Let do simple thing, we have a cloud, which client draws, and server which sends commands to move cloud. Assume what client 1 runs on 60 fps and Client 2 runs on 30 fps and we want kinda smooth cloud transition.
First problem – server have different fps with clients and if send move command every tick, it will start spamming commands much faster, then clients will draw.
Possible solution 1 – client sends “i want update” command after finishing frame.
Possible soolution 2 – server sends move cloud commands every x ms, but then cloud will not move smoothly. Can be combined with solution 3.
Possible solution 3 – server sends – “start move cloud with speed x” and “change “cloud direction” instead of “move cloud to x”. But problem again is what checks for changing cloud dir on edge of screen, will trigger faster then cloud actually drawned on client.
Also Client 2 draws 2 times slower then Client 1, how compensate this?
How sync server logic with clients drawning in basic way?
Solution 3 sounds like the best one by far, if you can do it. All of your other solutions are much too chatty: they require extremely frequent communication between the client and server, much too frequent unless servers and clients have a very good network connection between them.
If your cloud movements are all simple enough that they can be sent to the clients as vectors such that the client can move the cloud along one vector for an extended period of time (many frames) before receiving new instructions (a new starting location and vector) from the server then you should definitely do that. If your cloud movements are not so easily representable as simple vectors then you can choose a more complex model (e.g. add instructions to transform the vector over time) and send the model’s parameters to the clients.
If the cloud is part of a larger world and the clients track time in the world, then each of the sets of instructions coming from the server should include a timestamp representing the time when the initial conditions in the model are valid.
As for your question about how to compensate for client 2 drawing two times slower than client 1, you need to make your world clock tick at a consistent rate on both clients. This rate need not have any relationship with the screen refresh rate on either client.