class ClientEngine
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.
Constants
- 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.
Attributes
Public Class Methods
# 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
Public Instance Methods
# File lib/game_2d/client_engine.rb, line 90 def add_delta(delta) at_tick = delta[:at_tick] fail "Received delta without at_tick: #{delta.inspect}" unless at_tick if at_tick < @tick warn "Received delta #{@tick - at_tick} ticks late" if at_tick <= @earliest_tick warn "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
# File lib/game_2d/client_engine.rb, line 170 def add_entity(space, json) space.add_entity (o = Serializable.from_json(json)) if o.is_a?(Player) && @game_window.player_name == o.player_name # This can be news, if the server is ahead of us. The server # promises that we always have exactly one entity assigned to # each authenticated player, and each connected player must # have a unique name at any time -- so this entity has to be # ours. @game_window.player_id = o.registry_id end end
# File lib/game_2d/client_engine.rb, line 162 def add_npcs(space, npcs) npcs.each do |json| on_create = json.delete :on_create space << (entity = Serializable.from_json(json)) on_create.call(entity) if on_create end end
# File lib/game_2d/client_engine.rb, line 140 def add_player(space, hash) player = Serializable.from_json(hash) puts "Added player #{player}" space << player player.registry_id end
# File lib/game_2d/client_engine.rb, line 147 def add_players(space, players) players.each {|json| add_player(space, json) } end
# File lib/game_2d/client_engine.rb, line 105 def apply_deltas(at_tick) space = space_at(at_tick) @deltas[at_tick].each do |hash| players = hash.delete :add_players add_players(space, players) if players doomed = hash.delete :delete_entities delete_entities(space, doomed) if doomed updated = hash.delete :update_entities update_entities(space, updated) if updated snap = hash.delete :snap_to_grid space.snap_to_grid(snap.to_sym) if snap npcs = hash.delete :add_npcs add_npcs(space, npcs) if npcs move = hash.delete :move player_name = hash.delete :player_name player_id = hash.delete :player_id if move fail "No player_id sent with move #{move.inspect}" unless player_id apply_move(space, move, player_id.to_sym) end score_update = hash.delete :update_score update_score(space, score_update) if score_update leftovers = hash.keys - [:at_tick] warn "Unprocessed deltas: #{leftovers.join(', ')}" unless leftovers.empty? end end
# File lib/game_2d/client_engine.rb, line 151 def apply_move(space, move, player_id) player = space[player_id] if player player.add_move move else # This can happen if, say, the player sent an action just before # death or disconnection. warn "No such player #{player_id}, can't apply #{move.inspect}" end end
# File lib/game_2d/client_engine.rb, line 49 def create_initial_space(at_tick, highest_id) @earliest_tick = @tick = at_tick space = @spaces[@tick] = GameSpace.new(@game_window). establish_world(@world_name, @world_id, @width, @height) space.highest_id = highest_id space end
# File lib/game_2d/client_engine.rb, line 201 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
# 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) @preprocessed = at_tick end
# File lib/game_2d/client_engine.rb, line 86 def space @spaces[@tick] end
# File lib/game_2d/client_engine.rb, line 57 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(@game_window).copy_from(last_space) apply_deltas(tick) new_space.update new_space end
Discard anything we think we know, in favor of the registry we just got from the server
# File lib/game_2d/client_engine.rb, line 219 def sync_registry(server_registry, highest_id, at_tick) return unless world_established? @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
# File lib/game_2d/client_engine.rb, line 70 def update return unless world_established? # 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 warn "Lost connection? Running ahead of server?" return space_at(@tick) end space_at(@tick += 1) end
Returns the set of registry IDs updated or added
# File lib/game_2d/client_engine.rb, line 183 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) my_obj.grab! else add_entity(space, json) end end registry_ids end
# File lib/game_2d/client_engine.rb, line 211 def update_score(space, update) registry_id, score = update.to_a.first return unless player = space[registry_id] player.score = score end