css - Background-image in keyframe does not display in Firefox or Internet Explorer

Question

I have several animations on my site that I just realized do not even show up in Firefox or Internet Explorer. I have the background-image within the keyframes. I do this because I have different images in different percentages with the animation.

Why doesn't the background-image display within the keyframes in Firefox and Internet Explorer and is there a way to make this work?

Answer 1

As per the specs, background-image is not an animatable or a transitionable property. But it does not seem to say anything about what or how the handling should be when it is used as part of transition or animation. Because of this, each browser seem to be handling it differently. While Chrome (Webkit) is displaying the background image, Firefox and IE seem to do nothing.

The below quote found in an article at oli.jp provides some interesting information:

While CSS Backgrounds and Borders Module Level 3 Editor’s Draft says “Animatable: no” for background-image at the time of writing, support for crossfading images in CSS appeared in Chrome 19 Canary. Until widespread support arrives this can be faked via image sprites and background-position or opacity. To animate gradients they must be the same type.

On the face of it, it looks like Firefox and IE are handling it correctly while Chrome is not. But, it is not so simple. Firefox seems to contradict itself when it comes to how it handles transition on background image as opposed to animation. While transitioning background-image, it shows up the second image immediately (hover the first div in the snippet) whereas while animating, the second image doesn't get displayed at all (hover the second div in the snippet).

So, conclusion is that it is better to not set background-image inside keyframes. Instead, we have to use background-position or opacity like specified @ oli.jp.

div {
  background-image: url(https://placehold.it/100x100);
  height: 100px;
  width: 100px;
  margin: 10px;
  border: 1px solid;
}
div:nth-of-type(1) {
  transition: background-image 1s ease;
}
div:nth-of-type(1):hover {
  background-image: url(https://placehold.it/100/123456/ffffff);
}
div:nth-of-type(2):hover {
  animation: show-img 1s ease forwards;
}
@keyframes show-img {
  to {
    background-image: url(https://placehold.it/100/123456/ffffff);
  }
}

<div></div>
<div></div>