Someone else mentioned that the 3D background will be 2X as wide. I don't see how that is possible unless you make the fish smaller
Nope.
Or did they mean the back will be 2X farther away?
Nope.
I think changing the vantage point would make it seem a lot more 3D as you could see over objects to other objects behind them and fish swimming behind them, that sort of thing.
Which is why the camera will pan back and forth over the double-width background. The fish aren't getting any bigger or smaller.
I am also still unclear why the number of creatures needs to be limited by the program.
For asthetic reasons.
It has been explained as a collision detection problem.
Correct. If you have more fish, they bump into each other or fight trying to around each other. It looks really ugly. I usually have my Aquarium set to 6 fish to minimize the 'bumper cars' look.
It has also been stated that the new 3D background version might be able to 'fit' 10 fish because it is bigger.
A conscious choice has been made to allow 10 fish with the double-width 3D background.
I don't understand why the tank size matters. If you have 7 fish all in one corner, isn't that like cramming them into a smaller tank?
Which is why the 7 fish are spread out and no more are allowed. You can have 8 fish if you use the Widescreen background.
Originally I thought that collision detection calculations increases exponentially as you increase fish and therefore it would be a CPU limitation
This Aquarium has something few other screen savers have -- collision AVOIDANCE. Instead of waiting until there is a problem and then trying to gracefully solve it, this Aquarium makes efforts using basic math to keep fish from ending up in the same place at the same time. A subtle but important distinction.
However, because they tend to have complex surfaces it becomes a CPU limitation.
It's not a CPU issue, it's simply an aesthetic choice. Things will really get hairy if you have many invertebrates trying to crawl over the same terrain.
All of the developers out there using advanced physics models and Calculus, and Jim came up with something that looks more graceful using pre-Algebra. Go figure!