javascript - 如何使悬停在 PNG 中的透明度上不算悬停？

Question

当我将鼠标悬停在 PNG 的透明部分上时，它仍然表现得好像我将鼠标悬停在实际图像上一样。有什么办法可以防止这种情况发生吗？以便仅当我将鼠标悬停在图像的可见部分而不是透明部分时它才会采取行动？

我试图裁剪掉透明度，但找不到方法。

Answer 1

可以通过将png转换为canvas元素来完成

这通过将 png 加载到 HTML-5 canvas 元素中，然后查询 Canvas 以获取单击像素的 alpha 值来实现。

工作演示:http://jsfiddle.net/x9ScK/3/

HTML如下...

<!-- create a canvas element to hold the PNG image -->
<canvas id="canvas1" width="500" height="500"></canvas>

像这样的 Javascript...

// 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