Related
I want to make a little painting app using canvas. So I need to find the mouse's position on the canvas.
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
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().
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;
}
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,
};
}
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;
}
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.
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;
}
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
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
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:
Do as little as possible during mousemove or touchmove events.
Do as much as possible during mousedown or touchstart events.
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">
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
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 );
} );
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
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}`);
}
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.
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).
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)
})
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)}
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>
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 :)
function myFunction(e) {
var x = e.clientX - e.currentTarget.offsetLeft ;
var y = e.clientY - e.currentTarget.offsetTop ;
}
this works ok!
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
you can get it by
var element = document.getElementById(canvasId);
element.onmousemove = function(e) {
var xCoor = e.clientX;
var yCoor = e.clientY;
}
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);
});
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>
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,
};
}
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 )
});
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
}
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);
});
I'm trying to make a jquery function to follow the mouse coursor with a div, when it is on mousedown and when it is on mouseup it stay in the last position it was.
any sugestion.
Why not simply use drag and drop by jquery:
<script>
$(function() {
$( "#draggable" ).draggable();
});
</script>
Jquery draggable
I've put together a simple working example that defines a Draggable object. You specify the drag item (the element that you're moving around), as well as a drag boundary (the space—or element—that you are moving the item inside of). The concept of a boundary is important if you ever want to restrict a draggable item to a certain space on the page (such as a container), or define a relative coordinate system on which to base your math.
My solution isn't the fastest, but it demonstrates the concept:
$(function() {
window.mousedown = 0;
$(window).on('mousedown mouseup', function(e) {
if(e.type == 'mousedown') { this.mousedown++; }
else { this.mousedown--; }
});
var Draggable = function(dragItem, dragBoundary) {
this.item = $(dragItem).css('position', 'absolute');
this.item.on('mousemove', $.proxy(this.handleDragEvent, this));
this.boundary = $(dragBoundary).css('position', 'relative');
};
Draggable.prototype.handleDragEvent = function(e) {
if(window.mousedown) {
var mousePosition = this.mapToBoundary([e.clientX, e.clientY]);
var mouseX = mousePosition[0],
mouseY = mousePosition[1];
if(typeof this.prevMouseX == "undefined") this.prevMouseX = mouseX;
if(typeof this.prevMouseY == "undefined") this.prevMouseY = mouseY;
this.itemX = this.item.offset().left - this.boundary.offset().left;
this.itemY = this.item.offset().top - this.boundary.offset().top;
var deltaX = mouseX - this.prevMouseX,
deltaY = mouseY - this.prevMouseY;
this.item.css({
'left': this.itemX + deltaX,
'top': this.itemY + deltaY
});
this.prevMouseX = mouseX;
this.prevMouseY = mouseY;
}
};
Draggable.prototype.mapToBoundary = function(coord) {
var x = coord[0] - this.boundary.offset().left;
var y = coord[1] - this.boundary.offset().top;
return [x,y];
};
var draggable = new Draggable($('.draggable'), $('.container'));
});
Notice that we are maintaining a mousedown value on global, allowing us to determine when it would be appropriate to drag around our element (we only add a mousemove listener to the drag item itself). I've also included a spacer div above the boundary div to demonstrate how you can move the boundary anywhere around the page and the coordinate system is still accurate. The code to actually restrict a draggable item within its assigned boundary could be written using simple math.
Here is the fiddle: http://jsfiddle.net/bTh9s/3/
EDIT:
Here is the start to some code for restricting a Draggable item within its container.
Draggable.prototype.restrictItemToBoundary = function() {
var position = this.item.position();
position.right = position.left + this.item.outerWidth();
position.bottom = position.top + this.item.outerHeight();
if(position.left <= 0) {
this.item.css('left', 1);
} else if(position.right >= this.boundary.outerWidth()) {
this.item.css('left', this.boundary.outerWidth() - this.item.outerWidth());
}
if(position.top <= 0) {
this.item.css('top', 1);
} else if(position.bottom >= this.boundary.outerHeight()) {
this.item.css('top', this.boundary.outerHeight() - this.item.outerHeight());
}
};
This method should be called inside of Draggable.handleDragEvent just after you update the CSS positioning of the drag item. It seems this solution is glitchy, but it's a start.
How do I get the x and y pixel value of the mouse click on the image after a canvas translate & scale? What's the needed calculation from the event x and y?
I am using panning & zooming code from this answer:
var zoom = function(clicks) {
var pt = ctx.transformedPoint(lastX,lastY);
ctx.translate(pt.x,pt.y);
var factor = Math.pow(scaleFactor,clicks);
ctx.scale(factor,factor);
ctx.translate(-pt.x,-pt.y);
redraw();
}
var handleScroll = function(evt) {
var delta = evt.wheelDelta ? evt.wheelDelta/40 : evt.detail ? -evt.detail : 0;
if (delta) zoom(delta);
return evt.preventDefault() && false;
};
Example website
If you're just trying to get the mouse X and Y position after a click, then you should attach a function to the mousedown event in Javascript. This is called event binding. In short, while in the DOM you can bind events to elements within the page. Here's an example I made which shows an event bound to the #box element.
document.getElementById("box").onmousedown = function() {
var posx = 0;
var posy = 0;
if (!e) var e = window.event;
if (e.pageX || e.pageY) {
posx = e.pageX;
posy = e.pageY;
}
else if (e.clientX || e.clientY) {
posx = e.clientX + document.body.scrollLeft
+ document.documentElement.scrollLeft;
posy = e.clientY + document.body.scrollTop
+ document.documentElement.scrollTop;
}
alert("Mouse x: " + posx + "\nMouse y: " + posy);
};
This code finds an element with an ID of box and tells the code in the function to run every time after the mouse is depressed. In this example we also fall back for older system to ensure that it works cross-platform and cross-browser. If you wanted to bind this event to the whole webpage rather than just an element then you can replace document.getElementById("box") with window.
This however does not compute the relative position within a DOM element. There's multiple ways to do that which I won't go into detail on here, but I'll include a few methods below. Best of luck!
RESOURCES
More on handling mouseclicks in Javascript
Relative position of mouse clicks within an element
jQuery solution for the previous link
So i just recently got into canvas and decide to play around with it by making a simple game.
However it doesn't work in chrome but it does work in firefox. The game is supposed to be a very simple RTS. You select a box and when you right click you can move the box from one point to another.
This works in firefox. In chrome however, it draws the boxes but doesn't register any clicking (can't select/move boxes). Also in chrome nothing appears in the firebug console. I am running the script off of xampp in case that would be relevant.
EDIT: ha, I'm sorry. I honestly didn't know where to start looking before so i just posted the whole thing up. I took the above code down and replaced it with a much shorter version below. also edited formatting
EDIT2: narrowed down below code even more
/*Game mouse controls*/
_screen.mousemove(function(e){
var playerUnitHover = _game.onUnit(playerUnits, e),
enemyUnitHover = _game.onUnit(enemyUnits, e);
if(typeof(playerUnitHover)=='number') _screen.css('cursor','pointer');
if(typeof(enemyUnitHover)=='number') _screen.css('cursor','not-allowed');
});
The code above handles the mouse functions. This is where the problems would probably occur. In firebug chrome i can get the variables to show in the console but it fails to register when the cursor is over the box. This is the function below that handles that.
/*If mouse coordinates are ontop of unit, then return index of that unit from supplied array argument*/
this.onUnit = function(array,e){
var numOfUnits = array.length,
mouseOffsetX = e.pageX - offsetX,
mouseOffsetY = e.pageY - offsetY;
for(var i = 0; i < numOfUnits; i++){
var unit = array[i],
xRange = mouseOffsetX > unit.x && (unit.x+unit.width) > mouseOffsetX,
yRange = mouseOffsetY > unit.y && (unit.y+unit.height) > mouseOffsetY;
if (xRange && yRange){
return i;
}
if(!xRange || !yRange) _screen.css('cursor','crosshair');
}
}
The problem is that
mouseOffsetX = e.pageX - offsetX,
mouseOffsetY = e.pageY - offsetY;
is not enough for consistent cross-browser mouse coordinates.
There are probably many valid ways to get mouse coordinates for a canvas. The bullet-proof way that I use might be overcomplicated but it does work in all browsers and is aware of things like CSS borders:
getMouse = function(e, canvas) {
var element = canvas, offsetX = 0, offsetY = 0;
if (element.offsetParent) {
do {
offsetX += element.offsetLeft;
offsetY += element.offsetTop;
} while ((element = element.offsetParent));
}
// Add padding and border style widths to offset
offsetX += stylePaddingLeft;
offsetY += stylePaddingTop;
offsetX += styleBorderLeft;
offsetY += styleBorderTop;
// We return an javascript object with x and y defined
return {
x: e.pageX - offsetX,
y: e.pageY - offsetY
};
}
The stylePadding and styleBorder are probably not necessary unless you have padding/border. You can get the canvas' stylePadding like this:
var stylePaddingLeft, stylePaddingTop, styleBorderLeft, styleBorderTop;
if (document.defaultView && document.defaultView.getComputedStyle) {
stylePaddingLeft = parseInt(document.defaultView.getComputedStyle(canvas, null)['paddingLeft'], 10) || 0;
stylePaddingTop = parseInt(document.defaultView.getComputedStyle(canvas, null)['paddingTop'], 10) || 0;
styleBorderLeft = parseInt(document.defaultView.getComputedStyle(canvas, null)['borderLeftWidth'], 10) || 0;
styleBorderTop = parseInt(document.defaultView.getComputedStyle(canvas, null)['borderTopWidth'], 10) || 0;
}
I want to make a little painting app using canvas. So I need to find the mouse's position on the canvas.
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
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().
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;
}
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,
};
}
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;
}
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.
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;
}
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
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
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:
Do as little as possible during mousemove or touchmove events.
Do as much as possible during mousedown or touchstart events.
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">
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
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 );
} );
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
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}`);
}
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.
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).
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)
})
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)}
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>
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 :)
function myFunction(e) {
var x = e.clientX - e.currentTarget.offsetLeft ;
var y = e.clientY - e.currentTarget.offsetTop ;
}
this works ok!
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
you can get it by
var element = document.getElementById(canvasId);
element.onmousemove = function(e) {
var xCoor = e.clientX;
var yCoor = e.clientY;
}
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);
});
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>
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,
};
}
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 )
});
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
}
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);
});