Key Concepts
Skeletal animation is great for organic-looking character animations. It allows meshes to be deformed by only animating a few 3D points (which are hierarchically organized into a “skeleton”) instead of having to animate each and every mesh vertex.
If you upload a 3D file with a skeletal animation to the console and open it in the scene editor, you will see your animated model.
In the example above, “Enable Debug Lines” and “Draw Skeleton” was toggled in the scene settings to see the skeleton as well (the yellow hierarchy). The animated model came from Mixamo.
Once the animated model was uploaded to the console, the animation-related assets generated were the following: Animation, Skeleton, Animation Set, and Animation Graph.
The two assets that are 3dverse-specific are the animation graph and the animation set.
The mesh, the skeleton and the animations can usually be exported quite easily from other tools (Blender, 3ds Max, etc.), but the logic that governs the choice of animation cannot be. This is where the animation graph comes into play.
Assets
Animation
A series of key poses. Each key pose correspond to a frame of the animation. A key pose is a pose of the skeleton, with transforms for each bone of the skeleton.
Skeleton
A skeleton is an asset which represents a 3D hierarchy of bones. A bone has a name and a transform, and is linked to other bones in a skeleton. Think of a bone more like a joint (point) than a bone (edge between two points).
Skinned Mesh
A mesh asset whose vertices are influenced by bones of a skeleton. A skinned mesh is a mesh with a bone id channel and a weight channel.
Animation Graph
An animation graph is an asset which applies some logic to animations. While it is running, the animation graph outputs a pose at each frame. Animation graphs run automatically at the start of each session.
To have control over animation transitions you will have to create a state machine in your animation graph.
While it is running, the animation graph is either in a state or in a transition between states. If it is in a state it computes and outputs the pose of that state. If it is in a transition between states, it blends between the pose of the initial state and the pose of the next state to generate the final pose.
The animation graph is an asset which describes the logic that governs animations. For example, if you want an animation to transition to another one (e.g. an idle animation transitioning to a walking animation), you can configure this in an animation graph.
Animation Set
The animation set is an asset which is simply a list of animations. The animation set works alongside the animation graph to provide the animations the graph will work with.
Components
Animation Controller
The animation_controller component has an animation graph reference and an animation set reference. If the animation graph has any inputs specified, they will show up in the animation controller.
In the scene itself the animation graph and animation set assets are linked to an entity via the animation controller component.
Bone
The bone component links the entity to a bone in the skeleton with its bone index attribute. The root bone (boneIndex=0) entity should also have a skeleton reference.
If set up correctly, the entity with bone component will be impacted by that bone’s animated transform. It is useful for incorporating external entities to your animation. For example, if you wanted to give your animated avatar a sword, you could parent the sword to the hand bone entity, and the sword will follow the animated hand movement.