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My First Animation Clip

What does it show?

This sample shows how to play an animation clip in a loop on an existing model in a scene.

Overview

The entry point to this sample is the root GameObject in the subscene. There are two important Unity components attached to this GameObject:

  1. The RigComponent component (from the Unity.Animation package) which defines the rig for the object. During entity conversion, it is converted to a Rig ECS component.
  2. The ClipPlayer component. This allows you to choose an animation clip to play on the rig. It is converted to a PlayClipComponent ECS component.

The only part left to understand is the PlayClipSystem. The system does the following:

  • for every PlayClipComponent, it creates an animation graph, and registers it to the AnimationGraphSystem from the Unity.Animation package.
  • it keeps track of the generated graphs by attaching a PlayClipStateComponent to the entity;
  • when a PlayClipComponent is deleted or changed, the corresponding graph is deleted or updated.

Note that this system is not doing any of the actual computation involved in performing the animation. The AnimationGraphSystem executes the graphs, and the AnimatedData buffers are updated on the entity by the ComponentNode.

The Animation Graph

The animation graph is using the Data Flow Graph (DFG) to compute an animation. The animation graph is the central concept that drives the animation.

When an animated entity is added, the PlayClipSystem creates a ClipPlayerNode and a ComponentNode (associated with this entity). It sets up parameters (like the clip to be played) on the ClipPlayerNode by sending it messages. It also connects the output of the ClipPlayerNode to the input of the ComponentNode. This will set the data of the AnimatedData buffer on the entity. When a PlayClipComponent changes, the PlayClipSystem sends another message to the graph to update the clip in use.

The AnimationGraphSystem from the Unity.Animation package automatically updates the graphs and applies the output to the entity.

When the PlayClipComponent is removed from an entity, the PlayClipSystem needs to release the nodes created for this instance to avoid a leak. This is why PlayClipStateComponent exists.

Time Management

Each rig entity has a component DeltaTime. This component is updated by the UpdateAnimationDeltaTime system. Using a ComponentNode, the graph connects the value of the DeltaTime component to the converter node ConvertDeltaTimeToFloatNode, and the output of the node is used as an input to evaluate the clip.