Gem Drop Deluxe

Bill Kendrick, 2015-2021


Gem Drop Deluxe is an updated version of my game for the Atari 8-bit line of home computers, Gem Drop.

The original Gem Drop was written in 1997, in the Action! programming language on the Atari. (In 1998, it was ported to C for Xlib, then Simple DirectMedia Layer library (libSDL), and is available as Gem Drop X for Linux, Windows, Mac OS X, and a variety of other platforms.)

This new Deluxe version, under development in 2015, is a port to C for Atari 8-bits, via the cc65 6502 cross-compiler.


The goal of this project, aside from learning more about, and practicing coding with, cc65, is to produce an updated version of the game, adding new features.


Note: Gem Drop Deluxe, like the original Gem Drop, uses a special graphical effect that switches between two images every frame (50 (PAL) or 60 (NTSC) times per second). Human eyes' persistence of vision (POV) blends the two images together. The game utilizes this to simulate more colors on the screen than are actually shown. "Interlaced" screenshots from Atari800 smoothly blend frames together to show the full spectrum of colors. Single frame screenshots will show an image normally only visible for a fraction of a second, with shapes that may appear blockier or more distorted. You can disable/re-enable this feature by pressing the [F] key.

2021_03_21 version, new title screen. Atari800 emulator window.
2021_05_13_beta version, interlaced screenshot from Atari800 emulator.
2015_08_15_1_alpha version, single frame screenshot of Atari800 emulator window. "NTSC Filter" display mode enabled.


Currently, the program should run on any Atari 8-bit computer with 48KB of RAM, including the 800. (It does not use RAM under the OS ROM.)



Currently (2021-05-13) it's released as a ZIP archive containing three versions:

    • Version: 2021_05_13_beta
    • Date: 2021-05-13
    • Description: A feature-complete build, based on the original 1997 release of Gem Drop. All new title screen with fancy graphics, copyright and version info, last and high scores, and settings options displayed. A few minor bug fixes and some minor gameplay flourishes. "Super IRG" flicker mode can be disabled (press [F] key). A help screen has been added (press [H] from the title).

Source Code

The source code to the game, data files, as well as some of the artwork source, are maintained in the gemdrop_deluxe git repository at GitHub.

A snapshot of the latest release's source code, as a ".tar.gz" archive, can be downloaded here: gemdrop_deluxe_2021_05_13_beta-src.tar.gz