ObiRope Mesh Renderer

[josemendez]

Thanks! Just to clarify - can I use the shark, as shown in the attached photo, with the Obi Rope Mesh Renderer and have it behave exactly like the default Obi Rope and collisions will work without visual problems?

No. The mesh used for rendering the rope is only used for rendering, it is not taken into account during simulation in any way. Obi is a particle-based engine, everything in it is entirely particle-based including collision detection.

In general, the more your mesh resembles a rope the better. There's certain meshes that are more "rope like" than others. The shark in the example scene is an example of taking this to the limit - though it's longer than wider, a shark is obviously not a rope and has parts that stick out like fins, tail, etc that cannot be accurately approximated as a chain of particles. While it works well for the use case shown in the scene - to represent a hanging shark carcass - the illusion will break down when collision detection takes place, as parts of the mesh will just clip trough nearby geometry. You can work around this to some extent by adjusting rope thickness, but a rope will never be able to provide accurate collision detection for an arbitrary mesh.

The same principle applies to any physical object in any engine: visual and physical shape are often decoupled for practical reasons, it's up to you to decide whether your visual and physical shape choices are a good enough fit for your purpose.

For example, Unity has primitive colliders like boxes, spheres and capsules. If your object is roughly sphere-shaped (say, an apple), you can simulate it using a sphere collider. However using a sphere to simulate a shark may be oversimplifying things, and you might need to use a convex mesh collider - which still doesn't perfectly represent the shape of the shark, but it's closer to it than a sphere. Another example would be player characters: in many games the player is represented using a capsule. This works well in many cases, but if you need detailed collision detection this approach will break down, as character limbs stick out and will be able to clip trough other objects.

If you want to simulate a mesh that's not close in shape to a rope, using a softbody might be a better option as it does not make assumptions about the shape of the object or how particles are laid out to represent it.

kind regards,