Shape dynamics dialog

The shape dynamics dialog is part of the shape dialog. The dialog displays the dynamics settings and parameters of the last selected shape. If no object is selected, the dialog is inactive. If more than one shape is selected, then some parameters can be copied from the last selected shape to the other selected shapes (Apply to selection-buttons):

[Shape dynamics dialog]


  • Static: when disabled, then the shape's position and orientation will be influenced in a dynamics simulation. See the designing dynamic simulation section for more details.
  • Start in sleep mode: a respondable shape that is dynamically simulated can start in sleep mode, in which case it doesn't react to constraints (e.g. gravity) until it first collides with another respondable shape.
  • Parent follows: if enabled, then the parent object will follow the shape during dynamics simulation (normally the child follows the parent, not the other way round!). This option is useful if your dynamic model (e.g. a vehicle) uses an object not dynamically enabled as model base (e.g. a dummy object).
  • Body is respondable: if enabled, then the shape will produce a collision reaction with other respondable shapes, however only if the respective respondable masks overlap (see the item below). See also the designing dynamic simulation section for more details.
  • Respondable mask: indicates when a collision response is generated (above respondable item needs however to be enabled). The mask is composed by two 8-bit values, local and global. If two colliding shapes share any of their parents (direct or indirect), then the local masks are used, otherwise the global masks are used. If two shapes' AND-combined masks (local or global) is different from zero, then a collision response will be generated.
  • Adjust engine specific properties: allows adjusting engine specific parameters. Refer to the Bullet or ODE documentations for more details.
  • Mass: the mass of the shape. Selected shapes can have their masses easily increased or decreased by a factor 2 with the M=M*2 (for all selected shapes) and the M=M/2 (for all selected shapes) buttons. This is convenient to quickly find stable simulation parameters by trial-and-error.
  • Principal moments of inertia / mass: the mass-less (i.e. divided by the mass of the shape) principal moments of inertia. Selected shapes can have their mass-less inertia values easily increased or decreased by a factor 2 with the I=I*2 (for all selected shapes) and the I=I/2 (for all selected shapes) buttons. This is convenient to quickly find stable simulation parameters by trial-and-error.
  • Set inertia matrix: opens the inertia matrix dialog, allowing to specify non-diagonal inertia matrices:
  • [Object custom data dialog]


  • Inertia matrix divided by the mass: the inertia matrix or tensor. Values are mass-less (i.e. divided by the mass of the shape). The matrix must be expressed relative to the center of mass of the shape.
  • Position of the center of mass (COM): the position of the center of mass
  • Inertia & COM are relative to shape frame: indicates that the inertia matrix (orientation) and center of mass are relative to the shape's reference frame.
  • Inertia & COM are relative to absolute frame: indicates that the inertia matrix (orientation) and center of mass are relative to the absolute reference frame.


  • Position/orientation of inertia frame: the configuration of the inertia frame expressed relative to the shape's reference frame (shape frame) , or relative to the absolute reference frame (World). Be aware that if the inertia frame configuration is expressed relative to the world, and you apply the settings in this dialog to the selection (i.e. Apply to selection button), then this will set the same absolute position/orientation of all inertia frames.

  • Recommended topics

  • Shapes
  • Shape reference frame
  • Dynamics module
  • Bullet Physics Library
  • Open Dynamic Engine