Seasnails' Guide to Portals

Guide to Portals

A few years ago, I published a track called Computer. Since then, no one has done much interesting with portals, which I think is a shame, so I'm making this post to demystify some of the things I learned while making the track.

Some boring but vaguely important disclaimers/points I want to say first but which you can probably ignore:

• In all the images below, portal pairs will be indicated by a line between them.
• I will not being showing how I fully made a computer in this post, only the basic idea, but, if anyone wants more info, dm me here on the forums and I'll try to find out/remember for you and, if I deem it interesting enough, I'll add it to this post.

The Idea

The teleport powerup is unique in Free Rider in that it consists of two part. Often tracks are designed so that one teleport is the entry, and one is the exit. This is a lie perpetrated by many trackmakers. You can enter either portal and be transported to the other.

Another important (and fairly unique) aspect of the portal is its expendability. You can only use a portal pair once. Once it's used, it's gone, doesn't matter which portal you entered from, no getting them back.

Both of these properties are key.

Say you are falling, you fall into a portal and are transported to location B.



But what if that portal had already been activated? Well then you would fall straight past the portal to location A.



In this way, where you end up is dependent on some prior input.


The Basics

The Splitter - Where the player ends up depends on whether some "switch" has been activated
In this setup a player will enter via portal E and exit via portal B.



However, if the player activates the switch, by entering via S and exiting via SE, then, when the player enters via E, they will instead exit via A.




The Combiner - The player may start in different locations, but will end up in the same place.
In this setup whether the player enters via E1 or E2, they will exit via A.



Here are some combiners for 3 and 4 entrances.




The Tricky Stuff

Any computer can be broken down into logic gates. These are functions which take two inputs and give an output, all inputs and outputs being either a 0 or a 1. A common example is an AND gate which outputs a 1 only if both inputs are 1, and else outputs 0. Google "logic gates" for a full explanation.
Say we made a Splitter with two switches. If the switch HAS NOT been activated this can represent a 0 and if the switch HAS been been activated, this can represent a 1. Then, when the player enters the system, there are four possible exits: 00 (neither switch was activated), 01 (the first switch wasn't activated, but the second one was), 10 (the first switch was activated, but not the second), and 11 (both switches were activated).



From here a combiner can be used to combine the 00, 01, 10 "signals" together into a 0, and then the 11 "signal" can be rethought of as a 1. Hence this is an AND gate. Similarly you could combine the signals together in any other way to get any gate. (Also, when making specific gates you can also eliminate some redundant switches, for example the AND gate doesn't need a switch between 00 and 01 as both of these would output a 0. (Also also, when making my track, I used some switches that activated for a 0 signal to even out "processing time".)) The signal outputs from one gate can be used to activate the switches in the another gate, and in this way any digital circuit can be designed.

If you look online, you can find plenty of computer systems broken down into gates. For the track, I used a four-bit adder-subtractor and figured out the rest.


Conclusion

Don't settle for boring. Do something creative with your portals.

Endnotes

• I like to use the setup with the blob being crushed to a point to eliminate any sideways movement when falling and not have to worry about portals being activated when they're not supposed to be because the player is at some weird angle or whatever. You can of course just use a bike, etc. but you will have to deal with these complications, maybe use some boost barriers to keep the player on the right track.
• Above a portal that the player may emerge from, make sure to keep space, so the player won't go into another portal or hit something, with the crushed blob I found 7 10x10 grid squares was the minimum. Any portal that is intended only for the player to enter doesn't need any empty space above.

• In the track I used a cypher to label systems, gates, and any portal pairs not near each other. Labelling them with letters I found difficult to draw and see at the scale. If anyone wants to try to understand the original track here are the alphabet and numbers in the cypher.

 

there's serious unexplored potential to do crazy sh*t with portals that no one else has done before and it's a real shame that not much people actually attempt to do so. i know me and many other people were completely flabbergasted when computer dropped and it's not something that often happens on this site lol

 

Oh sweet, a guide from our local resident portal expert! I've attempted to do stuff with portals a little bit before (such as this), but for whatever reason, I never thought to make logic gates. This is seriously cool, though, and I may have to invest more time into trying to make interesting portal things.
Something that I found during my experimentation that you might also find cool is a slightly different way to use portals. Essentially, the way the rider interacts with powerups is (barring weird physics things) deterministic - when the code is parsed, powerups are added in a specific order, which means that when checking collisions, powerups are checked and interacted with in (I believe) the same order as they were in the code. For a powerup like, say, the teleporter, which instantly transports you away and prevents any further collision checking in that spot, this can be extremely powerful (as an example, in the above track, the 'mechanism' that combines all of the inputs into one and sends the rider off to the correct next portal to give the next number is all in the same 'node' and thus takes 1 game update - half of a frame - to run, despite combining 20 inputs and then sending them to 20 outputs). Of course, creating such tracks - where every teleporter not only has to be placed in the right spot but also in the right order - by hand is, to put it simply, a massive pain (I say this from experience), especially given how much you'd potentially have to undo if you made a mistake and didn't catch it, but making a generator is honestly less work than coming up with a teleporter machine in the first place. (tl;dr: portal stacking = cool and super quick teleporter stuff, although it does have limits)
I hope you'll consider making more with portals! There really is some seriously cool stuff waiting to be made with portals, and Computer was and has been a massive inspiration to me in attempting to create more dynamic levels and exploring the game more (even if I've barely made anything, oops!).

 

I never knew portal stacking was deterministic, I'll also experiment with it and see if I find anything

 

bump

 

pretty interesting

 

If anyone has ever done programming with FPGA's and VHDL youll know that anything can be broken down into logic gates.
a couple of years ago I made an FPGA project for a 12-bit calculator with addition, subtraction and multiplication/devision

imagine the complexity of the FRHD track if you made it, id love to give multiplication/division a shot if i have a bunch of free time.

 

Hmmm

 

I was able make these
https://www.freeriderhd.com/t/988735-instant-portal-coding

 

im trying to experiment with portals but i don't have any new ideas that no one had tried.

 

imagine if we tried to change the code so that teleports become logic gates
i mean the others, like NAND and XOR and vice versa