When I hover over the transparent part of a PNG, it still acts as though I\'m hovering over the actual image. Is there a way that I can prevent that from happening? So that it o
This works by loading a png into an HTML-5 canvas element, and then querying the canvas for the alpha value of the clicked pixel.
HTML as follows...
Javascript like this...
// select the canvas element with jQuery, and set up
// a click handler for the whole canvas
$('#canvas1').on('click', function(e) {
// utility function for finding the position of the clicked pixel
function findPos(obj) {
var curleft = 0, curtop = 0;
if (obj.offsetParent) {
do {
curleft += obj.offsetLeft;
curtop += obj.offsetTop;
} while (obj = obj.offsetParent);
return { x: curleft, y: curtop };
}
return undefined;
}
// get the position of clicked pixel
var pos = findPos(this);
var x = e.pageX - pos.x;
var y = e.pageY - pos.y;
// get reference to canvas element clicked on
var canvas = this.getContext('2d');
// return array of [RED,GREEN,BLUE,ALPHA] as 0-255 of clicked pixel
var pixel = canvas.getImageData(x, y, 1, 1).data;
// if the alpha is not 0, we clicked a non-transparent pixel
// could be easily adjusted to detect other features of the clicked pixel
if(pixel[3] != 0){
// do something when clicking on image...
alert("Clicked the dice!");
}
});
// get reference to canvas DOM element
var canvas = $('#canvas1')[0];
// get reference to canvas context
var context = canvas.getContext('2d');
// create an empty image
var img = new Image();
// after loading...
img.onload = function() {
// draw the image onto the canvas
context.drawImage(img, 0, 0);
}
// set the image source (can be any url - I used data URI to keep demo self contained)
img.src = "data:image/png;base64,iVBORw0KGgoAAAANS ... more image data ...TkSuQmCC"; // PNG with transparency