The Bound of Rigid Body (New for 5)

The Bound of a physics object is a range that causes collision with other physics objects. The shape of the bound can be default or customized. The more complex the mesh is, the more system loading you will encounter. Therefore, using the bound as simple as possible may produce physics reactions while minimizing the use of your PC system resources.

Bound and Collision

After you assign a bound type to a rigid body, the range for collision will be defined. The collision does not necessarily happen according to the shape of the rigid body, but to the shape of the bound instead. The basic bound types are Box, Sphere, Cylinder and Capsule; and the complicated types are Convex Hull, Bounding Mesh and Self Mesh.

A diamond is assigned with a Box bound.	The physics balls collide against the bound instead of the skin of the diamond.

Convex Hull and Self Mesh

Convex Hull

• If you select a Convex Hull as the bound for a rigid body, then you are actually wrapping the object with a virtual plastic film. Use the film to enclose a colliding range.

  A trophy-shaped rigid body applied with a Convex Hull bound.	The collision happens on the convex hull instead of the concave shape of the body.

Self Mesh

• In order to have the concaves of a rigid body collide against other physics objects, you may select the Self Mesh type for the rigid body. IClone will then use the "skin" of the object as the bound.

  The same rigid body applied with Self Mesh bound.	The collision happens on the real shape of the rigid body.

• For specific shapes such as tubes, U-shaped slide way or concave bowls, use the Self Mesh setting for getting correct collision effects. Remember to only use it for low polygon mesh objects (See also: Creating Custom Bounding Mesh) in order to maintain the speed and accuracy.

  The container is applied with a bound type other than the Self Mesh. The ball is hindered from dropping into the opening of the container by the bound.	The container is set as Self Mesh. The ball drops into the container.

Bounding Mesh

The Bounding Mesh is a representative model, mostly a box, surrounding an object. By displaying the bounding mesh instead of the true mesh of the object, you may ease the system loading and increase the processing speed of iClone. In iClone, the prop templates in the 3D block category all contain a bounding mesh in a box shape. Therefore, if you choose to use this bound type for the 3D blocks, then their collision area will all be like boxes.

Viewing Bounding Mesh

If you wish to check the bounding mesh of an object, then you may follow the steps below:

1. Select the cone.
   
2. Right click on it. Select the Display item in the right-click menu.
3. Pick the Bounding Mesh command to show the object in bounding mesh mode.
   

If you choose to use the Bounding Mesh as the collision area for the rigid bodies, then you will actually be using the boxes surrounding them.

The bounding meshes of the three objects.	Use the Bounding Mesh as the bound type.

Creating Custom Bounding Mesh

By default, all object's bounding meshes are mostly boxes; you may create custom bounding meshes by using external 3D modeling tools.

Since real-time physics collision detection depends on the simplicity of a collision bound, for high-polygon-mesh objects, it is highly suggested that you create custom collision bounds to approximate the shape and keep speed and correctness.

1. Launch your favorite 3D modeling tools (Maya, 3DS Max or any one that can export models in FBX format)
2. Create a model, name it. (Helix for example)
3. Create another model.
   • If you want an exact collision result in iClone, then copy and paste the new model at the same position.
     
   • If you want to keep the speed in iClone, then you need to downsize the pasted model with the Optimize feature; the number of the mesh will decreased while keeping a similar shape.
     
4. Name this new model as Helix_Boundingmesh (case sensitive).
   
5. Export them together in FBX format.
6. Load this FBX into 3DXchange 4. Convert it to .iProp for use in iClone.
   • Although 3DXchange 4 supports .obj, .skp, .3ds and .fbx formats, it is highly recommended that you export in FBX since it assures correct results.
   • If you are not able to see the model named with the suffix, _Boundingmesh, in the tree view, then your process is correct. Except .fbx format, sometimes other formats may cause the bounding mesh model to be shown in 3DXchange 4, which fails to convert it into the bounding mesh.
7. Import the converted prop and display its bounding mesh. You will then see that the bounding mesh is a differnt one than the one you created in the 3D modeling tool.

   Bounding meshes with a high mesh number.	Bounding meshes with a low mesh number.