In 1992, I wrote a game for the Commodore Amiga computer called Gravitoids. It is like Atari's classic arcade game Asteroids from 1979, except each asteroid generates a gravitational field influencing the trajectories of everything else on the screen. The links below can be used to download Gravitoids as an Amiga floppy disk image (ADF format) or as an RP9 file for use with Amiga Forever. Links are also provided for downloading a non-gravitational version of the game called Asteroids.

Both games detect the speed of the computer (or emulator) and adjust the gameplay accordingly. For Gravitoids, this automatic adjustment is important, because the time required to compute the gravitational forces between every pair of asteroids is proportional to the number of asteroids squared. A faster computer allows the game to handle more asteroids on the screen. Each RP9 file contains configuration settings for things like the Amiga computer model (A500), the Amiga OS version (1.3), the amount of additional memory (1MB fast RAM), the emulation speed (fastest), the video format (NTSC), and a few hardware compatibility adjustments to improve the game's efficiency.

The ADF files do not contain emulator settings because they are just images of Amiga floppy disks. To run either game in UAE, open Hardware ➜ Chipset, and in the Chipset panel, do two things:

• Check the box for NTSC
• Remove the check in the box for Cycle-exact

Then, in the Options panel:

• Check the box for Immediate Blitter

Next, open Hardware ➜ CPU and FPU, and in the CPU Emulation Speed panel:

• Select Fastest possible

Finally, open Quickstart, and in the Emulated Drives panel, select the floppy image file as follows:

• Floppy drive DF0: ⇦ Gravitoids or Asteroids ADF file

Each ADF file boots directly into the game without needing a separate Workbench ADF file.

If you run into problems running these games in Amiga Forever or UAE, send me a note with a description of the problem. It may be possible to change some settings to make it work properly.

The ADF files will work in the online Scripted AMIGA Emulator. The Kickstart ROM file and keyfile must be supplied by the user. In this emulator, the games become noticeably slower with many asteroids on the screen, but they are still playable. The emulator was configured as follows:

On the Welcome! screen, start by clicking Config near the bottom.

From the menu on the left, select CPU:

• For Model, choose 68000
• For Speed, choose Maximum

From the menu on the left, select Chipset:

• For Type, choose Enhanced Chip Set (ECS)
• For Region, choose NTSC
• For Blitter?, choose Immediate

From the menu on the left, select RAM:

• For Chip, choose 1M (1024K)
• For Slow, choose 1M (1024K)

From the menu on the left, select ROM:

• For Kickstart, select your Kickstart v1.3 ROM file
• For Keyfile, select your ROM keyfile

From the menu on the left, select Floppy:

• For DF0, select Gravitoids.adf or Asteroids.adf

If someone finds other settings for this emulator that fix the slowness problem, please send them to me, and I will post them here.