Rocks

The goal of the game is to destroy the floating space rocks, so, now that you can shoot, it's time to add them. Like the ship, the rocks will also be RigidBody2D, which will make them travel in a straight line at a steady speed unless disturbed. They'll also bounce off each other in a realistic fashion. To make things more interesting, rocks will start out large and, when you shoot them, break into multiple smaller rocks.

Scene setup

Start a new scene by making a RigidBody2D, naming it Rock, and adding a Sprite using the res://assets/rock.png texture. Add a CollisionShape2D, but don't add a shape to it yet. Because you'll be spawning different-sized rocks, the collision shape will need to be set in the code and adjusted to the correct size.

Set the Bounce property of the Rock to 1 and both Linear/Damp and Angular/Damp to 0.

Variable size

Attach a script and define the member variables:

extends RigidBody2D

var screensize = Vector2()
var size
var radius
var scale_factor = 0.2

The Main script...