have have to use offsetX and offsetY on the dragover-mouse event.

onDragOver(event){
 var x = event.offsetX;
 var y = event.offsetY;
}

Upvotes: 11

Letokteren
Letokteren

Reputation: 809

Based on @Spider's solution, my non JQuery version is this:

// Get the container element's bounding box
var sides = document.getElementById("container").getBoundingClientRect();

// Apply the mouse event listener
document.getElementById("canvas").onmousemove = (e) => {
  // Here 'self' is simply the current window's context
  var x = (e.clientX - sides.left) + self.pageXOffset;
  var y = (e.clientY - sides.top) + self.pageYOffset;
}

This works both with scrolling and zooming (in which case sometimes it returns floats).

Upvotes: 3

kungfooman
kungfooman

Reputation: 4892

canvas.onmousedown = function(e) {
    pos_left = e.pageX - e.currentTarget.offsetLeft;
    pos_top = e.pageY - e.currentTarget.offsetTop;
    console.log(pos_left, pos_top)
}

HTMLElement.offsetLeft

The HTMLElement.offsetLeft read-only property returns the number of pixels that the upper left corner of the current element is offset to the left within the HTMLElement.offsetParent node.

For block-level elements, offsetTop, offsetLeft, offsetWidth, and offsetHeight describe the border box of an element relative to the offsetParent.

However, for inline-level elements (such as span) that can wrap from one line to the next, offsetTop and offsetLeft describe the positions of the first border box (use Element.getClientRects() to get its width and height), while offsetWidth and offsetHeight describe the dimensions of the bounding border box (use Element.getBoundingClientRect() to get its position). Therefore, a box with the left, top, width and height of offsetLeft, offsetTop, offsetWidth and offsetHeight will not be a bounding box for a span with wrapped text.

HTMLElement.offsetTop

The HTMLElement.offsetTop read-only property returns the distance of the current element relative to the top of the offsetParent node.

MouseEvent.pageX

The pageX read-only property returns the X (horizontal) coordinate in pixels of the event relative to the whole document. This property takes into account any horizontal scrolling of the page.

MouseEvent.pageY

The MouseEvent.pageY read-only property returns the Y (vertical) coordinate in pixels of the event relative to the whole document. This property takes into account any vertical scrolling of the page.

For further explanation, please see the Mozilla Developer Network:

https://developer.mozilla.org/en-US/docs/Web/API/MouseEvent/pageX https://developer.mozilla.org/en-US/docs/Web/API/MouseEvent/pageY https://developer.mozilla.org/en-US/docs/Web/API/HTMLElement/offsetLeft https://developer.mozilla.org/en-US/docs/Web/API/HTMLElement/offsetTop

Upvotes: 5

Nino Filiu
Nino Filiu

Reputation: 18551

The mouse coordinates inside a canvas can be obtained thanks to event.offsetX and event.offsetY. Here's a little snippet to prove my point:

c=document.getElementById("c");
ctx=c.getContext("2d");
ctx.fillStyle="black";
ctx.fillRect(0,0,100,100);
c.addEventListener("mousemove",function(mouseEvt){
  // the mouse's coordinates on the canvas are just below
  x=mouseEvt.offsetX;
  y=mouseEvt.offsetY;
  // the following lines draw a red square around the mouse to prove it
  ctx.fillStyle="black";
  ctx.fillRect(0,0,100,100);
  ctx.fillStyle="red";
  ctx.fillRect(x-5,y-5,10,10);
});
  
body {
  background-color: blue;
}

canvas {
  position: absolute;
  top: 50px;
  left: 100px;
}
<canvas id="c" width="100" height="100"></canvas>

Upvotes: 1

Smertrios2007
Smertrios2007

Reputation: 1

Original answer said to put it in an iframe. The better solution is to use the events offsetX and offsetY on a canvas that has the padding set to 0px.

<html>
<body>
<script>

var main=document.createElement('canvas');
main.width="200";
main.height="300";
main.style="padding:0px;margin:30px;border:thick dashed red";
document.body.appendChild(main);

// adding event listener

main.addEventListener('mousemove',function(e){
    var ctx=e.target.getContext('2d');
    var c=Math.floor(Math.random()*0xFFFFFF);
    c=c.toString(16); for(;c.length<6;) c='0'+c;
    ctx.strokeStyle='#'+c;
    ctx.beginPath();
    ctx.arc(e.offsetX,e.offsetY,3,0,2*Math.PI);
    ctx.stroke();
    e.target.title=e.offsetX+' '+e.offsetY;
    });

// it worked! move mouse over window

</script>
</body>
</html>

Upvotes: 0

FutureSci
FutureSci

Reputation: 1760

I realise I'm a little late , but this works with PURE javascript, and it even gives you the coordinates of the pointer within the element if the element is bigger than the viewport and the user has scrolled. 

var element_offset_x ; // The distance from the left side of the element to the left of the content area


....// some code here (function declaration or element lookup )



element_offset_x = element.getBoundingClientRect().left  -  document.getElementsByTagName("html")[0].getBoundingClientRect().left  ;

....// code here 




function mouseMoveEvent(event) 
{
   var pointer_location = (event.clientX + window.pageXOffset) - element_offset_x ; 
}

How it works.

The first thing we do is get the location of the HTML element (the content area) relative to the current viewport. If the page has scrollbars and is scrolled, then the number returned by getBoundingClientRect().left for the html tag will be negative. We then use this number to compute the distance between the element and the left of the content area. With element_offset_x = element.getBoundingClientRect().left......;

Knowing the distance of the element from the content area. event.clientX gives us the distance of the pointer from the viewport. It is important to understand that the viewport and the content area are two different entities, the viewport can move if the page is scrolled. Hence, clientX will return the SAME number even if the page is scrolled.

To compensate for this , we need to add the x position of the pointer (relative to the viewport) , to the x position of the viewport (relative to the content area ). The X position of the viewport is found with window.pageXOffset.

Upvotes: 3

Eli Mashiah
Eli Mashiah

Reputation: 230

You have to know the structure of your page, because if your canvas is a child of a div which in turn is a child of another div... then the story gets more complicated. Here's my code for a canvas which is inside 2 levels of div s:

canvas.addEventListener("click", function(event) {
var x = event.pageX - (this.offsetLeft + this.parentElement.offsetLeft);
var y = event.pageY - (this.offsetTop + this.parentElement.offsetTop);
console.log("relative x=" + x, "relative y" + y);

});

Upvotes: 0

Jonathan H
Jonathan H

Reputation: 7962

Taken from this tutorial, with corrections made thanks to the top comment:

function getMousePos( canvas, evt ) {
    var rect = canvas.getBoundingClientRect();
    return {
        x: Math.floor( ( evt.clientX - rect.left ) / ( rect.right - rect.left ) * canvas.width ),
        y: Math.floor( ( evt.clientY - rect.top ) / ( rect.bottom - rect.top ) * canvas.height )
    };
}

Use on a canvas as follows:

var canvas = document.getElementById( 'myCanvas' );
canvas.addEventListener( 'mousemove', function( evt ) {
    var mousePos = getMousePos( canvas, evt );
} );

Upvotes: 5

user3105222
user3105222

Reputation:

None of the above answers are satisfactory IMO, so here's what I use:

// Cross-browser AddEventListener
function ael(e, n, h){
    if( e.addEventListener ){
        e.addEventListener(n, h, true);
    }else{
        e.attachEvent('on'+n, h);
    }
}

var touch = 'ontouchstart' in document.documentElement; // true if touch device
var mx, my; // always has current mouse position IN WINDOW

if(touch){
    ael(document, 'touchmove', function(e){var ori=e;mx=ori.changedTouches[0].pageX;my=ori.changedTouches[0].pageY} );
}else{
    ael(document, 'mousemove', function(e){mx=e.clientX;my=e.clientY} );
}

// local mouse X,Y position in element
function showLocalPos(e){
    document.title = (mx - e.getBoundingClientRect().left)
        + 'x'
        + Math.round(my - e.getBoundingClientRect().top);
}

And if you ever need to know the current Y scrolling position of page :

var yscroll = window.pageYOffset
        || (document.documentElement && document.documentElement.scrollTop)
        || document.body.scrollTop; // scroll Y position in page

Upvotes: 5

Matt
Matt

Reputation: 278

I +1' Mark van Wyk's answer as it got me in the right direction, but didn't quite solve it for me. I still had an offset on painting in elements contained within another element.

FOllowing solved it for me:

        x = e.pageX - this.offsetLeft - $(elem).offset().left;
        y = e.pageY - this.offsetTop - $(elem).offset().top;

In other words - i simply stacked all the offsets from all elements nested

Upvotes: 9

rob waminal
rob waminal

Reputation: 18429

you can get it by

var element = document.getElementById(canvasId);
element.onmousemove = function(e) {
    var xCoor = e.clientX;
    var yCoor = e.clientY;
}

Upvotes: 0

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