Shock

The Channel->Shock custom effect in the Motion module allows you to simulate real-time dynamic collision between models. Shock supports the collision between the bounding spheres of single objects on a plane using both the Custom and Channel menu cell commands to exchange data with SOFTIMAGE 3D.

Procedure

1. Create or load the models to participate in the collision as follows:

• The models must be parented to a single null. Only the bounding sphere of each object is considered during the simulation. Object types considered correctly are polygon meshes and patches. The null parents of the spheres must not be translated nor rotated from the global centre of coordinates.
• The hierarchy cannot exceed three levels. The hierarchy of the selected model is not taken into consideration during the simulation, so each object moves separately. The hierarchy is used only for an easy association of object properties.
• If you are creating a collision between groups of models, all models in a group that will have the same properties must be parented to a null; you can then apply the properties to the null so that they are inherited by all its children.
• The collision is detected only in the xz plane: the y movement of the object is considered, but forced to zero. You must create the models in the xz plane aligned on the same y value.
• If points or vertices of a model pass below y=0, the setup is invalid and the Shock effect will not work. For example, assume you have a B-Spline sphere sitting just above y=0. Since the control points on a B-Spline sphere reside outside its surface, they will probably pass below y=0 and invalidate the setup for the Shock effect. To avoid this kind of problem, you can use a Cardinal sphere because the points are located on the surface of the model.

2. Choose the Channel->Shock command in the Motion module. The Shock dialogue box is displayed:
3. Enter the name of the moving objects and their properties.
4. Set the simulation parameters.
5. Click Ok.
6. Select the model root.
   
   The system calculates the resulting simulation data and saves it to a file (usually /usr/tmp/Shock.data).
   
   
7. Choose the Channel->Get Channel Setup command in the Motion module.
   
   In the specified database, select the file called rebels_setup. This file contains all the information that the channel driver needs to read from the data file.
   
   Note:
   
   Next time you run the Shock effect, make sure to delete this file before starting. This ensures that you will avoid any problems overwriting it.
   
   
8. Choose the Channel->Channel Run->Sequence I/O command.
   
   The data coming from the data file is applied to your models.
   
   Note:
   
   Make sure that the time line pointer is at the frame you selected as the starting frame for your simulation.
   
   Your model hierarchy must be selected.
   
   
9. Play back your animation to view the results.

You can edit parameters by choosing the Channel->Channel Run->Sequence I/O command. You don't need to recall the Channel Setup since you didn't change the model used.

Parameters

Start Frame

Start frame for the simulation: the default is 1.

End Frame

End frame for the simulation: the default is 100.

Frame Rate

Frame rate set in SOFTIMAGE 3D: the default is 25.

Precision

Simulation precision level. It describes the sampling rate per frame. A higher value results in a more accurate simulation, but it takes longer to calculate. The values range from 1 to infinity: the default value is 3.

Z Gravity

The gravity value along the z-axis. If this value is more than 0, all the objects, except those designated as fixed, are attracted. The default is 0.

Bound X

This is the x-dimension of the simulation field in the plane, or floor. The field is always centred according to the world. The default is 40.

Bound Z

This is the z-dimension of the simulation field in the plane, or floor. The field is always centred according to the world. The default is 40.

Roughness

The amount of plane, or floor, friction. A value of 0 means that the floor doesn't affect the object's simulation. The range is 0 to 1, with 0 as the default.

Random

This global value describes the "surface quality" of the floor. A value of 0 means that the floor surface is perfectly "clean." A value of 0.1 produces a fuzzy random movement of the objects. Suggested values are close to 0 (the default).

Simulation Data File

Path and name of the file where the simulation data is placed. The default is /usr/tmp/Shock.data. If you change this path, you must also change the path in the DataFileDrive.drv file.

Working Database

Database where Shock stores the channel setup for the simulation. You must have the environment variable SI_DBDIR in your account and specify a valid Database Name as found in the DatabaseDir.rsrc file. The default database is TEST.

Verbose

Prints simulation statistics in a shell, as well as the percentage of simulation completed. The default is selected.

Node Name

Name of the object or the parent of models with the same physical properties.

Speed X

Node linear speed along the x-axis. The default is 0.

Speed Z

Node linear speed along the z-axis. The default is 0.

Density

Defines the object density and mass. Values range from 0 to infinity, with 1 as the default (water density).

Elasticity

Defines the object elasticity. The higher the value, the more the object bounces against the others. Values range from 0 to infinity. The default is 1, where no energy is lost after a collision.

Roughness

Defines the object friction. Values range from 0 to 1, with 0 as the default.

Fixed

This means that the object does not change the starting velocities; if it is still, it becomes a fixed obstacle for moving objects.

Shock Channel Driver

The Shock custom effect comes with its own channel driver. It allows SOFTIMAGE 3D to read the animation from the data file created by the effect. The installation program automatically installs two files called DataFileDriver and DataFileDriver.drv in the specified directory (usually the one pointed to by the SI_CHNL_DRIVER environment variable).

Note:

If you change the Simulation Data File, you must also change it in the DataFileDriver.drv file in your channel directory.

This driver can also be used with other applications that can produce ASCII data in the DataFileDriver format. The format is:

3
0.1 0.0000 0.0000 1.0000 33.1245 -1.8211 321.1224  
0.1 9.3221 0.0000 7.1000 33.1245 -1.8211 -65.3244 
0.1 0.0030 0.0060 1.0800 33.1245 -1.8211 11.1243  
0.2 0.0210 0.0000 1.0000 33.1245 -1.8211 63.1224  
0.2 0.0123 0.0000 1.0000 33.1245 -1.8211 -0.1524  
0.2 0.0121 0.0000 1.0000 33.1245 -1.8211 21.2124  
...

where:

• The first number is the number of objects animated per frame
• One row for each object is at each frame with 7 float fields where
  • field 1 is the time in seconds
  • fields 2, 3, 4 are the translation values
  • fields 5, 6, 7 are the rotation values

Last updated 03-apr-1998