Collision mesh

A collision mesh is a cheap 3D mesh used by VPhysics. It is sometimes called a collision model, after the object that loads it into the engine, but as far as creating models is concerned it is a vertex mesh more or less like any other.

Collision meshes are invisible, and should be extremely low-detail compared to the model's visible components (see the images to the right for two examples). The lack of precision will not be noticed, except in that it doesn't grind the simulation to a halt!

Caveats

• Collision meshes must be convex. To create an accurate collision mesh for a concave model create multiple, separate convex objects, intersecting them if necessary.
• Each face on a given convex object must be assigned the same texture and (if applicable) smoothing group if it is to be exported to a collision mesh.
• Unlike a reference mesh, a collision mesh must be solid on all sides. Errors similar to "WARNING: Model has 2-dimensional geometry" mean there is a missing face somewhere.
  Tip:This can happen if two convex objects become merged; in 3DS Max ensure you have applied at least one smoothing group before exporting.

See also

• $collisionmodel - QC command for collision meshes without moving parts
• $collisionjoints - QC command for collision meshes with moving parts
• VPhysics
• Physics and Ragdolls
• SMD Collisionmodel Prep 3DS Max Tool Version 1.0