This article introduces an animation system for Cocos Creator(3D). "NewGenAnim" is its name during development.
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Animation graph is a kind of asset which describes how multiple animation states are combined, how control flow is determined by a group of variables.
Animation graph by itself is a directional graph. Edges are called as transitions. In distinction to scene node, nodes in animation graph are called as graph nodes(however in term of this article "node" is an alias of graph node).
In general, every node may have a motion associated or not. Motion is the abstract of an animation representation.
There may be four kinds of nodes:
- entry node;
- exit node;
- "any" node;
- and, plain nodes, those do not belong to above.
Entry node, exist node and "any" node are built-in nodes which was borned once the graph is created. As their name suggested, the entry node is the initial node when the animation graph is constructed. The exit node has meaning of stopping the control flow. The "any" node is pretty special: outgoing transitions from the "any" node are considered as if that transitions are also emitted from other nodes, except for transition destination.
As their special meanings, no incoming transition is allowed for entry node or "any" node, and no outgoing transition is allowed for exist node. Motion on "any" node would take no effect.
There are two kinds of motion: state motion and blend tree.
State motion is a motion controls the playback of an animation clip. It internally wraps an animation state for that purpose.
Blend tree is a more complex type of motion. Every blend tree has a blender controlling how a group of sub-motion are blending together according to some blend arguments. The blender yeilds weights for each sub-motion.
The blend arguments usually reflect specular game logic. Such as speed, velocity, timing and so on. Depend on dimension of those argument value, there are also different blenders.
The 1D Blender accepts a single number argument. It records a threshold for each motion it's going to blend. If the blend argument matches the threshold, the corresponding motion was taken to play. Or if the blend argument is in bettwen two thresholds, the two corresponding motions were blended according to the ratio.
The most common use case of 1D blenders is to model blending of idle/walk/run of a character by it's speed.
{
nodes: {
'movemotion': {
motion: { // blend tree, 1D blender
motions: ['idle', 'walk', 'run'], // every sub-motion is a state motion
thresholds: [0, 0.5, 1.0], // threshold of every sub-motion
argument: 'speed',
}
},
},
variables: {
speed: 0,
},
}{
nodes: {
'movemotion': {
motion: { // blend tree, 2D blender
algorithm: 'freeform-directional',
motions: [ // every sub-motion is a state motion
'idle', 'walk', 'run',
'turn-left', 'walk-left', 'run-left',
'turn-right', 'walk-right', 'run-right',
],
thresholds: [ // threshold of every sub-motion
[0.0, 0.0], [0.5, 0.0], [1.0, 0.0],
[0.0, -1.0], [0.5, -1.0], [1.0, -1.0],
[0.0, 1.0], [0.5, 1.0], [1.0, 1.0],
],
argument: ['speed', 'turnSpeed'],
}
},
},
variables: {
speed: 0,
turnSpeed: 0,
},
}