Unity Non-Convex Mesh Colliders

Non-convex collider approximations that work with rigid bodies

This project provides three different approaches to approximate non-convex MeshColliders in Unity while remaining compatible with rigid bodies.

Unity does not allow non-convex MeshColliders on non-kinematic rigid bodies.
The systems in this repository work around this limitation by decomposing complex meshes into multiple simpler colliders that can safely participate in Unity’s physics simulation.

The focus is on:

• Robust runtime behavior
• Editor-time baking
• Configurability and clarity
• Minimal assumptions about mesh topology

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▶ Demo: https://www.youtube.com/shorts/yHOCyl136nw

🧩 DecompositionCollider

Voxel-based mesh decomposition into multiple MeshColliders

The DecompositionCollider splits a mesh into spatial regions using a voxel grid.
All triangles overlapping a voxel are grouped together and converted into a separate MeshCollider.

Each voxel group produces a small, locally convex (or nearly convex) mesh, allowing the resulting colliders to work reliably with rigid bodies.

Key characteristics

• Voxel grid based on mesh bounds
• Triangle grouping via AABB overlap
• One MeshCollider per voxel group
• Optional convex enforcement
• Editor-time baking

Use cases

• Large, complex static or dynamic meshes
• Objects that must interact physically with rigid bodies
• Replacing expensive or invalid non-convex MeshColliders

🧊 VoxelCollider

Solid voxel-based BoxCollider approximation

The VoxelCollider fills the interior of a mesh using a voxel grid and generates BoxColliders for all voxels that lie inside the mesh.

An optional greedy merge step combines adjacent voxels into larger boxes, drastically reducing collider count while keeping a good approximation.

Key characteristics

• Inside-test using ray–triangle intersection
• BoxCollider generation (physics-friendly)
• Optional voxel merging
• Very stable for dynamic rigid bodies

Use cases

• Performance-critical collision
• Rough but solid volume approximation
• Physics-heavy scenes with many interacting objects

🔵 PoissonDiscCollider

Surface-based sphere collider approximation

The PoissonDiscCollider samples points on the surface of a mesh using Poisson disk sampling.
Each sample point generates a SphereCollider, resulting in an even, surface-aligned collider distribution.

The points can optionally be inset along triangle normals to avoid surface penetration issues.

Key characteristics

• Area-weighted triangle sampling
• Evenly distributed surface points
• SphereCollider output
• Adjustable density and radius

Use cases

• Organic or irregular meshes
• Soft or rounded collision behavior
• Low-cost approximation for complex shapes

⚠️ Limitations

• These are approximations, not exact replacements
• Very small voxel sizes may lead to high collider counts
• Convex MeshColliders still inherit Unity’s convex hull limitations