2D Physics EngineDone already for your convenience!

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Unity 2D Game Development

Table of Contents

1. 2D Physics Overview

2. RigidBody 2D

3. Colliders 2D

1.Circle Collider 2D

2.Box Collider 2D

3.Polygon Collider 2D

4.Edge Collider 2D

4. Forces

2

2D Physics OverviewRigidbodies, Colliders,

Joints, etc.

2D Physics Overview

All physics elements are normal components

Just add them toa game object

Set all needed properties The physics engine

will start using them Enjoy the effects

4

2D Physics Overview Rigidbodies

Main component for the Physics Engine to start

With Rigidbody the object will start to respond to gravity

If you enable Rigidbody, you should not try to change the Transform part of the object

Instead, you should apply forces and let the engine do the heavy lifting

If you need non-moving by the engine Rigidbody, check “Is Kinematic” option

5

2D Physics Overview Colliders

Define the shape of an object in terms of physical collisions

Most of the time invisible Use Box Collider and Circle Collider

whenever possible for performance reasons

Otherwise use Polygon Collider Colliders with Rididbody are

dynamic colliders Colliders without Rigidbody are the

static environment in your game – walls, floor, etc.

6

2D Physics Overview Physic Materials

Materials define the physics collision effect

For example – ice is slippery, rubber has friction

Usually parameters are found by trial-error

In 2D there are two parameters Friction – friction coefficient Bounciness – the degree to which

collisions rebound from the surface 0 – no bounce effect

1 – full bounce effect with no loss of energy

7

2D Physics Overview Joints

Attaching two rigidbodies to a fixed point

Allow restricted movement

Rotation by the three axes

Translation by the three axes

Stretching like a spring

You can set joint to break if certain force is applied

8

2D Physics Overview Different Types of Colliders

Trigger Collider – does not respond to physics calculations but sends event to which you can subscribe from the scripts OnCollisionEnter2D /

OnTriggerEnter2D – when two colliders starts colliding for the first time

OnCollisionStay2D / OnTriggerStay2D – when two colliders are colliding

OnCollisionExit2D / OnTriggerExit2D – when colliders are no longer colliding

Simply select “Is Trigger”

9

2D Physics Overview Different Types of Colliders

Static Collider – object with collider but no Rigidbody Used for level geometry and should

never move

Should not be disabled or enabled

If you do, major performance decrease may occur

Also – calculation errors in the engine may occur

If you want to alter it – add Rigidbody to it

10

2D Physics Overview Different Types of Colliders

Rigidbody Collider – object with collider and Rigidbody

Most common case

Fully simulated by the physics engine

Reacts to collisions

Reacts to forces from script

Collide with all other objects11

2D Physics Overview Different Types of Colliders

Kinematic Rigidbody Collider – object with collider and Kinematic Rigidbody

Has “Is Kinematic” property set

Does not react to collisions and forces from the engine

Should be moved by a script

They behave like static colliders but can be enabled/disabled/moved when needed

12

RigidBody 2DHow to use it?

RigidBody 2D Rigidbody 2D

Attach it to objects controlled by the physics

In 2D only the XY plane takes effect for translation and the Z axis for rotation

14

RigidBody 2D Properties of RidigBody 2D

Mass – mass of the object Linear Drag / Angular Drag –

coefficient for movements Gravity Scale – whether the gravity

should be more or less on this object

Fixed Angle – can be rotated or not? Is Kinematic – is the body moved by

forces and collisions

15

Box Collider 2DHow to use it?

Box Collider 2D Box Collider 2D

Rectangular shaped collider

Attached to an game object

With or without a sprite

17

Box Collider 2D

Properties of Box Collider 2D

Material – the material to use for the collider

Is Trigger – whether events should be sent

Offset – local offset of the collider geometry

Size – the size of the rectangular shape 18

Circle Collider 2DHow to use it?

Circle Collider 2D Circle Collider 2D

Circular shaped collider

Attached to an game object

With or without a sprite

20

Circle Collider 2D

Properties of Circle Collider 2D

Material – the material to use for the collider

Is Trigger – whether events should be sent

Offset – local offset of the collider geometry

Radius – the radius of the circular shape 21

Polygon and Edge Colliders

2DHow to use them?

Polygon and Edge Colliders 2D

Polygon Collider 2D and Edge Collider 2D

Complex shaped collider

Attached to an game object

With or without a sprite

Difficult to compute – performance impact

23

Circle Collider 2D

Properties of Polygon Collider 2D and Circle Collider 2D

Material – the material to use for the collider

Is Trigger – whether events should be sent

Offset – local offset of the collider geometry

24

ForcesHow to use them?

Forces

Two types of forces Constant Force 2D Effectors (Area Effector 2D for

example) They both are added to a

Rigidbody 2D Applied every Update of the game Good for in-game mechanics Have acceleration options

26

Summary

Rigidbody – component used by the physics engine for calculations

Colliders – components to register any colliding objects in the game

Different types of colliders – static, kinematic, etc.

Other physics elements – joint, forces, etc.

27

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2D Physics Engine

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