Overlay Lifecycle

All 23 overlays share one code window. When the game invokes an overlay function, the overlay runtime loads the corresponding body from CIV.EXE if needed, then transfers control to that function. A module can expose several entry points; see the overlay interfaces.

Only overlay code is replaced. Module-owned tables, strings and writable data remain in shared or separate resident data storage. Diplomatic and world-generation state therefore survives a change of overlay.

flowchart LR
    Caller[Resident game code] --> Request[Request overlay function]
    Request --> Check{Required overlay loaded?}
    Check -->|Yes| Run[Execute overlay function]
    Check -->|No| Load[Load code from CIV.EXE]
    Load --> Run
    Run --> Return[Return to caller]