Rigid Body
Rigid body enables simulation of physical bodies in accordance with Rigid body dynamics. This type of body is the most commonly used and the most efficient one in terms of performance.
See also#
- BodyRigid class
Assigning a Rigid Body#
To assign the Rigid body to an object via UnigineEditor perform the following steps:
- Open the World Hierarchy window.
- Select an object to assign a Rigid body to.
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Go to the Physics tab in the Parameters window and assign a physical body to the selected object by selecting Body -> Rigid.
- Set the body name and change other parameters, if necessary.
Parameters#
The set of Rigid body parameters in accordance with Rigid body dynamics includes the following:
| Immovable |
Toggles the static mode for a Rigid body on and off. If the flag is set, the body will ignore all forces in the world and keep its position while being a collider object. |
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| Gravity | Toggles the gravity for the body on and off. | ||||||||||||||||||
| Freezable |
Enables freezing physical simulation of the body when necessary. Notice
This flag is recommended to be always set for all rigid bodies except for Player Actor. Freezing a player causes it to react to the user's input with a time lag, small but nonetheless perceptible. |
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| Shape-Based |
Toggles automatic calculation of certain parameters of a rigid body (total mass, center of mass, and inertia tensor) on the basis of parameters determined for its shapes on and off. Volume of a Rigid body can be approximated by several shapes (e.g. a concave object divided into a set of convex hulls or a Ragdoll body). Each shape has its mass and density. Therefore certain parameters of a Rigid body, such as its total mass, center of mass, and inertia tensor, are determined by its shapes. These parameters can be calculated automatically if the Shape-based option is enabled. Notice
Setting the individual masses or densities of the shapes is the most intuitive method to achieve correct physical behavior of the body. Even if overridden by the body parameters, they are still used to determine the distribution of mass within the object. Disabling the Shape-based option makes it possible to manually redefine such total parameters for the body as Center of mass and moment of Inertia. |
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| High Priority Contacts |
On collision, contacts are distributed randomly between the interacting bodies to optimize performance: some are handled by the first body, others by the second. For a body, contacts that it handles itself are internal (access to them is fast), and contacts handled by other bodies are external. This option makes the body handle most of its contacts itself (so that most of them are internal). Thus, you can track collisions of a certain body with maximum efficiency. Notice
You can iterate through all contacts for a body, but for better performance it is recommended to process only internal ones. |
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| Name |
Name of the body. | ||||||||||||||||||
| Physical | Bit mask for interactions with physicals. Used to enable selective interaction: two objects interact, if they both have matching masks (one bit at least). | ||||||||||||||||||
| Mass |
Mass of the body, in kilograms. Notice
Do not use real masses, this can make physics simulation unstable. Adjust mass values when necessary to achieve realistic behavior (e.g. for a wheel mass of 25 kg it might be better to set 60 kg for a car body instead of 2000 kg). It is very important to ensure mass balance – avoid connection of too heavy bodies to very light ones, otherwise the joints may become unstable! |
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| Inertia |
The moment of inertia is a rotational analog of mass, describing the resistance of the body to rotation in different directions. It is determined by the distribution of mass throughout the body volume. The farther from the axis of rotation the center of mass is, the more rotational inertia the body has. The inertia tensor that allows to compute a moment of inertia about an arbitrary axis is represented as a matrix, I:
where Iij sets the moment of inertia around the i -axis when the body is rotated around the j-axis. Notice
To rotate the body evenly about the rotation axis, the matrix should be diagonal, i.e all values outside the main diagonal are set to 0. Otherwise, the body may start to rotate chaotically. As for values of the moment of inertia:
Values are corrected with respect to the average value to provide smoother movement. For example, the following illustration shows three boxes with different inertia tensors. The yellow box has very high inertia:
Because of that, it can only slide down when falling upon the tilted plane. The red box, on the contrary, has the lowest inertia and rotates most eagerly.
Different inertia tensors that override shape-based parameters
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| CMass |
An arbitrary point can be set to be a center of mass of the body. It may be necessary to correct the motion of an object to provide desirable look. For example, a tilting doll with a sphere shape requires an uneven mass distribution: its center of mass should be located closer to the bottom, so it always stands up when tilted. Notice
Center of mass is set as coordinates of the point in local space of the body. |
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| LScale | Multipliers for the body's linear velocity along the axes. Setting any value to 0, restricts movement along the corresponding axis. | ||||||||||||||||||
| AScale | Multiplier for the body's angular velocity along the X axis. When set to 0, rotation along this axis will be restricted. | ||||||||||||||||||
| LDamping |
Linear damping reduces linear velocity of the body over time and slows it down up to a complete stop. Higher values make the body slow down faster. Global linear damping is added to the linear damping of the body to calculate resulting value. |
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| ADamping |
Angular damping reduces angular velocity of the body over time and slows it down until its rotation ceases. Higher values make the body slow down faster. Global angular damping is added to the angular damping of the body to calculate resulting value. |
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| MLVelocity |
Maximum linear velocity defines the maximum possible velocity of the body. Values exceeding this limit will be clipped. There is also a global maximum linear velocity threshold, it is compared with the maximum set for the body, and the minimum is chosen for actual velocity clipping. |
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| MAVelocity |
Maximum angular velocity defines the maximum possible angular velocity of the body. Values exceeding this limit will be clipped. There is also a global maximum angular velocity threshold, it is compared with the maximum set for the body, and the minimum is chosen for actual velocity clipping. |
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| FLVelocity | Frozen linear velocity defines the value of linear velocity at which the body becomes frozen. Such body is excluded from physical simulation until it remains idle, which significantly reduces simulation load and improves performance. There is also a global frozen linear velocity, it is compared with the value set for the body, and the maximum is chosen for body freezing. | ||||||||||||||||||
| FAVelocity | Frozen angular velocity defines the value of angular velocity at which the body becomes frozen. Such body is excluded from physical simulation until it remains idle, which significantly reduces simulation load and improves performance. There is also a global frozen angular velocity, it is compared with the value set for the body, and the maximum is chosen for body freezing. |
The information on this page is valid for UNIGINE 2.20 SDK.