Patrick Walton d2624765d0 Implement animation masks, allowing fine control of the targets that animations affect. (#15013) ... This commit adds support for *masks* to the animation graph. A mask is a set of animation targets (bones) that neither a node nor its descendants are allowed to animate. Animation targets can be assigned one or more *mask group*s, which are specific to a single graph. If a node masks out any mask group that an animation target belongs to, animation curves for that target will be ignored during evaluation. The canonical use case for masks is to support characters holding objects. Typically, character animations will contain hand animations in the case that the character's hand is empty. (For example, running animations may close a character's fingers into a fist.) However, when the character is holding an object, the animation must be altered so that the hand grips the object. Bevy currently has no convenient way to handle this. The only workaround that I can see is to have entirely separate animation clips for characters' hands and bodies and keep them in sync, which is burdensome and doesn't match artists' expectations from other engines, which all effectively have support for masks. However, with mask group support, this task is simple. We assign each hand to a mask group and parent all character animations to a node. When a character grasps an object in hand, we position the fingers as appropriate and then enable the mask group for that hand in that node. This allows the character's animations to run normally, while the object remains correctly attached to the hand. Note that even with this PR, we won't have support for running separate animations for a character's hand and the rest of the character. This is because we're missing additive blending: there's no way to combine the two masked animations together properly. I intend that to be a follow-up PR. The major engines all have support for masks, though the workflow varies from engine to engine: * Unity has support for masks [essentially as implemented here], though with layers instead of a tree. However, when using the Mecanim ("Humanoid") feature, precise control over bones is lost in favor of predefined muscle groups. * Unreal has a feature named [*layered blend per bone*]. This allows for separate blend weights for different bones, effectively achieving masks. I believe that the combination of blend nodes and masks make Bevy's animation graph as expressible as that of Unreal, once we have support for additive blending, though you may have to use more nodes than you would in Unreal. Moreover, separating out the concepts of "blend weight" and "which bones this node applies to" seems like a cleaner design than what Unreal has. * Godot's `AnimationTree` has the notion of [*blend filters*], which are essentially the same as masks as implemented in this PR. Additionally, this patch fixes a bug with weight evaluation whereby weights weren't properly propagated down to grandchildren, because the weight evaluation for a node only checked its parent's weight, not its evaluated weight. I considered submitting this as a separate PR, but given that this PR refactors that code entirely to support masks and weights under a unified "evaluated node" concept, I simply included the fix here. A new example, `animation_masks`, has been added. It demonstrates how to toggle masks on and off for specific portions of a skin. This is part of #14395, but I'm going to defer closing that issue until we have additive blending. [essentially as implemented here]: https://docs.unity3d.com/560/Documentation/Manual/class-AvatarMask.html [*layered blend per bone*]: https://dev.epicgames.com/documentation/en-us/unreal-engine/using-layered-animations-in-unreal-engine [*blend filters*]: https://docs.godotengine.org/en/stable/tutorials/animation/animation_tree.html ## Migration Guide * The serialized format of animation graphs has changed with the addition of animation masks. To upgrade animation graph RON files, add `mask` and `mask_groups` fields as appropriate. (They can be safely set to zero.)		2024-09-02 17:10:34 +00:00
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Fox.animgraph.ron	Implement animation masks, allowing fine control of the targets that animations affect. (#15013)	2024-09-02 17:10:34 +00:00