© 2021 David Given
Portable Object reLocation Force: the game of objects, holes, and dubious physics
POLF is a game of the Commodore PET. You are placed in a maze; your goal is to search the maze for the Portable Object, and use your Impulse Pusher (space bar) to move the Object into the Hole. There is no plot; please feel free to make up your own.
It should run on any 40-column PET with 16kB of RAM or more. (If anyone knows how to switch an 8032 from 80-column to 40-column mode, please get in touch.) It supports both Business and Graphics keyboards.
POLF is written with the 64tass assembler.
Simply assemble the polf.asm file with the --cbm-prg option and you should
have a working .prg file. Transfer this to your pet by whichever means makes
you happy. There is a Makefile which will build it for you.
Load the program, then RUN it. POLF should start.
Instructions: use WASD to move; use , and . to turn left or right (or ,
and ; on a graphical keyboard). Press SPACE to push the Portable Object if
you're close enough. The radar instruments at the bottom of the screen will
tell you how close you are to both Object and Hole.
There's a secret feature! You can use A and D on the level overview screen
to select any level (there are 100).
I wanted to write a proper 3D game for the Commodore PET. Given that the PET cannot actually display graphics, this seemed like a pleasantly futile task.
I originally wanted to use block graphics, which would have allowed a 80x50 graphics resolution, but it actually turns out that given the usual small-computer angle representation of 256 b-radians in a circle, then a comfortable field of view of 56° corresponds to 40 b-radians. This controls the highest possible resolution, because the program can't represent smaller angles than that. This is probably a good thing, as the rather feeble 1MHz 6502 processor produces a small enough frame rate as it is.
To draw the maze, raycasting is used, following Lode's Computer Graphics
Tutorial. The demo directory
contains a considerably hacked version of Lode's demo program, ported to use
8-bit fixed point graphics. POLF's number representation is 3.5 fixed-point,
which allows numbers to be represented from 0 to 7 31/32 at 1/32 intervals.
This is why the map is only 8x8, which is uncomfortably small.
In fact, this isn't really enough precision, even switching to 16-bit precision for a few operations. I've managed to special-case most of the graphical glitches but there are still some. Entertain yourself by finding them!
It should be easily portable to any other 6502 platform with a 40x25 text-mode screen and 16kB of RAM.
There's about 2.5kB of actual code, and 6kB of lookup tables.
POLF is © 2021 David Given, and is distributable under the terms of the MIT
public license. See the LICENSE file for the full text.
POLF was written by me, David Given. You may contact me at dg@cowlark.com, or visit my website at http://www.cowlark.com. There may or may not be anything interesting there.