CSS3 - Fading an image/element diagonally - css

Question

I am trying to fade an image diagonally. I know there are dozens of questions regarding fading images and I've gone through a lot of them but they all are either about fading left-to-right, top-to-bottom, or moving while fading.
I'm trying to make it so that an image will have a fade effect from one corner to another. The best I could come up with was rotating a white block and increasing the width of it in place.
$(document).ready(function() {
setInterval(function(){
$('.white-fade').toggleClass('white-fade-reveal');
$('.block').toggleClass('block-hide');
}, 2000);
});
.wrapper {
position: relative;
}
.block {
width: 100px;
height: 100px;
opacity: 1;
transition-delay: 1s;
transition: opacity 0.75s ease-in-out;
}
.white-fade {
position: absolute;
top: -25px;
left: -20px;
transform: rotate(45deg);
transform-origin: 75px 75px;
transition: width 1s ease-in-out;
width: 0%;
height: 150px;
background: -moz-linear-gradient(left, rgba(255,255,255,1) 0%, rgba(255,255,255,0) 100%); /* FF3.6+ */
background: -webkit-gradient(linear, left top, right top, color-stop(0%,rgba(255,255,255,1)), color-stop(100%,rgba(255,255,255,0))); /* Chrome,Safari4+ */
background: -webkit-linear-gradient(left, rgba(255,255,255,1) 0%,rgba(255,255,255,0) 100%); /* Chrome10+,Safari5.1+ */
background: -o-linear-gradient(left, rgba(255,255,255,1) 0%,rgba(255,255,255,0) 100%); /* Opera 11.10+ */
background: -ms-linear-gradient(left, rgba(255,255,255,1) 0%,rgba(255,255,255,0) 100%); /* IE10+ */
background: linear-gradient(to right, rgba(255,255,255,1) 0%,rgba(255,255,255,0) 100%); /* W3C */
filter: progid:DXImageTransform.Microsoft.gradient( startColorstr='#ffffff', endColorstr='#00ffffff',GradientType=1 ); /* IE6-9 */
}
.block-hide {
opacity: 0;
}
.white-fade-reveal {
width: 150px;
}
<script src="https://ajax.googleapis.com/ajax/libs/jquery/2.1.1/jquery.min.js"></script>
<div class="wrapper">
<img class="block" src="http://images.clipartpanda.com/smiley-face-transparent-background-awesome-smiley-background-2549-hd-wallpapers.png" alt="smiley"/>
<div class="white-fade"></div>
</div>
I was wondering if there was a cleaner approach to achieving this effect? It seems inevitable that some JavaScript is necessary. I added a gradient to make it cleaner but I'm not sure if there's a way to do it with CSS3 animations?

Answer 1

You could use a rotated Pseudo element for this.
So, in effect you would have:
+---+
| | <-- pseudo element (rotated 45 deg)
+---+
+---+
| | <-- image element
+---+
And the on hover, bring the pseudo element over the top of the image, giving the effect of the 'fade' by transitioning the opacity of the pseudo as well:
div {
height: 300px;
width: 300px;
background: url(http://placekitten.com/g/300/300);
position: relative;
transition: all 0.8s;
overflow:hidden;
}
div:before {
content: "";
position: absolute;
height: 150%;
width: 150%;
top: -150%;
left: -150%;
transition: all 2.3s;
background: white;
opacity: 0;
transform: rotate(45deg);
}
div:hover:before {
top: -25%;
left: -25%;
opacity: 1;
}
<div></div>

Answer 2

One thing I'd suggest is set height and width property on wrapper so you don't increase height,
I also animated width just on one selector with linear-gradient so it's slimmer, and the result looks good!!!
$(document).ready(function() {
setInterval(function(){
$( ".white-fade" ).animate({
width: "toggle",
}, 2000);
});
});
.wrapper {
position: relative;
width:100px;
height:100px;
overflow:hidden;
}
.block {
width: 100px;
height: 100px;
opacity: 1;
transition: opacity 0.5s ease-in-out;
}
.white-fade {
position: absolute;
top: 0;
left: 0;
top: -25px;
left: -20px;
transform: rotate(45deg);
transform-origin: 75px 75px;
width: 300px;
height: 150px;
background: white;
background: linear-gradient(to right, rgba(255,255,255,1) 0%,rgba(255,255,255,1) 66%,rgba(255,255,255,0) 100%); /* W3C */
opacity:1;
}
/*.block-hide {
opacity: 0;
}
.white-fade-reveal {
width: 100%;
}*/
<script src="https://ajax.googleapis.com/ajax/libs/jquery/2.1.1/jquery.min.js"></script>
<div class="wrapper">
<img class="block" src="http://images.clipartpanda.com/smiley-face-transparent-background-awesome-smiley-background-2549-hd-wallpapers.png" alt="smiley"/>
<div class="white-fade"></div>
</div>