Components

All game objects have one or more components.

Here are the ones you’re most likely to encounter.

This is not actually a component, but it lives at the top of the inspector panel, above all the components. Here you can give your object a meaningful name as well as attach a tag, which is useful for identifying things during collisions.

All GameObjects have a transform component, which manages the position, rotation and scale of the object in the scene.

Most game objects will appear on the screen in the form of some kind of image. The sprite renderer handles drawing that image. You can disable the sprite renderer by unchecking the box by the title. This is useful if you need an invisible object for some reason.

2D vs 3D: There is a Rigidbody2D for 2D games, and a Rigidbody for 3D games. Make sure you have the right one!

The Rigidbody component makes the object available to the physics engine. This means it will be affected by gravity, if your game has gravity enabled, and it can have forces applied to it. (You will mostly have a collider attached to any object with a Rigidbody as well.)

2D vs 3D: There are types of Collider2D for 2D games, and types of Collider for 3D games. Make sure you have the right one!

There are several colliders of different shapes and complexities; the BoxCollider2D is the simplest (others you might use are CircleCollider2D, CapsuleCollider2D and PolygonCollider2D). Colliders are responsible for determining when objects start and end colliding with other objects. If two colliders overlap, there is a collision. Note that a collision between two objects will only be registered if both objects have collider components.

You can modify the size/shape of the collider to better match your sprite by clicking the button next to Edit Collider.

When a collision begins (i.e. colliders start to overlap) the method:

void OnCollisionEnter2D(Collision other)

will be called, and when the collision ends, the method:

void OnCollisionExit2D(Collision other)

will be called, if they exist in a script attached to the object. You only need to define those methods if you want to do something particular in your game. If your objects also have Rigidbody components, the physics of the collision will be handled automatically by the physics engine.

If you need an object to respond when something passes over it, but you don’t want it to get in the way (think of the start/finish line on a top-down racing game), select the Is trigger option in the object’s collider, and now object won’t cause collisions. Instead of any OnCollision methods being called, these methods will be called:

void OnTriggerEnter2D(Collider2D other)

and

void OnTriggerExit2D(Collider2D other)