Initial State Node

The InitialState node is used to store a snapshot of the geometry and transforms of objects contained in a Rigid Set. This information, along with the physics attribute settings, are passed to the solver to define the initial state of the simulation.

Collision Attributes

Lets you specify the type of object, or the mesh that to use to approximate the solve object. Select Box, Sphere, Capsule, Hull, or Cylinder.

Note: It is a good idea to match the shape of your object as closely as possible as the collision behavior is affected by this shape.

Collision Shape Type

Collision shapes let you simulate collisions with different objects. They are attached to rigid bodies and shown as primitive shapes, although they do not have a world position. You can give multiple rigid bodies the same collision shape, which helps to speed up the solve. See Rigid Set Options.

Using collision shapes based on primitives such as hulls, spheres, boxes, and cylinders simplifies the collision algorithms and creates a smoother, faster solve and are recommended. You can choose from the following shape types:

Tip: Consider which shape will best represent the simulation effect you want to have. For example, using a box collision shape type to simulate marbles dropped on the ground may solve quickly, but they will not roll.

Box

A very fast-solving and simple shape.

Sphere

Recommended for faster solves and more realistic rolling behavior. There is no need to override the Collision Shape Margin value for spheres.

Capsule

A cylinder with sphere caps, useful for modeling humanoid characters.

Cylinder

A cylinder is similar to the box shape but has better rolling action.

Hull

This is the most costly shape type, and while the solve behaves accurately, it is not fast. The hull shape type is defined by a cloud of vertices but the shape formed is the smallest convex shape that encloses the vertices.

Collision Filter Type

Lets you specify the collision groups for this rigid body, by default the rigid body belongs to the DefaultFilter group. The first 16 bits of the integer determine the collision filter groups. The display names for the collision filter groups are defined by the Bullet Solver's collision filters attribute.

Collision Filter Mask

Lets you specify which other rigid bodies may collide with this body, by default this rigid body will collide with bodies belonging to the DefaultFilter group. The first 16 bits of the integer determine the collision filter mask. The display names for the collision filter masks are defined by the Bullet Solver's collision filters attribute. same as collider filter mask (collides with). Enter the bitmask value for which groups of objects you want the object to collide with. For example, if you specify 1, this object can collide with objects that belong to group 1.

Collision Shape Margin

Defines the size of the gap between Rigid objects for them to collide.

The Collision Shape Margin acts like a buffer around each collision shape.

Turning Collision Shape Margin on speeds the simulation up, as well as makes it more stable.

Notes on Collision Shape Margin Behavior:

The default setting for the Collision Shape Margin is 0.040, (equal to 4 centimeters), and any objects that touch will react the moment the solve is activated. If you use the Glue Shapes option, and your glued objects touch or intersect, set the Collision Shape Margin slider to 0.00 so you do not create an instant collision. Setting the Collision Shape Marginto 0.00 reduces the margin to nothing and the solver is aware that the pieces will automatically collide.

By default, Bullet uses a small collision margin for collision shapes to improve the performance and reliability of the collision detection. We recommend that you do not modify the default Collision Shape Margin of 0.040, as if you use a positive value, the zero margin might introduce problems.

Depending on which collision shapes you use, the collision margin has a different meaning. Generally, the Collision Shape Margin expands the object, creating a small gap. To compensate for this gap creation, some shapes subtract the margin from the object's actual size. For example, the Bullet Box collision shape subtracts the collision margin from the half extents, where the Sphere collision shape uses its entire radius as the collision margin so that no gap occurs. (There is no need to override the Collision Shape Margin for spheres and it is not recommended.)

For convex hulls, cylinders and cones, the margin is added to the extents of the object, so a gap occurs unless you adjust the graphics mesh or collision size.