[Freeciv-Dev] Unit fog of war

[Artur Biesiadowski <abies@xxxxxxxxx>]

This subject was mentioned few times, so sorry if I'm repetitive in some
ideas.

Here is proposed way to implement it.

Every unit has a field last_seen, which is bitfield for each player that
specify if unit was seens by that player last turn/move. After move,
before packets are send following tests are performed

for each tile in max_visibility_radius from unit.x,unit.y
  for each ounit on this tile
    if can_see(ounit, unit)
      ounit.owner can see unit
    if can_see(unit, ounit) and not ounit.last_seen by unit.owner
      send add packet about ounit to unit.owner
  if city on this tile
    if can_see(city, unit)
      city.owner can see unit
    if can_see(unit,city)
      send city info to unit.owner
  // maybe also 
  //if specific improvement on this tile 
  // ? I'm thinking about radar towers from CCTP, but maybe
  // they can be made as special units that do not move etc ?


send remove/add unit packets to unit.owner

for each other player
  if ( player can see unit now )
  {
    send remove/add unit packets to player
    last_seen |= player
  }
  else
  {
    if ( player last_seen unit )
      send shadow unit packet
    last_seen -= player
  }






Shadow unit packet is special packet that informs client that unit has
moved from last position, but player do not know where. It is up to
client (maybe configurable) if it want's to show this unit with some
special outline/greyed out, or plainly remove it.

Problems: when player x moves his unit A so he do not longer see unit B,
unit B is not shadowed for as long as it moves. So even with such fog of
war, players knows if not visible unit is still on old place. This could
be avoided by adding another check for for fields that was previously
visible by moving unit - for each stack/unit there check would be
performed if there is a player unit in max_visibilty radius that can see
it. I'm not sure if it is worth the effort - it at least doubles the
time and gives only small improvement.

Of course can_see_unit_unit, can_see_city_unit etc could be done as
scripts :)

Artur