Handle animations

3D models in .glTF and .glb format can include as many animations as you want in them. Animations tell the mesh how to move, by specifying a series of keyframes that are laid out over time, the mesh then blends from one pose to the other to simulate continuous movement.

Most 3D model animations are skeletal animations. These animations simplify the complex geometry of the model into a “stick figure”, linking every vertex in the mesh to the closest bone in the skeleton. Modelers adjust the skeleton into different poses, and the mesh stretches and bends to follow these movements.

As an alternative, vertex animations animate a model without the need of a skeleton. These animations specify the position of each vertex in the model directly. Decentraland supports these animations as well.

See Animations for details on how to create animations for a 3D model. Read Shape components for instructions on how to import a 3D model to a scene.

💡 Tip: Animations are usually better for moving something in place, not for changing the position of an entity. For example, you can set an animation to move a character’s feet in place, but to change the location of the entity it’s best to use the Transform component. See Positioning entities for more details.

Check a 3D model for animations #

Not all glTF files include animations. To see if there are any available, you can do the following:

• If using VS Code(recommended), install the GLTF Tools extension and view the contents of a glTF file there.
• Open the Babylon Sandbox site and drag the glTF file (and any .jpg or .bin dependencies) to the browser.
• Open the .glTF file with a text editor and scroll down till you find “animations”:.

💡 Tip: In skeletal animations, an animation name is often comprised of its armature name, an underscore and its animation name. For example myArmature_animation1.

Automatic playing #

If a 3D model includes any animations, the default behavior is that the first of these is always played on a loop.

To avoid this behavior, add an Animator component to the entity that has the model, and then handle the playing of animations explicitly. If an Animator component is present in the entity, all animations default to a playing: false state, and need to be manually played.

Handle animations explicitly #

An Animator component is used to access all the animations of the entity and can be used to explicitly tell the entity to play or stop an animation. The Animator component includes an array of states, this list must include one object for each one of the animations that the 3D model can perform. A single Animator can include as many states as needed.

// Create entity
const shark = engine.addEntity()

// Add a 3D model to it
GltfContainer.create(shark, {
	src: 'models/shark.glb'
})

Animator.create(shark, {
	states:[{
			name: "swim",
			clip: "swim",
			playing: true,
			loop: true
		}
	]
})

Each state object keeps track of if an animation is currently playing.

Fetch an animation #

Fetch a clip from the Animator by name using the .Animator.getClip() function. This function returns a mutable version of the animation state object.

const swimAnim = Animator.getClip(sharkEntity, "swim")

Animator.getClip requires the following parameters:

• entity: The entity of the Animator component that you want to query.
• name: The name of the animation state you want to fetch. If the animation state has no matching name property, it looks for matching clip properties.

Animator.getClip fetches a mutable version of the animation state, so you can modify values freely on what this function returns.

const swimAnim = Animator.getClip(sharkEntity, "swim")
swimAnim.looping = false 

📔 Note: If you attempt to use Animator.getClip() to fetch a clip that exists in the 3D model, but is not listed in the Animator component, it returns null.

Play an animation #

The .playing field in an animation state determines if the animation is currently playing. Note that multiple animations may be playing in a single 3D model at the same time.

Use the Animator.playSingleAnim() function on an AnimationState object.

Animator.playSingleAnim(sharkEntity, "swim")

If the entity was playing any other animations, Animator.playSingleAnim stops them.

Animator.playSingleAnim requires the following parameters:

• entity: The entity of the Animator component that you want to affect.
• name: String for the name of the animation state you want to play. If the animation state has no matching name property, it looks for matching clip properties.
• resetCursor: (optional) If true, it plays the animation from the start, even if the animation was previously paused. If false, it will keep playing the animation from where it was paused. Default: true.

Animator.playSingleAnim(sharkEntity, "swim", false)

The following table summarizes how Animator.playSingleAnim() behaves, using different values for the resetCursor property:

Looping animations #

By default, animations are played in a loop that keeps repeating the animation forever.

Change this setting by setting the loop property in the state object.

Animator.create(shark, {
	states:[{
			name: "bite",
			clip: "bite",
			playing: true,
			loop: false
		}
	]
})

If looping is set to false, the animation plays just once and then stops, staying on the posture of the last frame.

Stop an animation #

To stop all animations that an entity is playing, use Animator.stopAnims().

Animator.stopAnims(shark)

Animator.stopAnims requires the following parameters:

• entity: The entity of the Animator component that you want to affect.
• resetCursor: (optional) If true, it returns to the posture in the first frame of the animation. If false, stays paused in its current posture. Default: true.

📔 Note: When playing an animation with Animator.playSingleAnim, this function handles stopping all other animations behind the scenes. You don’t need to explicitly stop other animations in that case.

When an animation finishes playing a non-looping animation, by default the 3D model remains in the last posture it had. To change this default behavior so that when the animation ends it goes back to the first posture, set the shouldReset property to true.

Animator.create(shark, {
	states:[{
			name: "bite",
			clip: "bite",
			playing: true,
			shouldReset: true,
			loop: true
		}
	]
})

You can also use Animator.stopAnims() at any time to explicitly set the posture back to the first frame in the animation.

📔 Note: Resetting the posture is an abrupt change. If you want to make the model transition smoothly tinto another posture, you can either:

- apply an animation with a `weight` property of 0 and gradually increase the `weight`
- create an animation clip that describes a movement from the posture you want to transition from to the default posture you want.

Handle multiple animations #

If a 3D model has multiple animations packed into it, a single Animator component can deal with all of them.

// Create entity
const shark = engine.addEntity()

// Add a 3D model to it
GltfContainer.create(shark, {
	src: 'models/shark.glb'
})

Animator.create(shark, {
	states:[{
			name: "swim",
			clip: "swim",
			playing: true,
			loop: true
		}. {
			name: "bite",
			clip: "bite",
			playing: true,
			loop: true
		}
	]
})

In the example above, two animations are handled by separate state objects, and they are then both assigned to the same Animator component.

Each bone in an animation can only be affected by one animation at a time, unless these animations have a weight that adds up to a value of 1 or less.

If one animation only affects a character’s legs, and another only affects a character’s head, then they can be played at the same time without any issue. But if they both affect the character’s legs, then you must either only play one at a time, or play them with lower weight values.

If in the above example, the bite animation only affects the shark’s mouth, and the swim animation only affects the bones of the shark’s spine, then they can both be played at the same time if they’re on separate layers.

📔 Note: Animator.playSingleAnim() stops all other animations that the entity is currently playing. To play multiple animations at the same time, modify the playing property in the animation states manually.

Animation speed #

Change the speed at which an animation is played by changing the speed property. The value of the speed is 1 by default.

Animator.create(shark, {
	states:[{
			name: "swim",
			clip: "swim",
			playing: true,
			loop: true,
			speed: 2
		}
	]
})

Set the speed lower than 1 to play it slower, for example to 0.5 to play it at half the speed. Set it higher than 1 to play it faster, for example to 2 to play it at double the speed.

const swimAnim = Animator.getClip(sharkEntity, "swim")

swimAnim.speed = 0.5

Animation weight #

The weight property allows a single model to carry out multiple animations on different layers at once, calculating a weighted average of all the movements involved in the animation. The value of weight determines how much importance that animation will be given in the average.

By default, weight is equal to 1. The value of weight can’t be any higher than 1.

Animator.create(shark, {
	states:[{
			name: "swim",
			clip: "swim",
			playing: true,
			loop: true,
			weight: 0.2
		}
	]
})

The weight value of all active animations in an entity should add up to 1 at all times. If it adds up to less than 1, the weighted average will be using the default position of the armature for the remaining part of the calculation.

For example, in the code example above, we’re playing the swim animation, that only has a weight of 0.2. This swimming movement will be quite subtle: only 20% of the intensity that the animation defines. The remaining 80% of the calculation takes values from the default posture of the armature.

The weight property can be used in interesting ways, for example the weight property of swim could be set in proportion to how fast the shark is swimming, so you don’t need to create multiple animations for fast and slow swimming.

You could also change the weight value gradually when starting and stopping an animation to give it a more natural transition and to avoid jumps from the default pose to the first pose in the animation.

📔 Note: The added weight value of all animations that are acting on a 3D model’s bone can’t be more than 1. If more than one animation is affecting the same bones at the same time, they need to have their weight set to values that add to less than 1.

const swimAnim = Animator.getClip(sharkEntity, "swim")

swimAnim.weight = 0.5