Armature Capture geometry node

Represent a pose as a float point attribute.

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Overview
Proxy Geometry
Constraints
Parameters
Inputs
Outputs

Overview ¶

This is a capture node for Armature Deform. It allows you to prepare a proxy geometry used by Armature Deform to run a simulation.

Armature Deform is used together with Armature Capture. Armature Deform performs the quasistatic simulation and deformation, while Armature Capture prepares the proxy geometry for simulation.

For most cases, the internals of Armature Capture cook once, allowing you to apply Armature Deform efficiently on various different poses. Make sure the Animated Pose input is the only input of Armature Capture that is time dependent. Having other inputs of Armature Capture time dependent would trigger expensive re-cooks.

Proxy Geometry ¶

Armature Capture creates a proxy geometry used for simulation by Armature Deform. This proxy geometry is optimized for simulation and has a connectivity independent of the skin mesh connectivity.

The Element Size controls how fine the proxy geometry is A smaller Element Size results in more fine details in the deformations. Make sure to avoid choosing an Element Size too small that the proxy geometry’s details exceeds the skin geometry’s details. The Element Size very roughly corresponds to the average distance from each primitive (triangle or tet) centroid to each of the primitive’s vertices.

The proxy geometry can have less fine details compared to the skin mesh. If you use a coarse proxy geometry and you see visible artifacts, try increasing the Smoothing Level. It’s not recommended to use a proxy geometry that is more detailed than the skin. The final skin output by Armature Deform won’t be able to reproduce the extra detail present in the deformed proxy geometry.

Lowering Element Size will increase the number of primitives (tets) in the proxy geometry. This may cause Armature Deform to become slower and cause problems for the simulation as well. For basic use cases, tune Element Size use a few ten thousands tets. For detailed models, use a few hundred thousand tets. If you exceed a million tets, the results may be less stable and lower quality from Armature Deform. You may need to increase the Steps and Iterations parameters on Armature Deform to make the simulation work.

Constraints ¶

Armature Capture includes constraint points in the proximity of bone surfaces. Armature Deform puts these constraint points in animated positions, controlled by the Animated Pose input. To generate them properly, make sure the bone surfaces are contained within the skin.

For best results, make sure to use bone surfaces that are not too close to the skin. This allows more space to put tets between the bone surfaces and the skin. The results has more visible effects of tissue deformation on the skin. Moving the bone surfaces deeper into the interior allows the tissue deformation to show better without needing to increase the proxy geometry resolution, which has performance and potential stability implications.

The proximity geometry has a color attribute Cd which indicates:

Points that are unconstrained (white).
Bone proxy points that are constrained (blue).
Skin proxy points that are constrained (red).

Parameters ¶

Proxy Geometry

Element Size

Controls the size of each primitive in the proxy geometry that undergoes a tissue sim. Smaller numbers adds more details but makes the tissue sim more expensive.

Quality Threshold

Primitives with quality below this threshold are eliminated from the proxy geometry. The higher this value, the higher the minimum quality that is enforced. Eliminating poor quality primitives can help keep a simulation more stable. Setting this value too high may lead to problems where the proxy geometry has noticable holes.

Relative Volume Threshold

Tets whose volume is strictly less than this relative threshold times the average volume of all tets will be discarded. This can help keep a simulation more stable. Setting this value too high may lead to problems where the proxy geometry has noticable holes.

Skin Capture

The amount of smoothing applied at the skin capture stage. This helps get smoothly deformed skin when you use a large Element Size.

Constraints

Constrain to Bones

When on, the bone surfaces incorporated as constraints in the tissue simulation.

Constrain Skin

When on, a group of skin points can be constrained to the skin animation during the tissue simulation. This only works if the skin has valid capture weights for the capture pose on the Rest Point Transforms input. If Constrain to Bones is enabled as well, it is essential that both the bone geometry and the skin geometry match up properly in constrained regions when animated by bone deform.

Use Skin Target Strength

Enable the use of a multiplier for the Skin Target Strength.

Target Strength

This point attribute acts as a multiplier for the Skin Target Strength. This attribute can be assigned values between 0 and 1 that act as multipliers for the strength of the skin constraint force.

Inputs ¶

Skin to Deform

The skin deformed by a proxy geometry that undergoes a tissue simulation.

Capture Pose

The capture pose for the capture weights on the Bone Surfaces.

Animated Pose

A deformed pose. Not used and is passed to the corresponding output.

Armature Geometry

This is the Bone Surfaces. This geometry inside of the skin must have capture weights. It can be deformed using Bone Deform. This geometry can represent anatomical bone surfaces, muscles, or a combination.

Outputs ¶

Proxy Geometry to Simulate

A geometry used in a tissue simulation. After the simulation, this geometry deforms the skin.