blastar (./20) :
what classic console-game handles 80 enemies at the same time on screen? 20 enemies should be enough for 2d-shooters or most other games.
in my opinion doing a collision-check in the correct order is more important than any other optimization, collision zones are overrated because you need additional checks for every object. a successful collision-check needs 4 CMP.W but most will fail after 1st or 2nd check -> no collision! checking each object and sorting to a different zone is wasting of time!
VRAM access is slow but moving all bullets (changing x- & y-pos incl. check 'out of screen') without updating VRAM takes more time than collision-checks!

Apologies for late reply Blastar

Yes you make a good point! There are very few schmups that feature lots of enemies on screen at the same time. Maybe if you have a boss that fires lots of destructible bullets (missiles?) you would need zones. For example the crab boss in viewpoint which fires those bubbles you can destroy. If you had a gameplay mechanic in the game where you could destroy bullets they would be useful. Also 2 player games could need them - More enemies, bullets on screen etc. Viewpoint again being an example since the 2nd player mode was hidden possibly because they found it hard to add more enemies and keep the speed up.

Maybe an updated version of Asteroids on a less powerful system could make use of them if you really had a lot going on, on screen. Hmmm but yes not many games would need zones. I always assumed that you would need them in a bullet-hell game - but I guess not!

blastar (./20) :
@CosmicR
What's your solution or routine for a collision check?

I am not a very experienced coder in 68k so I don't know the best method. I was just trying to learn from you A lot of people online suggest quadtrees. I did use rectangular collision zones in a demo I made a few years back. And I can confirm the game did slow down before i added them. (it was written in a high-level language though - BlitzMax) I only originally made this demo at the time to test collision zones out. It was a a lot of work adding them - I think I had to keep record of the four corners of each object and I used linked-lists added to each zone and then added or removed objects form the lists as the aliens,bullets etc moved about. Then I just cycled through all the zones doing collision checks for each one. You could probably maintain a linked list of collision zones too if you wanted. It's a bit buggy but it works pretty much and displays how many collision checks are being done each frame at the top of the screen. But like you say not worth doing unless you want a lot of enemies onscreen at same time.

https://www.youtube.com/watch?v=iMPbbvQmOW0