Class: ClientEngine

Inherits:
Object
  • Object
show all
Defined in:
lib/game_2d/client_engine.rb

Overview

Server sends authoritative copy of GameSpace for tick T0. We store that, along with pending moves generated by our player, and pending moves for other players sent to us by the server. Then we calculate further ticks of action. These are predictions and might well be wrong.

When the user requests an action at T0, we delay it by 100ms (T6). We tell the server about it immediately, but advise it not to perform the action until T6 arrives. The server rebroadcasts this information to other players. Hopefully, everyone receives all players’ actions before T6.

We render one tick after another, 60 per second, the same speed at which the server calculates them. But because we may get out of sync, we also watch for full server updates at, e.g., T15. When we get a new full update, we can discard all information about older ticks. Anything we’ve calculated past the new update must now be recalculated, applying again whatever pending player actions we have heard about.

Constant Summary collapse

MAX_LEAD_TICKS =

If we haven’t received a full update from the server in this many ticks, stop guessing. We’re almost certainly wrong by this point.

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Instance Attribute Summary collapse

Instance Method Summary collapse

Constructor Details

#initialize(game_window) ⇒ ClientEngine

Returns a new instance of ClientEngine.



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# File 'lib/game_2d/client_engine.rb', line 32

def initialize(game_window)
  @game_window, @width, @height = game_window, 0, 0
  @spaces = {}
  @deltas = Hash.new {|h,tick| h[tick] = Array.new}
  @earliest_tick = @tick = @preprocessed = nil
end

Instance Attribute Details

#tick ⇒ Object (readonly)

Returns the value of attribute tick.



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# File 'lib/game_2d/client_engine.rb', line 30

def tick
  @tick
end

Instance Method Details

#add_delta(delta) ⇒ Object 



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# File 'lib/game_2d/client_engine.rb', line 103

def add_delta(delta)
  at_tick = delta.delete :at_tick
  if at_tick < @tick
    $stderr.puts "Received delta #{@tick - at_tick} ticks late"
    if at_tick <= @earliest_tick
      $stderr.puts "Discarding it - we've received registry sync at <#{@earliest_tick}>"
      return
    end
    # Invalidate old spaces that were generated without this information
    at_tick.upto(@tick) {|old_tick| @spaces.delete old_tick}
  end
  @deltas[at_tick] << delta
end

#add_entity(space, json) ⇒ Object 



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# File 'lib/game_2d/client_engine.rb', line 177

def add_entity(space, json)
  space << Serializable.from_json(json)
end

#add_npcs(space, npcs) ⇒ Object 



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# File 'lib/game_2d/client_engine.rb', line 173

def add_npcs(space, npcs)
  npcs.each {|json| space << Serializable.from_json(json) }
end

#add_player(space, hash) ⇒ Object 



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# File 'lib/game_2d/client_engine.rb', line 155

def add_player(space, hash)
  player = Serializable.from_json(hash)
  puts "Added player #{player}"
  space << player
  player.registry_id
end

#add_players(space, players) ⇒ Object 



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# File 'lib/game_2d/client_engine.rb', line 162

def add_players(space, players)
  players.each {|json| add_player(space, json) }
end

#apply_all_deltas(at_tick) ⇒ Object 



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# File 'lib/game_2d/client_engine.rb', line 150

def apply_all_deltas(at_tick)
  apply_deltas_before_update(at_tick)
  apply_deltas_after_update(at_tick)
end

#apply_deltas_after_update(at_tick) ⇒ Object 



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# File 'lib/game_2d/client_engine.rb', line 138

def apply_deltas_after_update(at_tick)
  space = space_at(at_tick)

  @deltas[at_tick].each do |hash|
    npcs = hash[:add_npcs]
    add_npcs(space, npcs) if npcs
  end

  # Any later spaces are now invalid
  @spaces.delete_if {|key, _| key > at_tick}
end

#apply_deltas_before_update(at_tick) ⇒ Object 



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# File 'lib/game_2d/client_engine.rb', line 117

def apply_deltas_before_update(at_tick)
  space = space_at(at_tick)

  @deltas[at_tick].each do |hash|
    players = hash[:add_players]
    add_players(space, players) if players

    doomed = hash[:delete_entities]
    delete_entities(space, doomed) if doomed

    updated = hash[:update_entities]
    update_entities(space, updated) if updated

    move = hash[:move]
    apply_move(space, move) if move

    score_update = hash[:update_score]
    update_score(space, score_update) if score_update
  end
end

#apply_move(space, move) ⇒ Object 



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# File 'lib/game_2d/client_engine.rb', line 166

def apply_move(space, move)
  player_id = move[:player_id]
  player = space[player_id]
  fail "No such player #{player_id}, can't apply #{move.inspect}" unless player
  player.add_move move
end

#create_initial_space(at_tick, highest_id) ⇒ Object 



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# File 'lib/game_2d/client_engine.rb', line 46

def create_initial_space(at_tick, highest_id)
  @earliest_tick = @tick = at_tick
  space = @spaces[@tick] = GameSpace.new.establish_world(@world_name, @world_id, @width, @height)
  space.highest_id = highest_id
  space
end

#create_local_player(player_id) ⇒ Object 



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# File 'lib/game_2d/client_engine.rb', line 91

def create_local_player(player_id)
  old_player_id = @game_window.player_id
  fail "Already have player #{old_player_id}!?" if old_player_id

  @game_window.player_id = player_id
  puts "I am player #{player_id}"
end

#delete_entities(space, doomed) ⇒ Object 



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# File 'lib/game_2d/client_engine.rb', line 199

def delete_entities(space, doomed)
  doomed.each do |registry_id|
    dead = space[registry_id]
    next unless dead
    puts "Disconnected: #{dead}" if dead.is_a? Player
    space.doom dead
  end
  space.purge_doomed_entities
end

#establish_world(world, at_tick) ⇒ Object 



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# File 'lib/game_2d/client_engine.rb', line 39

def establish_world(world, at_tick)
  @world_name, @world_id = world[:world_name], world[:world_id]
  @width, @height = world[:cell_width], world[:cell_height]
  highest_id = world[:highest_id]
  create_initial_space(at_tick, highest_id)
end

#player_id ⇒ Object 



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# File 'lib/game_2d/client_engine.rb', line 99

def player_id
  @game_window.player_id
end

#space ⇒ Object 



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# File 'lib/game_2d/client_engine.rb', line 87

def space
  @spaces[@tick]
end

#space_at(tick) ⇒ Object 



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# File 'lib/game_2d/client_engine.rb', line 53

def space_at(tick)
  return @spaces[tick] if @spaces[tick]

  fail "Can't create space at #{tick}; earliest space we know about is #{@earliest_tick}" if tick < @earliest_tick

  last_space = space_at(tick - 1)
  @spaces[tick] = new_space = GameSpace.new.copy_from(last_space)

  # Certain deltas, like add_npcs, need to be processed post-update
  # to match the server's behavior.  An object created during tick T
  # does not receive its first update until T+1.
  apply_deltas_before_update(tick)
  new_space.update
  apply_deltas_after_update(tick)

  new_space
end

#sync_registry(server_registry, highest_id, at_tick) ⇒ Object

Discard anything we think we know, in favor of the registry we just got from the server



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# File 'lib/game_2d/client_engine.rb', line 217

def sync_registry(server_registry, highest_id, at_tick)
  @spaces.clear
  # Any older deltas are now irrelevant
  @earliest_tick.upto(at_tick - 1) {|old_tick| @deltas.delete old_tick}
  update_entities(create_initial_space(at_tick, highest_id), server_registry)

  # The server has given us a complete, finished frame.  Don't
  # create a new one until this one has been displayed once.
  @preprocessed = at_tick
end

#update ⇒ Object 



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# File 'lib/game_2d/client_engine.rb', line 71

def update
  return unless @tick # handshake not yet answered

  # Display the frame we received from the server as-is
  if @preprocessed == @tick
    @preprocessed = nil
    return space_at(@tick)
  end

  if @tick - @earliest_tick >= MAX_LEAD_TICKS
    $stderr.puts "Lost connection?  Running ahead of server?"
    return space_at(@tick)
  end
  space_at(@tick += 1)
end

#update_entities(space, updated) ⇒ Object

Returns the set of registry IDs updated or added



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# File 'lib/game_2d/client_engine.rb', line 182

def update_entities(space, updated)
  registry_ids = Set.new
  updated.each do |json|
    registry_id = json[:registry_id]
    fail "Can't update #{entity.inspect}, no registry_id!" unless registry_id
    registry_ids << registry_id

    if my_obj = space[registry_id]
      my_obj.update_from_json(json)
    else
      add_entity(space, json)
    end
  end

  registry_ids
end

#update_score(space, update) ⇒ Object 



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# File 'lib/game_2d/client_engine.rb', line 209

def update_score(space, update)
  registry_id, score = update.to_a.first
  return unless player = space[registry_id]
  player.score = score
end