Ultimate Tron II for C64

Ultimate Tron II is a game for C64 developed by Oliver Stiller in 1989 and published in 64'er Sonderheft 54 in 1990.

This is a reverse-engineered version that can be compiled into the same binary, using the cc65 suite.

Credits

MASTERS' DESIGN GROUP'S ULTIMATE TRON II
        WRITTEN BY OLIVER STILLER
DEVELOPMENT HISTORY:
ULTIMATE TRON PUBLISHED BY 64'ER IN 1988
ATARI ST ESCAPE-TRON WRITTEN AT COLOGNE
UNIVERSITY IN AUGUST '88
HEX-TRON WRITTEN IN MAY '89, PLAYED BY  
MDG AND CYBERSTYLE
IMPROVED VERSION: 'ULTIMATE TRON II'    
PROGRAMMED IN NOVEMBER 1989

Reverse-engineering by Michael Steil mist64@mac.com, http://www.pagetable.com/

Files

• basic.prg, asm.prg: The original BASIC and assembly binaries.
• basic.bas: The ASCII/PETSCII representation of the BASIC part.
• asm.s: The reverse-engineered assembly part.
• Makefile, asm.cfg: Needed for building the assembly part.

Some implementation details

• The game consists of two parts: A BASIC program that evaluates and keeps track of the scores, and an assembly program that is the actual game. BASIC calls into assembly for every round.
• The main program sits in a busy waiting loop, while the game is run based on a raster interrupt triggered by line 230.
• The code explicitly checks for keys to be pressed for at least 20 ms.
• The game state is the hi-res bitmap itself, collisions are detected by reading back pixels of the bitmap.
• Escaping is detected by comparing whether the player's most recently drawn pixel was at the screen edge - which can only be the case if another player's explosion has already removed the border pixel.
• Killer detection is done using a ring buffer for every player that holds the most recent 32 positions. Since the game only saves the lower 8 bits of the x coordinate, and the screen has a horizontal resolution of 320, it could in theory happen that the wrong killer is detected.