Client-server Action Synchronisation

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074 wrote:

In other news, this is a demonstration of PoE's hardcore gameplay, showing the advantages of desync preventing any cheating to take place in the first place.

http://www.twitch.tv/jmyers123/c/4289878

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Chris wrote:

Why some other games appear to not have similar problems
Games using the "wait until server responds" method (RTS and MOBA games) have much higher input latency but don't have the same sync issues that we do. They have their own class of game state synchronisation problems that we thankfully don't have to deal with.

Games using client action prediction like ours run into exactly the same sync issues that we do unless they cheat on certain aspects of the simulation. For example, it's common for Action RPGs to do some combination of the following:

• Entities can hit each other from a long distance away
• There's no chance to hit - all hits occur for sure
• Various speed/collision concessions that make it easy to speedhack and/or walk through monsters with modified clients
• Attack animations cannot be interrupted (i.e. what we treat as Stun).
  

Unfortunately, we don't want to do any of those things! They each individually ruin part of the hardcore experience: by allowing combat/movement cheats, preventing accuracy from existing as a mechanic, prevent stunlock, preventing people getting blocked in, etc.

Due to the fact that we want to have hardcore game mechanics (i.e. ones where position matters and it's difficult to cheat in PvP), the only option for us has been to put a lot of work into improving our combat simulation and resync code.

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074 wrote:

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wakko wrote:

Then why wouldnt GGG do the same for PoE? That system sounds way better than PoE's system. Is it just a bad design choice or somehow limited to the engine or whatever?

For D3 system, you need fast servers with low ping to run smooth.

For whatever reason, PoE has poor ping (50-200ms, again, if you are used to any form of online games, is pretty bad). For PoE having such a high ping, "predictions" emulates the experience of low ping.

But in the end of the day, you can't escape lag, which messes up "predictions", aka desyncs.

TLDR:

Best system is "no prediction+low ping".

PoE is "prediction+high ping", although *feels* smoother than "no prediction+low ping", but you have desyncs as side effect.

So it's covering up the effects of the real problem without solving it: lag.

Why PoE is like this? I don't know, poor design choice from the creators probably.

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Nicholas_Steel wrote:

The main difference is that Diablo III features a lack of game mechanics that can't easily be predicted and thus its prediction engine works a heck of a lot better/desyncs a ton less often.

Things such as stun, dodging an attack by moving the character out of the way in time, chance of an attack missing etc. and a couple other mechanics are the main cause of desync in POE. Remove them and you end up with a much more streamlined gameplay experience and less desync.

They want to keep those mechanics though as they're essential to creating the experience/game they prefer to play. I'm indifferent/leaning towards keeping the mechanics as it does add a bunch of diversity to the gameplay and removing them would make the gameplay considerably bland.

Just to emphasize this, Diablo III uses prediction technology as well otherwise it would simply be straight up unplayable for anyone over 100ms. The only reason why their system works "better" is due to them having a more streamlined (less diverse) gameplay experience.

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Nicholas_Steel wrote:

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074 wrote:

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wakko wrote:

Then why wouldnt GGG do the same for PoE? That system sounds way better than PoE's system. Is it just a bad design choice or somehow limited to the engine or whatever?

For D3 system, you need fast servers with low ping to run smooth.

For whatever reason, PoE has poor ping (50-200ms, again, if you are used to any form of online games, is pretty bad). For PoE having such a high ping, "predictions" emulates the experience of low ping.

But in the end of the day, you can't escape lag, which messes up "predictions", aka desyncs.

TLDR:

Best system is "no prediction+low ping".

PoE is "prediction+high ping", although *feels* smoother than "no prediction+low ping", but you have desyncs as side effect.

So it's covering up the effects of the real problem without solving it: lag.

Why PoE is like this? I don't know, poor design choice from the creators probably.

The main difference is that Diablo III features a lack of game mechanics that can't easily be predicted and thus its prediction engine works a heck of a lot better/desyncs a ton less often.

Things such as stun, dodging an attack by moving the character out of the way in time, chance of an attack missing etc. and a couple other mechanics are the main cause of desync in POE. Remove them and you end up with a much more streamlined gameplay experience and less desync.

They want to keep those mechanics though as they're essential to creating the experience/game they prefer to play. I'm indifferent/leaning towards keeping the mechanics as it does add a bunch of diversity to the gameplay and removing them would make the gameplay considerably bland.

Just to emphasize this, Diablo III uses prediction technology as well otherwise it would simply be straight up unplayable for anyone over 100ms. The only reason why their system works "better" is due to them having a more streamlined (less diverse) gameplay experience.

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MortalKombat3 wrote:

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Nicholas_Steel wrote:

The main difference is that Diablo III features a lack of game mechanics that can't easily be predicted and thus its prediction engine works a heck of a lot better/desyncs a ton less often.

Things such as stun, dodging an attack by moving the character out of the way in time, chance of an attack missing etc. and a couple other mechanics are the main cause of desync in POE. Remove them and you end up with a much more streamlined gameplay experience and less desync.

They want to keep those mechanics though as they're essential to creating the experience/game they prefer to play. I'm indifferent/leaning towards keeping the mechanics as it does add a bunch of diversity to the gameplay and removing them would make the gameplay considerably bland.

Just to emphasize this, Diablo III uses prediction technology as well otherwise it would simply be straight up unplayable for anyone over 100ms. The only reason why their system works "better" is due to them having a more streamlined (less diverse) gameplay experience.

There IS stun in D3 - lots of skills (especially Monk's skills) stun, stagger or knockback enemies. Some skills even force enemies to wander randomly (blind). But still, monsters dont desync.
There are also TONS of monster's skills, that ARE intended to avoid by movement - most skills, used by elite mobs. And it is well-possible to avoid those by movement. Of course, sometimes you may get hit if you stop really near, but at least, you wont suddenly rubberband over half of the room as it happens in PoE. Furthermore, whole "life globes" system relies on movement in combat to regain health when you need it.
Monsters also have a chance ti miss when hitting you, though i dont know, HOW that can be relevant to desync.
D3 also has lots of movement skills, similar to those in PoE. The only difference is that in D3 desync from those skills is barely noticeable.

So, all you arguments are irrelevant. The only thing D3 really does to reduce desync is that ground isnt covered by tiny debris and doors are supposed to force-open (via attacks). You didnt mentioned that even.