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A port of Williams Defender for the Atari ST/STE/Falcon
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therealsark02/defender
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DEFENDER FOR THE ATARI ST/STE/FALCON ------------------------------------ Defender supports Atari ST/STE, Mega ST/STE, and Falcon030 computers with at least 1MB RAM. High quality sound samples are used on machines with DMA sound (STE/Falcon) and at least 2MB RAM. The game may be played with the keyboard, a joystick attached to port 1, or a joypad attached to Enhanced Joystick Port 0 (where available). ABOUT DEFENDER -------------- This program is a port of the Williams Defender arcade game, based on the published 6809 assembler source code and artistic assets: www.github.com/Historicalsource/defender Original game design and programming by Eugene Jarvis, Sam Dicker, Larry Demar, Paul Dussault, et al. Originally produced and Copyright (c) 1980 Williams Electronics, Inc. NON-AFFILIATION STATEMENT ------------------------- This program is not affiliated with Williams Electronics, Inc. in any way whatsoever. The Williams Electronics, Inc. logo and trademark are used under Fair Use to preserve the historical accuracy of this port. Williams Electronics, Inc. has not endorsed, sponsored, nor supported the production of this program. ABOUT THE PORT -------------- Gameplay -------- This Atari ST port attempts to replicate the original gameplay experience by importing as many original game functions and algorithms as possible. Original gameplay functions were translated from 6809 assembly into 'C', and modified as required to work in the new environment. Changes to constants for framerate-based delays and speeds have been scaled for 50Hz PAL timing, from their original 60Hz. Some algorithms related to graphics effects were re-created from scratch based on on-screen observation rather than code analysis. Graphics -------- The original Defender's screen bitmap layout is ridiculously well-suited to its 8-bit 6809 microprocessor, which allows its 1MHz processor to do so much on-screen without hardware support such as hardware scrolling or hardware sprites. In contrast, the Atari ST's 16-bit plane-based screen requires sprites be shifted and masked onto the screen so as to not clobber what is already there. This taxes the ST's 8MHz 16-bit 68000. At 320x200 4bpp, the Atari ST screen is a good match for Defender, which has 320x256 4bpp. Rather than use the standard ST resolution, requiring the game playfield be squeezed vertically, lower border overscan is used on ST/STE to extend the ST screen. This may result in the very bottom of the gameplay area being not visible on some monitors. For monitors on which it is visible, the trade-off is worth it. On the Falcon the screen is configured with more vertical resolution, and starts a little higher on the display for a more centered picture. Sound ----- The Defender hardware includes a separate sound board with its own microprocessor and software to generate sounds algorithmically (essentially a soft wave generator). The sound board is attached to the main 6809 via a parallel port, and the game sends single-byte commands to the sound board whenever it wants to play a sound. In this port, sounds were sampled from the original game and processed in two ways: - For the original ST without wave DMA, the samples were converted into YM2149 direct volume samples, using 1, 2, or 3 sound channels depending on the shape of the original wave. For example, sounds based on square waves can be reproduced reasonably using a single YM2149 channel, whereas sounds based on sine waves require multiple channels to reproduce the shapes more accurately. These samples are played using a timer interrupt up to 12.3kHz (i.e. ~12,300 interrupts/sec). - For STE and machines with wave DMA, the samples were used directly, with playback in hardware up to 25kHz. Input/Output ------------ Original Defender uses a PIA GPIO port to read joystick/switch positions, and saves game settings and high scores to CMOS RAM (essentially a 1980s equivalent of what flash memory is today). For the Atari ST, keyboard or joystick input is via the Intelligent Keyboard Controller via its ACIA, joypad input via the Enhanced Joystick Port (where available), and configuration and high scores are saved to GEMDOS drive. Programming Credits ------------------- Original design and gameplay algorithms: Eugene Jarvis, Sam Dicker, Larry Demar, Paul Dussault, et al. Atari ST/STE/Falcon platform, graphics, sound, and I/O programming: sark02 If it feels like Defender, then that's because of them. If it doesn't, then that's because of me. 3rd-Party Code -------------- This program incorporates liblzg by Marcus Geelnard (gitlab.com/mbitsnbites/liblzg) Sound sample conversion utilizes the ym2149_fixed_vol data, created by Paulo Simoes, from the Hatari project. Production Tools ---------------- Production of this program made use of the following tools: Microsoft Windows 11 Professional (www.microsoft.com) Ubuntu Linux (ubuntu.com) Crosstool-NG (crosstool-ng.github.io) GNU toolchain (www.gnu.org) Hatari (www.hatari-emu.org) STEEM SSE (sourceforge.net/projects/steemsse) MAME (www.mamedev.org) GIMP (www.gimp.org) Audacity (www.audacityteam.org) Community Play-Testing ---------------------- Thanks to the following users from atariage.com and atari-forum.com for playtesting and encouragement: Atari030 Eero Tamminen chronicthehedgehog AtariCrypt Kroll danboid Chris23235 Marakatti darwinmac Cyprian Philsan jd DarkLord Straker krupkaj DrTypo TwiliteZoner Free Software ------------- This program is free software. www.github.com/therealsark02/defender
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A port of Williams Defender for the Atari ST/STE/Falcon
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