I am quite sure that there are already Space Invaders games available for TI calculators, but all of them (at least, that I saw) are written in assembly. This one is written in TI-BASIC (as it's colloquially called). As you might be able to understand, getting such a complicated game as Space Invaders to work in such a slow environment and end up with a game that's fun to play is difficult.
The end result is fast enough (though a bit slow), fairly fun, and extremely difficult. The high difficulty was on purpose and the most recent change. It was because I found that the high score list seemed completely meaningless; clearing the aliens once was just too easy. In the most recent update, the aliens move faster downward, so clearing them once is difficult; you can't win a round if you miss more than a few shots.
There are some simplifications I had to make:
- There are only two rows of aliens (12 in total).
- No shields
- The aliens are treated as a single object, which means the aliens don't move all the way to the edge of the screen unless they were edge aliens to begin with (it's hard to explain; play it and you'll see what I mean)
- The player is represented by an "A", and the aliens are represented as "M"s. Less noticeably, bullets are colons (":").
Do let me know what you think!