This version of Space Invaders supports Steve Gray's colour PET module. I imagine that means two people on planet Earth can use it, though it works on normal PET's too.
It doesn't support joystick just yet because I've given in to frustration.... there is a bug in the game which exists in the original PET game too. When you fire and hit something (an alien) with the fire button held down, it shoots the next bullet of yours at the X position of the last hit.
So if you're at position 20 X-wise, and you hit an invader and then scroll to the very left of the screen and press fire, the bullet comes from the old X position where you hit the invader at the 20th X-position character. It doesn't occur if you let go of the keyboard.
L0585 is the left and right movement routine.
This happens in the original ROM as well. If anyone wants to tackle this, awesome. Source code is provided.
I've tried to reproduce the wrong firing/bullet position using Vice, emulating a PET4032, but no luck.
My idea was to set up breakpoints in the code.
- Holding down the fire button a bit after hitting an alien then moving the ship into a new x position
and firing again puts the bullet to the correct x position.
- Holding down the fire button after a hit and keeping it down while repositioning the ship (fire is seems to be inhibited during this),
then releasing and pressing the fire button again also puts the bullet to the correct x position for me.
Source code is provided.