Bevy-Space

Space invaders in Bevy, why not?

Small experiment to assess complexity of getting a simple thing done from scratch.

So far:

• Basically a working game, with title screen, waves, extra lives, etc.
• Both keyboard control and joy stick control, the latter plug and play at run-time. Tested only under arch linux (Manjaro) running KDE/wayland and Windows 10. No extra drivers or any other specifics, should work out the box, if not rise an issue.
• Simple particle system for bullet traces and explosions on impact.
• Audio (for now just a proof of concept with title music and an in game alien killed sample).

Todo:

• Mystery ship, possibly shooting homing missiles.

• More alien types perhaps?

• Varying speed of dropped bombs?

• Weapon upgrades? Double cannon might be useful...

• Leader board (for now its just a place holder). Potentially with on-line world wide scoring.

• Whatever you like to see in an modernized version of the 1978 classic.

• Stretch goals

  • Screen projection shader to replicate CRT.
  • Screen blur and suitable noise effects to get low quality video, VCR like shaders.

Tools used

• Pixelorama, well never used it before so why not trying it out.

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Setup

See Cargo.toml

• dynamic_linking (for reduced compilation time)
• log (settings for removing logging in release builds), seems not to work though
• `profile dev/release (for reasonable performance)

See .cargo/config.toml

• mold linker (for compilation speed)

All in all, after initial build, compile times are within seconds.

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How to play

• Keyboard

  • [Enter] to insert coin (start game)
  • [A]/[Left arrow], [D]/[Right arrow] to move
  • [LeftShift], to slow down movement
  • [Space]/[Up arrow] to shoot

• Gamepad

  • X on PS controller, A on X-Box to insert coin (start game).
  • LeftStick to move, speed determined by analog stick reading.
  • X on PS controller, A on X-Box to shoot. Only one missile at the time.

Hysteresis set at 0.01 to avoid drift, see common.rs for tuning.

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Design Documentation

The game uses the Bevy ECS to partition state and functionality. The initial design used Resources shared among the Components to determine the game logic. While adding more Components (and functionality) the number of dependencies between the systems grew. This is not necessarily a problem, however the amount of code duplication was increasing (and it started to become messy to accomplish desired behavior). This is not a unique problem the this particular game, instead an expected effect of shared state. The problem can be addressed in various ways, e.g., by implementing methods on the state holding Resources and/or by using Events. I opted to migrate towards Events primarily.

Events

Technically, events (if used correctly) increase available parallelism among systems (as under the Bevy hood, the need for "locking" of shared resources are reduced). For this particular application, this is not any major concern but in a realistic game parallel execution is in general desirable.

Events are currently declared along with their main Resource, so e.g., the game_state module defines the GameStateEvent. (Alternatively, all Event could be declared or re-exported by a separate module for convenience.)

The events declared are summarized as follows:

• PlaySoundEvent, play a one shot sample
• PlayMusicEvent, control background music
• GameStateEvent, request change of game state

The Events are listed by Component below.

Module	Declared	Reader	Writer
alien	-	-	-
audio	PlaySoundEvent	X	-
	PlayMusicEvent	X	-
bunker	-	-	-
common	-	-	-
game_state	GameStateEvent	X	PlayMusicEvent
hit_detection	-	-	PlaySoundEvent
	-	-	GameStateEvent
keyboard_input	-	-	FireLazerEvent
	-	-	PlayerEvent
	-	-	GameStateEvent
gamepad	-	-	FireLazerEvent
	-	-	PlayerEvent
	-	-	GameStateEvent
lazer	FireLazerEvent	X	-
lib	-	-	-
main	-	-	-
overlay	-	-	-
player	PlayerEvent	X	-

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Known Bugs

Bevy occasionally report an attempt to despawn a non existing Entity, it occurs rarely so not obvious to pin down. It is not a fatal bug as Bevy/Rust holds our back, but it would be nice to "iron out".

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License

Bevy-space is free, open source and permissively licensed! Except where noted (below and/or in individual files), all code in this repository is dual-licensed under either:

• MIT License (LICENSE-MIT or http://opensource.org/licenses/MIT)
• Apache License, Version 2.0 (LICENSE-APACHE or http://www.apache.org/licenses/LICENSE-2.0)

at your option. This means you can select the license you prefer! This dual-licensing approach is the de-facto standard in the Rust ecosystem and there are very good reasons to include both.

Some of the assets in this repo are cloned from Bevy game engine (under different licenses).

Your contributions

Unless you explicitly state otherwise, any contribution intentionally submitted for inclusion in the work by you, as defined in the Apache-2.0 license, shall be dual licensed as above, without any additional terms or conditions.