Simulate Bullet Rigid Bodies

Description

Moves particles as if each of them were rigid bodies (non deforming) using the Bullet physics engine. Particles will intercollide based on their shape, and collide with the input obstacle objects. More specifically, the node updates the position, velocity, orientation, and angular velocity of particles based on the following attributes:

PointPosition
PointVelocity
Orientation
AngularVelocity
Shape
Size
Scale
StaticFriction
Mass
Force
Elasticity

For information on using this node, see ICE Rigid Bodies.

The collision geometry used for the rigid body collision objects (obstacles) can be either actual shape or a convex hull approximation of the shape.

The following shapes are use for the collision geometry of the rigid body particles:

Convex hulls or bounding boxes (set in the Instance Shape node) can be used for instanced geometry
Bounding spheres are used for the Sphere and Blob shapes. Points are approximated by very small spheres
Bounding boxes are used for the Box, Disc, and Rectangle shapes
Bounding capsules are used for the Capsule, Cylinder, and Segment shapes
Bounding cones are used for the Cone shape. The bounding cone's center of mass is set close to its bottom so that a rotation that is more indicative of a cone results during collision.

For information on collision geometry, see Collision Geometry for Rigid Body Particles and Obstacles.

TipYou can choose the Particles

Simulation

Inspect Simulation Node command to open up the selected point cloud's Simulate Particles or Simulate Bullet Rigid Bodies node property editor without the ICE Tree view needing to be open.

TipIf you create collisions with particles using any of the Surface Interaction compounds (such as Bounce Off Surface), you cannot also make those particles into rigid bodies in the same ICE tree. This is because the Surface Interaction compounds use the Simulate Particles node, while rigid body particles use either this node or the Simulate Rigid Bodies node.

For information on creating other types of collisions with particles, such as bouncing, sticking, or sliding, see About ICE Particle Collisions.

Parameters

Simulation environment

You can choose the simulation environment to be based on the CPU or GPU (CUDA).

In the GPU (CUDA) mode, you can adjust the simulation parameters in ICE Bullet Rigid Bodies. This provides the flexibility to fine tune the performance and accuracy of the simulation. The parameters that you can set in the GPU (CUDA) simulation environment are:

Dimension	Increase or decrease the minimum and maximum values of X, Y, and Z to change the default dimension of the simulation area.
Cell Size	Increase or decrease the X, Y, Z values to change the default size of each cell in the simulation area.
Max body count	Set the number of objects that you want to simulate in the GPU or CPU-based simulation environment. By default, the maximum body count is limited to 1 million. If the GPU-based simulation environment is configured to use more body count than the available limit, then the following warning message appears and Softimage will use the CPU-based simulation environment. ImportantSimulation is switched to CPU based mode due to the Max body count exceeding the maximum number for a stable simulation. Please adjust this value to a value below NNN to use the GPU based mode again. You may increase the maximum available body count by setting system environment XSI_BULLET_GPU_MAX_BODY_CNT to the required value. NoteUsing unlimited number of body count for GPU-based simulation may cause Softimage to crash or hang.
Max body count per cell	Set the number of rigid bodies that you want to accommodate in each cell. By default, the maximum cell count is set to 100 million. If the GPU simulation environment requires more cells than available, then the following warning message appears and Softimage will use the CPU-based simulation environment. ImportantSimulation is switched to CPU based mode due to the number of cells exceeding the maximum number for a stable simulation. Please adjust the values for Dimensions and Cell Size to reduce the number of cells below NNN to use the GPU based mode again. You may adjust the maximum available cell count by setting the XSI_BULLET_GPU_MAX_CELL_CNT system environment variable to the required value. ImportantUsing unlimited number of cells for GPU-based simulation may cause Softimage to crash or hang.

TipIf you encounter inter-penetration issues, then try to enhance the Max body count per cell value.

Inputs

Mute	Turns off the rigid body simulation.
Collide	Specifies whether the particles collide with each other and with the obstacles.
Precision	Specifies the maximum simulation frequency allowed. A precision of 60 means that the longest simulation substep would be 1/60 seconds.

Obstacle

Active	Specifies whether the obstacle collides with the particles.
Exact Shape	The exact shape of the collision object's geometry is used for the collision shape, including if that geometry deforms over time. If this option is off, the collision shape is approximated to be the convex hull of the collision object's geometry.
Elasticity	The elasticity of the obstacle material. The elasticity is combined with the Elasticity attribute on each particle to determine how much each particle bounces off this obstacle.
Static Friction	The static friction of the obstacle material. The static friction is combined with the StaticFriction attribute on each particle to determine how each particle starts sliding on the obstacle when it is at rest. Static and dynamic friction are not recognized separately by the Bullet physics engine: it combines the two to support just one friction value.