Program Dream•3y ago

Let's talk about netcode

Recently I've started playing around with Godot. So far I got a basic "walker" type of game logic, so I decided to go for adding multiplayer support. And that got me thinking: what is really the best way to do exactly that? Most multiplayer solutions just update entities' positions across multiple clients. Older ones such as Doom just sends player commands, so the client does the simulation and updates positions based on commands. And there is probably something else that I left out. I thought I'd open this topic up for discussion.

89 Replies

keith•3y ago

I dont know if im explaining this well enough, but im going to go ahead and try. This is probably very inefficient, but i would go along the lines of something like the game is stored as an object (im going to visualize it with JSON) say you have the following game

const game = {
  player1: {
    position: {
      x: 546,
      y: -86
    }
  },
  player2: 
    position: {
      x: 546,
      y: -86
    }
  }
}

const game = {
  player1: {
    position: {
      x: 546,
      y: -86
    }
  },
  player2: 
    position: {
      x: 546,
      y: -86
    }
  }
}

this needs to be kept up to date between all players now saw player one moves in a direction 3 units in this example, on the x axis

const game = {
  player1: {
    position: {
      x: 549,
      y: -86
    }
  },
  player2: 
    position: {
      x: 546,
      y: -86
    }
  }

const game = {
  player1: {
    position: {
      x: 549,
      y: -86
    }
  },
  player2: 
    position: {
      x: 546,
      y: -86
    }
  }

instead of resending the new object in full, check what changed and only send what changed so instead of sending

const game = {
  player1: {
    position: {
      x: 549,
      y: -86
    }
  },
  player2: 
    position: {
      x: 546,
      y: -86
    }
  }
}

const game = {
  player1: {
    position: {
      x: 549,
      y: -86
    }
  },
  player2: 
    position: {
      x: 546,
      y: -86
    }
  }
}

this to all the players, send this

const update = {
  player1: {
    position: {
      x: 549
    }
  }
}

const update = {
  player1: {
    position: {
      x: 549
    }
  }
}

and then merge game (the data the players currently have on their local device) with update (the new data the server just sent) this is bound to have its issues, but for someone who has never actually looked into how online gaming data sending works, id say this is a pretty good idea @polyzium

polyziumOP•3y ago

Quake 3 uses the same pattern here I mean that would make total sense to only update what has changed but for compiled languages this may pose a problem if you unmarshal the data into a struct. position.x is the only value updated, then what's position.y? Zero? That's UB right here

keith•3y ago

can you not merge objects in go? for example

const $1 = {
  x: 1,
  y: 2
}

const $2 = {
  x: 2
}

// This becomes
const $3 = {
  x: 2,
  y: 2
}

const $1 = {
  x: 1,
  y: 2
}

const $2 = {
  x: 2
}

// This becomes
const $3 = {
  x: 2,
  y: 2
}

polyziumOP•3y ago

Nah it's not in Go

keith•3y ago

oh wait i misunderstood you said godot i thought go

polyziumOP•3y ago

In JS this could be done nicely with things like Object.assign, dunno about other languages, never did C# Currently using GDScript for prototyping, which is loosely based on Python But I'm sure I'll figure something out Anyways, another problem to tackle is: does the server do the gamesim and send the player positions, or should that be relied on clients? The latter would take some load off, but would introduce vulnerability to hacks. I believe that's what Minecraft does.

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Let's talk about netcode