The first big issue and main reason why the seat limit was assumed to be hardcoded, was the control binding. Normal BF2 only has controls for switching to seats 1 to 8, but if those 8 seats were filled, you would enter the normally unreachable seats. While that would work for normal gameplay, it would make testing seats nearly impossible. With v1.6 we added new server side capabilities to hook and interact with the engine through Python code. [R-DEV]AlonTavor used these to change the F8 key binding to cycle you to the next open seat instead of switching to seat 8. This will only work on dedicated servers.
Next up was COOP. The AI module does not like any vehicle with more than 8 seats and crashes instantly on map load. This could have been avoided by creating copies of every vehicle for coop mode. Luckily the crash was fixable through some binary editing, so coop players can enjoy the same amount of seats as everyone else.
With these two issues out of the way, BF2 would support up to 10 seats per vehicle without any further changes. The limit of 10 comes from the client side HUD showing the seat positions and names of players in the vehicle. The code for that has no out of bounds check and would start accessing part of the memory it should not touch which results in a crash. Even if the seats would not show up on the HUD, it would still result in a crash. We fixed this by injecting an overflow protection through the Launcher. However this also means the normal HUD will not work for any seat above 10.
That brings us to the next step: Making a nicer HUD for used seats. While non-essential for this to work, it ties everything together. As the BF2 HUD only supports 10 seats, we started making our own HUD that gets controlled by the Launcher. For that we count the amount of currently occupied seats that do not have a seat dot in the HUD and show this number as the passenger counter in the bottom left. We decided to use this counter even for vehicles that do not go past 10 seats to ensure consistency and easy recognition across all vehicles. As such only the vehicle crew gets position dots for their seats. The crew is roughly defined as pilot/driver, co-pilot/co-driver and any gunner.
Passenger numbers in v1.6.3(in game values may have changed since list got updated):
Land vehicles:
Air vehicles:
Sea vehicles:
