Bone Attachemnts

CPU Animator

CPU Animator writes animated bone positions back to the LocalTransform components of corresponding bone entities. No special preparation step is needed to work on bone attachments properly. Just make the attachment entity a child of required bone entity.

GPU Animator

Bone entities cannot be moved by the GPU animation engine. The simple attachment process used in the CPU Animator would not work. Because bone calculation is performed on GPU, all frame bone placement data is stored in GPU memory and cannot be copied to the main memory to be used by entities at the same frame. Nevertheless, a special shader can be created, which will move all model vertex positions according to the animation frame.

Bone attachment shader using ShaderGraph

The process is similar to the making of a deformation-aware shader for an ECS skinned mesh renderer.

• Create a new shader graph according to the render pipeline used in your project.
• Open it and add the Custom Function node.
• Set Type to File.
• Set Name to GPUAttachmentMeshMover.
• Set Source to GPUAttachmentShaderNode.hlsl (located at Rukhanka.Runtime/GPUAnimationEngine/Resources/GPUAttachment directory).
• Configure three input ports of this custom node:
  • vertex with type Vector 3.
  • normal with type Vector 3.
  • tangent with type Vector 3.
• Configure three output ports:
  • animatedVertex with type Vector 3.
  • animatedNormal with type Vector 3.
  • animatedTangent with type Vector 3.
• Create three additional nodes in the shader graph:
  • Geometry Position with Space property set to Object.
  • Geometry Normal Vector with Space property set to Object.
  • Geometry Tangent Vector with Space property set to Object.

• Connect the Out port of the Position node with the vertex port of the GPUAttachmentMeshMover (Custom Function) node.
• Connect the Out port of the Normal Vector node with the normal port of the GPUAttachmentMeshMover (Custom Function) node.
• Connect the Out port of the Tangent Vector node with the tangent port of the GPUAttachmentMeshMover (Custom Function) node.
• Connect the animatedPosition, animatedNormal, and animatedTangent output ports of the GPUAttachmentMeshMover (Custom Function) node to the vertex position, normal, and tangent ports in the master node respectively.

You should get the following shader graph:

• Complete fragment part of the shader graph with appropriate texture sampling (albedo, normal map), color modulation, etc.

Use the created shader as a material shader of your GPU-attached meshes.

Marking mesh as GPU attachment

Rukhanka must supply a GPU attachment shader with appropriate rig data. To be able to do this, you must add GPU Attachment Authoring Unity component to every authoring mesh in authoring GameObject:

Important

Object with GPU bone attachment shader but without GPU Attachment Authoring will be rendered incorrectly, or will completely disappear from the scene.

info

GPU attachments will work normally as ordinary CPU attachments