JA Invaders

Full title	JA Invaders
Year of release	1983/2017
Publisher	P Marshall
Producer / Author(s)	P Marshall
Memory	19K
Type	Game
Cost :	Never Sold / PD
Download	JA Invaders [CRC32 17BF1C19] Distribution Permission Allowed | Group 1

JA Invaders

A space invaders clone for the Jupiter Ace microcomputer. This is my attempt to rewrite a game that I orginally wrote when I was a kid. It's a clone of a clone. Unfortunately the game will not run on an unexpanded Ace as it weighs in at about 5K. Forth and machine code are supposed to be fast and compact but mine, not so much.

The original game was written partly in Forth and partly machine code. An unusual design feature is that the player ship was able to move through all pixel positions whereas the invaders moved through character positions. There is something dishonest about having the player work in a different resolution to the invaders but for some reason it was important to me back then and I have to say, I do like the effect now. The original game had sound but this version does not (mostly because xAce does not emulate sound). The original sounds (or shall we call them beeps?) would have been short bursts as making beeps was not a background task and would have used up precious cycles.

If you want to alter the game, be aware that the machine code routines defined by the hex create sequences refer to the variables defined early on in the source code and to some of the other machine code routines. So, avoid redefining anything up to and including the machine code routines. Also, some of the constants are restated in the machine code so changing these values will not be propogated to the whole code. Other than that, changing the code after the machine code routines should be fine.

To load the game enter 'invaders' then PLAY to run.

Keys

Z left
X right
Space fire

Screen shots