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Space Instigators 20th Anniversary Edition

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(I know 20 years - WTF?!?)


;Updates since original release:

; Slow down UFO
; Use UFO score table from arcade version
; Make UFO start position based on shot count
; Aliens drop one row lower
; Title screen with settings menu
; Implement Sound setting in game
; Implement NTSC/PAL colour settings in game
; 20th anniversary logo


;To Do
; Improve Shot Display (less flicker) (may not be possible)
; Optional Multicolour Instigators (Non-trivial - need to free ROM space or expand to another bank)
; Ensure smooth transition between Title Screen and Game Screen (no roll caused by too few or too many scanlines)
; Verify UFO scoring is correct (shot counting)
; Verify stable scanlines during game

Note: Demo version, requires hard reset after each game.
















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23 hours ago, sramirez2008 said:

I let the game play (2nd pic) and the UFO came out before I fired any shots.

Hmm... Is it not supposed to?


I just tried the arcade version on emulator and I got UFOs without ever firing a shot...


I'm not sure where I copied this from anymore, but these are the notes I have as far as UFO behaviour from when I was fixing the UFO. Th one thing I now notice I haven't done is preventing the UFO from appearing before the first row descends. Which would be a really simple flag if I had either RAM or ROM space available :)

Put it on the todo list since I need to find ROM space anyway and I probably have an available bitflag somewhere. (I don't remember how I determine when the UFO shows up may or may not be every 20 seconds)


;To the UFO show in arcade, the invaders need to be below the first row in the first wave. I mean, in the first wave, the program will wait for the invaders go down a 
;row before starting computing the UFO. For the next waves, they already start below this row.
;After that, the UFO will show every 600 frames, supposing you have a 30 frames per second frame rate (it leads to 20 seconds)…
;About the correct UFO velocity, enough to say the arcade moves just a game object per frame, beside the invaders themselves. So you have your base, base shot, 3 invaders
;shots and the UFO… The UFO increment is 2 pixels every move and the side it will show (right or left) will be randomly decided.
;Here is the ordered UFO score table. It is a circular list, and the pointer moves every shot you fire.
;The flying saucer’s direction is linked to the player’s shot count. The lowest bit of the count determines which side of the screen the saucer comes from. 
;If the saucer appears after an even number of player shots then it comes from the right. After an odd number it comes from the left. 
;The saucer object structure is re-initialized every time the player’s shot blows up. Here is the code in Object 1 (player fire):



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  • 2 weeks later...

ZeroPage Homebrew is playing Space Instigators 20th Anniversary Edition on tomorrow's ZPH stream LIVE on Twitch, hope you can join us!






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