Animation: Layered Blend Per Bone / Additive Blending #14395
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A-Animation
Make things move and change over time
C-Feature
A new feature, making something new possible
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ethereumdegen
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One way we could do this simply is by allowing for the animation system to define a 'BoneSet' which is a group of bones, and then you can have weights PER bone set as opposed to weights per the entire AnimGraph . |
alice-i-cecile
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Looks somewhat related to #14230 (the additive blending part) |
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#15013 implements most of this, but not the additive blending part. |
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…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.)
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pcwalton
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Oct 3, 2024
*Additive blending* is an ubiquitous feature in game engines that allows animations to be concatenated instead of blended. The canonical use case is to allow a character to hold a weapon while performing arbitrary poses. For example, if you had a character that needed to be able to walk or run while attacking with a weapon, the typical workflow is to have an additive blend node that combines walking and running animation clips with an animation clip of one of the limbs performing a weapon attack animation. This commit adds support for additive blending to Bevy. It builds on top of the flexible infrastructure in bevyengine#15589 and introduces a new type of node, the *add node*. Like blend nodes, add nodes combine the animations of their children according to their weights. Unlike blend nodes, however, add nodes don't normalize the weights to 1.0. The `animation_masks` example has been overhauled to demonstrate the use of additive blending in combination with masks. There are now controls to choose an animation clip for every limb of the fox individually. This patch also fixes a bug whereby masks were incorrectly accumulated with `insert()` during the graph threading phase, which could cause corruption of computed masks in some cases. Note that the `clip` field has been replaced with an `AnimationNodeType` enum, which breaks `animgraph.ron` files. The `Fox.animgraph.ron` asset has been updated to the new format. Closes bevyengine#14395.
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#15631 implements this. |
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*Additive blending* is an ubiquitous feature in game engines that allows animations to be concatenated instead of blended. The canonical use case is to allow a character to hold a weapon while performing arbitrary poses. For example, if you had a character that needed to be able to walk or run while attacking with a weapon, the typical workflow is to have an additive blend node that combines walking and running animation clips with an animation clip of one of the limbs performing a weapon attack animation. This commit adds support for additive blending to Bevy. It builds on top of the flexible infrastructure in #15589 and introduces a new type of node, the *add node*. Like blend nodes, add nodes combine the animations of their children according to their weights. Unlike blend nodes, however, add nodes don't normalize the weights to 1.0. The `animation_masks` example has been overhauled to demonstrate the use of additive blending in combination with masks. There are now controls to choose an animation clip for every limb of the fox individually. This patch also fixes a bug whereby masks were incorrectly accumulated with `insert()` during the graph threading phase, which could cause corruption of computed masks in some cases. Note that the `clip` field has been replaced with an `AnimationNodeType` enum, which breaks `animgraph.ron` files. The `Fox.animgraph.ron` asset has been updated to the new format. Closes #14395. ## Showcase https://github.com/user-attachments/assets/52dfe05f-fdb3-477a-9462-ec150f93df33 ## Migration Guide * The `animgraph.ron` format has changed to accommodate the new *additive blending* feature. You'll need to change `clip` fields to instances of the new `AnimationNodeType` enum.
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What problem does this solve or what need does it fill?
I want to be able to have apply a normal 'running' animation to my characters whole body, but then also be able to apply a bone-layer-masked animation to just the torso of the character on TOP of that running animation at will.
What solution would you like?
I would like for the bevy animation system to be able to support 'Layered Blend Per Bone' , the ability to apply an animation to a particular set of bones ( by bone [node] name ). Ideally, I also want the blend to apply in such a way that my layered animation is FULLY expressed, not averaged down by a division of the total weights of all animations. This is because I want the sword slash on the torso to look complete and not weird like it does when trying to blend it in 0.14 .
To be honest, an example with a humanoid who is running and sometimes doing a sword slash would be preferable to the fox example because i dont think the fox example is powerful enough to full express and capture what is needed.
What alternative(s) have you considered?
Additional context
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