Examining Portal's Teleportation Code

Gamasutra is running a story deconstructing the mechanics of Portal's teleportation programming. They present a snippet of Portal's code and a downloadable demo. They ran another article in this series earlier this year with an analysis Mario Galaxy's unique take on physics. We've discussed the development of Portal in the past. "Teleport mechanics in video games are nothing new. Puzzles from the original Gauntlet were memorable -- and more than likely, that wasn't the first game to use teleportation as a gameplay mechanic. The difference between Portal and all those that came before it is that Portal's teleportation acts as a frictionless tube between point A and point B. Physics are still hard at work inside the frictionless tube. Instead of simply repositioning an object from point A to point B, the player enters point A with full velocity and exits point B with the same speed, but moving in a new direction." Update: 8/26 at 19:37 by SS: Dan notes that the code was not directly from Portal; it was written to approximate Portal's physics.

Comments

Frictionless tube?

[Anonymous Coward]

Your mom has a frictionless tube.

First post?

Re:Frictionless tube?

[Chris Burke]

For friction to be present, the object being inserted into the tube must be large enough to touch the sides. That must be your problem.

Re:Frictionless tube?

[jollyreaper]

For friction to be present, the object being inserted into the tube must be large enough to touch the sides. That must be your problem.

THAT'S WHAT SHE SAID! -er, shit. *self pwn*

Re:Frictionless tube?

[ndnspongebob]

the problem was he accidentally played puddle and just got embarrassingly wet

Re:Frictionless tube?

[Anonymous Coward]

From Sex and the City

Samantha : Your dick's too small.
James: Have you ever thought that maybe your vagina is too big?

Posting anonymously for the obvious reason

Re:Frictionless tube?

[Anonymous Coward]

Whores do tend to be pretty loose.

Re:Frictionless tube?

[Anonymous Coward]

get back to FYAD, scum

Re:Frictionless tube?

[Anonymous Coward]

either that or she's Mrs. Goatse

Re:Frictionless tube?

[noundi]

Your internet has a series of frictionless tubes. *high fives Ted Stevens*

Re:Frictionless tube?

[Anonymous Coward]

You sir, have managed to get modded +5 funny for a combo mom joke and a FP. Nicely played :)

Portal

[CaptainPatent]

Regardless it's a lot better than quantum teleportation.

Re:Portal

[Impy the Impiuos Imp]

Duke Nukem 3D's teleporters would teleport your weapon shots, too.

I loved shooting the rocket launcher into it only to hear a buddy die on the other side of the map as the rocket appeared and continued on its way.

I don't recall if you jumped into the teleporter if you'd exit and continue your jump arc, but there is precident for "movement in progress" teleportation.

Re:Portal

[ElizabethGreene]

First thought: "Hey, if it can work within or near the event horizon of a black hole we could time travel!".

Second thought: "Wound this violate one of the laws of thermodynamics?"

Third thought: "I need a life."

Re:Portal

[pushing-robot]

That's not entirely correct, from a programming standpoint.

In most old games, "physics" were limited to jumping (and, occasionally, explosions knocking players around). Rather than try to simulate ballistic trajectories for every object in the game, rockets and other projectiles were simply moved forward a certain distance for every "tick" of game time.

So the transporter didn't preserve the rocket's momentum - it just put the rocket at a new location, and the game then resumed moving the rocket forward.

Re:Portal

[ElizabethGreene]

Fourth thought: "s/wound/would/g"

Re:Portal

[lgw]

Whether or not that would work is one of the more interesting questions in physics IMO. I think that Portal-style discontinuities "near" a black hole would not create any such weirdness, but sadly the math physisists used to model this stuff is so complex and abstract that the math simply can't model a discontinuity. It's amusing when someone claims it's impossible on the basis that it doesn't fit the model, though.

"Within" black hole ... that would be very weird indeed.

And don't worry, here on /. no one has a life.

Re:Portal

[Anonymous Coward]

Can anyone make a mod based on the books Eon, Eternity and Legacy (by Greg Bear) with all this information? I'd love to see The Way represented in a game... Watch out for the Jarts!

Re:Portal

[SanityInAnarchy]

I don't recall if you jumped into the teleporter if you'd exit and continue your jump arc,

To some extent, I'd guess. It wouldn't be perfect, but let me put it this way: Duke 3D was a two-and-a-half-D game, not a 3D game.

This implies, among other things, that the engine didn't actually support rooms on top of one another -- that all had to be faked in some way.

So how could you swim underwater? The simple answer is, the surface of the water was a silent teleporter -- it might even have to be marked "water" -- and the "underwater" was actually a completely different place in the map.

Going upstairs was a different trick -- the fact that the game could handle two rooms, or "sectors", occupying the same space, so long as you couldn't see both at once. There was a lot of really creative level design involving staircases and the like to make it seem as though you had a two-story building, while never actually letting you see both stories at once.

If you want to get a really good idea of what the Duke3D engine was, find one of the secret levels -- the one with a big room in the middle, and a hallway ringing around the outside (kind of a donut shape) -- don't remember what it was called. I do remember that you could turn right three times, and end up in a different room -- there were four separate rooms (or "sectors") set in the same physical space.

Re:Portal

[Anonymous Coward]

No need to be greedy ;)

Re:Portal

[10101001 10101001]

You're right. A better example would be something like Subspace, where a good 90% of a game was considering one's own momentum and the ballistic tragectories of bouncing bombs/shots. I've personally never played Portal and while I assume it's a fun game, I'm still quite perplexed on why so many people seem so awed by its concept.

Re:Portal

[nine-times]

If you could get portals working, then it would mean faster-than-light travel, which would all by itself raise the possibility of time travel.

Apparently, I need a life too.

Re:Portal

[Anonymous Coward]

I do believe the level you speak of is called Dreadnought. It was one of the best multiplayer maps for the game I can think of... well... there is Duke Burger!

Re:Portal

[FoolsGold]

Quake 4 would teleport your rockets in the same manner. I thought it was pretty neat - didn't know DN3D had done it a decade ago. :)

Re:Portal

[grahamd0]

I'm still quite perplexed on why so many people seem so awed by its concept.

It's not the concept, it's the execution.

Re:Portal

[zmollusc]

Hehe, just reminded me of the level in DN3D with 4 rooms with teleporters at each end leading to the previous/next rooms (like a linked list). You could fire a rocket into the teleporter so that it would go 'round and round' the rooms forever (or until it hit you or some other shmuck in the deathmatch).
Good times.

Re:Portal

[Anonymous Coward]

You insensitive clod!
http://www.vgcats.com/comics/extras/stillalive.php

Re:Portal

[beav007]

It's not the execution, it's the cake.

Note that, in Portal, execution and cake seem to be linked...

Re:Portal

[lysergic.acid]

i'd say Doom was 2.5D, and Duke Nukem 3D was more-or-less 2.99...D

having a screwed up map editor doesn't detract from the fact that you could move along all 3 axes. this is especially clear when you strap on a jet pack and can fly freely over buildings, or climb over obstacles and move between different elevations (without the help of "elevator" platforms) throughout the game's wide variety of terrain, or walk across bridges and other assort overhanging paths.

i mean, it wasn't like Doom, where the ground was always completely flat (and you were glued to it) and there weren't any diagonal slopes. you also had full vertical aiming in Duke Nukem 3D, whereas you didn't in Doom. all the 2d sprites could be placed/move in a fully 3D coordinate system (which is how bridges were created). that's why you can see projectiles moving non-parallel to the horizontal plane at any odd angles.

Re:Portal

[grahamd0]

It's not the execution, it's the cake.

I didn't want him to think of me as a liar.

Re:Portal

[SanityInAnarchy]

you could move along all 3 axes.... i mean, it wasn't like Doom, where the ground was always completely flat... you also had full vertical aiming in Duke Nukem 3D, whereas you didn't in Doom.

That last one, I didn't know about. I do know that quite a lot of Doom source ports support mouselook and (optional) jumping (optional, because it let you cheat quite a lot).

all the 2d sprites could be placed/move in a fully 3D coordinate system (which is how bridges were created).

I don't remember -- could you align those diagonally?

Regardless, from what I remember, Duke 3D mostly added a lot of hacks to Doom-style tech.

Sloped floors added a lot of realism, and there was the fact that sectors could intersect, without problems, so long as you didn't see both at once.

And then there were the teleporters, and the water...

So, we can argue over the version number, but it was nowhere near, say, Quake.

Re:Portal

[Schnoogs]

Actually it was a 3D game since the player could move in....wait for it....hold....ALL THREE AXIS!

The reason it and games like Doom were called 2.5D is because the data used to construct the 3D world was 2D in nature. The final output though was in fact 3D.

How about I get some of those insightful points you stole.

Re:Portal

[lysergic.acid]

well, i used to spend a lot of time creating custom maps in DN3D's build program, so i know how much of a pain in the ass it is, and the wide variety of hacks that are often employed--but isn't this true with every game engine? unless you can actually model the natural laws of physics, you're going to have to use hacks to fake most of it.

i know that Quake was a huge improvement over DN3D--for one it didn't use 2d sprites--but i still think it's a much bigger jump from Doom to Duke Nukem 3D than it is from Duke Nukem 3D to Quake. i just remember the first time i played Duke Nukem 3D, dropping down from that vent shaft in Hollywood Holocaust at the beginning of Episode 1: L.A. Meltdown, it totally blew my mind how "realistic" this game was. having only played games like Wolfenstein and Doom before this, it was completely amazing to me that i could actually look around in any direction i wanted to using the mouse (including up and down). and when i discovered that you could actually climb onto the buildings, walls, tables, etc. and interact with the environment so freely (especially with the jet pack) rather than being restricted to set paths or hallways, it was like a door to a whole new world of virtual reality was opened to me.

there are a lot of games that would be better classified as 2.5D than Duke Nukem 3D--for instance Crash Bandicoot, which although fully 3D graphically, still limited player movement to a fixed 2D "track." i mean, in Duke 3D you could actually have aerial deathmatch battles with the jet pack and literally fly over or under the other player. so the vertical layering issue is strictly limited to the map engine, and inside every "room" you had a fully 3d environment.

Re:Portal

[SanityInAnarchy]

The reason it and games like Doom were called 2.5D is because the data used to construct the 3D world was 2D in nature. The final output though was in fact 3D.

When Doom doesn't allow me to build something as simple as a ramp -- when neither Doom nor Duke3D allow me to do something as simple as a two-story building (and see both stories at once!) -- I call that 2.5D.

And yes, the final output was 3D... somewhat. Not a single 3D model to be seen, just sprites everywhere.

Compare to Quake.

Re:Portal

[SanityInAnarchy]

unless you can actually model the natural laws of physics, you're going to have to use hacks to fake most of it.

True.

My point here is that Quake was a milestone in avoiding such hacks -- most levels built in most modern FPSes could have been built in Quake, it's just that the performance would suck. These levels really couldn't have been built in Duke3D.

dropping down from that vent shaft in Hollywood Holocaust at the beginning of Episode 1: L.A. Meltdown, it totally blew my mind how "realistic" this game was.

Yeah, I remember that -- it was my first FPS. The explosions surrounding that were pretty cool, too -- camera shaking and everything.

Of course, it was also my first abuse of cheats. DNKROZ.

so the vertical layering issue is strictly limited to the map engine, and inside every "room" you had a fully 3d environment.

Well, you have a fully 3D column of air. I still find it quite a lot more interesting to explore a fully 3D environment -- Half-Life was probably the next game that blew my mind. (Though, to be honest, it was probably Counter-Strike first.)

Re:Portal

[lysergic.acid]

i agree that today's games offer a lot more possibility in terms of what kind of environments you can create. but i still miss playing in co-op mode with a friend over the phone line in Duke3D's epic outdoor missions--like walking across a narrow catwalk bridging a massive canyon. you really felt like you were inside the game's narrative, almost role-playing-like.

i don't know what it is, but today's games just don't have that kind of gameplay quality. it's all about deathmatch or team deathmatch these days. i guess it's hard to immerse yourself into the virtual world of the game when other players are shouting "PWNed!!!!11 U nUBZ!!!!11"

Re:Portal

[TheThiefMaster]

Most people seem to miss that the "portals" in portal aren't just teleporters, there is complete continuity of physics across the boundary. The game's own commentary explains that they have everything near the portal exist in another physics world, one centred on the portal and with the portals matched up so that they are in the same place (or something like that). An object half-through a portal is rendered so that you can see it sticking out both sides, and you can collide with it on both sides and it will react correctly.

Everyone can do a flat teleporter that preserves velocity/momentum, but it's not the same thing at all.

Re:Portal

[somersault]

IMO the portal 'physics' are pretty easy to understand - it's a very similar idea to sending a 2D character off one side of the screen and making them appear on the Other. The interesting thing to me is that you can see things through the portals - that is a bit more mindbending in programming terms, considering you can see yourself and other parts of the level recursively. I think there is a limit to the amount of graphical recursion it does though, it was maybe even specifiable in the options. I only played Portal once. It was a fun enough concept, and 'original' for me at least, but it's pretty gimmicky and has no long-lasting appeal, in the way that most puzzle games are. Apparently the story is interesting/amusing, but it's never been enough of a draw to make me go back and finish the game.

Re:Portal

[somersault]

DN3D had some great multiplayer gameplay elements that IMO have only just come through again in recent years - combining security cameras with pipe bombs, and having laser trip mines were a lot of fun :) I remember me and my bro having a lot of fun playing in a White House map and laying lots of traps for each other. The only online game I've been able to lay traps in since then is Battlefield: Bad Company, but admittedly my online gaming experience over the years tended to focus on Counter-Strike.

I think it just goes to show how game designers tend to get obsessed over shiny graphics and to some extent even 'the story' over gameplay elements. I'm still expecting Duke Nukem Forever to be a pretty original gaming experience (although perhaps I'll be disappointed, who knows?).

Re:Portal

[Cormacus]

there is complete continuity of physics across the boundary

I disagree. There is a discontinuity on the plane of the portal itself. Example: blue portal on the wall, orange portal on the ceiling somewhere else. If you stand next to the blue portal, you are not drawn towards the wall

What you do have is conservation of momentum. The player will exit the portal with the same momentum vector as he entered (albeit reoriented to the frame of reference as the exit).

I understand your argument about items halfway through the portal, but that is another issue. Those items exist on both sides of the discontinuity. Maybe the distinction isn't all that important, but this is madness. I mean /.

Re:Portal

[Nurgled]

The sprites in the BUILD engine could only be angled in one dimension, so it wasn't possible to tilt things up and down. Given that the original engine used flat sprites this wasn't a big limitation, but the more recent enhancements to the engine which allow full 3D models to be used in place of sprites really show off this limitation every time you fire a rocket diagonally up or down.

My favourite BUILD engine trick was using multiple rendering passes to defeat the limitations of the engine. DN3D did it for mirrors, but the subsequent games such as Blood used it to do room-over-room, water you could actually see into and various other things that we take for granted in today's fully-3D engines.

Re:Portal

[Anonymous Coward]

If you haven't finished the game, then you have no idea what you're talking about. I mean, it's clear from your 2D character comparison that you didn't even get to the complicated stuff, much less the....well, I don't know do you want me to spoil it?

And "long-lasting appeal"? I played it all the way through just days after finishing it. I've never done that with a puzzle game before.

Re:Portal

[TheThiefMaster]

The point is that you actually walk INTO the portal, you don't teleport on contact. The physics in portal has been written to allow you to essentially walk into the wall the portal is on.

Perhaps a better way of putting it would be that there is continuity of collision detection across the portal.

No attempts to imitate it have done this, they've just done the traditional "teleport on contact", which means that there is an obvious jump as you touch the portal. Including in TFA's attempt.

Re:Portal

[somersault]

No, the 2D comparison was simply from the game engine point of view and moving a character from one place to another, it wasn't a comment on the gameplay at all. I've done a bit of OpenGL coding and I'm well aware of the differences between 2D and 3D, and I'm not too shabby with my physics and engineering stuff so I know the differences and challenges involved between going from a 2D to a 3D system.

I got through plenty of rooms, never really got stuck (there was one point where I hadn't realised a technique and did one challenge a really awkward way by having myself drop infinitely from ceiling to ground and then fire the exit portal into the vertical platform at just the right time - later I realised that this was totally unecessary, but at least I had fun doing it). I don't know how far I was but probably about halfway considering my friend completed it in a couple of hours (and raved about the game for weeks which kind of just turned me off it, I get like that if something is overhyped), and we are of similar intelligence and FPS experience. That involved teleporting myself and other objects obviously, burning the friend cube etc. Can't remember if I went much beyond that. While it's possible to create interesting puzzles with Portal, I'd find it a lot more fun in a multiplayer environment rather than it just being yet another puzzle game. Once you work out a puzzle, that's it. Multiplayer games are constantly changing and need subtle reworkings of tactics, etc and I just find that more interesting.

I just want to point out that I have completed Half-Life, all the add-ons apart from Blue Shift and Half-Life 2 and the Lost Coast (not to mention the probably thousands of combined hours I spent playing Counter-Strike, which started off with me making my own bots just so that I could play offline back in the 56k days), but ever since then I just have drifted away from PC gaming and not taken the time to play any of the new stuff, even though I think I own Episode 1 and 2. Some games I just play for a day or two and then never touch them again because they didn't have the right hook for me, or I completed them and they weren't worth replaying (about the only game I've ever replayed was Uncharted! on the PS3, I really enjoyed it and it had good rewards for completing challenges on each difficulty mode). Puzzle games generally fall into that category. I loved Lemmings as a kid, but these days I'm more interested in action oriented games. I still enjoy playing more cerebral stuff like Chess too occasionally, but I guess overall I've become a bit of an ADHD addled adrenaline junkie. Anyway, if I was going to go back to PC gaming I'd yet again probably end up addicted to MUDding, though perhaps I'd go and complete Portal first.

Other games which you may be suprised to find I've just left hanging halfway through (even though I enjoy them) are Metal Gear Solid 4 and GTA4. I actually took a couple of days off work to play GTA4 and slept very little during that time, and likewise I played MGS non-stop over a weekend, but since then I just haven't gone back to them because I've been doing other things (anime, cinema, other games.. whatever).

Meh I'd better stop ranting :p In summary, Portal is a great concept, but I think they could have made more of the execution. It quickly started feeling like 'just another puzzle game' to me, because that's what it is. Perhaps the character escapes and the level designs get more interesting and realistic later though, I don't know.

Re:Portal

[Anonymous Coward]

Meh I'd better stop ranting :p In summary, Portal is a great concept, but I think they could have made more of the execution. It quickly started feeling like 'just another puzzle game' to me, because that's what it is. Perhaps the character escapes and the level designs get more interesting and realistic later though, I don't know.

Hmmm... That'd be pretty wild, wouldn't it?

Re:Portal

[Graywolf]

Mod parent up, this seems to be the important distinction making Portal's technology "next gen". TFA actually fails to recognize this.

Re:Portal

[somersault]

lol. My interest is slightly more piqued now actually, it would make the whole concept a lot more fun. Since I knew from talking to my friend that I'd done about half the game then I wasn't too fussed about the rest if it just continued along the same lines.

Re:Portal

[somersault]

A quick google of "portal escape" show that indeed it would get more fun later on. If the PS3 port of the HL2 engine wasn't so reputedly awful (due to EA London doing the port rather than Valve themself) then I'd definitely get the Orange Box on PS3 :/

Re:Portal

[drew]

I think there were a lot of gameplay elements of DN3D that have still never been fully replicated in any game that I've played. (Admittedly I've fallen a bit out of the FPS gaming scene since the later days of Return to Castle Wolfenstein.) I still remember the first time I walked into a room full of pipe bombs left waiting for me, and frantically backpedaling to get out of the room before they went off. I also liked how you could trigger pipe bombs even after you had died. It made for some great revenge moments.

One of my favorite tactics was placing the laser tripmines into door frames. If done right they were completely undetectable when the door was closed, and would give anyone who opened the door a nasty surprise. The catch was that their blast radius wasn't that large, so for a big doorframe you needed to put them on both sides, which was pretty tricky to accomplish without getting blown up yourself. After a while the people I played with got pretty good at avoiding the explosions, but they still made for a good way to keep track of where people were on the map.

Re:Portal

[Anonymous Coward]

but sadly the math physisists used to model this stuff is so complex and abstract that the math simply can't model a discontinuity

You mean calculus? Yeah, real complex and abstract there...

Re:Portal

[Impy the Impiuos Imp]

Duke Nukem had bridges, ledges, and so on. The map was true 3D in that sense, though the rendering was not true 3D.

Duke Nukem and predecessors all used a trick of matrices to do what amounts to a 3D rendering -- by preventing you from looking up and down* they could remove an entire set of multiplications in the 3D rendering matrices, effectively speeding it up a magnitude, highly useful for old PCs. Yes, this ran just fine on pre-Pentium class 486 and even 386 machines.

Now Quake was the first true 3D game in that it included not just maps with bridges, etc. but the renderer was true 3D too. I.e. it didn't use that matrix reduction trick. You could tilt up and down and even flip over (though this wasn't allowed) to your heart's content.

* You could tilt up and down, but that was a distortion overlay trick, not an alteration of the rendering angle. This is why things started looking odd when you did that. Also, whether objects are "sprites" or true 3D objects is irrelevant for this discussion. Even the most modern games use sprites for particle effects, though that stretches the definition of sprite -- in this context it means a 2-D flat plane rendered in a 3D world, rather than a 3D object = a bunch of 2D planes assembled into some geometric object. Originally, a sprite was a 2D visual tied to hardware, with hardware-level control over it. And you didn't "redraw" them the hard way, you used the sprite mechanics independent of whatever background and other things you did draw "the hard way." And thus the number of sprites were fixed -- 4 I think for the old Atari, more for Colecovision.

Re:Portal

[lgw]

Yeah, tensor calculus over a non-metric space is trivial, what was I thinking.

Re:Portal

[Masami Eiri]

No, actually it wouldn't. You're not moving across space between the Portals, the fabric of space-time is contorting to connect those two points. So, you're only stepping across a narrow threshold, even if those portals are miles apart.

Re:Portal

[nine-times]

It doesn't matter very much how the faster-than-light travel happens, it's a function of relativity that if I can travel faster than light, I should also be able to travel through time. Or... at least it raises the question, "Will I be able to travel backward in time?"

Because the whole issue with faster-than-light travel and relativity is that, for events that happen outside of each other's light cone, there is no absolute sequence of events. Just to be clear, I'm not saying that the sequence of events cannot be determined, but that there is no absolute sequence of events.

Admittedly, it's kind of hard to think about, but the upshot is that if I could travel faster than light, I could move to a point in space-time outside of the light cone of a given event. So lets say the event at the vertex of the light-cone is my leaving earth, and I travel 500million light-years away from Earth in 1 second. Suddenly I'm WAY outside the light cone of the event of my leaving earth, so the point in space time that I'll then occupy could be said to be either before or after the event of my leaving, depending on the frame of reference you measure from. If I then had the ability to travel back to Earth without being bound within my light cone at the new location, then there's no reason (according to physics) that I shouldn't be able to return at a point in time earlier than when I left.

Not being able to travel outside of the light cone you occupy is what guarantees that things can't go back in time. That's why so much is made about sending information faster-than-light. If any signal could be sent faster-than-light, then one of two possibilities should fall out of that: either (a) Einstein's theories are somehow wrong; or (b) you can send information back in time.

Re:Portal

[Schnoogs]

Again...that has nothing to do with what makes a game either 2D or 3D. Doom allows for movement along all 3 axis therefore it is 3D. The fact that you can't make a ramp is meaningless.

Even Quake used sprites for certain things...does that make it 2.5D also?

FAIL

Re:Portal

[SanityInAnarchy]

Doom allows for movement along all 3 axis therefore it is 3D.

It does not, however, allow for building over all 3 axes. Therefore it is 2D.

Since it can kind of look like 3D, and since both positions are valid, I call it 2.5D.

Even Quake used sprites for certain things...does that make it 2.5D also?

The things which Quake used sprites for, it didn't have to. The things Duke3D used sprites for (like bridges), it really did. That's the difference.

Re:Portal

[SanityInAnarchy]

My favourite BUILD engine trick was using multiple rendering passes to defeat the limitations of the engine.

My favorite was simply exploiting the limitations of the engine. Elevators that went both up and sideways, rooms that curved back into themselves (with walls that appeared out of nowhere), and "water" that you would fall through into a different part of the map -- possibly out of the ceiling and back into the same water...

Much of this can be faked with newer engines, but that's the main reason portals appeal to me -- the fact that you can use them to screw with people's minds.

Re:Portal

[Schnoogs]

News flash for you...Doom's levels exist along all 3 dimensions.

The game was 3D...the criteria you are using to call it 2.5D is INVALID. The criteria for being 2.5D is simply the fact that it used 2D to generate its 3D world.

Movement along all 3 axis makes it 3D no matter how much you want it to be something else. I guess when id called it Wolf3D they should have consulted you first and called it Wolf2.5D (rolls eyes)

Re:Portal

[KeatonMill]

This has been a hilarious thread to follow. Next up, somersault will be expounding unto all of us his LOVE FOR PORTAL!

Re:Portal

[SanityInAnarchy]

the criteria you are using to call it 2.5D is INVALID.

What criteria would you use? Or are you arguing there's no such thing as 2.5D?

As to the rest of your post, saying the same exact thing all over again, but more insulting, isn't going to make me agree with you. Hopefully it made you feel better -- otherwise, it was a waste of time.

Re:Portal

[somersault]

Not really, I still am not bothered enough to resurrect my old gaming PC (fried PSU). I could maybe expound my love of Anime or something, that's mostly what I've been taking up my time with.

I'm pretty sure I know what it would feel like to play Portal. I've played enough FPSes to know what it feels like to fight your oppressors, break free, yada yada. I wouldn't mind hearing the song and seeing the actual situation that spawned the 'the cake is a lie' crap, but I'm in no rush. I'd rather spend this evening watching the second half of Elfen Lied, and perhaps read more of my go karting book :p

Re:Portal

[Schnoogs]

No offense but simply pointing out that you're wrong doesn't count as insulting you...unless you're ego is beyond fragile. Is this the standard response you give someone when they disagree with you?

There's a reason I repeated myself 4 times...I was hoping the correct definition of 2.5D would finally sink in with you but I can see that it hasn't.

You can lead a horse to water but you can't make them drink.

Re:Portal

[SanityInAnarchy]

No offense but simply pointing out that you're wrong doesn't count as insulting you...

And I quote:

I guess when id called it Wolf3D they should have consulted you first and called it Wolf2.5D (rolls eyes)

I didn't say I was insulted, I said you were insulting. There's a difference. But here you come again, with another, subtler (barely) attack:

unless you're ego is beyond fragile.

Counterproductive and pointless.

I'm telling you for your own sake, and because I'd rather have a constructive discussion with you than a pissing contest. It doesn't really bother me if you have nothing to add other than insults -- in fact, it's reassuring to know that you actually can't find anything wrong with my argument.

There's a reason I repeated myself 4 times...I was hoping the correct definition of 2.5D would finally sink in with you

The definition of insanity is doing the same thing over and over again and expecting different results. (Albert Einstein)

And by the way, dimensions don't come by halves. It's a question of made-up semantics. Closest thing to a "correct" definition states:

In early first-person shooters like Doom, one use of the term is to describe the use of 2D character and object sprites in a 3D world. This technology was also implemented with the Virtual Boy game system by Nintendo. It is also used to describe the lack of true so-called "room-over-room" situations.

Pretty much exactly describes both Doom and Duke3D.

Re:Portal

[Schnoogs]

Thanks for the good laugh...as I suspected your attack against me was completely baseless. If my comments meet your definition of an insult it only reinforces the fact that it's a waste of my time trying to discuss this with you.

You can continue to hold onto a definition that has meaning to you alone. Let's ignore the simple fact that industry geniuses such as John Carmack or Tim Sweeney use the one that is found in Wikipedia or any site dedicated to games and descriptions of their game engines.

I'm sure your response to this will consist solely of you crying about being insulted...that's about the only angle you can play since it's absurdity is a good distraction from the actual conversation at hand. You were corrected...didn't like the fact...so you counter with some absurd accusation about being insulted.

Re:Portal

[Schnoogs]

I think it's hilarious that you're suggesting that it's insane to try and explain things to you. You might want to think long and hard about that one and figure out why you're so reluctant to admit you were wrong. I am feeling a bit insane at this point having wasted so much time trying to enlighten you...oh well...I guess I can take the fact that I know what I'm talking about as some sort of consolation prize. Better to be informed than ignorant (I know...I know....that's an insult)

Oh and for someone who posts things like "Counterproductive and pointless" you probably shouldn't follow it up with 3rd rate deflections which are the epitome of fluff. You can stick your fingers in your ears all you want but that doesn't some how make the faults with your argument go away.

Re:Portal

[SanityInAnarchy]

as I suspected your attack against me was completely baseless.

And as usual, you provide no evidence that it's baseless, or even that I attacked you.

I'm sure your response to this will consist solely of you crying about being insulted...that's about the only angle you can play since it's absurdity is a good distraction from the actual conversation at hand.

Well, you did surprise me -- what is this, "I'm rubber, you're glue"? Am I missing something obvious, or am I the one who linked to Wikipedia? And "waste of my time" coming the very post after I said "counterproductive and pointless"...

Let's ignore the simple fact that industry geniuses such as John Carmack or Tim Sweeney use the one that is found in Wikipedia or any site dedicated to games and descriptions of their game engines.

Yeah... the one that I quoted? The one that specifically mentioned Doom as 2.5D?

Don't respond. That would really surprise me.

Re:Portal

[SanityInAnarchy]

I think it's hilarious that you're suggesting that it's insane to try and explain things to you.

Except, you haven't. You've said the same thing, over and over, expecting a different result -- expecting me to suddenly see the light.

Has it occurred to you that I might be right? Or, more likely, that it's a stupid question of personal semantics, and that we're both stupid for spending as much time on it, no matter who "wins"?

you probably shouldn't follow it up with 3rd rate deflections which are the epitome of fluff.

At least I actually deflect -- and, y'know, have a counterargument.

All you have are more attacks.

You could have actually told me why the Wikipedia quote I've got is wrong, or how I've misinterpreted it, if I have. You could have pointed out what the "real" definition is, and how this one differs -- and why the "real" definition is right, and this one is wrong.

Instead, you've opened with "I think it's hilarious that you... You might want to think... about... why you're so reluctant to admit you were wrong..." Not one bit of substance, just more trollish attacks.

And no, "better to be informed than ignorant" wasn't the insult. Blithely assuming that:
  - You're right, and I'm wrong
  - I know it, and just can't admit it
That's what's insulting.

Notice: I'm not doing the same thing. I actually have some substance -- I may have just taught you something about how to make a logical argument (point, counterpoint, etc), if you were paying attention. You haven't said anything of substance, other than repeating the point you made 9 posts back, and throwing in a nice big wad of Ad Hominim.

Re:Portal

[Schnoogs]

Move forward...check Move backwards...check Move to the left...check Move to the right....check Move up....check Move down...check Move arbitrary angles in between those already mentioned...check It's a 3D game bud. The game itself exists within a 3D world and you can move along all 3 axis. 2.5D simply describes how the gameworld is constructed....hence why both Wolf3D and Doom are described as 3D shooters and not Wolf2.5D. I'm gonna side with Carmack on this one...unless your resume also includes work that rivals Wolf3D, Doom, Quake, etc. Thanks for wasting my time...good luck in life.

Re:Portal

[SanityInAnarchy]

And the insanity continues! Not a single counterargument, just the same one again. Plus the repetition of your sad argument from authority:

I'm gonna side with Carmack on this one...

Yeah, and when, exactly, did Carmack explicitly comment on 2.5D vs 3D? When Wolf3D came out, and certainly by the time Duke3D was out, "3D" was a hot marketing term, kind of like "cloud computing" is today. Gets abused all the times by marketing types.

So where's your evidence that Carmack actually named the product? And not that he was simply toeing the company line when someone else did?

And supposing he did say that, doesn't solve the fact that it's an argument from authority, and thus a logical fallacy.

Re:Portal

[Schnoogs]

Sigh...now I know what it's like for an elementary school teacher trying to instruct their students via repetition.

This is borderline tedious...Wolf3D and Doom are 3D games. The gameplay exists within a 3D world and allows for movement in all three dimensions. This is both a matter of fact and common sense to anyone who has ever played them. You have played them haven't you? Do you have any evidence supporting your theory that the games are in fact not 3D and do not allow you to move along all three axis? Please let me know so I can spread this groundbreaking news to the entire internet and the creators of those games who to this day are convinced that they take place in a 3D world.

Wolf3D came out well before Duke Nukem 3D. Duke Nukem was actually competing against Doom...if you actually knew anything about first person shooters, id Software or PC gaming in general you would know this. Wolf3D wasn't called that because of some marketing gimmick.

Knock yourself out thinking that Wolf3D and Doom aren't 3D games. Ignore the fact that they exist in a 3D world and allow for movement along all three axis just like Quake, Halo, Half-Life or any other game that we would labeled as 3D.

2.5D is a term used to describe how the levels themselves are constructed...using 2D data to extrapolate a 3D world. Notice the latter part? A 3D world. Just like a heightmap is used to generate the terrain in Far Cry...you gonna call Far Cry a 2.5D game as well? It also uses sprites for its vegetation...you gonna start calling it 2.5D?

This is my last response to you...I see no reason as to why I should continue wasting my precious time educating you on something so trivial. I have no problem dishing insults your way because I don't think people should limit themselves to compliments. Sometimes people need to be treated harshly so they can learn from their own stupidity. Think of it as tough love. You're clearly either ignorant or simply argumentative. You've provided no evidence to support your ridiculous theory that Wolf3D is in fact not a 3D game. You're opinion is contrary to some of the most intelligent software engineers on the planet such as John Carmack.

Good luck in life...it's unfortunate that I had to verbally bitch slap you around but perhaps this is the wake up call you needed to educate yourself.

Re:Portal

[SanityInAnarchy]

Do you have any evidence supporting your theory that the games are in fact not 3D and do not allow you to move along all three axis?

What a fucking strawman. (You do know what I'm referring to when I say "strawman", right?)

Where have I said this? Ever? Point to one place where I say you can't move in three axes. (Granted, you probably can't in Wolf3D, and only barely in Doom, but use Duke3D as an example.)

No, I said that the games themselves are 2.5D -- referring to the fact that while they are partly 3D (the levels are rendered in a 3D space), they are generated from a 2D map, severely limiting what can be built.

Duke Nukem was actually competing against Doom...if you actually knew anything about first person shooters, id Software or PC gaming in general you would know this.

Strawman #2: I know Duke3D was competing against wrong.

With a side of factually wrong -- Duke Nukem was a sidescrolling 2D game, in every sense of the word. You're talking about Duke Nukem 3D.

Wolf3D wasn't called that because of some marketing gimmick.

Citation needed.

2.5D is a term used to describe how the levels themselves are constructed...

Correct. Are we done yet?

Just like a heightmap is used to generate the terrain in Far Cry...you gonna call Far Cry a 2.5D game as well?

Given that Far Cry also allows 3D structures (including interiors), no. But then, Duke3D really doesn't allow for such things, except in recent source ports, which can hardly be called the same game.

It also uses sprites for its vegetation...

And flat 2D textures for its triangles, I am aware. But it supports and uses actual 3D models -- things which can actually have a top and a bottom, and sides, and exist somewhere in 3D space.

And by the way -- that's another word that doesn't mean what you think it means. "Sprites" aren't necessarily 2D. A two-dimensional texture standing in for a three-dimensional object is pretty much the definition of 2D.

I see no reason as to why I should continue wasting my precious time

Obviously not precious at all. Look up at how much you've written already. Hell, you pounced on this one less than 20 minutes after I posted it -- you must be obsessed!

You've provided no evidence to support your ridiculous theory that Wolf3D is in fact not a 3D game.

I provided a Wikipedia quote which you have yet to counter. I've provided arguments of my own, that the term 2.5D doesn't necessarily mean what you think it means. All you've done is take the same point you made in your very first response and say it again, worded differently, as if maybe this time, I'll concede the point.

Two plus two is five. When you take the number two, and sum it with itself, you get five. 2+2=5. Two, incremented twice, results in five.

But you know what? It's not five, it's four. No matter how many different ways you express the same thing, doesn't make it any more right.

Re:Portal

[SanityInAnarchy]

Blech. Should have been:

Strawman #2: I know Duke3D was competing against Doom.

It was a Doom Clone after all.

Re:Portal

[Schnoogs]

David, your silliness will be forever immortalized in my blog. Your poor logic and stubbornness are just more proof as to how it's possible for someone like Bush to get elected (or Obamaa come Nov).

I created this to commemorate your FAIL. Good luck continuing to rationalize to yourself how a game can let you move forward and up those stairs without being considered 3D.

http://www.assassinworks.com/doom3D.jpg

But...

[i.r.id10t]

But... can they telefrag?

I just love the sound of 2 bodies trying to occupy the same space at the same time in the morning... or afternoon... or evening...

Re:But...

[Anonymous Coward]

I just love the sound of 2 bodies trying to occupy the same space at the same time in the morning... or afternoon... or evening...

And stop peeking into our windows, you're creeping my wife out.

Too verbose

[Anonymous Coward]

>>Physics are still hard at work inside the frictionless tube. Instead of simply repositioning an object from point A to point B, the player enters point A with full velocity and exits point B with the same speed, but moving in a new direction."

Should be "Speedy thing goes in; speedy thing comes out."

Re:Too verbose

[elrous0]

My ex-girlfriend used to use that exact phrase all the time.

Re:Too verbose

[Anonymous Coward]

your ex-girlfriend is an AC

Re:Too verbose

[alexandreracine]

This is slashdot, your ex-girlfriend was probably your immagination.

Ahoy, GlaDOS!

[Stanistani]

I want to see the nautical version, Porthole.

Re:Ahoy, GlaDOS!

[Darth_brooks]

I'm waiting on the hot grits version, Portman

Re:Ahoy, GlaDOS!

[Underfoot]

I want to see the white water version, Portage.

Re:Ahoy, GlaDOS!

[Captain Splendid]

I'm waiting on the drunken lawyer version, Port

-Rowley Birkin, QC

Re:Ahoy, GlaDOS!

[Anonymous Coward]

The grits are a lie :(

Re:Ahoy, GlaDOS!

[Anonymous Coward]

attn: flamebait, I think that's the ricer cflags version where you have to compile each level just before playing.

Re:Ahoy, GlaDOS!

[MobileTatsu-NJG]

I'm waiting on the drunken lawyer version, Port

I'm waiting for the Wii version, P.

Re:Ahoy, GlaDOS!

[HTH NE1]

I want to see the nautical version, Porthole.

I think they have that at Crazy Adam's Discount Warehouse and Import Emporium.

Re:Ahoy, GlaDOS!

[Anonymous Coward]

I'm waiting on the hot grits version, Portman

That'll be good, but I heard the Port-O-Potty version really stinks.

Re:Ahoy, GlaDOS!

[UncleTogie]

I'm waiting on the version for mushroom fanatics....Portabello!

Re:Ahoy, GlaDOS!

[shadwstalkr]

I'm waiting for the Wii version, P.

I'm waiting for the Scrabble version, Portmanteau.

Re:Ahoy, GlaDOS!

[Chris Burke]

Aw, I thought that was the Gentoo version!

Re:Ahoy, GlaDOS!

[PaganRitual]

And it's less popular sequel, Starboardhole

Yeah, I've got nothin'

Re:Ahoy, GlaDOS!

[Draek]

I'm waiting for the math version, Pi, even though the levels won't be able to be solved rationally.

Re:Ahoy, GlaDOS!

[Anonymous Coward]

Yes, officially denounced by Portman herself: http://www.insult-o-matic.com/?article=7

It would have been more fun

[hcdejong]

if they'd chosen the Discworld version of teleportation: two objects have to be teleported simultaneously in opposite directions, and the weight difference determines the exit speed of the lighter object.

Re:It would have been more fun

[Underfoot]

We need a Pratchett based online FPS! Dwarf Bread for weapons; you can play as a Gollum; Discworld based physics.

That would be super-sweet!

Re:It would have been more fun

[geekoid]

The weight difference AND the difference between there distances to the rim determin exit speed.

This is why you can use a multi-hundred pound canon to teleport a person and not have your brain go out your ears.

Re:It would have been more fun

[mike9989]

Meh... Probably not. By the way it's a GOLEM not a Gollum. One is a human made construct the other is a human made construct... Wait... what?

Re:It would have been more fun

[Punko]

Dwarves on Discworld don't fight golems. They fight trolls. This is why the internet needs more dwarves.

Re:It would have been more fun

[xouumalperxe]

multi-hundred pound canon

Omnianism has loads of holy books, but I don't think even those collected amount to several hundred pounds.

Re:It would have been more fun

[DeusExMach]

That's it... call a dwarf...

Re:It would have been more fun

[Atzanteol]

The weight difference AND the difference between there distances to the rim determin exit speed.

Where distances?

Re:It would have been more fun

[mrmeval]

One is the stuff of myth, the other is the stuff of trademarks, lawsuits and RIAA thugs.

Choose.

Re:It would have been more fun

[Anonymous Coward]

Rinswind would be the character to play!

bzflag?

[mikael]

You can do that with 'bzflag' portals. Take a jump through the portal or with the 'wings' flag. Then you appear at the other end like SG-1 stargate. Spins and backward movement work as well.

Re:bzflag?

[Smidge204]

Yes no but not really. Vertical velocity is still vertical and horizontal velocity is still horizontal - just pointing in a different direction.

With Portal (and it's predecessor Narbacular Drop) you can enter a portal on the floor and pop out a portal on a wall - vertical speed seamlessly becomes horizontal speed. And that works at any combination of angles. Add to that collision detection mid-portal and you have something just a little more than what BZFlag offers.

Regarding the portals in Prey - I don't recall the portals being multi-directional but that game had a lot of funky physics in it so maybe I just don't remember. Also, the portals were all scripted in-place so they might have taken 'shortcuts' in the code to make them work.
=Smidge=

Re:bzflag?

[Anonymous Coward]

You people realize that there is no up and down in a computer, don't you? It's all just vectors and matrices. If the programmer wants your character to fall to the "left" or stick to the "roof", she simply assigns a local force vector to your character.

Re:bzflag?

[Anonymous Coward]

honestly anon, what do expect from a bunch of CS majors ;). Sure they got their discrete maths down, but when it comes to analysis and linear alg, they really don't stand a chance.

Re:bzflag?

[mikael]

'bzflag' portals can be in any direction the level designer wants. They can be vertical (drive into them), horizontal (jump up or down into them), or any angle you like. A 'bzflag' portal is simply a plane equation and a bounding frame. But there is no collision-detection as portal transportation is instantaneous. Having a 'Stargate' tunnel would probably change the dynamics a bit, but maybe it would be just like a secret tunnel.

Re:bzflag?

[twistedsymphony]

In Prey velocity was maintained just like in portal. Though you're right that all of the portals were pre-created for you. Though I do believe there were one or two that changed position, and quite a few on angular surfaces.

The biggest difference was that you couldn't create the portals yourself, and there were no situations where you'd leave a portal and enter another one to keep building velocity. I suspect you're right about development shortcuts, else we would have seen more interesting use of Prey's portal system.

Physics is Phun

[CopaceticOpus]

A well made 2D Flash version of Portal:

http://portal.wecreatestuff.com/portal.php

Re:Physics is Phun

[Anonymous Coward]

2d DS version

Re:Physics is Phun

[Annymouse Cowherd]

As opposed to this badly made 3D Blitz Basic version of Narbacular Drop.

Prey

[AioKits]

Any thoughts on a nice little compare and contrast of the 'teleportation physics' between Prey and Portal?

Re:Prey

[Anonymous Coward]

Prey hat fixed portals, easier to do.

M.C.Escher has good OLD examples of the concept:

[Zymergy]

These two were my favorites:
http://www.mcescher.net/images/relativity.jpg (1953)
and
http://www.mcescher.net/images/houseofstairs.jpg (1951)

The code

[anomnomnomymous]

The code is a lie!


Ok, sorry...

Damn!

[khendron]

Reading that article makes me want to play Portal through again.

--sigh-- at least it won't take long.

Re:Damn!

[hansamurai]

You can always play with commentary on if you haven't done that yet.

Re:Damn!

[fprintf]

Played it with commentary on, tried (and have not succeeded yet) all the challenge maps, and then downloaded some additonal challenge maps from the 'Net. And yet, it still seemed like a game that was way too short.

I really loved this game, possibly better than anything else I have tried in years. So it was slightly disappointing that it only took me a few hours to get through it the first time, and subsequently takes less than an hour. (I am a slow player)

Re:Damn!

[Eli Gottlieb]

Try this. They claim it's 3.5 hours of game time, but the puzzles are *hard*, so it takes more like a day.

am i

[nimbius]

the only person not absolutely obsessed with portal? video games use physics.

projectile force in rise of the triad? doom? every fragging quake? I liked this game better when it was called narbacular drop.

Re:am i

[FiloEleven]

When it was ugly, buggy, and short?

Narbuncular Drop was a great student project showing off a new idea, and I'm glad it's still available to play with. Neglecting the gameplay polish, puzzle depth, and environmental detail improvements that went into Portal is, IMO, a gross error in judgment.

You forgot to end with "get off my lawn" =)

Re:am i

[Koiu Lpoi]

am i the only person not absolutely obsessed with portal?

No. Most people actually just enjoyed it. The obsessives are just loud.

video games use physics. projectile force in rise of the triad? doom? every fragging quake?

Show me where anything like Portal's physics appear in any of those you listed. A moped is not a Porsche.

I liked this game better when it was called narbacular drop.

With that comment, I highly doubt you've really played either. The gameplay between the two is actually rather different. Troll harder next time.

Re:M.C.Escher has good OLD examples of the concept

[Anonymous Coward]

Speaking of, whens he gonna put a new album out?

Next step?

[Aranwe Haldaloke]

Porting Portal's portal code?

Re:Next step?

[saboola]

I'm not a portal porter
I'm a portal porter's son
And i'm only porting portal
Till the portal porter comes

WTF

[4D6963]

The difference between Portal and all those that came before it is that Portal's teleportation acts as a frictionless tube between point A and point B. Physics are still hard at work inside the frictionless tube. Instead of simply repositioning an object from point A to point B, the player enters point A with full velocity and exits point B with the same speed, but moving in a new direction.

Are you fucking kidding? What's not completely obvious about this algorithm that should be Slashdot-front page worthy? I mean, it's fucking mind blowingly obvious, of course it keeps the velocity and translates it, how else could it do what it does? I can understand why it would be relevant to do a coding tutorial on the subject, but that's about as newsworthy as a Bresenham line drawing algorithm tutorial. TFS looks just like a "hey let's talk about how some super popular game is super awesome and post about it on a high traffic website".

Re:WTF

[77Punker]

The physics of the teleportation are pretty boring, but the fact that you can see through the portals and have an object go halfway through a portal are unusual.

I don't care enough about programming games to RTFA, but that could be something worth talking about. Chances are it's not what they're talking about, though.

Re:WTF

[rpj1288]

GlasDOS said how it worked in the game for crying out loud! "Speedy thing goes in, speedy thing comes out."

Re:WTF

[kestasjk]

It didn't answer the main question for me: How does the code which accelerates players downwards work?

It must be using some kind of vector mathematics for mapping acceleration onto velocity, and velocity onto position, but I'll be damned if I can figure out how they expressed that in an algorithm.

Re:WTF

[Millennium]

Um... aren't you referring to gravity here?

Re:WTF

[geekoid]

I lied it, and I like seeing how they did it differently. If comparing how different people implement game teleportation isn't nerdy, then nothing is.
I mean, you could treat it like a tube, or you could just save the movement information and reimplement it when using a spawn technique of teleportation.

The fact that you aren't clever enough to see all the variations is hardly Slashdots fault.

Re:WTF

[Coward Anonymous]

Don't you be denigrating Bresenham's line drawing algorithm. Truly a work of algorithmic beauty.

Re:WTF

[Goaway]

Well, the Super Mario Galaxies was total bullshit too, so that does seem to be their modus operandi. Take a popular game, bullshit something that sounds plausible to someone who's not experienced with game programming, and get linked on social media sites.

Re:WTF

[Steauengeglase]

I was wondering the same thing. Sadly, it really didn't go too far into that one, just the physics.

Re:WTF

[BigJClark]

Although I appreciate Gamasutra for its laymen-type articles, in reality the portal code is quite simple. Simple matrix-multiplication kids. Take the rate of entry into portal A(incoming), apply this by the normal of portal B(outgoing), then multiply the new vector to the matrix describing the actor (in this case, the player). Don't forget the gravity vector!
Not terribly difficult, as with the WII Mario gravity. Although, I can really appreciate the creativity.

Re:WTF

[Goaway]

Uh... That's game programming 101.

velocity_z += gravity * delta_t;
position_x += velocity_x * delta_t;
position_y += velocity_y * delta_t;
position_z += velocity_z * delta_t;

Then again, with the rest of the article being absolutely elementary bullshit, maybe it is a wonder they didn't cover that, too.

Re:WTF

[Anonymous Coward]

The Mona Lisa is just a portrait of a woman. It's special because it was done well. Any painter can see that it was done with the same kinds of brushes and paints as other paintings of its day but very few will ever aspire to birth such a creation. It's really easy to sit back and scoff at the simplicity of a brush stroke or an algorithm but the time wasted doing so would be much better spent putting your money where your mouth is.

Re:WTF

[ABoerma]

Physics major nitpick: It doesn't keep the velocity, it keeps the speed.

Re:WTF

[4D6963]

Yeah which is really the easiest and most obvious part. As the GP pointed out the algorithm for seeing through the portal must be less obvious/interesting, same for things standing in the portal, although I suspect there's no big challenge here, I'm ready to be that objects just go on either side of the portal without making any difference.

Re:WTF

[nine-times]

the fact that you can see through the portals and have an object go halfway through a portal are unusual.

There's also some potential that's not really unlocked in Portal itself. For example, seeing through the portal could allow you to shoot through it (Portal only allows you to drop things through portals). The game it's based on (Narbacular Drop) even allowed you to place portals (imagine being able to shoot the portal gun through the portal) while looking through the portals, which made for some interesting strategy.

So it is an interesting case of teleportation. I'm not entirely sure it even makes sense to call it teleportation, though. The effect is not that objects themselves are being transported through any special means, but instead space is twisted around.

Re:WTF

[4D6963]

Haha nice one, I didn't think about that ;-). Don't pay attention to the other posters, Slashdot is crowded with people insensitive to even the most blatant sarcasm.

Re:WTF

[Anonymous Coward]

Angry poster is angry.

Re:WTF

[4D6963]

What the hell are you drivelling about? It is obvious that the only straightforward and sensible way to do this is to do a line-full circle collision detection between your position (a point) between this frame and the previous frame (a line) and the portal (a flat full circle, well, oval), and that when the line and the circle cross you just translate positions and velocity according to a fairly simple function that relies on the 3D angle between both portals. And wtf is "a spawn technique of teleportation" if not a fancy (although near nonsensical) way to refer to something obvious to sound like you're in the know?

Re:WTF

[4D6963]

Oh I know, I use it, and I'm not denigrating it. Just saying, if Gamasutra wrote a tutorial about it, I wouldn't want to see that on the front page of Slashdot, no matter how elegant and efficient this algorithm is.

Re:WTF

[4D6963]

You're pretty much missing the point, or at least your comparison is quite flawed. The Mona Lisa isn't obvious, not anyone who wanted to a woman's portrait came up with the Mona Lisa. And neither is Portal as a whole. But the algorithm behind the teleportation in Portal is flat out obvious. Like, really, anyone can come up with it when they're thinking of teleportation. The idea behind the game is what's admirable and ingenuous, not the little necessary and obvious algorithm.

Re:WTF

[4D6963]

Angry poster is angry.

Anonymous Coward is anonymous.

Re:WTF

[lgw]

It made sense to me. People have been doing spawn teleports forever, and Portal was interesting because it used a new technique, though Prey was similar and has been around in development since Quake2. "Zoom" teleports, where your point of view moves very fast from source to destination, are cool as well.

Re:WTF

[Cornflake917]

*WOOOSH!* #1

Re:WTF

[xhrit]

>As the GP pointed out the algorithm for seeing through the portal must be less obvious/interesting

This is easy.

1) portal_1 & portal_2 are textures that are applied to the walls as decals. (just like every other bullet hole in just about every other non-GeoMod style shooting game)
2) create a pair ov cameras, one attached to each portal. aim the camera the direction ov the normal with its up vector aligned with the global up vector.
3) Render target portal_1 with sorurce ov portal_2 and vice versa.

I am using this method for the intersteller transit gates in my Zero Point War game series. I have not figured out how to preserve momentum using ODE yet tho - my simulation breaks.

Re:WTF

[billsnow]

velocity is the correct term. even though the moving object changes direction within the 3 dimensional space, the vector value must be retained in relation to the plane of the original portal and translated to the plane of the new portal. don't feel bad; as an engineer, i'm accustomed to correcting physics majors on such topics.

Re:WTF

[HTH NE1]

I think he means whether the teleportation is rendered continuously or discontinuously. A discontinuous teleport would be like Halo where you touch the teleporter and you're suddenly at the other end. A continuous one allows for a smoother transition or even reversal while being transported.

Compare also the Stargate (SG-1, Atlantis) method where it feels like you walk in on one side and walk out the other, but in fact you're being disintegrated as you step through and aren't reintegrated on the other side until you're fully disintegrated. But with some programming that reintegrates you if you pull out (I'm not sure how that works if you stick your head in; how does your disintegrated head tell your body to pull it back out, or even keep your body standing?). The wormhole traversal animations are a cinematic presentation of the "Zoom" effect to suggest it still takes time to travel from one end to the other. In a game, it could be an out-of-body disorientation effect that renders you vulnerable for a moment on the other end.

Re:WTF

[4D6963]

Wait, you don't put your portal camera in the portal, do you? You put them at a distance from the portal (same distance as the player is from the portal) and make sure nothing gets rendered in the way, correct?

Re:WTF

[Anonymous Coward]

Near as I can tell, they seem to use an infinite coordinate grid such that the player's X, Y, and Z are consistent and they move "down" based on the direction relative to the portal. They can actually do the vector reorientation ahead of time, since the portals neither move (relative to down; they may translate linearly, but down doesn't change) nor spin in place, so down relative to a given portal is fixed. This becomes even easier when you realize that the surfaces onto which you can affix a portal tend to be vertical, horizontal, or at a 45 degree angle.

This has the benefit of providing "free" momentum conservation, because the momentum is relative to the player's coordinate grid, not the world's.

Re:WTF

[Anonymous Coward]

it's talked about in the commentary of the game. They use a small, secondary physics world and the collision hulls are cloned into it when they're in the presence of a portal.

Re:WTF

[ABoerma]

If the direction is changed, the vector values are not retained. Or are you arguing that (3,4,5) and (-7,1,0), for example, have the same values?

Re:WTF

[Fractal Dice]

how else could it do what it does?

OK, I'll bite. What's the force of gravity through a wormhole? If one end is in space and the other end is at a planet's surface, does a floating person accelerate towards the wormhole at 9.8m/s/s? Or does the atmosphere escape out into space because gravity isn't holding it in? Does going through a wormhole give you the bends?

(asking a geeky open-ended question about mythical tech on slashdot is dangerous)

Re:WTF

[billsnow]

i'm arguing the velocity vector is the same, in relation to the plane of the portal

Re:WTF

[srjh]

Another physics nitpick: It doesn't translate the velocity either, it rotates it.

Translation is a completely different transformation.

Re:WTF

[DeKO]

"Preserving momentum" is just a matter of rotating the velocity to the new orientation. Some complications may arise when a complex system of interconnected bodies goes partially through the portal (e.g. you can't move just one body to the new location, or you'll violate the joints' constraints). Other than that, ODE can trivially support "portalling" bodies. Make sure to create contact joints in the proper places (they must be relative to the body).

Re:WTF

[duckInferno]

Matt Damon.

Re:WTF

[shaiay]

Actually it's PHYSICS 101, not game programming 101, and he was being sarcastic ..

Re:WTF

[Dutch Gun]

Lots of things sound pretty simple when described in nice, clean theory. As a game programmer, I can assure you that the devil is ALWAYS in the details. You're correct that the basic physics of conversation of momentum are simple enough. What's tricky is fixing all the edge cases that invariably pop up when trying to write physics code in a game.

I'd recommend listening to the Portal commentary to hear some of the specific difficulties involved in getting everything working smoothly in all cases. You'll notice that the descriptions tend to bear this out - that the basics were pretty easy to get right, but it gets harder as you find and fix all the edge cases and optimize.

Re:WTF

[Goaway]

If he was, it was pretty clever.

Although it's still not really physics.

Re:WTF

[Steauengeglase]

I get that the portal is just a decal, the part that bugs me is when you have a portal that can view another portal.
How many portals do you draw before you decide to simply put a little orange or blue blob in the center/side/where ever. Also when you are in a large area and you fire two opposing portals at a far end whose textures haven't been loaded yet, how do you keep the game from crashing (I've had the big room towards the end slow down to a crawl but never actually crash)?

Re:WTF

[BigJClark]

This is true, this is true... but it is still fun to read people overcomplexify (yes, a word I just made up on the spot) an issue that at bare bones (save edge cases, as you described above) is 2nd year linear algebra :)

Re:WTF

[Anonymous Coward]

You're right in the context of the portal, but in general, the GGP would be right if there were no additional contextual clues.

slashdot version

[extirpater]

According to portal theory in some place, this comment is the first!

My big question

[Zerth]

If you could put a portal on a fast falling object, when it lands on you while you are standing still would you have momentum at the other of the portal or would you just poke through since the portal has the initial momentum? (IE nonplayer movement being different than player movement)

What would that say about your reference frame? Could you use that to distinguish which of two objects had "universal frame" movement? That'd be kinda neat, theoretically, but it'd be way more interesting to be able to put a portal on a crate hanging from a crane, then make the crate fall while standing under it to catapult yourself from a low position.

Re:My big question

[geekoid]

You could use to portals to create a geekoid friction bomb.

Just put one on top of another and but a steel ball so it keeps passing from one portal to another until it gets so hot to ignites the air.

Re:My big question

[director_mr]

I think you just helped Valve come up with some concepts for Portal2. That would add a bunch of fun to the game.

Re:My big question

[Erbo]

Well, in Portal, if an object that has an open portal on it moves, the portal disappears, and the "other end" of the portal is blocked. Hence tricky puzzles like the one in Test Chamber 18 to reach the storage cube. That one was a cast-iron bitch to figure out the first time. (Not going to give it away for the six people who've never played Portal...)

Re:My big question

[ikkonoishi]

Ah but the air would also be falling through at the same speed. If you put a portal on the ceiling and floor of a closed room then soon the small difference in air pressure from the top of the room to the bottom would create a howling vortex.

Re:My big question

[pla]

Just put one on top of another and but a steel ball so it keeps passing from one portal to another until it gets so hot to ignites the air.

The portals don't actually increase the velocity of what passes through them, they just redirect it. So the trick of putting two portals vertically aligned basically simulates "falling" for a much greater distance.

You would still (if in an atmosphere) reach terminal velocity rather quickly, however, so no vaporized metal (or human) explosions will happen.

Re:My big question

[Zerth]

Well, those were part of the "test". They (or the mechanics of the portal) were coded to dispel on movement. If that weren't the case, I'm curious how portal velocity would affect player velocity.

They already used the "portal keeps you from being slowly squished" trick, I'd like to see it with faster SMB-Thwomp style traps.

Re:My big question

[Apache]

Your velocity relative to the old portal's frame of reference becomes the velocity relative to the new portal's frame of reference.

For example, if a person falls straight down into a portal on a platform moving 5 m/s, and the exit portal is on a stationary floor, the person will hurl upward out of the stationary portal with a horizontal component of 5 m/s. Which way the person goes depends on the orientations of the portals. Flip either the exit or entrance portal and you'll go the opposite direction.

Sounds like a fantastic idea for portal 2. :D

Re:My big question

[Anonymous Coward]

It doesn't make a difference if the portal is moving to swallow you, or if you are moving into the portal.

You have a certain velocity WITH RESPECT TO the portal when you enter the it. Keywords: with respect to. This is all that matters. The velocity is calculated into momentum and that equals how much momentum you have exiting the portal on the other side.

So whether you were entering the portal or it was swallowing you, you will always be shot out of the portal a bit.

Furthermore it would technically be impossible to enter the portal without having respective momentum in relation to the portal. You would always get shot out of the portal, if only a smidgen.

Re:My big question

[Anonymous Coward]

Think of it in reverse. If you stepped through a stationary portal, but the other side was speeding along, you'd either wind up becoming a fine mist spread all across the space that the portal was moving through, or squished into a pancake, depending on which way it was going.

I believe that a portal should only convey motion of objects passing through. Of course, anything that can be expressed in code can be done in a video game, and it would make an interesting game mechanic...

Re:My big question

[Z80xxc!]

Portals cannot be placed on moving surfaces. Furthermore, if a surface begins to move, then any portals on it will self-close. For example, in level 18 (iirc), there is a panel that comes out from the wall and sticks out at a 45 degree angle. You need to place a portal on there in order to jump across the water and get one of the cubes. The panel only stays out for about 10 seconds; after that it goes back in and the portal closes as soon as the panel begins to move. If portals could exist on moving objects, then imagine if you put one portal on the floor, and took a piece of plywood just big enough for the other portal, placed the portal on it, and chucked it through the first portal. BOOM! Divide by 0 and the whole world ends.

Re:My big question

[meringuoid]

Portals on objects in relative motion lead to serious business.

Consider: we attach a blue portal to a wall aboard the starship Aurora, and an orange portal to a wall aboard the starship Borealis. Aurora stays home, while Borealis takes off on a high-velocity cruise to Alpha Centauri. On its return, thanks to relativity, the Borealis ship's clock shows an elapsed time of one month, while the Aurora ship's clock shows an elapsed time of eight years. At the blue end of the portal, many years have passed, while at the orange end only a few weeks.

Are my two portals now a time machine? Can I enter the portal at the Borealis end and emerge on the Aurora seven years and eleven months ago?

This is probably why portals can only exist in an inertial frame of reference, and disappear when subjected to any acceleration.

Re:My big question

[dhTardis]

If you could put a portal on a fast falling object, when it lands on you while you are standing still would you have momentum at the other of the portal or would you just poke through since the portal has the initial momentum?

It would only make sense for the falling crate to launch you; when it has fallen enough to put your head through the portal, obviously just your head sticks up out of the other end (on the floor, say). Then, a moment later, all of you exists on the other side, so your head must have been rocketing up at the same rate as the crate was falling (to make room). Your head could not then suddenly stop just because your feet happened to make it through. (So it would suck if you were standing in a foxhole and the crate were stopped by hitting the edges of it!)

If it could: suppose that you were standing on a narrow tower which would also fit through the portal as the crate fell. Then, if you stopped moving when you finished the traverse, you would immediately be skewered by the tower coming up after you. (We could say that you would keep going because you were standing on something that was coming through, but then the slightest of hops as the portal passed your feet would suddenly change everything.)

What's interesting about this is that the air that the crate is falling through (around?) does the same thing, and erupts from the other portal as a jet. No fluid could exert a pressure on the (part of the) bottom of the crate covered by the portal, so the crate should get sucked down even faster than gravity and create quite an updraft. A styrofoam block could be sunk into the ocean by attaching a portal to its base, creating a rush of hundreds of thousands of gallons of seawater from the other end. Putting one end of a portal on top of something and the other end on one of its sides would create an airplane as the pressure was applied only to its bottom and the other sides.

There's a way around these bizarre results: say that at each portal, the momentum that each object carries into or out of it (in the portal's reference) frame is assigned to or derived from the object backing the portal. That is to say, a heavy object entering a portal would bend the wall the portal was on in the same fashion it would if the portal weren't there and the object were simply hitting the wall. Then the falling crate would still have air pressure on it; the downdraft it should be creating (but isn't because the air isn't being forced aside) would simply be felt wherever the other end was. And when the crate engulfed you, it would slow down drastically (unless it were much heavier than you) and the result would be rather like it was launching you off the other end of a normal springboard, except that it would pull you up by your head — the part of you that encountered it when it was moving fastest.

you are doing it wrong

[Anonymous Coward]

the comments go in the code

Portalized

[TypoNAM]

Somebody using Ogre3D has been working on a portal like project for nearly a year and has made pretty damn good progress for somebody who was new to game programming:
http://www.ogre3d.org/phpBB2/viewtopic.php?t=37376

He also has a blog which seems quite lacking though.

Physics?

[sanosuke001]

I don't know... without RTFAing this seems to be a pretty straightforward problem.

If you wish to "teleport" an object, find the objects vector, find the difference from the portal's normal, move said object to front of connecting portal, dot the difference vector you got from before with the new portal's normal, keep velocity/acceleration constant.

Now, there's more to be done with making it look like the player is actually travelling through the portal. But, the movement itself seems quite simple...

Re:Physics?

[sanosuke001]

Note: you would have to reorient the initial offset from the first portal's normal to match the orientation of the second portal's normal. Oh, and normalize all vectors.

Re:Physics?

[KeatonMill]

The problem is that this is an instantaneous teleportation. The portal is more like you take the destination room and paste it into the starting room. Objects can go halfway through the portal, sit at rest, and collide with things on both sides of the portal *at the same time*.

According to the commentary, what they do is create a sort of hybrid collision zone when objects that are subject to dynamic physics calculations (i.e. the player, blocks and balls) near a portal.

The big question you are all missing is:

[Anonymous Coward]

Could we use these highly advanced computer programs for these portal tubes on the tubes that power the internet?

blitz3d & coding... while we are here

[erbbysam]

this isn't even coded correctly in blitz3d...
When you align the portals they flicker because blitz3d cannot handle 3d objects right on top of each other. The easiest fix for this is to move the portals .001 "blitz3d distances" away from the wall.

... my copy of blitz3d is lost but there definitly right about using it to create quick 3d stuff

Portal Physics 101

[xPsi]

In the game, GlaDOS says "momentum is conserved through the portal." Assuming our physical system is the character, momentum definitely is not conserved. Neither is energy. The description "the player enters point A with full velocity and exits point B with the same speed, but moving in a new direction" is exactly correct: a textbook example of momentum non-conservation. However, what drives the exciting "flinging" effect, which makes Portal's teleportation so unique, isn't just momentum redirection. It's that you instantly obtain the potential energy of your exit location. This new potential energy can be converted back into kinetic energy, increasing your speed...mix in a little momentum redirection at the portals then wash, rinse, repeat. Although GlaDOS describes the game physics incorrectly, there is a game walkthrough where the programmers do describe it correctly. If you take any physics courses from me, you can expect to see some Portal questions on future quizzes :) Nice article overall.

Re:Portal Physics 101

[Tacvek]

TO be fair, the magnitude of momentum is the same. Most regular people consider velocity to the the magnitude of the physics velocity vector, and momentum as the magnitude of the physics momentum vector.

The potential energy change is not very unique though, as games do not care about potential energies. Only current kinetic energy is ever important. Thus any sort of portals in a game where the that have different 'z' values would have that attribute.

What is really unique about Portal is the portal visuals.

Re:Portal Physics 101

[rk]

I never really thought about that before, but you're right. The portal gun is also a perpetual motion engine. Put a portal above a paddle wheel, and a portal below the paddle wheel. Add enough water to get the paddle going, and poof. Power until enough water evaporates that it can't turn the wheel anymore.

Re:Portal Physics 101

[lgw]

Nope, momentum *is* conserved, it's just that space is no longer a metric. Portal's portals don't teleport, they join distant portions of space so that you pass through them continuously. You do *not* conserve potential energy - teleporting from higher to lower does not "fling" you: your speed is the same as before.

Re:Portal Physics 101

[ThePiMan2003]

Isn't momentum conserved from the frame of reference of the person traveling through the portal? From a fixed frame you are right, I head into a portal going one way, and come out going another... but from the frame of reference of the person entering the portal you keep moving the same way the entire time.

Re:Portal Physics 101

[xPsi]

The difference is that person's frame is non-inertial because it is accelerating (i.e. their velocity vector and speed are changing). Motion is usually best analyzed in an inertial frame (e.g. the fixed frame of the infrastructure).

Re:Portal Physics 101

[Atzanteol]

Sooo... Speedy thing goes in, speedy thing comes out?

Re:Portal Physics 101

[Anonymous Coward]

TO be fair, the magnitude of momentum is the same. Most regular people consider velocity to the the magnitude of the physics velocity vector, and momentum as the magnitude of the physics momentum vector.

if what 'most regular people' thought about physics was remotely important, i think we'd all be screwed. if people are going to talk about a physics term in a physics context, it should be used correctly, no?

Re:Portal Physics 101

[daver00]

So on a slightly off topic note, does that invalidate the theory of 'wormholes' for some hypothetical FTL space travel? Surely, were it possible to create a wormhole in spacetime, you could set up a perpetual motion machine that works exactly like you describe, thus violating the second law. A nice simple thought experiment, I like it.

Re:Portal Physics 101

[Agripa]

Larry Niven's "Theory and Practice of Teleportation" goes into some of the fun ways such a system can cause some really large problems culminating with building a thruster capable of changing the earth's orbit. A more likely result though would be a short war until we get back to pre-portal technology.

Re:Portal Physics 101

[Anonymous Coward]

No, because the theory is to open that wormhole and keep it open, requires enormous amounts of energy, enormous amounts of energy. Plus, everything you send through that wormhole, increases the energy the wormhole demands by mc^2 or something. And what happens to your own personal wormhole? Well, unless you have enough energy, it starts to close and gets clogged up.

Re:Portal Physics 101

[DanielLC]

(Note: I'm not very good at explaining these things, so if someone paraphrased it, you should read that version. If not, then please paraphrase this so everyone else can understand it.)
She doesn't say that momentum is conserved, she says it's conserved "through the portal". This may very well be a mistake, but it makes perfect sense for the following reason:
The definition of momentum involves direction, but using the portals, it is possible travel from point a, through the portal, and back to point a, without turning, but still be facing a different direction. Since you haven't turned, you must still be facing the same direction. The only way to reconcile this is to make direction dependent on the path taken. You end up facing a different direction taking the path through the portal (comparing the two directions without going through the portal, of course) in a similar manner as how you may go further taking the portal, but still end up in the same place. This all applies to momentum too, so your momentum is conserved through the portal, but not, for want of a better word, around the portal.
As for the programmers talking about it differently, this could be due to it being a mistake that coincidentally works, it be interpreted differently by the programmers then by the script writers, or it could be because in the actual program, rather than the story, direction not only comes out the same no matter how you compare it, but there's actually absolute directions. For that matter, there's also an absolute rest, an absolute origin position (i.e. the coordinates (0,0,0)), and many other things that don't exist in real life.

Incidentally, everything I said about the Half Life universe applies in real life. It makes an all-but-imperceptible difference which path you take (unless you get really close to a black hole or something like that), but it makes a difference nonetheless.

Re:Portal Physics 101

[DigitAl56K]

Assuming that it takes less energy to transport the matter and energy through the portal than the wheel generates, and that gravity is never exhausted, which sounds like an obvious assumption but if the gravity is being converted to energy doesn't that mean that whatever is causing gravity must be changed so that it looses energy/mass?

Re:Portal Physics 101

[Dr. Cody]

Actually, there's a "conservation whipping boy" in a hidden room of each level getting pummeled against the wall of his cell to account for inconsistencies arising from use of the gun.

Re:Portal Physics 101

[Anonymous Coward]

No, momentum is conserved, but the portals make the co-ordinate system weird.

Going through a portal isn't equivalent to disappearing at one point in a room and reappearing at another, it's equivalent to moving from one room to another - oriented differently - through a hole with momentum conserved.

Re:Portal Physics 101

[Anonymous Coward]

moving while changing orientation implies momentum is changing too due to some force

Re:Portal Physics 101

[Anonymous Coward]

I would say that from the perspective of the Portal, momentum IS conserved. As far as the portals frame of reference is concerned, you're travelling in a straight line.

Re:Portal Physics 101

[Tacvek]

The audience of the game though was most certainly not physicists, and to that extent arguing about the game's internal claim of momentum conservation is quite absurd. Furthermore, as far as the object traveling through the portal can tell, momentum of itself was preserved, but the orientation of the rest of space-time was not conserved.

Re:Portal Physics 101

[pfafrich]

It depends on how you model the topology of the space. If you take space to be standard R^3 with teleportation then momentum is not conserved. If however you take space as being a 3-manifold with some handles joining disparate parts and define local coordinate systems (i.e. charts) then momentum is locally conserved. You do however loose the convenience of having a global chart. Taking a 3-manifold approach does cause problems with gravity which becomes discontinuous field, which leads to some interesting physics.

Re:Portal Physics 101

[Anonymous Coward]

There's a very good Larry Niven essay on this topic of using portals (teleportation) for space travel, not sure of the name off of the top of my head, but definitely worth the read.

Re:Portal Physics 101

[MynockGuano]

The Ones Who Walk Away from OmeLAS?

So....

[jeffy210]

Instead of simply repositioning an object from point A to point B, the player enters point A with full velocity and exits point B with the same speed, but moving in a new direction.

In other words, speedy thing goes in, speedy things comes out?

The physics is actually fake.

[Animats]

There's a fair amount of fake physics involved. Properly, the parts of the character on one side of the portal should have the gravity and momentum of that inertial frame, and as the character passes through the portal, the new frame should begin to act on the character. But the sample code in Gamasutra treat the character as a single rigid body.

It's a neat problem to make the physics correct as the character moves though a portal. It could certainly be done, even for ragdoll characters. From a gameplay perspective, it would drive players nuts. To make the gameplay tolerable, the designers of this game added a pseudo-force that tends to align the character with the local vertical. Otherwise, characters would have execute proper parachute landing falls when moving through a gravity vector change.

Character physics almost has to be fake. Trying to drive a real car via a game pad is very difficult, and trying to drive a human body via a game pad is worse.

Re:The physics is actually fake.

[brkello]

Hate to burst your bubble...but video game characters have no mass...so ALL physics in the game would have to be fake ;)

Re:The physics is actually fake.

[lgw]

Technically, the force of gravity should also pass through the portal, providing a smooth transition of forcesm, not a discontinuity. That would be interesting, but I think less fun. The way that the direction of gravity changes abruptly as you move through a portal is part of the charm.

Re:The physics is actually fake.

[4D6963]

A bit off topic but it may also be of interest to note that there's a fair disregard for air drag. The proof is that if you make two portals in a same floor, and jump into one, you'll reach the same heights indefinitely whereas air drag should gradually make you go lower and lower.

On and as for the points you brought up, the Portal "character" is one of the "singularity in a box" type. I.e. it's treated like a singularity but is inside an invisible box that keeps it to a certain distance from anything to act like it's a body. The human appearance is very accessory.

Re:M.C.Escher has good OLD examples of the concept

[isomeme]

http://www.phespirit.info/momus/19980102.htm

They omitted what Portal actually does.

[Sockatume]

Portal exploits portal rendering technology - a technique for graphics optimisation which incidentally allows you to take a given map layout and provide a different subjective layout for the player. It's actually a fairly trivial problem to do the portals themselves, as most graphics engines these days should have portalling built in. All of the interesting physics comes in when they start making it work as gameplay, for example by giving portal entrances "push" or "pull" to steer players into and out of them. The article is a good description of how to make a game that behaves a bit like Portal, but it's got nothing to do with that game's actual physics.

Re:M.C.Escher has good OLD examples of the concept

[Anonymous Coward]

Ahhh, good ol' Momus. Does he ever change that eyepatch?

Havok...

[Enki X]

Halo 3's teleporters do this...I had loads of fun in forge making portals to cliff edges in front of 'human propulsifiers'

Re:M.C.Escher has good OLD examples of the concept

[Chris Burke]

Speaking of, whens he gonna put a new album out?

Are you talking about M.C. Escher who designed the crazy staircase house? Or David Bowie, who lives there?

the cake is a lie

[Anonymous Coward]

the cake is a lie

No kidding

[Moraelin]

No kidding. The whole "frictionless tube" thing is just thinking too hard about it. Yes, instead of simply repositioning an object from point A to point B, you also take the normal of both holes and change the direction of the velocity. That's it. It solves the same problem and produces the exact same result without doing physics for a frictionless tube.

Re:No kidding

[RobinH]

What's more interesting to me is that you can look through the portal and see what's on the other side, including the object that just went through. In fact, you can put two portals on the floor beside each other, drop an object into one and you basically see two copies of the object oscillating alternately. If you stand near the portals you can see the object in two places. I just think that's neat.

Re:No kidding

[Ahnteis]

Serious Sam had some incredible portals like that. :)

Re:No kidding

[Scott Carnahan]

Yes, instead of simply repositioning an object from point A to point B, you also take the normal of both holes and change the direction of the velocity.

If you want to get a uniquely defined map, you need to specify an identification of the tangent spaces of the holes. I agree that the reference to physics of a frictionless tube is superfluous, but in addition to your suggested transformation, the article presumes a specified framing, and gradually rotates the character to be oriented upward upon exit.

Re:No kidding

[poopdeville]

Normal to the hole? Since when are holes surfaces? I don't think you realize how difficult topologically characterizing a hole is.

Pacman

[BattleHawk]

"that wasn't the first game to use teleportation as a gameplay mechanic...the player enters point A with full velocity and exits point B with the same speed, but moving in a new direction"

Sounds like they re-invented (ms)Pacman(jr)

Re:Pacman

[SBacks]

Pacman just ripped that off from Asteroids.

Grossly Oversimplified

[p0tat03]

Portal's physics go *way* beyond what the article implies.

Article basically says: it's not a simple teleport, direction of movement and momentum are preserved.

This is far too much of an oversimplification. Portal was probably a technically difficult game to code for - mostly due to collision physics. The problem is that something does not instantly teleport from one end of the portal to another. You can have an object on BOTH sides of the portal. This makes physics calculations very difficult, since you essentially have a single object of a small finite size, colliding with different objects across the room, affected differently by gravity, etc.

If I get the right gist from the developer commentary in the game, their solution was the CLONE the two sides of the portal in a mini physics-only environment and run the simulation there.

Definitely much more complex than the article.

Re:Grossly Oversimplified

[hvm2hvm]

Yeah and the commentary also said that the calculations involved were too complex to make it work fast enough so they had to lower the resolution of calculations in the portals.

Re:Grossly Oversimplified

[electrosoccertux]

What you just described is nothing I didn't do in calculus-- splitting an object somewhere and calculating the volume->momentum of that piece, doing the other side, and summing the resultant vectors.

Re:Grossly Oversimplified

[Anonymous Coward]

Yes, but did you write a physics engine based around that that was fast enough to run in realtime on hundreds of objects at once on your average desktop computer?

Re:Grossly Oversimplified

[4D6963]

Allow me to disagree with that statement. In my view, objects are treated as a singularity (their barycentre) with a "collision shape" around (the actual object you interact with). Since you only have two portals anyways, all you have to do with keep calculating the physics for just the singularity, and as for the collisions, calculate them once for the side of the portal the singularity is on, and just do them once more for the other side, simply by translating the shape's coordinates there.

Please do point out any flaw in my reasoning, but the way I see it it's nowhere near as complicated as you make it out to be.

Re:Grossly Oversimplified

[Workaphobia]

As long as we're ragging on the column, I read this in the Galaxy article:

Intensity of Gravity = 1 / Distance2

This means that as an object moves closer to a planet, the gravity between them
increases dramatically due to the exponential effect applied by distance.

I *hate* it when people abuse the word exponential.

Re:Ahhh

[MobileTatsu-NJG]

I got a great blow-job last weekend. It was like she was making out with my dick.

It was wonderful.

And when you were done, did you type 'afk' and light a cigarette?

Cake...

[AnomaliesAndrew]

I wonder if that's where the cake got to...

Re: You sooo Phunny.

[IdeaMan]

I played that one all the way through too. It seemed to me that the portals worked a little differently than in 3d portal.

What was confusing to me in the 3d portal was how your orientation on exiting the portal would change based on the orientation you shot the portal from.

teleportation vs. wormhole travel

[dwights]

i actually thought that the portal travel method seemed more like wormhole travel, something liek stargates in Stargate, than teleportation, as we are accustomed to in the startrek generation (geek reference).

Wormholes create a direction connection between two points in space/time that allow energy and matter to pass through directly. In the case of the portal game, you can actually see through the wormhole in both directions (rather than what looks like a 'water' event horizon", even to the point of looking at your self in both sides of the event horizon.

As I understand the physics of teleportation, the device would deconstruct the matter into energy, sends it from point a to point b along a 'path', and recontructs it at point b.

thoughts? :)

dwight.

Actually not obvious

[Anonymous Coward]

The article talks about the easy part, and not the hard part. If you listened to the game's commentary (or just tried using your brain, maybe) turns out it's not obvious at all.

For instance, how do you handle mechanics where an object can collide with something while it's half-way through the portal? Or two things that are half-way through a portal colliding with each other? How do you write graphics for something that can display an object in two places, two environments at once, as well as see-through holes to different parts of space?

Re:Actually not obvious

[4D6963]

You said it yourself, the article talks about the easy part, which is obvious. The harder problems you raised are more interesting.

With this and the LHC documentation...

[Anonymous Coward]

Teleportation is at hand. Maybe even quantum teleportation!

First game to have teleportation...

[slashname3]

Wasn't the first game to have teleportation Zork?

XYZZY

Re:First game to have teleportation...

[Mr2001]

XYZZY appeared in Colossal Cave before Zork, but Spacewar had teleportation (hyperspace) over a decade earlier.

Not really

[Sycraft-fu]

Started neat but quickly degenerated in to something all to typical with flash games: You have to have really fast reflexes and figure you the logic apparent only to the designer. Neat technically, but the gameplay needs work.

Re:Not really

[LordKronos]

Wow. I thought it was excellently done. There was nothing at all unintuitive about the game, and I played it all the way through. Yes, it was challenging to figure out some of what you need to do, but it's a puzzle game. I didn't think it needed much in the way of reflexes. I mean, sure my grandma couldn't complete it, but anyone reasonably agile with a mouse and only average reflexes could accomplish what needs to be done. Figuring out the solutions was way more challenging than executing them.

For ever cool idea, there is already an SF short.

[kohaku]

And with that, I give you "Approaching Perimelasma" by Geoffrey A. Landis: http://www.infinityplus.co.uk/stories/perimelasma.htm

M.C.Hammer has good OLD examples of the concept:

[Anonymous Coward]

These two were my favorites:

http://www.mcescher.net/images/relativity.jpg (1953)

and

http://www.mcescher.net/images/houseofstairs.jpg (1951)

The last one could be done in prey with the adjustable gravity vector. Now as for the Duke 3D engine. We lost that whole sector ability when we went with true 3D.

Original source

[Anonymous Coward]

I'm not a pheasant plucker
I'm a pheasant plucker's son
And I'm only plucking pheasants
Till the pheasant plucker comes!

Re:Original source

[Anonymous Coward]

I'm not a pleasant fucker
I'm a pleasant fucker's son
And I'm only fucking pleasant
Till the pleasant fucker comes!

Asteroids anyone?

[mfnickster]

Didn't Asteroids have prior art on this..? :)

Re:Asteroids anyone?

[MagusSlurpy]

Didn't Asteroids have prior art on this..? :)

That's what I thought when I read this sentence:

Puzzles from the original Gauntlet were memorable -- and more than likely, that wasn't the first game to use teleportation as a gameplay mechanic

Re:Asteroids anyone?

[ZerdZerd]

I didn't see any companion cube in Asteroids.
Hidden level?

Portal, shmortal... Unreal had this in 1998 :)

[Roman Mamedov]

Unreal had better-made portals in 1998. Too bad we don't see more of those in today's games.

Not a tube, direction doesn't actually change.

[Anonymous Coward]

His programming may certainly work to duplicate the effect of the Portal, but the physics portrayed by the game world are a little different.

First, it's not a tube, it may have an effective 'depth' of Zero. It certainly doesn't exceed 1cm at the worst case. Find a spot in the game with a corner, you can arrange things so you can see yourself from both Portals. It's very apparent at that point that their is either no 'depth' to the Portal, or it's so small you really can't perceive it in the game.

Second, objects passing through do not change direction. Their direction and velocity are the same as when they entered. To an outsider, it appears as though they change, but that is an illusion. Just remember that the Portal is a connection through space. Relative to the object passing through, it hasn't changed direction, rather everything else changed location. As far as it's concerned (or her, if you really want to stress the game character)a simple continous vector was followed. Though it may have been a ballistic or falling arc, and the forces of gravity may have shifted direction, the subject was simply following a basic newtonian trajectory through the local spacetime. (A spacetime with a doorway or wormhole in it.)

Like I was saying, the authors coding of the software to duplicate this effect was fine, but it's not the same thing as the physics it represents in the game. After all, even our most complex simulations of reality take very liberal and unrealistic shortcuts to make things happen that do not represent the physics involved.

(It's like someone watching original Star Trek and proclaiming that the Transporters use a photon based array transfer because I can see the Christmas lights they used in the transporter pad...)

Re:Not a tube, direction doesn't actually change.

[BlackCobra43]

So what you're saying is it's more like a portal truck then a tube.

nothing new

[Anonymous Coward]

What the hell? the original unreal had the same portal technology as "portal" so it is nothing new techwise. All they did new was base the gameplay around it.

Pac-Man?

[Anonymous Coward]

Pac-Man had the slide door....

Prior art patent, from 1995

[Anonymous Coward]

Prior art?
http://www.patentstorm.us/patents/5414801/description.html

Once a plurality of three-dimensional polyhedra are defined, the connections therebetween are also specified. A connection is a logical construct which relates a surface on one polyhedron to the surface of another polyhedron. In one implementation, connection may only be maintained among polyhedra surfaces that lie in a single plane. However, the planes do not have to be in the same physical space, with overlapping and congruent surfaces. Since the connections are logical connections, any polyhedron can be connected to any polyhedron regardless of their physical connection to one another. The renderer, upon finding the logical connection, will start rendering the model based on the connection. This property allows portals between volumes that do not necessarily map into the same space. For example, several large rooms that would normally conflict in space could be connected to a surface of a small lobby to allow easier, quicker navigation between the large spaces.

It's exactly the same.

[DrYak]

So the transporter didn't preserve the rocket's momentum - it just put the rocket at a new location, and the game then resumed moving the rocket forward.

From a engine coding point of view, i fail to see how there's any difference.

In both cases, you have a vector attached to an object which describes how an object move :
- you can call it "trajectory" for shots
- you can call it "momentum" for portal
but technically it's just plain stupid "speed" vector. As in "derivative of the position" (= how the position is updated between each turn).

Eventually, if it's not a rocket, it will also obey to an acceleration (most of the time : gravity. But it can be buoyancy).

In both situation, all you have to do for any object entering a teleport, is simply change the current coordinate of the object, and eventually perform a transformation on the speed vector if both teleport end point aren't facing the same direction.

From a coding point of view portal doesn't introduce anything new for the physics that wasn't already done by any of all the multiple game that allow shooting through a portal or *jumping* through a teleport.

The new thing are the rendering engine (not all engine can easily render see-through portals - due to the way the work, Duke 3D's and Descent [portal based] and Wolfenstein and Doom [raycasting] could do them, but Quake 1 & 2 [BSP polygons] can't)

and the gameplay (before portal, teleporting thing other than the player was a fun by-product of how teleport work and can enable a couple of giggles. Portal in contrast has all its puzzle based around throwing object through portals)

Law of Conservation of Energy

[kaos07]

Portal breaks it!

Say I have my entrance portal at the base of a cliff and my exit portal at the top of the cliff. At the bottom, I have zero energy. Once I enter the portal and end up hovering for that split second at the top of the cliff, I have quite a lot of potential energy. Doesn't work!

Portal renderer

[DrYak]

Because the duke engine is basically a (2D) portal renderer.

The world is represented as a series of convex sectors.
Then sectors are connected together by sharing 1 side. The renderer works by painting the wall of the current sector. When a sector edge isn't a wall but a connection to another sector, the renderer start painting the opposite wall for the connected sector.

The good thing is that, as you mention, it is possible to design things that can't be laid on an actual 2D map, simply by allowing sectors to be connected in more original ways (is possible to build staircases which point to 2 different sectors, it's possible to build strange design were 3 square rooms are all connected together, etc...)

This approach also come with support for see-through portals and mirrors for free (a mirror is simply a sector connected back to itself). Although I don't remember if they actually used the see-through ability in Duke.

The other good thing (the main reason it was done this way) is that it speeds up considerably the render speed as the system knows very precisely which walls are visible. (If i remember correctly, Descent used a similar approach but in full 3D - in order to consider for rendering only the couple of room connected to the current one).

Re:Portal renderer

[SanityInAnarchy]

The world is represented as a series of convex sectors.

They couldn't be concave? I'm not sure.

Although I don't remember if they actually used the see-through ability in Duke.

I think that's what the glass was -- I seem to remember much more flexibility in shaping the glass than you might have with a simple sprite.

The good thing is that, as you mention, it is possible to design things that can't be laid on an actual 2D map

Indeed -- though I would imagine that a modern 3D portal system (even partially), given a good map editor, could allow similar things. (Speaking here of things you could do in Duke which you can't even do in a proper 3D map.)

Re:Portal renderer

[Anonymous Coward]

This approach also come with support for see-through portals and mirrors for free (a mirror is simply a sector connected back to itself). Although I don't remember if they actually used the see-through ability in Duke.

IIRC the Build engine mirrors used another sector (added by the map designer) that mirrored objects, walls, etc. when player was within sight of it and in the mirror sector's area

This dwarf?

[Anonymous Coward]

The dwarf with a huge dick fucks the shit out of our heroine and it seems like the best sex in her life...

"Haven't you ever seen such a big toy, Frau? Especially if a dwarf has it, right? Haven't you been fucked by such a big dick? Well, check it out!"

I was overwhelmed by curiosity and fear. His dick looked really luring but it was so big it could literally tear me apart. But⦠I just wondered what I would feel with such a cock inside me?

His hands spread my hips.

"See you're leaking girl! I'm gonna show you what a real hardcore fuck is like!"

He entered my snatch with his dick. At one thrust! When I regained consciousness I felt his dick screw me. The frictions seemed to echo in every single cell of my body. I was crying and... trying to impale myself more on his prick. It hurt but it was so awesome! What a wonderful penis he had! C'mon boy, fuck me harder! I was cumming...

He told me to turn round and get on my knees. His shaft got back to my stretched pussy, getting deeper in my womb. He was trying to reach for my tits with his short hands. I was trying to help him with it... But I just couldn't move, his stem didn't let me move. Well, seemed he realized it was mission impossible and he just started squeezing and caressing my hips and my ass. Wait a minute... he wasn't caressing my butt. He was lubricating it!

"You shouldn't do this sir..."

"Oh, yes, I should Frau!"

Hardly had I had rest after that wonderful orgasm as his stem entered my asshole⦠it was more than I could take, both literally and figuratively. He was drilling my ass getting deeper in my rectum. Man, those were brand new sensations, the feeling when my butt lost virginity two days ago was nothing in comparison with the dwarf's wild ass ramming.

The orgy was so exhausting for my body I lost consciousness for a couple of minutes. When I opened my eyes my lover was caressing my boobs. I felt like my butt hurt, guess he'd torn it apart... But there was no time for self-pity; I had to get back to work. My client told me to suck his shaft off. Man, the dick was so huge I just couldn't get it in my throat. Well, I'd better use my cunt...

He was lying on his back I mounted his member carefully and slowly. I started riding the dick, the dwarf moaned approvingly trying to screw me deeper. I stopped him gently and took full control over the tempo and the depth of penetration. That felt much better, for both of us. He was smiling, grinning, giggling, and moaning.

Damn, my ass hurt... I was probably too absorbed in my own sensations and didn't notice him push me downwards and enter me very-very deep. Ohhh God!

When I opened my eyes, my client was zipping up his pants. He gave me several crispy bills and said:

"Thank you so much Frau Lotta! You're the first woman for the last three years who managed to satisfy me. Sorry for hurting you."

I couldn't even reply, all I could do was moan and blink my eyes. Yeah, it was the most unforgettable fuck for my entire life! My holes were swollen, red and aching. I had to get up and go to the hall but I couldn't move.

Loren knocked on the door.

"Hey don't move Liz... it's ok. Frau Dort said it's enough for you for today. You're the first who managed to please babe Henrich!"

"What???"

"Well, you saw his pecker. He can't find a woman to have sex with, no street whore or brothel slut agrees to sleep with him. You were great, girl! We were watching your show on TV in the hall. There were all the girls and all clients there. You've earned a hell of money today, babe!"

"What about your show, Loren? How many hours did you spent with Schulz? Seven? More?"

Loren screwed up her eyes, caressing her boobs automatically.

"You know Liz, I'm getting married. To Schulz!"

WHAT??!!

"How come?" I asked, still not believing my ears.

"Well, we just thought we could make a nice couple -- a scientist and a whore. He will teach and I will please. We'll marry as soon as I'm through

Wrong

[justinlee37]

Pac-Man, however, never changed his acceleration, so the speed at which he entered and exited any portal was never in issue, it was constant. Additionally, the teleportation happened off-screen -- in Portal, you can actually look THROUGH the portal out to the other side. In summary, Portal is more complicated than Pac-Man by many degrees of magnitude because the portals themselves entail more variables.

Re:Wrong

[Anonymous Coward]

Pacman didn't really have a speed. IIRC he had a 32 bit bitstring of which each bit which meant move/don't move one pixel, which was evaluated twice per (60Hz) frame. So it sort of was a speed, predithered over a quarter of a second. The string was different for the tunnels. I don't know why they didn't use fixed point arithmetic and a fractional speed instead though.

Re:Ahhh

[yanyan]

+1, Touche.

This thread has been a triumph

[Cormacus]

I'm making a note here, huge success!

Teleporting?

[LunarCrisis]

The coolest part about Portal is that you don't feel like you're teleporting, you feel like you're just going through a hole in the wall.

XYZZY

[Anonymous Coward]

Google it if you don't understand that.

Re:M.C.Escher has good OLD examples of the concept

[Anonymous Coward]

That is hilarious. I watched The Labryinth just a couple of days ago for the first time.