How do I get the coordinates of a mouse click on a canvas element?

Question

What\'s the simplest way to add a click event handler to a canvas element that will return the x and y coordinates of the click (relative to the canvas element)?

No

Answer 1

Here is some modifications of the above Ryan Artecona's solution.

function myGetPxStyle(e,p)
{
    var r=window.getComputedStyle?window.getComputedStyle(e,null)[p]:"";
    return parseFloat(r);
}

function myGetClick=function(ev)
{
    // {x:ev.layerX,y:ev.layerY} doesn't work when zooming with mac chrome 27
    // {x:ev.clientX,y:ev.clientY} not supported by mac firefox 21
    // document.body.scrollLeft and document.body.scrollTop seem required when scrolling on iPad
    // html is not an offsetParent of body but can have non null offsetX or offsetY (case of wordpress 3.5.1 admin pages for instance)
    // html.offsetX and html.offsetY don't work with mac firefox 21

    var offsetX=0,offsetY=0,e=this,x,y;
    var htmls=document.getElementsByTagName("html"),html=(htmls?htmls[0]:0);

    do
    {
        offsetX+=e.offsetLeft-e.scrollLeft;
        offsetY+=e.offsetTop-e.scrollTop;
    } while (e=e.offsetParent);

    if (html)
    {
        offsetX+=myGetPxStyle(html,"marginLeft");
        offsetY+=myGetPxStyle(html,"marginTop");
    }

    x=ev.pageX-offsetX-document.body.scrollLeft;
    y=ev.pageY-offsetY-document.body.scrollTop;
    return {x:x,y:y};
}