Spring Joint
Wheel Collider

Cloth

The Cloth component works with the Skinned Mesh Renderer to provide a physics-based solution for simulating fabrics. It is specifically designed for character clothing, and only works with skinned meshes. If you add a Cloth component to a non-skinned Mesh, Unity removes the non-skinned Mesh and adds a skinned Mesh.

To attach a Cloth component to a skinned Mesh, select the GameObject in the Editor, click the Add Component button in the Inspector window, and select Physics > Cloth. The component appears in the Inspector.

Properties

Property Function
Stretching Stiffness Stretching stiffness of the cloth.
Bending Stiffness Bending stiffness of the cloth.
Use Tethers Apply constraints that help to prevent the moving cloth particles from going too far away from the fixed ones. This helps to reduce excess stretchiness.
Use Gravity Should gravitational acceleration be applied to the cloth?
Damping Motion damping coefficient.
External Acceleration A constant, external acceleration applied to the cloth.
Random Acceleration A random, external acceleration applied to the cloth.
World Velocity Scale How much world-space movement of the character will affect cloth vertices.
World Acceleration Scale How much world-space acceleration of the character will affect cloth vertices.
Friction The friction of the cloth when colliding with the character.
Collision Mass Scale How much to increase mass of colliding particles.
Use Continuous Collision Enable continuous collision to improve collision stability.
Use Virtual Particles Add one virtual particle per triangle to improve collision stability.
Solver Frequency Number of solver iterations per second.
Sleep Threshold Cloth’s sleep threshold.
Capsule Colliders An array of CapsuleColliders which this Cloth instance should collide with.
Sphere Colliders An array of ClothSphereColliderPairs which this Cloth instance should collide with.

Details

Cloth does not react to all colliders in a scene, nor does it apply forces back to the world. When it has been added the Cloth component will not react to or influence any other bodies at all. Thus Cloth and the world do not recognise or see each other until you manually add colliders from the world to the Cloth component. Even after that, the simulation is still one-way: cloth reacts to those bodies but doesn’t apply forces back.

Additionally, you can only use three types of colliders with cloth: a sphere, a capsule, and conical capsule colliders, constructed using two sphere colliders. These restrictions all exist to help boost performance.

Edit Constraints Tool

You can apply constraints to specific vertices of the cloth to give them more or less freedom of movement.

In the Inspector, select Edit cloth constraints (top-left button) in the Cloth component. When the tool is active, small spheres appear in the Scene view on all vertices of the mesh. They represent the cloth particles to which you can apply constraints. The Cloth Constraints tool window also appears at the bottom right of the Scene view.

The Cloth Constraints Tool being used on a Skinned Mesh Renderer.
The Cloth Constraints Tool being used on a Skinned Mesh Renderer.

Constraint types and colors

For each cloth particle, you can set and display two types of constraints: * Max Distance – the maximum distance a cloth particle can travel from its vertex position. * Surface Penetration – how deep the cloth particle can penetrate the mesh.

The color of a particle represents the relative value of its constraint within the cloth, according to the type of constraint currently selected.

Constraints visualization

The visualization properties of the Cloth Constraints Tool.
The visualization properties of the Cloth Constraints Tool.
Property Function
Visualization Allows you to select which constraint type and which particles to display.
Max Distance Displays only the Max Distance values of the cloth particles.
Surface Penetration Displays only the Surface Penetration values of the cloth particles.
Manipulate Backfaces Enable this option to visualize and manipulate particles that might be hidden behind the current facing part of the cloth.
[ Color spectrum ] Provides the correspondance between particle colors and constraint values for the above selected constraint type, according to the mimimum and maximum values currently applied within the whole cloth. Black always means that the particle has no constraint.
Constraint Size The display size of the spheres that represent the cloth particles. Adjust this value at your convenience to ease your constraints edition. This property has no effect on the constraints themselves.

Constraints edition modes

You can use 3 different modes to edit the cloth constraint values.

Mode Description
Select Allows you to apply a fixed constraint value to a pre-selected group of particles.
Paint Allows you to apply a fixed constraint value by painting the cloth particles with a brush.
Gradient Allows to apply a left-to-right linear gradient of constraint values to a pre-selected group of particles.

The tool properties and the steps that you need to perform are different according to the mode you are using. In all cases, the last step corresponds to the action that applies the constraint values.

With the Select mode:

The Cloth Constraints Tool in Select mode.

  1. Use the mouse cursor to draw a selection box or click on particles one at a time.
  2. Enable the constraint type that you want to apply to your selection: Max Distance, Surface Penetration, or both.
  3. Set a value according to the constraint type you just enabled.
With the Paint mode:

The Cloth Constraints Tool in Paint mode.

  1. Adjust the Brush Radius according to the area you need to cover with the brush.
  2. Enable the constraint type you want to apply: Max Distance, Surface Penetration, or both.
  3. Set a paint value according to the constraint type you just enabled.
  4. Paint the constraints on the particles with the brush.
With the Gradient mode:

The Cloth Constraints Tool in Gradient mode.

  1. Ensure to toggle on the 2D view in the Scene view (the tool cannot apply a gradient when in 3D view).
  2. Use the mouse cursor to draw a selection box or click on particles one at a time.
  3. Set the limit values of the gradient you want to apply left-to-right within your selection: Gradient Start and Gradient End.
  4. Enable the constraint type that you want to apply to your selection: Max Distance, Surface Penetration, or both.

Self collision and intercollision

Cloth collision makes character clothing and other fabrics in your game move more realistically. In Unity, a cloth has several cloth particles that handle collision. You can set up cloth particles for:

  • Self-collision, which prevents cloth from penetrating itself.
  • Intercollision, which allows cloth particles to collide with each other.

To set up the collision particles for a cloth, select the Self Collision and Intercollision button in the Cloth inspector:

The Self Collision and Intercollision button in the Cloth Inspector
The Self Collision and Intercollision button in the Cloth Inspector

The Cloth Self Collision And Intercollision window appears in the Scene view:

The Cloth Self Collision And Intercollision window
The Cloth Self Collision And Intercollision window

Cloth particles appear automatically for skinned Meshes with a Cloth component. Initially, none of the cloth particles are set to use collision. These unused particles appear black:

Unused cloth particles
Unused cloth particles

To apply self-collision or intercollision, you need to select a single set of particles to apply collision to. To select a set of particles for collision, click the Select button:

Select cloth particles button
Select cloth particles button

Now left-click and drag to select the particles you want to apply collision to:

Selecting cloth particles using click and drag
Selecting cloth particles using click and drag

The selected particles appear in blue:

Selected cloth particles are blue
Selected cloth particles are blue

Tick the Self Collision and Intercollision checkbox to apply collision to the selected particles:

Self Collision and Intercollision tick box
Self Collision and Intercollision tick box

The particles you specify for use in collision appear in green:

Selected particles are green
Selected particles are green

To enable the self collision behavior for a cloth, to go the Self Collision section of the Cloth Inspector window and set Distance and Stiffness to non-zero values:

Self Collision parameters
Self Collision parameters
Property: Function:
Distance The diameter of a sphere around each particle. Unity ensures that these spheres do not overlap during simulations. Distance should be smaller than the smallest distance between two particles in the configuration. If the distance is larger, self collision may violate some distance constraints and result in jittering.
Stiffness How strong the separating impulse between particles should be. The cloth solver calculates this and it should be enough to keep the particles separated.

Self collision and intercollision can take a significant amount of the overall simulation time. Consider keeping the collision distance small and using self collision indices to reduce the number of particles that collide with each other.

Self collision uses vertices, not triangles, so don’t expect self collision to work perfectly for Meshes with triangles much larger than the cloth thickness.

Paint and Erase modes allow you to add or remove particles for use in collision by holding the left mouse button down and dragging individual cloth particles:

Self Collision parameters
Self Collision parameters

When in Paint or Erase mode, particles specified for collision are green, unspecified particles are black, and particles underneath the brush are blue:

Particles being painted are blue
Particles being painted are blue

Cloth intercollision

You specify particles for intercollision in the same way as you specify particles for self collision, as described above. As with self collision, you specify one set of particles for intercollision.

To enable intercollision behavior, open the Physics settings (from the main menu in Unity: Edit > Project Settings, then select the Physics category) and set Distance and Stiffness to non-zero values in the Cloth InterCollision section:

Enable intercollision behavior in the Physics settings
Enable intercollision behavior in the Physics settings

Cloth intercollision Distance and Stiffness properties have the same function as self collision Distance and Stiffness properties, which are described above.

Collider collision

Cloth is unable to simply collide with arbitrary world geometry, and now will only interact with the colliders specified in either the Capsule Colliders or Sphere Colliders arrays.

The sphere colliders array can contain either a single valid SphereCollider instance (with the second one being null), or a pair. In the former cases the ClothSphereColliderPair just represents a single sphere collider for the cloth to collide against. In the latter case, it represents a conic capsule shape defined by the two spheres, and the cone connecting the two. Conic capsule shapes are useful for modelling limbs of a character.


  • 2017–12–05  Page amended

  • Cloth self collision and intercollision added in 2017.3 NewIn20173

Spring Joint
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