Sceneform animation

Sceneform lets you import models with animation. You can use Sceneform APIs to play back and control the animation, and attach nodes to a model's skeleton.

For instance, the Sceneform Animation sample includes files used to build models of Andy the android and a baseball hat. The Andy model contains animation data, while the baseball hat is a non-animated model. When you run the sample, Andy breakdances and waves his arms while the hat remains fixed to his head using a node.

Sceneform model animation vs Android property animation

It's important to differentiate between model animation in Sceneform versus property animation in Android.

• Model animations are created ahead of time by artists using modeling and animation software. They contain skeletal animation data. These animations must be exported as *.fbx files, then imported into a *.sfb file to be used in Sceneform.

• Property animation is a fundamental Android concept and is not specific to Sceneform. This kind of animation can change any mutable value on a Java object that has a getter and a setter. The animated values can be set dynamically, but cannot be packaged into an *.sfb file.

  Both property and model animation support Android's Animator API . They both support listeners, playback control (start/stop/end/pause/cancel), duration, and start delay.

  Only limited support for TimeInterpolators playback is provided in the model animations. Reverse playback is not supported in model animations.

• To see Sceneform animation modeling in action, review the Animation sample.

• To see property animation using Sceneform in action, review the Solar System sample.

Model animation concepts

Before you start working with animated models, it's a good idea to understand specific concepts relating to skeletal animation, as well as related restrictions and features that apply to Sceneform.

• Bones. An animated model contains bones that are connected together, forming parent-child relationships in a hierarchy. Animation alters the position and orientation of bones during playback.

  In the same way that moving a parent Node in Sceneform causes all child Nodes to also move, moving a parent bone in Sceneform moves the children. Bones are movable by animation or accessed as a node via the SkeletonNode class. When bones are accessed as a Node, the new positions are overwritten every frame by animation if one is playing.

• Skeleton. The skeleton comprises all of the bones together, forming a hierarchy of parent-child relationships.

  For example, a model of a human arm might contain bones such as "left shoulder", "left upper arm", "left elbow", and "left forearm" and so on. Starting from the "left shoulder" as the parent of this hierarchy, "left upper arm" would be assigned as a child. The children of "left upper arm" might be the "left elbow" and lower bones. When the shoulder bone is rotated, the upper arm, forearm, elbow and any bones below would move in tandem.

  Sceneform doesn't have an API for changing the parent-child relationships between bones in the skeleton. This must be done ahead of time in an external modeling and animation package.

  Even models depicting inorganic objects can utilize skeletons to facilitate realism. For example, a model of a couch could have bones and a skeleton.

• Skin. The skin is a weight applied to the drawn surface mesh of the model. The position and shape of the skin mesh is calculated from the nearby bones. This bone to skin connection maps to how the model deforms, providing for more realistic movement.

  The skin must be prepared ahead of time using a modeling and animation package. Sceneform can alter the material of the skin mesh to change a model's appearance.