Font-Weight CSS Transition in Chrome

Question

Trying to get font-weight to gracefully transition from \'400\' to \'600\' using CSS but it doesn\'t appear to be working in Chrome. Is this a known bug or am

Answer 1

Font-weight animation is currently not supported in Chrome and IE-10 based on numerous tests. This may change in the future.

Answer 2

I came here to find out the answer myself for how to transition font weight, and was disappointed when I read the approved answer above saying that it can't be done (or at least not very well).

With font-weight animation unavailable, I decided to try another effect, which actually gives you a font-weight effect... which I didn't even think would work for this type of transition.

Here is how to make the weight grow:

.weightGrow:hover {
    text-shadow:
    -1px -1px 0 #2DD785,
    1px -1px 0 #2DD785,
    -1px 1px 0 #2DD785,
    1px 1px 0 #2DD785;
    -webkit-transition: all .5s;
    -moz-transition: all .5s;
    -o-transition: all .5s;
    transition: all .5s;
}

Perfectly smooth and exactly what I was looking for when I first arrived on this page. Hope it helps someone.

Answer 3

I seem to have obtained a "font-weight" transition effect accidentally, by doing a quick color transition (light gray to dark blue) at the same time.

Answer 4

The problem is that font weights, when represented numerically, must be a multiple of 100. To animate between 400 and 600, the font would change from 400 to 500 to 600 (3 'frames', if you like) and wouldn't look very smooth. An animation wouldn't increment the weight by 1 each time (400, 401, 402...) it would increment the weight by 100 (400, 500, 600). If your animation lasted 2 seconds, after 1 second the weight would suddenly become 500, and after 2 seconds the weight would suddenly become 600; there are no in-between variations.

A further problem with what you're attempting here is that the font you're using (or JSFiddle's default, at least) doesn't have anything different for font-weight:500, meaning it defaults to 400:

<p style="font-weight:400;">a - 400, normal</p>
<p style="font-weight:500;">a - 500 (no support, defaults to 400)</p>
<p style="font-weight:600;">a - 600 (bold)</p>
<p style="font-weight:650;">a - 650 (not valid, defaults to 400)</p>

http://jsfiddle.net/r4gDh/6/

Numeric font weights for fonts that provide more than just normal and bold. If the exact weight given is unavailable, then 600-900 use the closest available darker weight (or, if there is none, the closest available lighter weight), and 100-500 use the closest available lighter weight (or, if there is none, the closest available darker weight). This means that for fonts that provide only normal and bold, 100-500 are normal, and 600-900 are bold.

https://developer.mozilla.org/en-US/docs/Web/CSS/font-weight

This basically means that you can't smoothly animate font-weight. Even if you had support for all weights between 100 and 900 the change wouldn't be pleasant and there would be a dramatic change between 500 and 600 (where lighter weight meets darker weight).

Answer 5

Fonts are not simple vector image collections (that's why svg fonts never took off). Opentype fonts include all kinds of magic to clamp fonts to the pixel grid, which makes it unrealistic to expect a font family to ever include every possible weight value.

Because fonts are not simple vector image collections they will also never resize linearly – there will be bumps to take the pixel grid into account.

This Google whitepaper explains why linear resizing does not work for text on current screens https://docs.google.com/document/d/1wpzgGMqXgit6FBVaO76epnnFC_rQPdVKswrDQWyqO1M/edit

which is why no browser will attempt it and they will all rely on pre-computed font weights.

That may change in a decade when retina displays are the lowest common denominator but current font tech targets current screens.

This Microsoft whitepaper documents some standard font weight values http://blogs.msdn.com/cfs-filesystemfile.ashx/__key/communityserver-components-postattachments/00-02-24-90-36/WPF-Font-Selection-Model.pdf

(but just because they are documented does not mean the number of fonts that actually include all of them is not quite small)

You can probably achieve the effect you want with an svg font and some javascript. The svg font will be crap for text use though.

Answer 6

Although there is no direct way to get the font-weight to smoothly transition, I have found a way to do this indirectly (although with some limitations).

In essence you can simply use one of the pseudo elements in order to make a mirror copy of the element whom font you want to transition to bold, where the font-weight on the pseudo element is bold and the opacity is 0. And on hover simply transition the pseudo element's opacity and that does the trick with a very smooth transition.

You can see a demo here:
http://jsfiddle.net/r4gDh/45/

HTML:

<div class="element" data-text="text will turn to bold on hover">
  text will turn to bold on hover
</div>

In the HTML you can already see one of the limitations, because we are using pseudo elements we need to pass the contents of the element as an attribute as well, so the content is duplicated.

CSS:

.element,
.element::before {
    background: red;
    font-weight:normal;
    font-size:40px;

    text-align:center;

    display: inline-block;

    padding: 0px 30px 0px 30px;

    position: relative;
    top: 0;
    left: 0;
}
.element::before {
    position: absolute;
    top: 0;
    left: 0;

    width: 100%;
    height: 100%;

    padding: 0;

    content: attr(data-text);
    opacity: 0;

    font-weight: bold;

    transition: all 1s linear;
}
.element:hover::before {
    opacity: 1;
}

The second limitation comes from the nature of the technique, namely because you are simply overlaying the pseudo element over the original, then the element needs to have a solid background or this will not work, because the original element will remain visible in the background.

One thing you should really keep an eye on is that the pseudo element and the original element have the same dimensions, to this end, in the demo, I've removed the padding on the pseudo element, so you may need to do something similar.

As you can see, this way of getting the font-weight transition is not without it's problems and far from ideal, but this is the best I can currently think of and in limited cases like for buttons and what not this is quite useful and if done correctly will look decent even in legacy browsers.