Animations

Note: This documentation is for the old 0.2.0 version of A-Frame. Check out the documentation for the current 0.5.0 version

Animations in A-Frame are defined by attaching an <a-animation> element as a child of the entity to animate. The API is roughly based after the Web Animations specification.

As an introductory example, to define a 5-meter orbit on an entity about the Y-axis that takes 10 seconds, we can offset its position and animate the rotation of a parent entity. This animation starts with the initial rotation about the Y-axis of 0 degrees and goes around to 360 degrees. It’s defined with a duration of 10000 milliseconds, maintains the final value on each cycle of the animation, and loops indefinitely.

<a-entity>
<a-entity position="5 0 0"></a-entity>
<a-animation attribute="rotation"
dur="10000"
fill="forwards"
to="0 360 0"
repeat="indefinite"></a-animation>
</a-entity>

Many attributes and values are used to define animations. We’ll delve into more detail below:

AttributeDescriptionDefault Value
attributeAttribute to animate. To specify a component attribute, use componentName.property syntax (e.g., light.intensity).rotation
beginDelay (in milliseconds) or event name to wait on before beginning animation.0
directionDirection of the animation (between from and to). One of alternate, alternateReverse, normal, reverse.normal
durDuration in (milliseconds) of the animation.1000
easingEasing function of the animation. There are very many to choose from.ease
fillDetermines effect of animation when not actively in play. One of backwards, both, forwards, none.forwards
fromStarting value.Current value.
repeatRepeat count or indefinite.0
toEnding value. Must be specified.None

Animating Different Types of Attributes

A-Frame’s animation system can animate several possible categories of attributes.

vec3 Attributes

A-Frame has several standard vec3 components (i.e., position, rotation, and scale). These components consist of three factors: X, Y, and Z. We can pass three space-delimited numbers to the from and to attributes just as we would define them on an entity. In this case, the animation system will assume we are animating a vec3 value.

For example, if we want to animate an entity going from one spot to another, we can animate the position component.

<a-entity>
<a-animation attribute="position" from="1 1 1" to="2 4 -8"></a-animation>
</a-entity>

Boolean Attributes

A-Frame has several standard components that accept a single boolean value. Boolean values can be “animated” as well by flipping the boolean at the end of each animation cycle.

For example, we can define an animation that toggles off the visibility of an entity after 5 seconds.

<a-entity>
<a-animation attribute="visible" dur="5000" to="false" repeat="indefinite"></a-animation>
</a-entity>

Numeric Attributes

We can animate numeric attributes as well. For example, we can animate the intensity of the light primitive.

<a-light intensity="1">
<a-animation attribute="intensity" to="3"></a-animation>
</a-light>

Component Properties

We can animate a certain property of a multi-property component. To do so, we select the component property using the dot syntax: componentName.propertyName.

For example, to animate a cone’s top radius, we can select the radiusTop value with geometry.radiusTop.

<a-entity geometry="primitive: cone; radiusTop: 1">
<a-animation attribute="geometry.radiusTop" to="0.5"></a-animation>
</a-entity>

Begin

The begin attribute defines when the animation should start playing.

This can either be a number, representing milliseconds to wait, or an event name to wait for. For example, we can define an animation that waits 2 seconds from when the animation is attached before scaling an entity.

<a-entity>
<a-animation attribute="scale" begin="2000" to="2 2 2"></a-animation>
</a-entity>

Or we can define an animation that waits for the parent element to trigger an event named fade before fading an entity.

<a-entity id="fading-cube" geometry="primitive: box" material="opacity: 1">
<a-animation attribute="material.opacity" begin="fade" to="0"></a-animation>
</a-entity>
// Trigger an event to begin fading.
document.querySelector('#fading-cube').emit('fade');

Direction

The direction attribute defines which way to animate between the starting value and the final value.

When an alternating direction is defined, the animation will go back and forth between the from and to values like a yo-yo. Alternating directions only take affect when the animation is set to repeat.

ValueDescription
alternateOn even-numbered cycles, animate from from to to. On odd-numbered cycles, animation from to to from
alternate-reverseOn odd-numbered cycles, animate from from to to. On even-numbered cycles, animation from to to from
normalAnimate from from to to.
reverseAnimate from to to from.

Easing

The easing attribute defines the easing function of the animation, which defaults to ease. There are too many easing functions to list, but we can implicitly explain what all of them are.

One possible value is linear. And the basic easing functions are ease, ease-in, ease-out, and ease-in-out.

Then there are additional groups of easing functions. Each group of easing functions are prefixed by the above basic easing functions. The groups of easing functions are cubic, quad, quart, quint, sine, expo, circ, elastic, back, and bounce.

For example, the cubic group of easing functions would consist of ease-cubic, ease-in-cubic, ease-out-cubic, ease-in-out-cubic.

Fill

The fill attribute defines the effect of animation when not actively in play. Think of fill as what values the animation sets on the entity before and/or after each animation cycle. Below are the possible values for fill and their effects.

ValueDescription
backwardsBefore the animation starts, set the starting value to the from value.
bothCombine the effects of both backwards fill and forwards fill.
forwardsAfter the animation finishes, the final value will stay at the to value. The default fill.
noneBefore the animation starts, set the starting value to the initial value. After the animation finishes, reset the value to the initial value.

Repeat

The repeat attribute defines how often the animation repeats. We call each repeat of the animation a cycle. Repeat can either be a number that counts down on each animation cycle until it reaches 0 at which point the animation will end, or it can be set to indefinite and the animation will loop continuously until the animation is manually removed or stopped.

Events

The <a-animation> element emits a couple of events.

Event NameDescription
animationendEmitted when the animation finishes. In case of repeats, emitted when the repeat count reaches 0. Not emitted for indefinite repeats.
animationstartEmitted immediately when the animation begins playing.