CSS animation-timing-function

The CSS animation-timing-function property allows you to specify how an animation will progress over one cycle of its duration. More specifically, it describes how the animation will change speed over the duration of each cycle. This effect is commonly called easing functions.

The animation-timing-function is specified using a cubic bézier curve, which is defined by four control points; P₀, P₁, P₂, and P₃. The points P₀ and P₃, which represent the start and end of the animation cycle, are always set to (0,0) and (1,1) repectively.

The animation-timing-function property includes a number of keywords that can be used as a quick way to get a nice transition. Alternatively, you can use the cubic-bezier keyword to specify your own cubic-bézier curve.

For a keyframed animation, the animation-timing-function property applies between keyframes, not over the entire animation. For example, in the case of an ease-in-out timing function, an animation will ease in at the start of the keyframe and ease out at the end of the keyframe. A animation-timing-function defined within a keyframe block applies to that keyframe, otherwise the timing function specified for the animation is used.

animation-timing-function: ease-out /* W3C */
-webkit-animation-timing-function: ease-out /* Safari & Chrome */
-moz-animation-timing-function: ease-out /* Firefox */
-ms-animation-timing-function: ease-out /* Internet Explorer */
-o-animation-timing-function: ease-out /* Opera */

Browser Compatibility

At the time of writing, CSS3 was still under development and browser support for many CSS3 properties was limited or non-existent. For maximum browser compatibility many web developers add browser-specific properties by using extensions such as -webkit- for Safari and Google Chrome, -ms- for Internet Explorer, -moz- for Firefox, -o- for Opera etc. As with any CSS property, if a browser doesn't support a proprietary extension, it will simply ignore it.

This practice is not recommended by the W3C, however in many cases, the only way you can test a property is to include the CSS extension that is compatible with your browser.

Be aware that if you choose to use the proprietary CSS extensions in a live environment, your code will not pass any W3C CSS validation, as the browser-specific properties are not valid W3C properties.

Many of the CSS3 examples on this website include these browser specific properties. If they weren't included, most of the examples wouldn't work for most users (at least, not until possibly years after the article was written).

The major browser manufacturers are working to support the W3C properties, and eventually, you will be able to omit these browser-specific properties.

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