[Emmet_]

Use a variable to contain the player's virtual world.

pawn Код:

new g_VirtualWorld[MAX_PLAYERS];

Then under OnPlayerUpdate, check if the value within the array doesn't match the player's current virtual world.

pawn Код:

public OnPlayerUpdate(playerid)
{
    new worldid = GetPlayerVirtualWorld(playerid);
 
    if (g_VirtualWorld[playerid] != worldid)
    {
        g_VirtualWorld[playerid] = worldid;

        // Player changed virtual worlds.
    }
    return 1;
}

Only way to do this, AFAIK.