Invade CTF: Design, Application, and Theory

Suna

What's a greybox?
aa
Nov 10, 2017
407
614
Introduction

I think the best way to start this off is to answer a pretty important question.
What is Invade CTF?

The obvious answer is:
It’s CTF, but there’s only one flag, and you deliver it to the enemy’s base rather than your own.
This is the simplest answer, and it’s how I describe it whenever anyone asks me what the gamemode is. It’s quick, and it lets people know how the gamemode is played. It does not, however, tell people how to design for this gamemode.

From this answer, one would assume that it is designed similarly to a CTF map, when that is absolutely not the case. I’m not saying that you can’t convert 2fort to an ICTF map, but it probably won’t go well.

So instead, let me give this answer:
ICTF is a gamemode similar to 3CP or PTOW (Payload Tug of War), where there is an emphasis on back-and-forth gameplay that moves throughout the map. The objective is to escort a neutral flag from the center of the map to the enemy base, while the other team tries to take the same flag to your base. It is a mode very reliant on teamplay and coordination as solo pushes very rarely succeed, and are more likely to aid the enemy team rather than your own.

This answer is a lot more complex and doesn’t really do a great job of describing the gamemode to a new player, which is why I don’t often respond with an answer like this. However, it does succeed at describing the main attractions of the gamemode, as well as how it’s played in practice which aids community map makers.

Of course, just that isn’t enough to tell people how to design for the gamemode. It gives them a pretty good picture, but the comparisons to other game modes can give the wrong impression. Although certain elements of ICTF are shared with other gamemodes, I don’t believe ICTF can be designed with another gamemode in mind, as a whole. It is its own, unique beast that requires a new way of thinking when designing around it.

So, let's get started!



The Basics of Design

To start, every good ICTF map requires three ‘stages’. Mid, Hold, and Last.

I’ll talk about these very soon, but before then, I've found that to create an effective layout for ICTF, there are several rules that must be followed. These rules can be bent (and I recommend you do!), but should not be broken.

They are as follows:
  • Mid should funnel players towards the flag spawn zone

  • There should be at least two ‘Main’ routes leading from Mid to Last.

  • Defenders should be encouraged to push forwards at all times.

  • Players should have an ‘escape route’ from every major area of the map.

  • Spawn times should be kept low

  • No forward spawns

  • Time taken to walk from spawn to mid should be less than 20 seconds
Why these rules? Well, remove just one of them, and the fun factor of an ICTF map can drop drastically. I have seen others attempt ICTF maps without knowing of these ‘rules’ and they unfortunately, failed to create a fun and well-designed ICTF map. Of course, that’s not wholly their fault. This is a very difficult gamemode to design for, and it took me several tries to finally get a layout that actually worked. Hopefully, if you follow these rules, you won’t need several tries like I did.

Mid
Mid should be designed to be an extremely neutral area, not giving any advantage to attackers or defenders, but with a layout interesting enough to create fun and fast combat. Some good examples of this are: Well, 5Gorge, Freight, Process, Badlands, and Highpass.

You may have noticed that those are all 5CP maps, with the exception of Highpass. This is because ICTF and 5CP share very similar goals with their design, though the execution is somewhat different. Unlike 5CP, Mid is not designed to be held in ICTF, and no forward spawns are provided to help with this. Apart from that, I could easily see any of those aforementioned Mids being repurposed for use in an ICTF map, though they would definitely need some tweaking to properly fit the gamemode. Of course, not every 5CP mid would be suitable. As I wrote earlier, Mid should funnel players towards the flag spawn zone. The Mids I mentioned do that successfully, not containing any flank routes to bypass Mid. However, many other 5CP maps, such as Granary and Gullywash, do allow players to ignore the point and continue onwards to the next point. This is a big no-no for ITCF. The flag, and the player carrying it, should always be the top priority. Additionally, sentries on many of these Mids can be very powerful. This is another thing which can not be allowed for ITCF. Player flow throughout the map, especially mid, is key, and a single sentry being able to lock down that area can ruin all of that. You shouldn’t try to make engineer useless, but be very careful about sentry spots on mid.

‘Main/Sub’ Routes
Continuing from mid, players should have several options available to them when it comes to picking a route to take. At least two of these should be larger, main routes that offer a degree of safety to the flag carrier whilst still allowing defenders to, well, defend. From these main routes, there should be several smaller routes that connect the two, or create an alternative way to traverse those main routes by providing some cover, high ground, or perhaps a sneaky way around a tough choke. How these routes are implemented is all up to you, but remember these are going to be used by both teams, for attack and defense! Therefore, keep things like dropdowns and one-way doors to an absolute minimum! These gameplay elements can work well for asymmetrical maps or maps with a fixed objective, but it’s rare to see them in game modes such as 5CP, for a good reason. These are tricky to balance, and can often feel unfair for whichever team is on the receiving end of those routes, and cannot even use them once they are able to attack. It also provides attackers with a safe space to set up for an assault, which should be discouraged in this gamemode.

Spawns
Unlike standard CTF, it is very important to not put spawns ahead of the capzone. In CTF, this is done so that teams have a chance to intercept an enemy attempting to leave the base with their flag, but in ICTF it would only server the purpose of making it very easy for attackers to cap once they had made it past the defender’s spawn. Instead, spawns should be positioned behind the capzone, similarly to most asymmetrical maps and 5CP maps. This prevents players from going the wrong way out of spawn, and guarantees that players are on their way to attack or defend.

But unlike those other gamemodes, there should, under no circumstances, be any forward spawns in ICTF. Adjust spawn times dynamically all you want, but forward spawns will only lead to disaster. It makes attackers have far too much pressure, creating a horrible situation for defenders where they are constantly focusing on defense and having no chance to push out.

Chokes
Chokes in ICTF are pretty hard to push through, but are necessary for a good and fair experience. They are mainly used to prevent one team from steamrolling through the other’s defense, and allowing them to build one up in the first place after losing the midfight. I recommend at least two chokes per main route, one on either end, with the harder of which being on the defender’s side. Be careful not to make these chokes too unforgiving, as they can result in a stalemate scenario where both teams are unable to make any progress, which is never any fun.



Nuclide Analysis
Nuclide was the result of a lot of trial and error, and about a year’s worth of accumulated research into how a map should be designed for this mode.

Mid was the area I made first, and has pretty much stayed the same for all of its development. I have the flag spawn on a small bridge, with a small stream underneath that connects to the secondary main route and allows for some sneaky plays by spies and pyros. I made sure there was a lot of cover around the area, with a small fence atop a concrete retaining wall and some rocks near the bridge to block some troublesome sniper sightlines. I also did my best to include as much interesting height variation as possible, going so far as to position the highest point of mid directly next to the lowest point. Pickups in the area are sparse to encourage players to retreat from the area, or push forward in order to heal/resupply.

Following that came the two main routes, and the accompanying sub-routes. These went through a lot of iteration but the final result turned out quite well. The sewer/pool route is very straight forward, with only one attached sub-route, acting as a ‘major flank route’ to the other main route, which has several attached sub-routes. One of which is a smaller, safer entrance into the route, another is a highground route with plenty of cover and some pickups, there’s another which provides a sneaky underground route into last, and finally a small connector to bring both main routes together. Defenders on these routes have the high ground, but not a lot of cover, whereas the attackers have a lot of angles to work with. There are a lot of pickups in these areas to encourage players to move into them as much as possible and take fights.

Lastly, comes Last. This was inspired by Sunshine’s last point, which has a raised rear area but a lowered entry point, though still has safe-ish ways for attackers to reach the high ground. I don’t really have too much to say on it, it is a rather basic design. This is the area where sentries are most powerful, but they are never able to lock down all four routes into last. While they are tough to take out, a quick-fix Uber can counter them rather easily as the flag carrier can choose to simply ignore the sentries and walk into the pit to cap. A demoknight can also charge into the pit from the jump pad to surprise defenders, though it is rather tricky to pull off.

There are also some features I integrated into Nuclide I'd like to comment on.

Firstly is the ‘revenge crits’ feature. A lot of players were confused with this at first, asking things like ‘why do the people doing bad get rewarded while those doing well get nothing?’. I am of the mindset that crits-on-cap is a bad mechanic, encouraging steamrolls and spawn camping. Revenge crits aim to do the opposite. Whenever a team caps, any dead players on the opposing team are instantly respawned and the entire team gains crits for a short time. This is done to push the attackers back out of spawn and remove any defense they may have created in the routes leading up to last, effectively ‘resetting’ the round back to mid. Players have warmed up to the feature now, but new players are still often confused by it at first.

Next are the mechanics attached to the flag itself. When the flag is carried by a player, any nearby teammates are provided with healing and ammo regeneration, equivalent to a payload dispenser. This was done to solve the problem of players seemingly refusing to group up and push as a team, instead opting to roam the map for frags. I tried many other effects to encourage players to group up and protect the carrier, though some were actually too effective. Originally, I applied a damage resistance to all players within a small radius of the flag carrier, as sentries were extremely powerful on last at the time. The downside to this was that sentries did essentially no damage to the flag carrier, and if they were a high-health/mobility class with a source of healing, they were able to almost ignore sentries entirely. This made rounds very short and also made all engineer gamers leave the server. Next up I tried health regen, which worked well but wasn’t useful enough to encourage players to get close to the carrier. I knew that health + ammo regen would solve the problem, but implementation was extremely difficult. Once I got it to work though, gameplay improved significantly.



Findings Through Failure
I wrote earlier that Nuclide was a product of trial and error. There were a lot of errors, and I'd like to talk about them now so you don’t make the same mistakes.

Isotope
This was my first foray into ICTF, and I made a lot of bad decisions with this map. I learned a lot about what works and what doesn’t with the gamemode on this map, with it essentially becoming a testing ground for a lot of different gameplay concepts. The layout of this map was choke-heavy and extremely linear, as that’s what I believed the gamemode needed at the time. Since after making Nuclide, I have seen others attempt the gamemode but fall into the same pitfalls as I did with Isotope, designing the layout to be far too linear. Last was also a hellhole. You could effectively guard all three entrance points from right above the pit, completely shutting down any attempt to cap. Most rounds of Isotope ended in stalemates. I designed mid similarly to a normal CTF, and it actually ended up being the high point of the map for me, but it definitely had its flaws.

Theia
Theia was my second attempt at an ICTF map that I made for the 72hr Jam of 2019. This attempted to solve many of the flaws of Isotope, and actually managed to succeed in a lot of areas. Obviously, I designed it to be far less linear, providing many larger, open routes for players to take, and it played pretty well. You may be asking “What was the problem?”. The problem was once again, last. I still hadn’t nailed it down, though I did admittedly have to rush last to meet the deadline for the jam. This time around, I opted to forego the pit and instead have a capture zone instead. Players were confused as to where the capzone actually was, and the highground route that dropped straight into the zone didn’t help things. Mid was decent, and some of it I even carried over into Nuclide, but as a whole this was a very ‘bleh’ map.



Gamemode Flaws
While I love ICTF, it definitely has some problems. It’s part of why it’s such a difficult mode to design for.

Spawn Camping
Since the gamemode, in paper and practice, is encouraging players to move into enemy territory, that also means that players are encouraged to move closer to the enemy spawn. It’s very easy to accidentally create scenarios where players are practically given the spawn camping golden ticket. Nuclide solves this through both the layout design as well the the ‘Revenge crits’ feature, which you are also free to use but do be mindful that it’s not a fix-all.

A lot a required entity work
ICTF is technically a supported gamemode in TF2, but only technically. A lot of things don’t work as you may expect them to. Setting the flag mode to ‘Invade’ is a good idea, but you are unable to change the cap limit if you do this. If you want a cap limit of 1, you can opt for SD instead, but this disables a lot of the benefits you receive for using Invade.

There are also no voice lines for this gamemode, so if you want a ‘full’ gameplay experience you may have to create your own soundscript for your map.

There are a lot of other bits of entity work you’ll likely discover are needed as you do more work, but I have a prefab available for download here to make it easier for y’all.

Stalemates
Like spawn camping, this is something which is very easy to accidentally create. A single choke point can be a make-or-break in the gamemode. Having a score limit of 3 also tends to create a few stalemates; if both teams have two points when the timer hits zero, what happens? Do you enter overtime until someone caps or do you just force a stalemate then and there? My personal solution is to enter a stalemate until the flag returns to the spawn point (and return time is massively reduced), but it’s really up to you how you want to approach this problem.

A player-based objective
This is, by far, the problem that is brought up most in tests. What happens if a team scores, is able to take the flag to their base and camps there with it? In Isotope, I saw this as a major problem and so turned the flag into a time bomb that explodes after 120 seconds. This is not a good approach. Generally, players will not do this. If they do, they may actually be putting their team at a disadvantage since all it would take is a single enemy to kill them, take the flag, and cap. The other problem of a player-based objective is as such: A team is able to clear out a defense, but the flag carrier dies in the backline and the flag resets to mid. That was a lot of wasted time and effort! Unfortunately, that problem cannot be solved, as far as i’m aware.


Conclusion
Overall, ICTF is a difficult game mode. I’d rank it about as high in terms of complexity as gravelpit or steel type CP to design for. Although the size of these maps are small, there is a lot of thought put into each area, as if even one doesn’t work well it can ruin the rest of the map.

I would like to say that i’m the expert on ICTF, as some others view me as, and with the amount of experience I have with designing maps for this gamemode i’m also inclined to believe it. However, as good as Nuclide is, I know and believe that there can be a lot better. I have seen others try their hand at ICTF and there have been some great attempts, with a lot of promise, but sadly not many of them have gone anywhere outside of early alpha stages.

I’m very passionate about this gamemode, and I want to see more of it! I understand that it is a very intimidating mode to design for given its success rate, but I believe in you.

To do better than I.

Good luck.
 

I dinne ken

Has currently had enough
aa
Apr 16, 2016
324
432
This is an interesting read, especially for me since I made ctf_transmission. My thought process for that map wasn't as developed as yours is but I had a couple of thoughts.

I posited that a gamemode such as invadectf is the most fun when the flag is about to be capped, both to defend against and to attack with. It's pretty fun during the initial midfight, gaining or losing the flag. But it's the least fun when moving the flag from mid to last. As such for transmission; I tried to design an interesting enough midfight, a blazingly fast transition, and a very heightened forward hold.

Particularly for the forward hold, I tried to make it a very strong position for the attackers to hold in. The forward hold has view over the surrounding area. And there aren't many good ways for defenders to get to it without going out into the courtyard outside.

upload_2021-6-28_18-6-6.png


Note previously I said "Heightened" forward hold. The strong forward hold the attackers are given is counteracted by the strong defensive qualities of the point courtyard. The push forward is very difficult, defenders occupy the entire space below, attackers have to give up a great high ground position to start capping.

upload_2021-6-28_18-15-47.png


Beyond this difference, there were some minor ones:
  • My flag becomes pickup-able by the enemy team after a short time.
    • This is to make sure attackers can't just continue holding in their forward hold while waiting for the flag to eventually come back to them. They're guaranteed to lose the flag if a push fails basically.
  • You have to cap a midpoint to gain initial control of the flag.
    • This gives defenders some buffer time so they can set up on the final point without immediately getting screwed.
And as far as I could tell my ideas worked, people had fun, and they told me so. The thing is, the map isn't yet great in my estimation. It has issues with gamemode clarity, which is minor, but more majorly it has layout problems. Or at least it feels like it does. I feel like the dynamic doesn't change frequently enough. Attackers sit in their forward hold and don't try a push to the point for a long time. And any pressuring that the defenders try to do by going around them is immediately quashed by the low ground they start in. I also need to fix some logic issues lol.

I have some ideas on how to address this. But I'll leave it here for now. This was a good read. Even if we're coming to slightly different ideas about what we want.

Like you said, iCtf has a fair bit of potential. I feel it's great for creating very strong layout dynamics since it forces players to deal with a flag. It's just that that's not immediately obvious, and I encourage others to give mapping for it a try.
 

Pawlakov

Deliberately incoherent
aa
Jun 1, 2013
194
42
Time taken to walk from spawn to mid should be less than 20 seconds

You have made a statement about the upper bound of a ICTF map's size. But I am now interested about the opposite - how short can we go?
Here are some timings of your maps I have measured (as Heavy).
Nuclide cap <-> flag: 16s
Toucan own cap -> flag: 14s
Toucan flag -> enemy cap: 20s

Would you say that it's possible to cut that in half (cap <-> flag in 6-10s as Heavy)? How far can we go before the game mode disintegrates?

To start, every good ICTF map requires three ‘stages’. Mid, Hold, and Last.

With a much smaller map I don't think keeping that structure will be possible without making all spaces overly cramped. Therefore wouldn't it make sense to compress Hold-Mid-Hold into a single Hold?

In case you're wondering "why all that?" - I am thinking about making a TC map with ICTF instead of 2CP and I don't think it will be viable to make every round a full-sized ICTF map.
 

Suna

What's a greybox?
aa
Nov 10, 2017
407
614
In case you're wondering "why all that?" - I am thinking about making a TC map with ICTF instead of 2CP and I don't think it will be viable to make every round a full-sized ICTF map.
I think you definitely could do exactly that, Hydro is not a good example of TC; and I think that the gamemode requires stages that are a little larger. If hold is made into a small lobby, you should have enough space for this to work fine!