Game Development

I have looked into some source codes of multiplayer games and i saw that they don't implement any kind of game loop on the server. Instead they work with events. If the game has physics handled by the server (i wanna use Box2D) shouldn't the server use a game loop to call the step method?

-1

Q: How to implement server side physics?

I am working on multiplayer 2d sidescroller. Client looks like this: The game is in the GameScreen and there are groups of 2 players that play it. How should I implement the physics on the server? Use one world for every game or use a big world in which I add every 2 player that start a game?

java 2d-physics server

Comments like this: "Box2D has the ability to stop certain objects from interacting with others"
make me think he's either trolling, or really wants to run multiple game instances with the same Box2D instance

ToddersLegrande

12:40 AM

maybe its the latter

since hes talking about server side

John McDonald

He is talking about server side stuff, but as per this answer that Byte has linked to:

5

A: Run a physics simulation on both client and server?

Definitely run the simulation on both the clients and the server. Anything else have too long latency. You should be sure that the simulations match by inserting objects in the same order, using a fixed time step and avoiding pointer comparison. I haven't tried this with Box2D but it is generally...

Run on both client and server

AND why only 1 Box2D instance on the server? I'd imagine you'd want (/need) one per game

ToddersLegrande

No clue :|

John McDonald

I guess I'm a little confused

yeah

You around @Romeo?

John McDonald

1:10 AM

:/ I just want to remove his image from the earlier question, and add in some info from the second question, then close the second one

ToddersLegrande

Yeah that picture really is irrelevant. "Here's my client. How do I do server side physics?"

John McDonald

Done

Byte tried to remove the image earlier, but Romeo edited it back in

(again, the question about trolling)

ToddersLegrande

lol

saw that

John McDonald

(cleaning my keyboard, lol)

ToddersLegrande

nice

Dave

1:50 AM

hello fellow devs

John McDonald

Yo

Dave

anything amazing to report the world of gaming industry

John McDonald

:/ not from me

Dave

what you been working on ?

John McDonald

Working on getting my hard-coded data into JSON files. But it's a bit tricky because I want 3 layers of data to define an object: generic, entity specific, and object specific.

Dave

2:01 AM

not sure i follow? i do alot of JSON for server to client exchanges

John McDonald

So trying to find ways to create a bunch of components from a bunch of json. Should make for a great result

Dave

is it server lingo to JS client?

John McDonald

Right, so I have a component based system, and each component is data-only and can be defined in json (or xml, or whatever)

I'm in C#

Dave

ah i do php to js

so you just looking to sort all the data in a logical way to process later?

John McDonald

Yeah, I'll be doing json -> C# -> js... heh

eg:
entity.json:

{
    "SpriteName" : "*",
    "componentDefaults" : {
		"EntityName" : {
			"Name" : "*"
		},
		"Position" : {
			"Center" : {
				"X" : "*",
				"Y" : "*",
			},
			"Solid" : true,
			"Radius" : "*"
		},
		"Animator" : {
			"Scale" : 1,
			"Tint" : {
				"R" : 255,
				"G" : 255,
				"B" : 255,
				"A" : 255
			},
			"FrameAngle" : 0,
			"Angle" : 0,
			"CurrentSet" : null,
			"CurrentAnimation" : null,
			"CurrentOrientation" : null
		}
    }
}

asteroid.json:

{
    "SpriteName" : "asteroid",
    "componentDefaults" : {
		"EntityName" : {
			"Name" : "Asteroid"
		},
        "Minable" : {
			"Minerals" : "*",
			"StartingMinerals" : "*"
		}
    }
}

So, everything in asteroid overrides everything in entity.json

but "*" still needs to be provided with runtime info

Dave

2:07 AM

surely it adds minable rather than replaces

John McDonald

Yes, it "extends"

So if it's new, it adds. If it was already there, it overwrites

Dave

so you need to look for:

if(entity[i].spritename == asteroid[i].spritename){ in a loop

John McDonald

Same with the next layer. And I need to create all these components using this data

Dave

that means replace

its guna be alot of if's :P

unless C# has a nifty built in function

John McDonald

Well... That's the beauty of json, you can merge these things together

in jQuery, its called Extend

Dave

2:11 AM

u will still need to loop though to see if they match unless there is only one object

in which case change [i] to [0]

or might not even need a position

are you doing the adding etc JS end or C# end

as i don't know C#

John McDonald

Kind of. I am using a library that handles the loops and other stuff. What I end up writing to merge the above json is:

	String entityJson = File.ReadAllText(@"..\entities\entity.json");
	EntityTemplate baseEntity = JsonConvert.DeserializeObject<EntityTemplate>(entityJson);
	EntityTemplate asteroidTemplate = (EntityTemplate)baseEntity.Clone();
	String asteroidJson = File.ReadAllText(@"..\entities\asteroid.json");
	JsonConvert.PopulateObject(asteroidJson, asteroidTemplate);

where EntityTemplate is something I wrote to hold a C# version of the json

Dave

i see thats complicated to follow as i am not familiar with the library of the language =/

currently im working on reducing ajax requests to a minimum of 1 per person

John McDonald

Essentially, it makes a C# baseEntity that's based on the json, then clones it, then extends it using the json for the Asteroid. Resulting in a C# representation of an asteroid

@Dave per update?

Dave

no i mean on connect to my server - it gets all the user's data + the layouts at same time in one json

all my html layouts are stored in json for js to display

John McDonald

Ah yeah, cool

Dave

2:18 AM

i have to worry about inflow of players

if my server lags the game is broken

John McDonald

oh?

Dave

my cron jobs need to work quickly so people login their data is updated

or they will be behind

John McDonald

Hmm, I always think that on-login stuff can be done on-login, as opposed to continuously

Dave

no the game continues when u log out etc

John McDonald

Are other affected by it?

I'm just imagining Travian right now

Dave

2:25 AM

yes think travian

John McDonald

So... is anyone else affected while I'm building my granary?

Dave

not really unless they attack you

ToddersLegrande

I am... emotionally.

Dave

so the state of the game needs to be up to date

LOL todders

John McDonald

I've always imagined that Travian was "completeTime" driven. Meaning that when you start your granary, it sets up the time at which the granary will be done. Your client will show you constant progress, but the server is actually doing nothing at all. If you log out, again... nothing happens on the server, period. When you log in, the server looks at your account and may (or may not) determine that your granary is complete and tell you that it was finished hours ago

Dave

2:31 AM

true but lets say you build defence stuff

John McDonald

You could also re-calc when someone attacks

Dave

yeh

currently i have it at 60 minute updates for those not logged in

John McDonald

Just an alternative, probably less server intensive

Dave

if they are logged in the client does all the timers

John McDonald

60 minutes? ah, that's no problem then

Dave

2:32 AM

im curious though how they make a world

where people are placed in the world in a spot spaced out from others

John McDonald

yeah, I didn't play long enough to figure any of that out

Dave

yeh probably

John McDonald

So yeah, what's this about the cron jobs needing to work quickly or players would be out of date?

Dave

well some buildings once constructed generate resources every X amount of time

if no one interacts with their city

i need to use crons to update it all the time

don't know how else to do it

John McDonald

Nah, just (CurrentTime - completedTime) * rate

On login

Elapsed time * collection rate

Dave

2:37 AM

so alot of persistant games dont use crons at all /

?*

if true that does stop me having to update cities that may be inactive!

John McDonald

I was kinda wondering when you asked the question earlier

Dave

your solution is far better than my current

now i have to re-code alot of stuff xD

John McDonald

(or maybe that was someone else that asked the question I'm thinking of)

On the plus side, it will be simpler. I hope

:/

Dave

yeh

lowers the maths as i dont have to loop all the users every hour

John McDonald

Yeah, just OnInteraction

like, OnLogin

Dave

2:40 AM

smart

wish i thought of that xD

John McDonald

If it's easier, you can always still have some OnTheHour calcs

Yeah, this is the question I was thinking of:

1

Q: Will running cron jobs every minute a good practice?

I'm trying to create a browser-based game (made in PHP, MySQL, Js, HTML, and CSS) that is heavily dependent on user's actions being carried out after a certain amount of time passed whether online or offline. Will running cron jobs every second/minute a good practice or a solution to my problem? ...

mmo browser-based-games php timer

:/ Maybe I should add an answer to this effect, even though this guy is down the cron path

ToddersLegrande

Hmmmmmmmmmmmm

John McDonald

Hmmm?

Dave

i think on interaction solves the problem to the point crons are not needed at all

except for back up purposes

ToddersLegrande

My only thought is what if something is supposed to happen while the user just sits there

John McDonald

2:46 AM

@Dave It's possible

@ToddersLegrande Like?

Dave

@ToddersLegrande what do you mean

ToddersLegrande

I'd upvote it @JohnMcDonald... it doesn't "answer the question" but I think its a good alternative that people searching on the same topic would benefit from.

I honestly don't know anything about Travian

but in the context of "building a grannary"

Dave

but that can use client end

ToddersLegrande

That would solve it :)

so nevermind :P

Dave

javascript would do that so server does no work :P client's pc does

ToddersLegrande

2:47 AM

Client would just have to confirm with the server when the user then interacts with whatever it is that happened. Problem solved

Good call

Dave

yup

John McDonald

3:03 AM

Well, I've added an answer: gamedev.stackexchange.com/a/57931/9366

anything I should clarify or change?

ToddersLegrande

Looks good overall

The only thing I realized myself is all these little things you have to update, you'll have to keep track of a last updated time for that thing

If I was logged out for 5 days, my army got attacked on the 3rd day, when I log in I should see the results of that + 2 days worht of training or whatever. Not 5 days worth.

I don't know if that needs clarification or not... just a "gotcha" I thought of while reading through it

John McDonald

Yeah.... there is certainly some data involved with that

There can be potentially complex interactions between events. I'm trying to think of a good, clear example

ToddersLegrande

Queue training for 3 days, log out for 5, get attacked on the second... its a good example. Don't know if its clear :P

John McDonald

Yeah... just getting it straight in my head

Because when you get attacked, your empire may get a complete re-calc (depending on the implementation)

ToddersLegrande

That's an idea

would simplify things

John McDonald

3:12 AM

So the re-calc data would get stored, then when you log in, it would only re-calc the last 3 days

ToddersLegrande

I approve of this plan

Maybe explain a complex example simply (kind of like I did) to show how messy this can get, and then explain the simple recalc scenario

John McDonald

3:27 AM

Alright, I added some kind of battle ex

ToddersLegrande

good enough!

John McDonald

heh, time is a tough subject though. I'm going to be having some interesting time issues in my game if/when I get multiplayer moving again

But, at least in this style of game, time only moves forward, just forward at... different times

>.> Yeah.. that makes sense, right?

ToddersLegrande

lol

I believe so

Seriously though... I've been practicing Super Mario Bros for like 4 hours

John McDonald

heh, I kinda wanted to use "High and Dry" in an email this morning, because I was quite literally "high" and "dry", as in, away from the flood

lol, nice

ToddersLegrande

same to you :P

John McDonald

3:34 AM

:p I ended up avoiding the phrase, simply because it usually means the opposite

I didn't really want to have my subject read: "High and Dry"

lol

ToddersLegrande

lol

indeed

Great news. I think I have a solid plan for level 8-2. The hard part is nailing the ending

John McDonald

:D

ToddersLegrande

Considering how well I do the entire level up to the final stairs... I'm gonna skip the YOLO strats at the end and just play it safe

John McDonald

4:20 AM

@Byte56, are you around to discuss that A* question?

all I do is talk

John McDonald

4:36 AM

@Byte56 :/ Alright, I'm just going to answer a code wall

:( shame

John McDonald

4:49 AM

When you do read this, I'm not quite clear on what I should be doing with questions that are effectively "debug my code", even if I have some local knowledge, and am bored/procrastinating. I looked over the code, and came up with a very likely reason his code was failing, and wasn't sure if I should really be answering the code wall because all that does is encourage that behaviour in the future. Here's the Q: gamedev.stackexchange.com/questions/57932/how-to-speed-up-astar

On one hand, I don't really want to encourage code walls. On the other, I think I can help. Are comments more appropriate? Is shutting this guy out what we need to be doing? I don't know.

Maybe I should start something on meta instead of asking a future diamond in chat

Byte56

@JohnMcDonald When I come across that situation, I post an answer and make it community wiki.

John McDonald

I'm not sure how that helps anyone.

ToddersLegrande

Doesn't sound like the answer to me either

Byte56

It gives the OP the answer they need

John McDonald

Yeah, but it's really the same, except without the show: "I don't need the rep", no?

I've got enough rep to do what I want here, but...

I don't really see the point

Byte56

5:01 AM

More like, "I'm not doing this for the rep".

It's just what I do. I don't want to get rep for "breaking the rules".

John McDonald

Noobs are still going to see an answer to a code wall and go "Hey, he got an answer, let's paste some code"

wiki or not

ToddersLegrande

This site is all sorts of screwed up IMO. And maybe I just need to see clear examples... but heres what I see

John McDonald

tbh, I'm not sure there's a right answer to this, :/

yeah

ToddersLegrande

Questions should be real world problems that you face

If you have a code problem, don't paste it in

Byte56

Sure, it's up to you.

ToddersLegrande

5:04 AM

And lots of times I think the real world problems a lot of us face are either code or subjective

Or often times "preoptimization" as you try to plan something out

I don't know what kinds of questions actually are allowed, honestly

John McDonald

well... SE is all about googleable answers

Byte56

If we allowed people to just paste in the code they're having trouble with, that's all the site would be.

John McDonald

yeah... totally

ToddersLegrande

I don't disagree

Byte56

It's highly unlikely anyone else is going to have the exact same problem as him, and even more unlikely they'd be able to find it if we kept it.

John McDonald

5:07 AM

Well... considering how active you are, what is going to happen to questions like these assuming you become diamond?

Do questions like these warrant answers?

I know it's a bad question for SE, and for google, but... I guess I'm struggling with the fact that I can help (maybe)

Byte56

I'd try to get him to generalize it.

I'm not really sure how it could happen.

John McDonald

:/ yeah

Considering what I think is his problem, it's quite specific

Byte56

Yeah. It's one of those, come to chat and talk to us questions.

Have him post a comment linking him asking it on reddit, then follow him there and answer it.

John McDonald

Is there a way to invite sub 20 rep users to chat?

Byte56

Nope. It's been requested a few times.

I'm not sure what the status on that is.

John McDonald

5:13 AM

Yeah, ok

ToddersLegrande

For fun... what are some good questions?

(examples)

Byte56

But I'd use whatever influence I had as a mod to try and get that implemented :)

John McDonald

So: use other channels, or fit it into 250 chars

Byte56

Heh, yeah.

@ToddersLegrande You want me to show you what I think are good questions?

John McDonald

@ToddersLegrande :D

51

Q: How to prevent homing entities from orbiting their targets

I am developing a 2D space game with no friction, and I am finding it very easy to make a homing entity orbit a target. I am curious about anti-orbiting strategies. A simple example is a homing missile that simply accelerates directly toward its target. If that target were to move perpendicular ...

2d ai

Byte56

5:14 AM

Or multiple comments :p

Yeah, that's a good one. Clear, to the point, with excellent visual examples.

ToddersLegrande

So basically if you can't get something to work, explain in general terms what you are trying to accomplish and ask for approaches to soliving that problem?

John McDonald

And applicable to a wide audience

Byte56

@ToddersLegrande Exactly.

19

Q: Calculating the rotational force of a 2D sprite

I am wondering if someone has an elegant way of calculating the following scenario. I have an object of (n) number of squares, random shapes, but we will pretend they are all rectangles. We are dealing with no gravity, so consider the object in space, from a top down perspective. I am applyi...

xna 2d vector rotation

ToddersLegrande

What if there are several approaches to such a problem?

Trying to think of a good one...

John McDonald

The top 2 answers to my question are both excellent answers

And totally different

Byte56

5:18 AM

The more ways there are to approach something, the more general the answers will get. Eventually it crosses into the too broad threshold.

ToddersLegrande

Ok... I think what I'm thinking comes down to a question quality issue then

@Byte56 kind of hit it

John McDonald

Right

ToddersLegrande

Also in there could be too subjective or even too localized if the wording isn't exactly right

I'd propose a gamedevoverlow for code based questions but we really don't have the numbers to split this community

John McDonald

Yeah... I was gonna mention earlier

Byte56

If they work as coding questions, they should be asked on SO

ToddersLegrande

5:21 AM

Are programming game dev questions not getting migrated?

John McDonald

Some are

ToddersLegrande

I mean... that's problem solved right there

I personally would prefer a dedicated game dev programming site.. but I can just follow tags on SO too

John McDonald

But you know what? I think we need more migration from SO to here. That's how I found out about this place

Byte56

Yeah they do need to do that.

John McDonald

Once I found gamedev, I never went back

(nearly)

Byte56

5:23 AM

The speeding up A* question would be too localized for SO too

John McDonald

Oh yeah

I'm not disagreeing that it's too localized

It is

let me vote that

Byte56

Yeah

ToddersLegrande

I think that was directed towards me :)

Byte56

Correct.

John McDonald

Yeah... I've often struggled with closing localized questions because I guess I feel more for the person crying out for help than I do for SE trying to keep the rif-raf at bay, :/

Byte56

5:27 AM

That "give a pass to chat" would solve a lot of those too localized and not constructive questions.

John McDonald

IF they have 20 rep

Byte56

Yeah, that's the "give a pass" part.

John McDonald

and IF they actually log in within the next 24 hours

Byte56

They could implement a "tip" system. I'd give 20 of my rep to get those people into chat and productive members of the site.

John McDonald

Right

ToddersLegrande

5:29 AM

5

Q: Gift reputation to users that need it to join chat

While I realize that for many users the chat is not a big part of the community but its really what keeps me engaged with the site and I think it would help keep other people (as in new users) here as well. Would it make sense to implement a feature where you can gift a user the gap amount of rep...

feature-request chat reputation

Byte56

That's the one (of a few).

It should at least be a moderator privilege.

John McDonald

@ToddersLegrande Nice

This may be more of an issue with a community that is trying to grow, like gdse

ToddersLegrande

Maybe I've got a new meta question / feature request here. I was thinking about this earlier today though I can't remember on which question...

CREATE ROOMS ON A PER QUESTION BASIS :O

make it a privilege that requires rep to activate

a rep level, not like lose rep in a bounty sense

1000 rep may be reasonable?

I dunno

OH

I was thinking about it on the many commented meta question/answer from earlier today

I wanted to bring it to chat because it was getting very discussion oriented

If you just create a room for a question or an answer then the messages don't need to get lost in the shuffle and askers / answers with low rep can join THAT room and be denied access the real rooms until they hit their mark?

Byte56

They could just removed the chat barrier for user created chat rooms.

ToddersLegrande

That would work too

Byte56

5:35 AM

The general chat rooms remain closed to < 20

ToddersLegrande

A button to generate a user created room on a question would be good

John McDonald

right, that would work for me

ToddersLegrande

but removing that barrier would be a good first step

Byte56

Make the meta, I'd vote for it.

ToddersLegrande

You're right... I need a break from Mario. It's been like 6 hours now

John McDonald

5:36 AM

:p

Alright, I'm out. gn

Byte56

Same. I will vote on that question though.

Nice deciding the future of GDSE with you guys.

ToddersLegrande

Haha :)

Ciao!

Stack Exchange

6:22 AM

1

Q: Proposal to remove the reputation barrier on chatting in user created chat rooms

As per usual, a few of us were in the chatroom talking about code dump questions, subjective questions, localized questions, and other general off topic questions trying to figure out what to do with them because some of us REALLY WANT TO HELP but the question is inappropriate for the site so we ...

feature-request chat

3

ToddersLegrande

Loophole... I can star my own meta question posted by "Stack Exchange" ... and I am going to abuse it in this case.

Kikaimaru

7:45 AM

Star? You can favourite any question, it doesnt do anything

ToddersLegrande

@Kikaimaru in chat

technically I starred the chat message which only contained a link to a question. Poor wording on my part

Kikaimaru

oh i get it

Alex M.

12:24 PM

hiya

Siddharth

1:29 PM

Hi Jon,

Alex M.

oh MY god

after years of searching, I managed to find an actual working torrent for Konung 1

only one peer (seeder), 2.6MB/s

LUCKY

you guys have no idea how hard it is to find an actual place to download this game

trying to buy it from eBay gets you, if you're lucky, the original version w/o any patch whatsoever

otherwise, it gets you nothing

Siddharth

Hi friends, I want to discuss some gaming related concept. You have free to answer me.

Alex M.

1:51 PM

well, ask away and see if someone answers

Alex M.

2:09 PM

Scapegoat tree

In computer science, a scapegoat tree is a self-balancing binary search tree, discovered by Arne Andersson and again by Igal Galperin and Ronald L. Rivest. It provides worst-case O(log n) lookup time, and O(log n) amortized insertion and deletion time. Unlike most other self-balancing binary search trees that provide worst case O(log n) lookup time, scapegoat trees have no additional per-node memory overhead compared to a regular binary search tree: a node stores only a key and two pointers to the child nodes. This makes scapegoat trees easier to implement and, due to data structure align...

should that "discovered by" not be replaced with "invented by"?

did Arne dig a hole outside and discover the scapegoat tree?

Icy Defiance

I would contend that mathematical things are discovered, not invented, but algorithms are kind of in the grey area between the two. In this case, I would probably agree with you, but I wouldn't be able to argue the point much.

Alex M.

technically, a tree was invented

a data structure first of all

a way to organize data

it's very different from discovering a mathematical relationship between two things

PythonInProgress

2:30 PM

hey all

PythonInProgress

2:59 PM

no one here @AlexM. @IcyDefiance

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