Javascript mouse click coordinates for image

问题

The assignment says "Your task is to write an HTML file that contains JavaScript that will randomly display one of the images above. If the page is refreshed in the browser, you should get another random image." so I did it.

Now it says "When the user clicks anywhere on the image, display an alert window that shows the X and Y position of where the click occurred relative to the image". Here is my code:

<html>
<head>
<title>Assignment 2</title>
<script type="text/javascript">
  var imageURLs = [
       "p1.jpg"
     , "p2.jpg"
     , "p3.jpg"
     , "p4.jpg"
  ];
  function getImageTag() {
    var img = '<img src=\"';
    var randomIndex = Math.floor(Math.random() * imageURLs.length);
    img += imageURLs[randomIndex];
    img += '\" alt=\"Some alt text\"/>';
    return img;
  }
</script>
</head>
<body>
<script type="text/javascript">
  document.write(getImageTag());
</script>
</body>
</html>

回答1:

You can actually use HTML for this. The image tag has an attribute known as ismap.

What this attribute does is specify that an image is part of a server-side image map. When clicking on such map, the click coordinates are sent to the server as a url query string.

Images must be nested under links for this to work. Here is an example

<a href="http://www.google.com">
    <img src="myimage.png" alt="My Image" ismap">
</a>

If you can't use image maps for this, here is a javascript/jquery solution

First, you need to include the jQuery library at the bottom of your body tag.

<script src="https://ajax.googleapis.com/ajax/libs/jquery/1.11.3/jquery.min.js"></script>

$(document).ready(function() {
    $("img").on("click", function(event) {
        var x = event.pageX - this.offsetLeft;
        var y = event.pageY - this.offsetTop;
        alert("X Coordinate: " + x + " Y Coordinate: " + y);
    });
});

<script src="https://ajax.googleapis.com/ajax/libs/jquery/2.1.1/jquery.min.js"></script>

<img src="http://vignette1.wikia.nocookie.net/seraphina/images/b/b2/Dragonseraphina.jpg/revision/latest?cb=20160103194957" height="200" width="200" alt="dragon">

You listen for the click event, and pass in event as the parameter.

The event.pageX property returns the position of the mouse pointer, relative to the left edge of the document.

回答2:

$(document).ready(function () {
    $("img").on("click", function (event) {

        $('#img_coordinate').html("X Coordinate: " + (event.pageX - this.offsetLeft) + "<br/> Y Coordinate: " + (event.pageY - this.offsetTop));
    });
});

html

<img src="img/sample.gif" />

<p id="img_coordinate"></p>

回答3:

The map solution will only give you the client side pixel coordinates. If you'd like to get the pixel coordinate relative to the original image you need the naturalHeight and naturalWidth information which has height and width of the original image.

code:

 // https://stackoverflow.com/questions/34867066/javascript-mouse-click-coordinates-for-image
  document.getElementById(imageid).addEventListener('click', function (event) {
    // https://stackoverflow.com/a/288731/1497139
    bounds=this.getBoundingClientRect();
    var left=bounds.left;
    var top=bounds.top;
    var x = event.pageX - left;
    var y = event.pageY - top;
    var cw=this.clientWidth
    var ch=this.clientHeight
    var iw=this.naturalWidth
    var ih=this.naturalHeight
    var px=x/cw*iw
    var py=y/ch*ih
    alert("click on "+this.tagName+" at pixel ("+px+","+py+") mouse pos ("+x+"," + y+ ") relative to boundingClientRect at ("+left+","+top+") client image size: "+cw+" x "+ch+" natural image size: "+iw+" x "+ih );
  });

$(document).ready(function() {
    $("img").on("click", function(event) {
        bounds=this.getBoundingClientRect();
        var left=bounds.left;
        var top=bounds.top;
        var x = event.pageX - left;
        var y = event.pageY - top;
        var cw=this.clientWidth
        var ch=this.clientHeight
        var iw=this.naturalWidth
        var ih=this.naturalHeight
        var px=x/cw*iw
        var py=y/ch*ih
        alert("click on "+this.tagName+" at pixel ("+px+","+py+") mouse pos ("+x+"," + y+ ") relative to boundingClientRect at ("+left+","+top+") client image size: "+cw+" x "+ch+" natural image size: "+iw+" x "+ih );
    });
});

<script src="https://ajax.googleapis.com/ajax/libs/jquery/2.1.1/jquery.min.js"></script>

<img src="https://upload.wikimedia.org/wikipedia/commons/7/77/Avatar_cat.png" height="256" width="256" alt="kitten">

example

click on IMG at pixel (445.5,334.125) mouse pos (148.5,49) relative to boundingClientRect at (483.5,64) client image size: 640 x 480 natural image size: 1920 x 1080

来源：https://stackoverflow.com/questions/34867066/javascript-mouse-click-coordinates-for-image

标签

javascript

html

image

mouseclick-event