Game Development

Grey

00:00

@AlexM. Take him off of ignore

This handsome avatar

HOW TO MAKE LE AFRO err.... err.... MOVE

I don't know jack.

hasherr

@Grey If he wants me on ignore, let him. As he is a large member of the community, I have a lot of respect for him, so I respect the fact that he doesn't want to hear me speak. I will do better to censor myself after this.

Alex M.

@Grey and just why would I do that

Grey

:/

Alex M.

@Grey well that's going to be slightly hard if the afro is not a separate layer

Grey

I have the original

svg

@AlexM.

layered and everything

Alex M.

00:03

hmm, apply a water wave algorithm to it or something

no idea, why does it even have to move

Grey

Itd be awesome?

Idk

Alex M.

better make a full avatar of yourself

and make it dance

I bet you got the moves like mick jakesoon

Grey

@mick

Alex M.

yeah, on this one

►

Grey

LOl

Alex M.

00:05

current favorite

MickLH

sup

Alex M.

nah jk

it doesn't beat butterflies

that one is just too smooth

1

Q: How do I convince my boss to get rid of our open office and give us individual offices?

My Job is a thinking job (programmer) and I work in an open style of office. I used to have a quiet area to work in and at one point, my own office. We are moving our office to a new building and the plan is to make it even more open. How can I convince management to move us into an office ...

/headphones on

I'd love a closed office though

I was half asleep this morning

and hearing everyone talk and make sounds around me felt really really bad

felt like taking a kitten and killing it

classical music tends to cover the noises

and still provide silence

Matt D

i like partially open offices

silence is... an artificial thing.

its why you invest in good headphones

Alex M.

I just want my morning silence and my permanent peace of mind

I hate noisy people in general

there are certain people who are always happy and go around shouting HEYAH HOW IS EVERYBODY DOING

Matt D

i dont think i'd be any more productive in a closed office of my own

Alex M.

00:13

I just can't

take it

Matt D

you need a nerf gun

Alex M.

lol I feel like yelling

Matt D

just nerf that sucka

Alex M.

"WOMAN WHY THE FUCK ARE YOU SHOUTING IN MY EARS

AND WHY THE FUCK ARE YOU ALWAYS HAPPY

Matt D

eventually the entire office will join in

Alex M.

00:14

DO YOU EVEN WORK"

Matt D

and prozac

Alex M.

being happy with your workplace is a good thing

being happy at your workplace isn't always a good thing

any sort of such extreme emotions can affect your performance in some way that is not desirable

also the performance of others

ideally, at work, one should do his job and then go home

nothing more

hasherr

@Grey What are you worknig on right now? :3

Grey

a screensaver

but I have to find a shader technique before I do it.

Alex M.

@Grey you know

hasherr

00:22

Cool. Still working on Down?

Alex M.

if you increase the hair in size, vertically (and progressively), and then go back

at different speeds on each loop

Grey

@hasherr yes

Alex M.

it will look like jelly without horizontal movement

hasherr

How's it going? Updated anything yet?

2

Grey

@AlexM. scale?

Alex M.

00:23

yeah just be sure to always keep it positioned properly

Grey

@hasherr it was ok. I'm kind of burnt out on it for now lol :p

Alex M.

imagine some sort of piece of elastic material

and someone pulls one of its extremities

it's the same effect

hasherr

@Grey It's okay. Just work on something else until you get back into it. I'm dropped off of DPA for now

Grey

@AlexM. Okay I'll give it a go

Alex M.

you can definitely get more realistic effects with those splines

but I'm sure a shader is overkill

Grey

00:25

hrm. k then

Alex M.

codepen.io/chinchang/pen/neKJD

see this too

hasherr

@Grey Do you know of anybody else who muted me? :(

Alex M.

Hooke's law

Hooke's law is a principle of physics that states that the force F needed to extend or compress a spring by some distance X is proportional to that distance. That is, :F = k X, where k is a constant factor characteristic of the spring, its stiffness. Hooke's equation in fact holds (to some extent) in many other situations where an elastic body is deformed, such as wind blowing on a tall building, a musician plucking a string of a violin, or the filling of a party balloon. An elastic body or material for which this equation can be assumed is said to be linear-elastic or Hookean. Hoo...

also this

Grey

@hasherr i don't think so

hasherr

Well, now I'm paranoid

Grey

00:34

lol

hasherr

Hmm, my pong is being funny

Grey

how so

hasherr

What happens is that my ball ends up touching the pong paddle but my collision handling is too fast so the ball ends up bouncing forward and back against the paddle until it either gets out and glitches and goes off map

Grey

hmmm

Alex M.

man I'm sleepy but can't get myself to go sleep

hasherr

00:44

@Grey What do you think?

Grey

@hasherr Record prev pos and when you get the collision set it to the prev pos and reverse ur vel

hasherr

@Grey Saving the old position is a pain.

Previous at: 503.7646, 139.4233 Now at: 503.7646, 139.4233
Previous at: 516.10785, 117.6877 Now at: 516.10785, 117.6877
Previous at: 528.6478, 95.60566 Now at: 528.6478, 95.60566

Grey

lol

hasherr

I'm honestly not sure how to do that

Grey

okay

so you have current and prev

//redacted

hasherr

00:49

@Override
public void update()
{
    handleWallCollision();
    pos.x += velocity.x * Gdx.graphics.getDeltaTime();
    pos.y += velocity.y * Gdx.graphics.getDeltaTime();
    System.out.println("Previous at: " + previousPos.x + ", " + previousPos.y + " Now at: " + pos.x + ", " + pos.y);
    previousPos = pos;
}

What's wrong with that?

Grey

Take the previousPos = pos and put it on top of handleWallCollision

hasherr

Previous at: 54.027756, 311.99744 Now at: 54.027756, 311.99744
Previous at: 66.52784, 289.9857 Now at: 66.52784, 289.9857
Previous at: 54.85086, 269.42334 Now at: 54.85086, 269.42334

Yeah that didn't work.

@Grey See what I mean?

Grey

Yes

What does handle Wall collision do

hasherr

Makes sure that the player can't leave the boundaries

public void handleWallCollision()
{
    if (pos.x <= 0f)
    {
        velocity.x = -velocity.x;
    }
    if (pos.y <= 0f)
    {
        velocity.y = -velocity.y;
    }
}

woops, that's the old method

Grey

Okay nvm lol. I thought you were messing with the position in there. MUCH WEIRD. NO DICE.

hasherr

00:55

Yeh

I'm not sure what to do

Grey

okaywait

System.out.println("Previous at: " + previousPos.x + ", " + previousPos.y + " Now at: " + pos.x + ", " + pos.y);
previousPos = pos;

You had this originally right.

Okay do this, but print your stuff out after you set previousPos to pos

hasherr

Previous at: 63.258484, 123.0803 Now at: 63.258484, 123.0803
Previous at: 50.825546, 144.97382 Now at: 50.825546, 144.97382
Previous at: 38.44003, 166.78383 Now at: 38.44003, 166.78383

Grey no

Grey

ffaaak

hasherr

Bad grey!

Grey

:((

hasherr

00:57

:(

I don't get it either.

Grey

wait

It works

I think

hasherr

Nope

Grey

Do you except the previous position to be such a significant change

Tell you what

do something like:

if(k pressed)
offset x by 5

do it now and tell me what happens.

hasherr

Wait, what?

Grey

I basically want you to make your ball jump

hasherr

01:00

why?

Grey

just do it v=v

It's a test.

hasherr

I'm not sure what you were trying to accomplish with that

Grey

Same thing?

hasherr

JYeah

WHYY

SO post?

Grey

I guess :/ I should know this tho lol

He's asleep I think

Matt D

01:04

?

Grey

a taker

goodluckmatt

bails

Matt D

>_>

Grey

@MattD Recording Previous Position

Matt D

<_<

hasherr

@MattD You want to help with the not-so-complicated pong issue?

Before I make yet another stupid SO post?

Matt D

01:05

sure

i havent had a chance to look at your other stupid SO post

i was busy getting drunk last night

im also at work, but ill do what i can

hasherr

What happens is that my ball ends up touching the pong paddle but my collision handling is too fast so the ball ends up bouncing forward and back against the paddle until it either gets out or glitches and goes off map

Matt D

hehehe

i knew that would be the problem

hasherr

lol

Matt D

because its the first problem everyone has with collision

Grey

^

Matt D

01:07

theres two parts to the collision process

hasherr

Yeah

Matt D

a) there's the detection of a collision and

hasherr

We're having trouble with it :P

Matt D

b) there's the resolution of the collision

hasherr

public void handleBallCollision(Ball ball)
{
    if (ball.boungingBox.overlaps(boungingBox))
    {
        ball.velocity.x = -ball.velocity.x;
    }
}

Matt D

01:07

its quite possible to detect collisions and decide to not do anything about it

hasherr

This method is inside of my playerPaddle class

Matt D

is that a member of something?

ok

i find physical examples help here

Alex M.

RuneScape
Which of these two RuneScape Community J Mods would you side with in an event?

none

hasherr

So it takes the ball object, detects the collision, and then handles the ball's velocity like you'd expect

Matt D

get yourself a coffee cup lid, or a tennis ball

Alex M.

01:08

siding with any one of them means kissing official ass

Matt D

something round

hasherr

I have a ball on my desk

Matt D

right. now you need something to bounce it against

hasherr

Wall on my left

Matt D

got a pad or something

wall wont work

you see, the problem is that the bounding boxes overlap. which means the ball is, by the time you detect that there's a collision, partially inside the wall

hasherr

01:10

What do you suggest? I have a clipboard around here somewhere

I see

Matt D

so, in reality, you can throw the ball against the wall, and the ball bounces off the wall (after compressing against the wall slightly). in games. you throw the ball at the wall, and we wait for the ball's bounding box to intersect the wall's bounding box (which means the ball is partially inside the wall) and then we decide to make it look like the ball bounced off the wall

hasherr

So I need to detect when they touch, not when they overlap.

Matt D

no. thats almost impossible

what you need to do, is work out when they touched

because then you can work out where they touched, and then you can move the ball back to that position, and then change its velocity

alright

hasherr

Partially troll thing I said.

sorry

Matt D

so. you have the starting position of the ball BS. you have the end position of the ball BE. somewhere along the line described by BS and BE we have the point where the edge of the box, intersects with the edge of the wall.

oh that reminds me.

hasherr

01:13

Right

Matt D

the other thing we dont want to use is use the bounding box at BE.

we want the swept volume of the bounding box from BS -> BE

because when we collide that with our wall bounding box. its much easier to work out where the collision actually happened

so when you throw the ball against the wall

the ball's discrete motion every 1/30th of second can be described as a capsule

the wall's not moving. so we can describe that as a plane

hasherr

Well the wall is moving in this case

Matt D

now we can work out where along BS -> BE the plane intersects

same deal then. the paddle "sweeps" an area

and you're comparing the swept area against the swept ball

now this is where it gets fun

because both objects are moving

hasherr

Suree.

Grey

yar

Matt D

01:16

so, lets say you take two balls. and you throw them so their paths will cross. but you throw one ball much faster than the other. if you sweep the areas of their motion, you would come to the conclusion that they actually hit each other. but where in time they cross determines that they actually didnt

collision is all about time :)

hasherr

Sure.

Matt D

so, what we're trying to do is find out when a collision occured. and then if a collision occured, and where it occured. then we can use that information to resolve the collision

but you kinda see that in your head right?

hasherr

Yeah

Matt D

right. so the maths for this are very well documented, and searching for it in google will get you the required maths

hasherr

It's like a crime scene. Get a call at a certain time. Find out if the call was real. Investigate it to find out where it happened.

Matt D

01:19

exaclty

it gets more fun when there's multiple things in motion

so, what you do is "broadphase" collision, which is typically very fast, but very innacruate. to throw out things that really wont collide

then, you sort your collisions by time

then, you do narrowphase detection which works out if things actually did hit

now. its possible that one object was marked in multiple collisions. and since we've altered the path of that object, we can remove it from any further collisions that happened later

(or we can resimulate, bu no one bothers to do that)

so, capsule/swept rectangle is broadphase

hasherr

I'm writing on my whiteboard how I would implement this

Matt D

then working out exactly where there was a collision is narrowphase

hasherr

The thing that confuses me is the timing

Matt D

hehe

the sweep of the capsule is time

well, its motion over time.

so, if the intersection is bang in themiddle of the capsule, it was at exactly half the timestep

hasherr

Now I'm confused again

I just don't understand the implementation for that.

Matt D

01:22

(also, the timesteps we're talking about are so small that you can cheat a lot)

gamasutra.com/view/feature/3383/…

swept sphere collision stuff is really really really well documented

hasherr

I'm not using spheres, what about rectangles?

Matt D

same concept

a sphere is just a little easier as you can assume distance from a single point

are the OOB or AAB

hasherr

gamedev.net/page/resources/_/technical/game-programming/…

Matt D

ok

here's one of the best collision tricks i ever learnt

hasherr

I didn't think there was this much to it

Matt D

01:25

there's a thing called the separating axis test. and it does what we're talking about. finds the axis between two things and then works out where they intersect

but there's a really really cheap way to fake it

alright

imagine your balls bounding box

in your pong game "space"

if you were to flatten that 2d object into a 1d line. by projecting the box down to the X axis, and across the Y axis.

we'd have a small line floating in space right?

hasherr

Um... sure?

I'm having trouble visualizing flattening a 2d object into a 1d line

Matt D

we'd have two small lines, one marking the flattened position on the X axis, the other marking the flattened position on the Y axis

hasherr

flattened position?

Matt D

so. you know how your browser has a scroll bar?

hasherr

Yeah, of course

Matt D

01:28

on the Y axis, your bounding box would look like that

hasherr

Okay

Matt D

on the X axis, your flattened line would be the same thing. just under the box

like a shadow

hasherr

okay

So we have 2 lines

Matt D

if you took a light. and shined it down from on top of the box. itd cast a shadow under the box on the X axis

and if you took a light and shined it onto the left side of the box, itd cast a shadow on the Y axis

thats basically flattening the 2D object down onto its cardinal axis

hasherr

Okay...

Matt D

01:29

ok. so what we then do. is we take the paddle. and we do exactly the same thing. and draw another line on the X axis, and another line on the Y axis

and we look at the X axis and go. HEY THESE LINES OVERLAP

if we look at the Y axis. and go HEY THEY OVERLAP HERE TOO

we've got a collision

hasherr

...

that's just detecting it though

Matt D

kind of

but where the intersection occurs tells us a lot as well

hasherr

I already understand that, I want to know how to get the time

Matt D

well that tells you the time ;) if you're using swept "lines"

hasherr

And I have to go in a few minutes, I've spent all night working on this when I should've been working on other things.

Matt D

01:31

hehe

this took me 6 months to work out on my own

and when it clicked

it was like lightbulb. and ill never forget it.

hasherr

Why when I look up 'Basic Pong collision' on Google does it come up with people saying

    public void handleBallCollision(Ball ball)
    {
        if (ball.boungingBox.overlaps(boungingBox))
        {

            ball.velocity.x = -ball.velocity.x;
        }
    }

fixed their solution

I found at least 5 people saying that.

Matt D

ok

hasherr

Not one of them learned about Sweep collision or anything like that

Matt D

what im trying to tell you is the complicated and correct way of saying "move the ball backwards along its motion until it stops colliding with the wall, then change its velocity and simulate it for as much time as you moved it backwards"

which is why just changing the velocity doesnt work

because the ball is still inside the damn wall

hasherr

But it works for them.

Right, but how do I get it out of the wall?

Matt D

01:34

move it backwards along is line of motion

hasherr

Until what?

Matt D

it stops colliding

hasherr

And that's the point where you place it?

Matt D

which is what we're trying to do by finding the time of actual collision, we're skipping the iterative approach of just moving it backwards, and working out exactly where to place it

yes. and if you want to be correct you can simulate it for however much time you just rewound

hasherr

Your use of the word time confuses me. You make me thing that it is actual time.

Matt D

01:35

well it is

hasherr

Like the time of collision, where you're really referring to it as a place

Matt D

no, i mean time.

hasherr

Moving backwards in time sounds hard

Matt D

one last thing. games work in discrete timesteps. 30fps is 1/30th of a second. so we have a snapshot at T0, and we have a snapshot at where we think T1/30th is. there's still 33ms between those snapshots.

so, within that discrete timestep, im moving my objects along a path over time. over that 33ms. and I can pretty much assume linearity unless there's insane acceleration. so. i can pretty much assume that the middle of the path my ball takes, is equal to half the elapsed duration of the discrete timestep

hasherr

That makes no sense to me.

HALF your path = time?

Matt D

01:38

yes. because the path is your motion for that timestep

the ball has a location at the begining of the frame

and it has a location at the end of the frame

hasherr

I don't know anymore. Thanks for the help, I'll think about it later.

Matt D

we can draw a line between those two points.

that line is the motion of the ball, over the time of the timestep

hasherr

I don't see how you can draw a line between time and a position

Matt D

if we had half as long a timestep, we'd only travel halfway along the path

well, thats what simulation is ;) its also what integrating/differentiation is

hasherr

Welp, I'll talk to you later.

Matt D

01:40

if it takes me an hour to drive from here, to your place

and i drive for half an hour

how far have I gone?

hasherr

Halfway

But how the hell do you get position out of that.

Matt D

if i have a ball, that takes 33ms to move from point A to point B, how long did it take to get to the middle?

hasherr

~16

Matt D

so. if i take two lines

and those lines describe the motion of two balls over 33ms. and the lines intersect each other at exactly in the middle. when did the collision occur?

hasherr

16.5...

Stop talking

Going to shower to think

Matt D

01:42

think about what happens if the lines intersect at halfway for one. and 3/4 for the other

time and position are intrinsically linked. meters per second

distance per time.

have fun man :)

oh yeah. exploding brains. ... and hey its lunchtime!

hasherr

02:08

@MattD I mostly understand what you're saying, but code implementing is gong to be soul-crushing.

Alex M.

am I the only one here who zooms in on sites? I kinda have to zoom in on all of SE (125%) to get a comfy experience at 1440x900 on a 19" monitor

Pip

meh

I get good default resolution on my 1600x900 monitor

hasherr

medium.com/cyber-security/24eb09e026dd

Alex M.

I find that it's easier to read text if it's big; I don't think I have sight issues

it's just that I kinda register characters more easily if they're big

I don't have to try as hard to read them

Pip

I gotta go to bed, night all

night @AlexM.

Alex M.

02:17

yeah me too, nite

Matt D

03:22

@hasherr nah. its mostly pretty simple. as i said, its well documented on the interwebs

@hasherr also, these days i just use box2d ;)

endrohat

07:58

hello

Lasse

hi

endrohat

whatsup

Lasse

not much

I just woke up

endrohat

oh

radical

Hey Lasse, endrohat

Lasse

08:05

hi radical

endrohat

heya

radical

It's afternoon here, but even I just woke up :p

Lasse

I'm trying to get a lot of sleep before the jam :P

radical

Heh cool

Lasse

and it's only 10am

endrohat

08:15

i just had lunch

radical

08:33

@endrohat, are you working on some game ?

endrohat

yes

a clone of "dangerous dave"

old dos game

radical

I remember the game

What are using to make it?

endrohat

libgdx

radical

Ah okk

I remember playing 'dangerous Dave', it was nice

endrohat

ya. i knw

what about you?

radical

08:43

Working on a little word game for ios. And thinking of stopping my 3d engine project :/

endrohat

oh

radical

Stopping it and working on a game instead :p

@lasse, planning to use Opentk for the jam?

Lasse

yeah

radical

Cool

I probably won't have more than a few hours over the whole weekend, for the jam :(

endrohat

what are you using to make your word game?

radical

08:48

Uikit actually. Graphically it is a simple game. My friend has been working on it mainly, and I am now helping in some areas

endrohat

oh ok

radical

Where in India are you from, if you don't mind me asking?

endrohat

mumbai

radical

Ok.. I am from Delhi

endrohat

ok. cool

Transcript for