Why video game doors are so hard to get right [video]

Where network replication matters a lot more though is on things like movement and shooting in competitive games. There is a great short series of blog posts by Gabriel Gambetta that covers different problems and solutions, but everything is a tradeoff https://www.gabrielgambetta.com/client-server-game-architect...

Desync is common and is caused by packet loss in UDP games. It's not usually worth while to compare your state with the authoritative state, because that requires a round-trip from client->server. Instead, the server can rank each piece of the state as important (has been altered recently is a good measure of importance), and just spam out a bunch of redundant game state packets hoping some of them arrive.

You can build a guaranteed delivery packet system on top of UDP, but a guarantee has to come from the client meaning you're waiting on round-trips to confirm that the states are fully in-sync. Most games (especially fast paced shooters) don't need this level of assurance, and heavy packet loss over a long period of time should just result in a disconnect for that player.

Half of games networking is finding out what you can "get away with" from an impact/user perception. Ex: play hit effects, sounds in a de-synched way locally but have major game events be authoritatively acked by the server, the local events also do a good job of masking the latency. The other half is really cool tricks like dead-reckoning or lock-step[1] which uses a completely deterministic game state to sync hundreds of entities over latent connections.

It's a really fun design space that's leverages heavily both the game design(designs where players "predict" are easier to keep in sync/fun), a level of deception to hide latency and cool technical approaches to hard problems in a non-deterministic environment.

[1] https://en.wikipedia.org/wiki/Lockstep_protocol

If doors synchronize closer than a player's sniper rifle range then a player can either stand just behind a door (that is open for them) and shoot people at range (who see the door as closed). Or the door defaults to open and a closed door that seems like cover allows you to get sniped.

While the ideal is to synchronize everything at the same distance, if you have 100+ players on a single map and a sniper rifle with 500m range you can be synchronizing the stage of hundreds of doors per player and eating bandwidth that would (usually) be better used synchronizing player position state. In practice you end up doing some amount of 'automatic' synchronization and some based on context... and a server that has the definitive world state that can 'undo' shots through closed doors etc.

Building rendering distances can also be an issue with doors, generally you switch to simpler building models as they get further from the player's camera. But you can't include doors in the lower level of detail models until you are at a distance that enemy players are also not visible. So while a building can be a 200 triangle shell at 400m it still has to have doorways and network synchronized doors, even if the doorway is 4 on-screen pixels it should still be possible to see a player move behind that open doorway (or not see them if the door is closed).

I think narrowing it to “seeing” the door might produce a limited result that closes a lot of doors on proper multiplayer handling of other game mechanics.

That is typically one of the conditions encompassed by "network relevancy".

https://youtu.be/OKSWkpC_SC4?t=946 Link starts at where the master sword gets knocked off but the premise of the speedrun is interesting on its own.

To be fair, it was _saving_ after having performed the glitch that persisted glitched data to the save RAM, but I only figured that out seven years later.

Redstone: The surprising complexity of a redstone torch does not confer complexity to a minecraft door, even though you could use that torch to open or close a door. A minecraft door has one binary state relating to redstone, powered or unpowered. That's it. The redstone functionality a minecraft door has is very simple by the standards of many other redstone-capable blocks in the game.

Piston doors: Can be arbitrarily complex, but these do not confer complexity to regular minecraft doors.

Placement: Minecraft doors are not the simplest block in this regard, but they are far from the most complex. Just compare them to stairs. Stairs have four attributes: facing[east,west,north,south], half[bottom,top], shape[inner_left,inner_right,outer_left,outer_right,straight]. There are 80 ways any stair block can be configured. There are only 64 configurations of a door block in minecraft (as far as the player need be concerned, it's only half of that since half a door implies the other half, similar to an extended piston.) Incidentally, there are 9 materials a door can be made out of, but 48 materials stairs can be made out of. And 8 of those 48 stairs have the special behavior of turning into other material, while only one of the 9 door materials has special behavior.

Waterlogging: Regular minecraft doors have never waterlogged. Waterlogging is complexity added to other blocks in the aquatic update, but doors were not changed. There was no complexity added here. And doors are not the only blocks which weren't updated for waterlogging; there are dozens of other blocks like this.

Trapdoors: Are more complex than regular minecraft doors. Trapdoors being complex does not mean that regular minecraft doors complex.

Players wishing doors had more complexity: Is not doors being complex.

> Doors are hard, no matter how simple the game.

Doors are extremely complex in some games, and significantly less complex in others. Complexity is not a binary trait. I claimed that minecraft doors are comparably simple, particularly when compared to the doors in TLOU2. I stand by that.

Given the current Java waterlogging mechanisms, even if doors acted like slabs and trapdoors, they would still hold out water source blocks present on one face. It would still break scuba diving though.

Another example from beenBoutIT: The Last of Us and its sequel have the same sort of style. The sequel has superior doors but is generally considered an inferior game. The quality of the doors really doesn't seem to be a major factor in how these games were received.

Minecraft itself: minecraft doors having no animation was not a foregone conclusion derived from the broader style of the game. Minecraft pistons do have animations when extending or retracting. I've never heard a player complain that minecraft doors are lack what minecraft pistons have.

I think that most video game players are accepting of doors behaving in unrealistic ways. Simple doors don't actually bother most players, and complex doors usually go unappreciated by most players. Contrary to what the video claims, doors can 'just magically fly open', and players don't care.

basically the argument I was trying to make is: if it wasn't simulated I wouldn't be looking at it, and I wouldn't find it strange at all because I would be living in a world where that thing doesn't exist

> and what, specifically, do you think you would notice if it was in some way simplified?

exactly, I wouldn't notice anything.

My argument is: if those beings are so smart that they created this awesome simulation, how could they be so dumb that they wasted time simulating unneeded details?

I am not a game dev, so at first look a level editor that is mostly drag and drop should solve this for the level designers, but for some reason you can still fall through floors.

While I never actually did any level editing, I did read a guide to the Unreal Tournament level editor, which said that UT was unusual in that a blank level was filled with mass and the level creation process involved subtracting that away to create empty space, rather than adding objects to an empty void.

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