Gem Drop Deluxe

Bill Kendrick, 2015


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.

2015_08_15_1_alpha version, interlaced screenshot from Atari800 emulator.
2015_08_15_1_alpha version, single frame screenshot of Atari800 emulator window. "NTSC Filter" display mode enabled.
2015_10_02 version, "Super IRG" flicker mode disabled. 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.)



The source code is maintained in the 'gemdrop_deluxe' git repository at GitHub. You'll also need the 'cc65_atari8bit_extended_headers' (also at GitHub).


Currently (2015-10-02) it's released as a ZIP archive containing an ".xex" Atari executable program (which can be run on a real Atari via your favorite DOS's "binary load" option, booted via a disk emulating device, such as SIO2SD, or run directly by your favorite Atari emulator, e.g. "atari800 -run gemdrop.xex")