Rope Body

Rope body enables physical simulation of ropes, cables, wires, etc. Ropes can be pinned to the following types of bodies:

• Rigid body
• RagDoll body
• Dummy body

To pin a rope to a body so it would hang freely, or tie several bodies, use a Particles joint. The Rope body can be torn as a Cloth body. Rope enhances the realism of simulated environment and saves the time of game artists as it replaces animation. However, simulation of this type of body is quite costly and it is strongly recommended to use distance optimization to avoid performance hits.

See also#

The only acceptable mesh type for a Rope body is a cylinder. You can use a standard primitive cylinder to create a rope. The workflow in this case is as follows:

1. On the Menu bar, click Create -> Primitive -> Cylinder.

2. Specify desired rope parameters (length, radius) for a cylinder, e.g. the following:

   

3. Click OK and place the cylinder somewhere in the world. It is created as a Static Mesh object. The object itself can be deleted, its mesh however is still available in the data/ folder.
4. Create a Dynamic Mesh object and use the cylinder mesh for it.
5. Assign the rope body to the created dynamic mesh object.

A Rope body is modeled as set of point masses (particles) located in the mesh vertices. Each particle is represented with a sphere shape and is linked together with other particles by inner spring joints that are located along the mesh edges. Inner joints allow to recreate mesh topology, on the one hand, and constrain stretching and folding, on the other.

Each particle is characterized by a position, mass and velocity and has a constant spherical shape with a set radius. The total mass of the whole body is equally distributed among them. In accordance with Newton's second law particles can be acted upon by a force or an impulse applied by inner joints and external forces (collision, gravity, air resistance, wind, etc.).

Self-collision of the particles and collisions between different rope bodies are not calculated. However, the rope interacts with environment by colliding with other physical bodies if the Collision box is checked. Its behavior in case of contact is controlled by such parameters as friction and restitution. Selective physical interaction is available via corresponding bitmasks.

Thus, Rope body can be regarded as a constrained system of rigid particles and therefore shares some parameters with Rigid body:

• Mass
• Friction
• Restitution
• Linear Damping and Angular Damping

Particle Radius#

Joints Solver Iterations#

A rope may be deformed by stretching and folding. These deformations are controlled with joint constraints of two types:

• Linear restitution controls stretching.
• Angular restitution controls folding.

With these types of constraints, it is possible to obtain the desired look and feel of the rope and simulate a variety of different deformable materials ranging from a stiff metal wire to an elastic rubber cord.

Linear Restitution#

Angular Restitution#

The Rigidity parameter is an additional constraint of the rope motion to make it stiffer and more inflexible. For that purpose, linear and angular velocities of each rope particle are corrected according to the total velocities interpolated for all the particles.

• The minimum value of 0, makes the rope elastic, flexible and easily deformable.
• The maximum value of 1, makes the rope stiffer and less prone to deformation.

When the rope is stretched or folded beyond its elastic limit, it tears and shreds into pieces. Tearing is caused by applying the force or collision with a physical body, and depends on the rope stiffness (controlled by linear and angular restitution parameters). The rope is torn only along the edges of rope triangles, splitting mesh vertices and duplicating particles.

Linear Threshold Distance#

Angular Threshold Angle#

Updating each frame a huge number of objects located far away from the camera that are hardly distinguishable or observed as a mass is a waste of resources.

To improve performance and avoid the excessive load, simulation of the rope can be updated with a reduced framerate. When the player is out of the area specified by the Update Distance Limit, the rope stops to be updated and freezes statically.

The set of frame rates given below enables you to specify how often the rope simulation should be updated when the object is visible, when only its shadow is visible, or when it is not visible at all.

This feature is enabled with default settings ensuring optimum performance and can be adjusted per-object in the UnigineEditor or via API at run time.

To assign a Rope body to an object via UnigineEditor perform the following steps:

1. Open the World Hierarchy window.

2. Select a dynamic mesh object to assign a Rope body to.

   Notice

   Make sure that the object's mesh meets requirements!

3. Go to the Physics tab in the Parameters window and assign a physical body to the selected object by selecting Body -> Rope.

   

4. Set the body's name and change other parameters, if necessary.

Ropes can be attached to the following types of bodies:

• Rigid body
• RagDoll body
• Dummy body

To attach a rope to a body, use the Particles joint. In case of Rigid body (either static or dynamic) and Dummy body, pinned particles stay fixed in their position and follow transformations of attached objects pulling the rope with it.

1. Select Rigid body, RagDoll body or Dummy body.
2. Add Particles joint.
3. Specify Rope body.
4. Adjust the pinning area using the Threshold and Size parameters of the Particles joint.

Attachment to Skinned Mesh#