Force COMP

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Force COMPs are used to added forces to a physics solver's simulation. Bullet supports linear/rotational forces and impulse forces (see Force page) and Flex supports force fields (see Force Field page).

Active Force

Active forces are enabled using the Active toggle parameter on the Force page.

An active force will create a force in the simulation that is applied over time. An active force can either be applied globally by being referenced on the Bullet Solver COMP, or it can be applied locally by being referenced on an individual Actor COMP. The active force applies its force each frame, and the force applied over 1 second is equivalent to an impulse force of the same value applied in a single frame.

The units for the force and torque parameters are in Newtons (N), equivalent to kg*m/s^2. This means that if a force of 10N is applied to an actor with mass equal to 5kg and no initial velocity, then after 1 second the velocity of that actor will be 2m/s => 10N / 5kg * 1 sec = 2m/s. If all the parameters were the same, but instead it was an impulse force, then the velocity would still be 2m/s. However, the impulse force's velocity would change instantaneously and stop increasing (unless pulsed again) whereas with the active force the velocity will continue to increase after 1 second.

The center of mass is assumed to be center of the bounding box of the mass. By default, if a body is not constrained and not colliding, the force will not cause the body to rotate, unless the Relative Position parameter is set to a non-zero value. If Relative Position is set to +1 in X and the force is +1 in Y, it will cause the body to rotate counter-clockwise around the Z-axis and translate in Y.

If the Torque is set to +1 in Z, it will cause the body to only rotate counter-clockwise in the Z-axis (a positive Z rotation), and not translate.

To apply force/torque to specific bodies use a Feedback CHOP (see Bullet Solver COMP or Actor COMP) and force[xyz] and torque[xyz] channels.

Impulse Force

Impulse forces are applied through the Impulse Force pulse parameter.

An impulse force pulse will create a force in the simulation that is applied for 1 frame. In the real world, impulse forces are forces applied over a very short duration, however in Bullet this is somewhat simplified, and they are instead applied instantly (for a single frame). Examples of impulse forces are kicking a ball or shooting a cannon. The velocities of the affected bodies are changed in an instant by the impulse force, and after that instant the force no longer has an effect unless applied again.

The resulting velocity of the bodies after the impulse force is applied is the same as an active force with the same values if the active force is applied for exactly 1 second. For example, if 10N of impulse force is applied to a body with mass 5kg then the resulting velocity will be 10N / 5kg * 1sec = 2m/s.

Force Field

Force fields are enabled through the Active parameter on the Force Field page.

Force fields are spherical with a radius defined through the Radius parameter. Positive strength pushes bodies outward and negative strength pulls bodies inward.

See also: Flex, Bullet Dynamics, Bullet Solver COMP, Actor COMP, Constraint COMP, Bullet Solver CHOP, Nvidia Flex TOP, Nvidia Flex Solver COMP.


Parameters - Force Page

Active active - Toggle the active force on/off in the simulation

Force force - - The linear force in Newtons that will be applied.

  • X forcex -
  • Y forcey -
  • Z forcez -

Relative Position relpos - - The position at which to apply the linear force, relative to the center of the body (Note: the physical center of the object, not the center of mass). Having a nonzero relative position will also cause the body to rotate due to added torque.

  • X relposx -
  • Y relposy -
  • Z relposz -

Torque torque - - The rotational force in Newtons that will be applied.

  • X torquex -
  • Y torquey -
  • Z torquez -

Impulse Force impulse - Applies an impulse force in the simulation for 1 frame with the above parameters.

Parameters - Force Field Page

Active ffactive - Toggle the force field on/off in the simulation

Strength strength - The strength of the force field. Positive strength pushes bodies outward and negative strength pulls bodies inward.

Radius radius - The radius of the force field.

Linear Falloff falloff - Applies linear falloff to the strength of the force field based on the distance from the center.

Parameters - Extensions Page

The Extensions parameter page sets the component's python extensions. Please see extensions for more information.

Re-Init Extensions reinitextensions - Recompile all extension objects. Normally extension objects are compiled only when they are referenced and their definitions have changed.

Extension Object 1 extension1 - A number of class instances that can be attached to the component.

Extension Name 1 extname1 - Optional name to search by, instead of the instance class name.

Promote Extension 1 promoteextension1 - Controls whether or not the extensions are visible directly at the component level, or must be accessed through the .ext member. Example: n.Somefunction vs n.ext.Somefunction

Parameters - Common Page

The Common parameter page sets the component's node viewer and clone relationships.

Parent Shortcut parentshortcut - Specifies a name you can use anywhere inside the component as the path to that component. See Parent Shortcut.

Global Shortcut opshortcut - Specifies a name you can use anywhere at all as the path to that component. See Global OP Shortcut.

Internal OP Shortcut 1 iopshortcut1 - Specifies a name you can use anywhere inside the component as a path to "Internal OP" below. See Internal Operators.

Internal OP iop1 - The path to the Internal OP inside this component. See Internal Operators.

Node View nodeview - - Determines what is displayed in the node viewer, also known as the Node Viewer. Some options will not be available depending on the Component type (Object Component, Panel Component, Misc.)

  • Default Viewer default - Displays the default viewer for the component type, a 3D Viewer for Object COMPS and a Control Panel Viewer for Panel COMPs.
  • Operator Viewer opviewer - Displays the node viewer from any operator specified in the Operator Viewer parameter below.

Operator Viewer opviewer - Select which operator's node viewer to use when the Node View parameter above is set to Operator Viewer.

Keep in Memory keepmemory - Used only for Panel Components this keeps the panel in memory to it doesn't reload every time it is displayed.

Enable Cloning enablecloning - Control if the OP should be actively cloned.

Enable Cloning Pulse enablecloningpulse - Instantaneously clone the contents.

Clone Master clone - Path to a component used as the Master Clone.

Load on Demand loadondemand - Loads the component into memory only when required. Good to use for components that are not always used in the project.

External .tox externaltox - Path to a .tox file on disk which will source the component's contents upon start of a .toe. This allows for components to contain networks that can be updated independently. If the .tox file can not be found, whatever the .toe file was saved with will be loaded.

Reload .tox on Start reloadtoxonstart - When on (default), the external .tox file will be loaded when the .toe starts and the contents of the COMP will match that of the external .tox. This can be turned off to avoid loading from the referenced external .tox on startup if desired (the contents of the COMP are instead loaded from the .toe file). Useful if you wish to have a COMP reference an external .tox but not always load from it unless you specifically push the Re-Init Network parameter button.

Reload Custom Parameters reloadcustom - When this checkbox is enabled, the values of the component's Custom Parameters are reloaded when the .tox is reloaded.

Reload Built-In Parameters reloadbuiltin - When this checkbox is enabled, the values of the component's built-in parameters are reloaded when the .tox is reloaded.

Save Backup of External savebackup - When this checkbox is enabled, a backup copy of the component specified by the External .tox parameter is saved in the .toe file. This backup copy will be used if the External .tox can not be found. This may happen if the .tox was renamed, deleted, or the .toe file is running on another computer that is missing component media.

Sub-Component to Load subcompname - When loading from an External .tox file, this option allows you to reach into the .tox and pull out a COMP and make that the top-level COMP, ignoring everything else in the file (except for the contents of that COMP). For example if a .tox file named project1.tox contains project1/geo1, putting geo1 as the Sub-Component to Load, will result in geo1 being loaded in place of the current COMP. If this parameter is blank, it just loads the .tox file normally using the top level COMP in the file.

Re-Init Network reinitnet - This button will re-load from the external .tox file (if present), followed by re-initializing itself from its master, if it's a clone.

Info CHOP Channels

Extra Information for the Force COMP can be accessed via an Info CHOP.

Common COMP Info Channels

  • num_children - Number of children in this component.

Common Operator Info Channels

  • total_cooks - Number of times the operator has cooked since the process started.
  • cook_time - Duration of the last cook in milliseconds.
  • cook_frame - Frame number when this operator was last cooked relative to the component timeline.
  • cook_abs_frame - Frame number when this operator was last cooked relative to the absolute time.
  • cook_start_time - Time in milliseconds at which the operator started cooking in the frame it was cooked.
  • cook_end_time - Time in milliseconds at which the operator finished cooking in the frame it was cooked.
  • cooked_this_frame - 1 if operator was cooked this frame.
  • warnings - Number of warnings in this operator if any.
  • errors - Number of errors in this operator if any.

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