• Advertisement
Sign in to follow this  

Abilities involving movement + state sync

Recommended Posts

Server Authoritative 

What I'm doing right now is syncing the players position periodically and using some interpolation while any ability the player uses gets sent and played as soon as possible. Everything seems to work ok in parallel if the abilities don't involve the player moving. If I were to use the same system for movement based skills I would have some trouble syncing VFX with the movement part of the skill because movement would only be managed by state sync. So my question is what would be the best approach to deal with this issue? Should the players position get "locked" at the start of the ability so the ability code could take care of the movement instead, should the state sync take care of both: positions and abilities or is there a better solution? I understand I can't just have state sync take care of the movement and ability code take care of the VFX because of abilities such as teleport for example.

Edited by Sparta

Share this post

Link to post
Share on other sites

I don't know what your network code looks like, but assuming you use something like a traditional "command" model, the best solution I know if is to have your "play ability X" command carry the state necessary to sync up the presentation of the relevant actor.

That's a mouthful, so here's a concrete example:

  • You have an ability "lunge" which starts with a rapid forward movement and then ends with a damage-dealing blast.
  • Player One is at position x0,y0,z0 at frame N
  • Player One sends an input packet from their PC to the server stating they wish to use the lunge
  • Server validates the ability as normal (e.g. is it off cooldown, whatever)
  • Assuming the input is valid, the server issues a command packet back to all the relevant players
  • The command contains the actual ability (lunge), combined with any position, velocity, acceleration, etc. necessary to describe the server's perspective of where Player One was at the time of frame N
  • Other players apply latency compensation as desired
  • Player Two's machine will now interpolate from "Player Two's idea of where One is at" -> "Server authoritative state of One" over suitable number of frames


Note that some parts of this may vary depending on your netcode, your simulation model, and your desired tradeoffs (e.g. is it ok to trade accurate positions for faster response times? etc.)

Share this post

Link to post
Share on other sites

First, make sure your simulation runs at a fixed step rate (whatever -- 30 Hz, 60 Hz, 120 Hz, 1000 Hz, ...)

You can run graphics asynchronously from physics -- check out the canonical game loop for one way of doing that. (On the server, there's no graphics, but time still needs to advance using a real clock.)

Then, timestamp both movement, and action commands, using "this takes effect at physics step X."

Then, you should be able to make positions and actions sync up, because you can play actions and positions back at the same timestep. Now, whether that timestep is the "global" time step X, or the "local" time step X for the viewer, or some time step X+Q where the lag from sender to receiver is Q, depends on the specifics of your networking and simulation models.


Share this post

Link to post
Share on other sites

Create an account or sign in to comment

You need to be a member in order to leave a comment

Create an account

Sign up for a new account in our community. It's easy!

Register a new account

Sign in

Already have an account? Sign in here.

Sign In Now

Sign in to follow this  

  • Advertisement
  • Advertisement
  • Popular Tags

  • Advertisement
  • Popular Now

  • Similar Content

    • By Timothy Sharp
      just to test out my animations, let's say i had a trip animation. How would I code a script to where my character would fall it mud and their clothes would become all muddy? I saw this in a game on Unreal 3 but is this possible with Unity?
    • By Manuel Berger
      Hello fellow devs!
      Once again I started working on an 2D adventure game and right now I'm doing the character-movement/animation. I'm not a big math guy and I was happy about my solution, but soon I realized that it's flawed.
      My player has 5 walking-animations, mirrored for the left side: up, upright, right, downright, down. With the atan2 function I get the angle between player and destination. To get an index from 0 to 4, I divide PI by 5 and see how many times it goes into the player-destination angle.

      In Pseudo-Code:
      angle = atan2(destination.x - player.x, destination.y - player.y) //swapped y and x to get mirrored angle around the y axis
      index = (int) (angle / (PI / 5));
      PlayAnimation(index); //0 = up, 1 = up_right, 2 = right, 3 = down_right, 4 = down

      Besides the fact that when angle is equal to PI it produces an index of 5, this works like a charm. Or at least I thought so at first. When I tested it, I realized that the up and down animation is playing more often than the others, which is pretty logical, since they have double the angle.

      What I'm trying to achieve is something like this, but with equal angles, so that up and down has the same range as all other directions.

      I can't get my head around it. Any suggestions? Is the whole approach doomed?

      Thank you in advance for any input!
    • By Alexander Nazarov
      Hello. I'm newby in Unity and just start learning basics of this engine. I want to create a game like StackJump (links are below). And now I wondering what features do I have to use to create such my game. Should I use Physics engine or I can move objects changing transform manually in Update().
      If I should use Physics can you in several words direct me how can I implement and what I have to use. Just general info, no need for detailed description of developing process.
      Game in PlayMarket
      Video of the game
    • By Dave Haylett
      Hi all. My project is coming along wonderfully, and am starting to consider alpha deployment, and would like your advice.
      My project need access to 10,000 small PNG image files at runtime, each is only a few kilobytes each, which during development I used to load in directly from a fixed path on my HDD whenever one was needed (obviously not a solution for go-live), using something like this:
      img = new WriteableBitmap(new BitmapImage(new Uri(@screenshotsPath + filename)));
      The image would then be blitted onto a buffer screen, etc. etc. At a time, a few dozen would be being used.
      Now I'm thinking about deployment, and also when I produce an update to my app, there could be more images to add to the folders. So I'm considering the best way of a) deploying the images to the user as part of the project, and b) how to most easily handle updates to the app, whereby more images will be added.
      I have just experimented with adding them all as a Resource (!). This inflated the exe from 10mb to 100mb (not a major problem), increased the compile time from 3 secs to 30 secs (annoying), increased RAM usage from 500mb to 1.5gb (not a major problem either), but means that it solves my fixed directory issue, distribution issue, and update issue, simply by having the files all stuck into the executable. Here's the new code I'm using:
      img = BitmapFactory.FromResource("Shots/" + filename);
      The next thing I was going to try was to mark them as Content > Copy if Newer. This would resolve the executable size and RAM usage (and also the directory issue as well), however it seems that I'd need to highlight them all, and move them from Resource to Content. As an up-front job this isn't too bad, but as I add new images to the project, I'll need to go in and do this every time, which gets annoying, as the VS2015 default is Resource. Also, I'm not sure how this would work in terms of updates. Would something like ClickOnce deployment recognise new PNGs and install them to the users?
      I also have 3,000 ZIP files (~500kb each) which also need deploying and updating in the same way. These are currently read directly from my HDD until I can find a permanent solution for adding these to the project as well.
      Can anyone thing of a better way of doing what I'm trying to achieve?
      Thanks for any help folks.
    • By Felis Nigripes
      I'm doing a test quest.
      The player gets a quest from an NPC to bring him fish.

      Once the player picks up the fish, the original NPC gets replaced by a new one with a new conversation trigger. The NPC tells the Player "Well done" and should give 200xp.

      The script tells the xp counter to go up by making a reference to the gameobject that holds the text component
      But it throws this error:

      I'm aware that the error may hide in plain sight. I just have to sort this out, since I'm writing the AI at the same time, and the time it takes to resolve everyone of these errors is tremendous.
      Plus, I think I'll learn something. I've been having trouble with some basic functionalities recently. There might be something wrong with my understanding on how programming works.
      Glad if someone could help (:
      Edit: I'm fully aware that the update function requires an input. I call the function in the editor when the dialogue ends, it still doesn't work.
  • Advertisement