Webkit Opacity Transition Issues with Text

问题:

Situation:

View the jsFiddle

Inside of a div I have an image followed by text which has a font-weight of 900 on it. In my locally hosted environment I'm using a custom font, but for the fiddle above I chose the "ever-so-stylish" Comic Sans to illustrate my point. Before anything happens I set the opacity of the entire div to 0.7. However, on hovering over the div, I want the opacity of everything to come to full opacity.

Problem:

I've noticed that in Webkit browsers only (more apparent on Chrome than it is on Safari however), upon hovering on and off the of the div tag, the text's weight will appear to change. In actuality, there's no change at all of course in the weight of the text. However, upon closer review you'll see the text appears at it's desired weight only on hover, but not in a non-hovered state.

Things I've Done:

• I've tested this in all the latest versions of Chrome, Firefox, and Safari.
• I am testing this currently on the new MacBook Pro which, in my case, is a retina screen. However, the colleague next to me tested the fiddle on her iMac (non-retina display) only to find the issue still apparent.
• Perhaps I'm just crazy, but I feel this actually may be how webkit browsers choose to render out elements with different opacities. Then again, that may be just me trying to avoid admitting I did something wrong.

---

And naturally I thought I could lighten the mood with Comic Sans. Here's a screen capture to help explain the issue:

回答1:

It's not an issue with the opacity itself (in fact, turning it back to 1 in @Zoltan's example doesn't change anything for me).

The issue is with the transitions, there are two anti-aliasing modes that webkit can use:

1. Subpixel (the default, but not supported during animations, transitions or transforms) or
2. Grayscale

This means that when an element is rendered using subpixel antialiasing and an animation is applied to it, webkit temporarily switches to grayscale for the duration of the animation and then back to subpixel once finished.

Given that subixel antialiasing results in a slightly heavier font face you get the unwanted artifact.

To solve the issue, add this to your css:

html {
    -webkit-font-smoothing: antialiased;
}

This forces grayscale antialiasing and all the text and you won't see the switching.

(end result: http://jsfiddle.net/ErVYs/9/)

回答2:

A possible solution would be to make the opacity transition not to 1, but .999 - http://jsfiddle.net/ErVYs/2/

div {
    width: 200px;
    text-align: center;
    opacity: 0.7;
    transition: opacity ease-in 0.25s;
    -webkit-transition: opacity ease-in 0.25s;
    -moz-transition: opacity ease-in 0.25s;
    -o-transition: opacity ease-in 0.25s;
}

div:hover {
    opacity: .999;
}