This is a Space Invaders clone made using SkookumScript and Unreal Engine 4. The goal of this project is to provide a fully working sample project that illustrates how to write a basic game in UE4 using the SkookumScript programming language. The game is also available as a stand-alone download on our itch page.
If you would like to discuss aspects of the project feel free to reach out in the official announcement thread. If you'd like to report a bug you can use the github Issue Tracker.
- UE4 4.23.1
- SkookumScript Plugin from github
Implements ability to fire classes of BP_Projectile. Defines:
- Max # of projectiles allowed on screen at a time
- Delay between shots
- Audio cues for firing sound and gun empty sound
- Spread firing pattern
All of the gun parameters are defined in the struct S_GunParams with the idea that the current gun can be overridden by collecting a BP_Powerup. The direction and location that the gun fires from is determined by the X direction of the gun component. This is the only component that is a SceneComponent (has a transform).
- Tracks current health/max health
- Automatically registers damage handling routines
- Spawns damage and death particles
- Plays death audio cue.
- Provides death callback to broadcast when its owner has expired.
Also squirreled away here is the number of points that something is worth when destroyed.
- Provides the typical space invaders movement scheme (right, down, left, down)
- Exposes parameters for speed and distance
Can also be used for things that travel in a straight line like BP_Saucer and BP_Powerup. Typical use requires knowledge of the game playfield and screen boundaries which are provided by BP_World.
- Provides ability to spawn a group of actors from an ASCII defined pattern of 0's and 1's
- Can spawn individual actors like in the case of
BP_Shieldwhich spawnsBP_ShieldBlockNewto create the destroyable shields. OrBP_Invasionwhich spawns groups ofBP_Invader - Can use instanced static mesh instances to create the pattern.
Patterns are enumerated in E_Pattern and defined in the SkookumScript method Pattern.pattern. Spawned patterns can be centered about an arbitrary index, for instance in the powerup pattern below, it would be ideal to center it on index 7 so that the pattern will be geometrically centered at the location it is spawned at:
1 1 1
1 0 1
1 1 1
1 0 0
1 0 0
The coordinator for a group of invaders. The invasion spawns the invaders, groups them together and then moves them down the playfield. It also coordinates:
- Firing amongst the remaining invaders
- Difficulty adjustment based on how many invaders are remaining and what level you're on
- Spawning saucers
- Determining if invaders have landed
The main entry point here is _invasion.
The actual invasion start/stop is controlled by GM_Invaders.
The bad guys. They pretty much just stand around and fire once in awhile. They also take damage and die, they are basically puppets controlled by BP_Invasion. There are also sub-classes BP_InvaderType1-3 which just change the color of the invader body and point light.
- Fly's to the right until it reaches its despawn destination
- Defines an array of
BP_Powerupand chooses one at random to spawn when it is destroyed by the player
- Defines a gun parameter
S_GunParams - Overlaps
BP_PlayerPawnwho overrides theS_GunParamsin herGunComponent.
- Spawns
BP_ShieldBlockNew - Parameterizes shield class, pattern and scale
Each individual shield is made up of an array of these things. They have some cool functionality that makes them connect to adjacent neighbors with their connector arms, see connect_neighbors. They also generate a spline on startup that is used to fly them in rapidly past the camera, see begin_play.
- Takes damage thanks to HealthComponent
- Also takes damage when overlapped by
BP_Invader
Fired by GunComponent, damages HealthComponent.
The single class in the game that can apply damage to anything it overlaps. This is also the only class that uses physics to move, I had thought of extending this later on to make guided projectiles.
Projectiles have a maximum lifetime after which they self-destruct. They also have a variety of other parameters to tune speed, look and feel.
There is 1 subclass BP_EnemyProjectile whose 2 key differences are:
- A different particle system
- A different collision profile on the sphere component
The player pawn.
- Handles overlaps with
BP_Powerup - Handles input and logic for moving and shooting
The satellites sitting in the background. These have lasers built in that can fire into the playfield. When the player picks up a powerup, the satellites will track to the Sat Start helper defined in BP_WorldSetup, fire their lasers and then sweep to Sat End. The actual firing happens in PC_Invaders.fire_sats, this was a somewhat arbitrary location to place this. Primarily I didn't want it tied to the player pawn so that if a player is killed, the satellites continue firing.
These are pretty cool models that are rigged to allow rotation and pitch control. There are default implementations to aim the base _aim_at and the tip _aim_tip_at and then another one that combines those two to look at a specific point in the world _look_at.
Does all of the heavy lifting for calculating game coordinates:
- Movement boundaries
- Player start
- Screen corners
- Saucer spawn/despawn
- Game Over line
- Invasion spawn point
- Shield spawn points
Shield, invasion class along with shield count and shield start location are all parameterized. Run the TEST_WorldBounds map and eject to see bounds and helpers drawn out. You can probably guess what most of these are.
The GameMode that defines the player controller PC_Invaders and the default pawn BP_PlayerPawn. This is also where the logic for starting, running and restarting the game is found (see _invaders_game).
This class is where the majority of the stage direction takes place.
The player controller.
- Is the primary entry point for everything UI related
- Handles input for the start UI
- Tracks number of player lives
- Tracks player score and high score
- Manages the firing of satellites
A simple UI that invites the player to press start. This screen is implemented in PC_Invaders _start_menu and is called by GM_Invaders _start_game.
Simply the words Game Over in the center of the screen. This is handled in PC_Invaders show_game_over and is called by GM_Invaders _handle_win_lose and _restart_game.
The primary game screen which displays:
- Number of player lives
- Score
- Highscore
This UI mostly uses UMG bindings that in-turn call SkookumScript code to perform updates. For instance, the update_score method which smoothly increments the player score from previous to current. However, you can also see an example of text being set directly in PC_Invaders _spawn_pawns where we directly set number of player lives when a player is killed.
- Erbos Draco Monospaced NBP font — Created in 2012 by total FontGeek DTF, Ltd
Music by Eric Matyas “Automation” "Mech Monsters Closing In" www.soundimage.org