The physics system helps you simulate physical phenomena such as collisions and forces in real life.

Physics module

Physics is a module that is loaded by default.

Here you can modify the global physics settings:

1. The direction and strength of gravity.
2. The default physics material. See the section on collisions – physics material below.
3. The global energy threshold. The kinetic energy of an object is calculated using the formula

$$Ek=1/2<em>m</em>v^2$$

where m is the mass of the object in kg.

v represents the physical speed in m/s.

When an object has a kinetic energy less than this threshold, it will stop moving. If the threshold is set to 0.5, an object weighing 1kg will stop moving after its speed falls below 1m/s.

4. Character controller collision threshold. Only applicable to the player module with [Use physics-enabled player controller] turned on or a fully customized character controller.

The momentum formula is:

$$p=mv$$

m is the mass in kg.

v is the speed in m/s.

In the event of a collision, the momentum of the player is subtracted from that of the rigid body being hit, and the magnitude of the component of the momentum difference normal to the collision normal is taken and compared with the character controller collision threshold. If it is less than this threshold, the rigid body will be pushed steadily, otherwise there will be a violent collision.

Roughly speaking, the parameters that affect whether there is a violent collision are:

1. The greater the mass of the player or character, the more likely there will be a violent collision.

2. The greater the relative speed of the player or character and the rigid body being hit, the more likely there will be a violent collision.

3. The greater the collision threshold setting of the character controller, the less likely there will be a violent collision.

For example, if the collision threshold for the character controller is set to 50, a 50 kg player moving at 1 m/s can collide violently with any stationary rigid body of similar mass to the player or character in a head-on collision.

5. Physics layer. Whether collisions occur at different layers depends on the physics configuration.

Configure a non-default physics layer for the player:

Disable collisions for the Custom and Default layers in the physics configuration:

You will notice that the player can pass through any object with the default physics layer without any effect:

Objects that depend on collisions being triggered also won’t trigger:

Collider shapes and Collider

Custom objects require two basic components to be applied to the physics system:

the Collider shape component and the Collider component.

For the vast majority of objects, you will only find a single Collider component.

This is because they are usually not custom objects:

For the need to customize the Collider shape and physical material, we recommend that you create a new empty node and operate on this empty node:

Collider shape

The Collider shape component determines the boundary within which objects collide.

Collider types:

The Collider type determines the basic shape of the Collider. We provide three basic shapes: Cube, Sphere, and Capsule, as well as Mesh Collider.

The Mesh Collider is a Collider shape that is simulated based on the boundary of the model and is almost the same as the visual appearance of the model.

For the empty node created, you need to add a custom render component to specify its grid shape and size.

For the Collider shapes of the basic shapes, you can modify their position, size, or adjust their shape manually:

Drag the yellow dot on the Collider box to adjust the Collider shape

The mesh Collider shape has an option for whether it is a convex polygon

Is Convex: Whether to collide with other mesh colliders. Mesh colliders without convex polygons are only supported on game objects without rigid body components. To use mesh colliders with rigid body components, check the convex polygon option.

Collider

physics material

The physics material determines some of the physical properties of the Collider.

For custom objects, the Collider physics material supports customization. However, for most officially provided non-custom objects, the physics material cannot be modified.

The physics material file can be created.

You can modify the following properties in the inspector panel of the physics material file, so that all objects mounted with this physics material will get the corresponding physical properties.

Is Trigger

When the Is Trigger checkbox is selected, the Collider object ignores physical Colliders but can trigger events.

This means that the object will not participate in the default physical collision logic:

but can trigger Collider events:

Physics layer

Determines the layer at which physics is located. Whether Colliders occur at different layers depends on the configuration in the physics module.

Rigid body

The rigid body component makes an object subject to physics, so that it is affected by forces.

To add a rigid body component, you must first have a Collider component.

There are static, dynamic and kinematic rigid bodies.

Static rigid bodies are mostly used for objects that have no speed and are not affected by forces, such as the ground, walls, and other objects that do not move. Modifying the position or scaling of these objects will increase performance overhead.

Dynamic rigid bodies are mostly used for objects that have mechanical properties such as mass and speed, and can be affected by forces.

You can modify physics-related parameters such as the center of gravity and mass under the dynamic rigid body option.

A kinematic rigid body can be manually controlled to move and rotate, but is not affected by Colliders or forces from other rigid bodies. It is often used in the production of animations and special effects.

Character controller

FF player controller

By default, player-to-player character control is inherited from the FreeFire player controller.

Player controller with physics

In the Player module, after checking [Use player controller with physics], you can modify some of the physics parameters of the player controller. In this case, the player will begin to participate to a certain extent in the in-game physics simulation, and the configuration of [Character controller collider threshold] in the Physics module will take effect.

Use Physical CCT: If you select this option, a controller with custom physics will be used, and the relevant configuration will be expanded.

Height: The height of the character capsule Collider body.

Radius: The radius of the capsule body, which cannot exceed 1/2 of the height.

Mass: The mass of the player.

Slope Limit: A slope beyond this angle cannot be climbed, and the player will start to slide down.

Step Offset: The distance the player is allowed to deviate from this configuration without leaving the ground or being blocked, often used when moving on stairs.

Min. Move Distance: If the distance the character controller is to move is less than this value, the player will remain motionless.

Skin Width: The layer to which other objects can be embedded in the character’s Collider body to avoid jitter or getting stuck.

Gravity: The acceleration due to gravity in three dimensions. For the player character, this setting overrides the global physics settings.

Enable Custom Push Force: When enabled, the force applied when the character pushes a rigid body can be customized. Expand the relevant configuration when enabled.

Custom Push force: the amount of force applied when the character pushes a rigid body.

Jump Height: the height of the jump when performing a multisegment jump.

Max. Jump Count: the maximum number of jumps supported per multisegment jump.

Move in Midair: when enabled, the player can change the movement speed and direction in the air.

Fully Customizable Character Controller

In the fully customizable character controller, you can completely customize the character controller without any restrictions, but this controller does not have any default functions.

To use the fully customizable character controller, you need to use the character controller component, and the object that is controlled as the character cannot have components such as Collider, Collider shape, or Rigidbody.

For specific usage methods, please refer to the example below.

Example

We will explain how to use the custom character controller by creating a simple horizontal board mode character controller.

Building the Scene

Build a simple scene.

Create a player character

Here we will only create a simple player character.

Create an empty object:

Add the Character Controller component to this object.

Add a custom property to the character controller: state. We will use state to control the player character’s left and right movement in the following steps.

The character does not have an appearance at the moment, so add an empty child node to this empty node to display an appearance.

Add a custom render component to the empty child node.

Select Mesh as the Cylinder.

Now select the parent node and observe our character in the Scene Editor.

The capsule grid is the parent object’s role controller component, and the cylinder is the child object’s custom rendering component. We found that the role controller seems to be a bit taller than it looks and has a smaller range than the model.

Adjust the relative height of the child object to match the appearance of the role controller roughly.

Please note that for the character controller, its height must be greater than twice the radius.

Set the created character as a Prefab and rename it to New_player (or whatever you like). Delete the empty object used for the creation in the Scene.

Initialization

Create a global script that is used to hide the default player, create a new player, and set the movement method.

1. Clear default UI

To use a custom character controller, you first need to solve the built-in player controller. The player character cannot be deleted from the game, but there are ways to make it impossible to control or see.

By using the Close Default UI interface, we can block all UIs that can directly control the default player.

2. Use a custom camera

The default camera follows the default player character. We need to use a new custom camera to only observe the new player character we created.

3. Store player data

Create a global variable to store each player’s custom character controller.

4. Set the movement method

We control movement by determining the state of the character controller. Setting 0 means no movement, 1 means left, and 2 means right.

The movement method is executed once for all custom controllers each time it is updated. The movement method checks the state of the player’s controller and, if it is in a moving state, moves it a small distance in the corresponding direction.

When the fixed frame is updated, the event is triggered 30 times per second, which is equivalent to the character controller moving at a speed of 30*0.1=3m/s.

Create a custom action UI

Create a UI to control the movement of the custom character controller.

The three buttons are used to make the player move left, move right and jump.

Add scripting to UI entities and use callbacks to handle logic:

1. Jump

Jumping is achieved by applying force to the custom character controller.

The force interface can directly select the applied speed, avoiding the calculation of force and mass.

2. Movement

We control movement by changing states, which we can do by handling the state of the player when they press and release the button.

Add callbacks to the buttons to call these methods respectively.

1. Jump

2. Move

Debug

Logic is working as expected.

Additional: Lens Debugging

When using custom lenses, it is sometimes difficult to determine an appropriate lens parameter.

We can adjust the lens during the development phase by adding a UI to control the lens. Using the same idea can help you continuously optimize the performance of your character controller during the debugging phase.

Create UI

We use buttons to control the movement of the lens up, down, left, right, forward and backward, and print the current lens offset with a button.

Write a script

Add a script to the UI entity.

Move the camera, using the up movement as an example:

Print the lens parameters:

Add callbacks

Add callbacks for each button:

Take moving up as an example:

Print the lens parameters:

This way, you can adjust the lens during game debugging to achieve the effect you want: