Simple Physics 为 Unity 提供了基于物理的轻量级、易于使用的行为（绳索、布料、软体）。
This project provides a collection of physics-based behaviors for Unity, including ropes, cloth, and soft bodies.
The focus is on simplicity and usability, aiming for minimal authoring effort while keeping the systems easy to understand, modify, and integrate into existing projects.
Using Rigidbodies and ConfigurableJoints
The rope system is split into a generator and a runtime component.
The generator instantiates a chain of prefab Rigidbody points and connects them using ConfigurableJoints, with configurable spacing and joint parameters.
The runtime Rope component handles visualization by collecting the generated segment transforms and updating a LineRenderer each frame so the rope follows the simulated rigidbody positions.
Demo: https://www.youtube.com/shorts/QTXzCxIQ-xY
Using Rigidbodies and ConfigurableJoints
The cloth system also consists of a generator and a runtime component.
The generator creates a 2D grid of prefab Rigidbody points and connects neighboring points using ConfigurableJoints to form the cloth structure.
The Cloth component is responsible for visualization and optional collision behavior.
It can render the cloth as a wireframe using line renderers or as a dynamically generated mesh whose vertices are updated each frame from the simulated point positions. Optional mesh collider updates prevent rigidbodies from passing through the cloth, provided the cloth points are not spaced too far apart.
Demo: https://www.youtube.com/shorts/QTXzCxIQ-xY
Joint-based volumetric soft body using mesh topology
SoftBody is an soft-body implementation that derives its simulation structure directly from a mesh.
At runtime, the mesh is cloned and its vertices are merged to remove duplicates. For each unique vertex, a prefab Rigidbody is instantiated and positioned at the corresponding vertex location.
Edges are extracted from the mesh triangles, and ConfigurableJoints are created between rigidbodies that share an edge. These joints use linear and angular drives to approximate elastic behavior based on the original mesh topology.
Each frame, the mesh is deformed by updating its vertices from the current rigidbody positions.
An optional mesh collider can be generated and updated dynamically, and collision impulses can be relayed back to nearby rigidbodies to improve interaction with external objects.
SoftBody variant with internal pressure forces
ClothBalloon works like SoftBody, deriving its simulation structure from a mesh by creating rigidbodies per unique vertex and connecting them using ConfigurableJoints.
In addition, the current mesh volume is evaluated each physics step and used to apply outward pressure forces to all surface triangles, allowing the object to inflate, compress, and behave like a balloon.
Mesh deformation, optional collider updates, and collision impulse handling work the same way as in SoftBody.
Surface-sampled joint soft body with mesh skinning
EmbeddedSoftBody distributes prefab rigidbodie points across a mesh surface using Poisson disk sampling.
These points are connected with ConfigurableJoints based on nearest neighbors to form the simulation structure.
At runtime, the mesh is cloned and bound to the simulated points.
Each vertex is influenced by up to four nearby rigidbodies using weighted skinning, and the mesh vertices are updated every frame from the current rigidbody transforms.
An optional mesh collider can be generated and updated dynamically.
Collision impulses can be relayed to nearby rigidbodies.
SoftMeshLight and SoftMesh used to be part of this project and have been removed from it.
Both components, including their demo scenes and assets, now live in their own repository: Unity Soft Mesh.
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