I had to take some liberties with the game play and alien design to make it playable. The spectrum version had a laser that zipped across the screen. That would have made the game too easy, so this uses minus signs like bullets. The difficultly levels adjust the number of aliens and bullets from four aliens/eight bullets to eight aliens/two bullets. Extra life at 2000 points. The bottom line of the screen tells you what your current task is such as assemble of fuel your ship etc.
Give it a go and see what you think.
There is a certain irony in using a 4.7Mb file to load 16k into a machine. Imagine if modern computers used every last drop of memory and processing power as efficiently as the early computers.
My site contains a few other minor ZX81 programs that I haven't posted here, at least not yet.
Have you considered including Chroma colour support in the game?
If you have a Window PC then you can use winTZX to create audio files from .p files as and when needed. The utility was improved last year to produce more accurate audio waveforms and also to include support for ZX80 files, and I've found it works remarkable well.
This game is excellent. Thanks for your hard work. It's a shame I'm no longer a writer as this is definitely review-worthy.
At least you get a chance at another extra life then?
I only get one extra life at 2000 points and have not made the score 'wrap around' yet, so good work