Agent Wander
for Atari 8-bit Home Computers

Message me on Reddit at u/devshinedotcom if you have any questions or feedback.

Designed for Atari 8-bit computers with 48K or more memory. This includes Atari 800, 800XL, 65XE, and 130XE.

Agent Wander was originally designed for NTSC computers. PAL support has been added to have correct colors and correct play speed. The game works slightly better in NTSC mode than PAL. If you have the option, play the game in NTSC mode.

 

The game is being developed in assembly language. Development is done on a Windows PC using VS Code and the MADS assembler. Testing is done using the Altirra emulator.

The game is being developed to fulfill my dream I had when I was a kid in the 80s to create a professional quality game for my Atari 800XL. My goal is to try different techniques I have read about to make full use of the hardware available in 8-bit Atari computers.

Features implemented to create the game:

Flipping between two character sets every other frame to blend colors to create more simultaneous on screen colors.

Background sound player that takes sound data as input and then plays the sounds automatically. Each item in the sound data specifies frequency, volume, noise, and duration in frames. Up to four sounds can play at once, one sound per voice.

Player/Missile multiplexer for the enemy sprites. Each character row can have a different horizontal position and color for P/M players 1, 2, and 3.

P/M player 0 is used for the player's sprite. Player 0 flips between two sets of graphics data and two colors every other frame. This creates a three color player sprite using a single P/M player.

Playfeld hit detection implemeneted by reading the character value of the characters around the player's position. A character meaning lookup table is used to quickly determine what each detected character code means.

Because the game was designed for NTSC, the timing and colors were incorrect on PAL machines. The color issue was solved by having a color table that gets modified if PAL hardward is detected. To solve the issue of the speed the game runs at, I am running the game engine update logic twice on every fifth frame on PAL hardware. This results in 60 game engine updates per second while showing 50 frames per second on PAL hardware. Movement is not quite as smooth on PAL hardware as a result. However, it does make the game play the same on both NTSC and PAL hardware.

More information about how the graphics are implemented.

Future Development Goals

More levels.

High score table saved to disk to persist between play sessions.

Built-in custom level editor.

Theme music.