Vice Invaders

**VICE INVADERS** is a Space Invaders tribute built for the humble, unexpanded Commodore VIC-20: 5K of RAM.

The whole game, graphics and sound included, is a 3.5 KB program.

Hold the line against four rows of invaders, hide behind your houses, shoot

the bonus saucer, and survive wave after wave as the invaders get faster and meaner.

### How it plays

- **32 invaders in four different types.** They march side by side, drop a row
when they reach the edge, and speed up with every one you shoot. The top row
is worth **40** points, then **30**, **20** and **10**.

- **Only the lowest invader in each column fires,** so the front line is the
dangerous one. Their white missiles fall slowly enough to dodge, but you can
only take **three** hits.

- **Four houses to shelter behind.** They crumble in three stages when hit,
from either side: your own shots damage them too. If the invaders reach them
they eat straight through.

- **Bonus saucer.** Once the invaders have started to come down, a red saucer
now and then crosses the top of the screen. Hit it for **100** points.

- **Fire is a tap, not a hold.** No auto-fire, and no more than two shots in
the air at once. Make them count.

- **Lose a life** when an invader missile hits you. **The game is over**
straight away if the invaders land on your ship or reach the ground.

- **Level after level.** Clear the screen and the next wave comes faster:
every level the invaders move **10% faster**, fire **10% more often**, and
their missiles fall **10% faster**. Your score and lives carry on.

### Controls

| Z | Move left |

| X | Move right |

| SPACE | Fire |

On the title screen, SPACE starts the game. 

### How to run it

This is a VIC-20 program, so you need a VIC-20 or an emulator. The download

has the game as a **.prg** and as a **.d64** disk image.

- **VICE (free):** `xvic -pal -memory none vice-invaders.prg` or attach the file from the menus and let it autostart.

- **Real VIC-20** with a disk drive or SD loader: `LOAD"VICE INVADERS",8` then
`RUN`. It needs a stock, **unexpanded** machine.

### About the making of Vice Invaders

The game was written in 6502 assembly using my own development tool called Dev20 for creating the source files. The code was written in Kick Assembler and tested in Vice.

The game fits in the VIC-20's unexpanded memory with just a few bytes to spare: the program and its 64-character custom character set come to 3,581 bytes in total. In the last 170 bytes I managed to include the top row ufo and two sound effects. There are only 4 bytes of free ram in the compiled code, else it would have corrupted the charset data at $1C00.

## System requirements

- Commodore VIC-20, unexpanded (no RAM expansion), or an emulator configured as one.

- Tested in VICE 3.10 (xvic), PAL

- [NTSC machines and real hardware have not been tested.

## First release

**v1.0 - 6 October 2026**

## Credits

- Game, Graphics, Sound and Code: Tony Brice

- Built with Dev20 (VIC-20 development environment) and KickAssembler, with Vice.

- This game is dedicated to James Black (Grandfather) for giving me my first computer - my beloved Vic 20.

- By completing this game, I have finally ticked off a bucket list entry of developing a 100% machine code Vic 20 game. It took me 45 years to get around to it.