State synchronization and frame synchronization

Sync , In fact, let all clients see the same content , for instance ： Glory of Kings ,5V5 when , When a player A Released a skill ,10 Players （ Include A） You should be able to see players synchronously on your mobile screen A Released skills . So let's say , It generally refers to online games , Players see the same thing on their respective devices . And stand-alone games , Play your own , Basically no synchronization is required . The mainstream synchronization methods are generally state synchronization and frame synchronization .

One . Realization principle ：

State synchronization ：

The client sends operation instructions to the server , After receiving the instruction, the server performs logical processing , Return the final processing result to the client . Then the client returns the result according to the server , Just play the corresponding effect locally .

Such as ：A Click the skill button （ Release a skill attack B）, Then the client will send the message of using skills to the server , The server will process this message , Is it enough ” blue “ Put skills , Skills are right for B How much damage is done ,B Death or not , And so on , The results will eventually be returned to all players , Then on all players' devices （ client ） Will play skill release effects ,B Hit animation , then B The effect of deducting blood floating words and so on .

Frame synchronization ：

The client sends instructions to the server , The server does nothing to forward instructions to all clients , Then, after all clients receive the instruction, they will execute logical processing locally , Then play the effect .

Two . Comparison of advantages and disadvantages ：

1. Server pressure

State synchronization ： Because the logical operation is on the server , Relatively speaking, the pressure will be relatively high .

Frame synchronization ： No server pressure .

2. Logical consistency

State synchronization ： Unified computing on the server , Absolutely consistent .

Frame synchronization ： It takes a lot of effort to ensure consistency . Such as ： Accept the random factor sent by the server at the beginning of the battle , To ensure that the random results of all clients are consistent . Try to avoid decimal point operation , To ensure that the calculation results on different devices will have errors, etc .

3. Break line reconnection ：

State synchronization ： It's easier to achieve , Because when reconnecting , The real-time data of the current round is on the server , The server only needs to send the data of the current server to the client , You can directly present the current combat interface state .

Frame synchronization ： Because the server only has all the operation steps of the client , When reconnecting , You may need to start with the first step , Until this step of the current game progress , To restore the state of the whole combat interface .

4. Battle replay ：

State synchronization ： You need to record and save all the status information sent to the client , The quantity saved is relatively large .

Frame synchronization ： Just save the operation records forwarded to the client , Playback implementation is more convenient .

5. Data volume ：

State synchronization ： More , Because the server needs to process all player States after logic , The processing results are sent to the client .

Frame synchronization ： less , Just forward the operation instructions .

6. Network delay ：

State synchronization ： It can be pre expressed , Make players look relatively less stuck , Flow a little .

Frame synchronization ： The whole game will be stuck , Poor effect .

7. anti-cheating ：

State synchronization ： It's simpler , Because the core computing logic is on the server , Even if the player modifies the client , Can only change his local display effect .

Frame synchronization ： More difficult , Because the logical processing is performed locally on the client . However, the results can also be verified by some means , Such as ： Verify the consistency of the results of all players , If a player cheats , Raised his attack , Then the player's client will show that a knife killed the other party , Other clients show that the other party is only normal blood deduction and does not die , This can also verify that the player's client exception . But there are also some cheating behaviors that are difficult to effectively stop , Such as ： Show full map , All player positions, etc

8. Development efficiency ：

State synchronization ： The client server needs to be clear about the requirements , Co produce , Joint commissioning, etc （ There is more communication cost ）. But because many games have battles PVE part , So in fact, there can be a client to uniformly develop the combat system , Single combat and networked combat use the same set of combat codes , This can save communication costs , However, you also need to add some special processing code related to the client or server .

Frame synchronization ： The server is only responsible for forwarding , All code has client-side development （ No communication costs ）, But also pay attention to ” Anti crack “,” Uniqueness of code execution results “,” Separation of logic and expression “ And so on .

9. Applicable scenario

State synchronization ： Applicable to almost all games .

Frame synchronization ： Not applicable to games with too many players （ High bandwidth ）; Not suitable for large maps MMO game , Because in the game of super map , The client only has the data of this part of the area displayed by the current mobile phone , Other data of the map exists in the server , The client does not have all the data and cannot do logical processing .  

PS： Most games can use two synchronization methods , Which is more suitable for , We need to consider the type of game 、 Combat mode 、 network bandwidth 、 Delay response 、 anti-cheating 、 Development cycle and other factors to choose different schemes , Even a mixture of the two , There is no best technology , Only the most appropriate technology . So which way to use can only depend on the specific needs of the project .

-------------------------------------------- Little knowledge -------------------------------------------

1. Early frame synchronization , The server will wait to receive all players' keyframe messages , Will be forwarded to all players , Cause a player to get stuck , All players are stuck , A terrible game experience when they all stop . Now the frame synchronization adopts ” Optimistic frame “, The server forwards the received message sent by the client to other clients at a fixed time interval , The one who doesn't wait for the card . In this way, only the player with the card will be stuck , Other normal network players play games normally , The experience is much better .