Arcen Talk A Valley Without Wind, Part 2

This is the second part of our extensive interview with Arcen Games’ Chris Park about their forthcoming procedurally-generated action-adventure survival game, A Valley Without Wind. Read on…

RPS: You’ve described AVWW as a ‘procedurally generated adventure game’, but from some of the other descriptions it seems to have more in common with RPGs than your typical adventure game.

Park: In terms of player/character progression, it is indeed a bit more RPG-ish. In terms of what you’re actually doing while you’re out adventuring and encountering monsters, that’s all action-RPG, though. You have to cast spells or hit monsters with weapons or lay traps for them to step in. This is all done in realtime, like any adventure game. It just happens that how much damage you deal when you strike a monster is based on your player stats and levels, and the stats of the weapon you’re using. And the monster’s health values are based on the level of the monster.

RPS: What’s going to be the meat of the player experience? Is it going to be puzzle based or combat based?

Park: This is where the uniqueness of the game really comes in, I think. It’s an adventure game, but the focus is neither on puzzles nor combat. “What’s left,” right? In our case, the core of the experience is going to revolve around impacting the world. You do these various deeds, and the world changes for the better or the worse in the affected regions. Kill a big overlord bad guy, and everybody who had been oppressed by him is happy to now be free. If your character dies, then a grave marker goes up and people that knew him/her reminisce about them (or are glad they are gone, I suppose).

When you help other survivors out, you can convince them to join your settlements, and over time those settlements grow and change and provide new equipment and abilities for you. Also, when your current character dies, you get to choose from among the characters that you’ve added to your settlements (and while your overall stats persist, each character brings their own flavor and crafting specialties). As already mentioned, you can make certain areas a lot safer by setting up wind shelters, too.

RPS: Despite being a post apocalypse, this is sounding like there’s a fair bit of player interaction with non-hostile NPCs, who are presumably not all horrific monster AIs. How deep is the player interaction with other people?

Park: Most NPCs will be pretty decent people just trying to survive, like you are. Most of the enemies are non-human monsters out to get all of you. Of course, you’ll run into some enemy humans, or entire settlements of enemy humans, but they’re more the exception than the norm. Most NPCs won’t care much about you at all until you do something to help them out and win their favor, and then they might join your proposed settlements or might not.

In terms of interaction with other NPCs, in early alpha it’s going to be extremely, extremely limited. Exactly what that would entail at that early stage depends on what we have time to fit in, honestly. For core gameplay reasons we need the ability to speak to NPCs to enlist their crafting services, but just about everything else lifts out if we have to for time reasons in early alpha.

In terms of where we’d like to take this post-alpha… the idea is that each NPC will have skills, desires, and problems, and you’ll be able to help them out with their problems or to realize their desires, and that has benefits from both of you. Or not — you can also just murder every NPC on sight if you want to. Probably not the best way to win, and the character that does all the murdering will get a pretty bad reputation (that dies with that character, conveniently for you), but the flexibility is there. Since the story is non-centralized and somewhat emergent, there are no “key characters” that the game can’t progress without.

If the game really takes off, then this is one of the aspects that we’d like to push further in new directions. But to start out with, our focus is on the adventuring, and the NPCs exist in service to that.

RPS: And how easy was it to move from AI behaving like an AI, and AI behaving like a human?

Park: Well, that’s one aspect we haven’t particularly gotten to yet in our implementation. That said, in the Alden Ridge game I was doing before AI War, I had exactly this sort of system for NPCs. And I’ve worked with that in numerous other past projects over the years. Honestly, most of this sort of thing is only what I would tenuously call “AI.” It’s all a matter of branching decision trees that are fairly limited and scripted. If you play long enough with any sort of RPG game, you start getting repetitive conversation at some point.

In AVWW, this is another area where player content submissions will be welcome, so that should help really minimize the amount of repetitiousness and make the characters seem more real and varied than they otherwise would. We’ll see how that works out. But honestly I don’t have hugely grand plans beyond the standards of the RPG/adventure genres when it comes to the NPCs — our goal is for a SNES-like poetic brevity of dialogue, and for a lot of unique-feeling characters, without going too crazy into a Heavy Rain direction or whatever (of course, that was heavily scripted, too).

RPS: But combat is still going to be a necessary part of the game?

Park: Combat is certainly still a key part of the game, but it’s a means to an end and avoiding some fights is just as valid as engaging in them. You don’t have to fight every monster just because you see them. In terms of puzzles, I think some degree of puzzles are also inevitable, but that’s not something we’ve thought a lot about yet.

Right now we’re still in pre-alpha, so we’re mostly focused on getting the art the way we want, and the general world-building aspects in there. It’s still very early days, but we’ve gone through a lot of intensive design and are really excited about what’s coming. The first public alpha versions will mostly be exploration with little motivating purpose (no settlement building, limited interaction with NPCs, etc). Those higher-level features will be built-up with player involvement through beta and the 1.0 release and hopefully beyond.

RPS: With the popularity of games like Minecraft, the experience of a world unique to each player, yet persistent, has struck a chord with gamers. What do you think the appeal of that is?

Park: This is actually something that happens with the galaxies in AI War, too, though that’s less of a creative situation and more of a historical “I remember anecdotes about this place that are unique to just me and the other players in this galaxy.” Other players have talked about this effect that AI War has on them, and I’ve certainly seen it, too. Remembering the scene of some epic battle if I load up an old save is pretty cool, because generally that battle played out in a way that was unique to me and that map — it feels more like a real life memory, rather than just another chapter in a book that someone else wrote.

So I think the appeal is multifold. In Minecraft, of which I’m a huge fan by the way, you get these massive worlds that you can reshape to your will. Starting with a world that is unique to begin with, and then adding on your own personality on top, is just a really special feeling. My wife and I have a private Minecraft server that we’ve played on since first encountering that game. We’ve never created more than one world, we’ve just kept expanding in that one single world. That’s particularly cool, because we can go back to places that we constructed six months ago, and which are just a distant memory now.

AVWW will be a mix of those two concepts when it comes to world persistence and growth. You can’t reshape the terrain or your surroundings like you can in Minecraft, but you can still affect the overall world in a a lot of persistent ways: settlements and wind shelters and stuff you do for NPCs being the three most obvious ways, but also including things like it remembering that you knocked down a bunch of trees in one area, if that’s what you wanted to do. And as you explore around, you can leave spraypaint markings to show where you’ve been. And no matter what happens to your specific characters, their deeds and their legacies live on. You can go visit their graves or even memorials to the bigger heroes, and the things that they accomplished have a lasting effect on the game world.

Our goal with AVWW is that individual players will never create more than a single game world. Why would they? Every bit of content, even future content or expansion content, can become available in that world simply by exploring into new regions. There’s a huge disincentive to ever start over, because all those older marks you made on the world would then be lost. Instead, even if I wind up exploring way out into the nether reaches of my world, I can always go back to the original starting area if I so desire, months or even years later. To me personally, that’s really exciting.

RPS: One of my problems with Minecraft is that I create all of these huge monoliths, and then there’s no one but me to witness their majesty. This makes me sad. Who will bear witness to my accomplishments in AVWW? Is there any thoughts towards multiplayer?

Park: Multiplayer is something we’re hoping to have by alpha. It will probably be buggy and rough right at first in alpha, just fair warning — but the player testing is what is needed to iron out those rough edges early on. Last week I’d said that I couldn’t confirm if we were going to have multiplayer or not, but as we’ve been progressing in the technical implementation of the game that’s been something that we just couldn’t ignore any longer. I think that the game really needs it, and I’m always a huge proponent of co-op. If we delayed on implementing it too long, we’d run into the lengthy sort of refactoring period that Minecraft has seen, and I wanted to avoid that sort of pain.

The reason why multiplayer was ever a question mark for this game was that, as an action game, its networking model will be entirely different than that of AI War or Tidalis. RTS games in general use a really unique lock-step-synced sort of model, and for Tidalis we were able to make that work there, too. With an FPS, racing, adventure, or other action-oriented game, the networking model is based on an entirely different premise. Supposedly its easier to do than the RTS method, but it’s new to me and so makes me wary for the time being. We’ve been preparing for the new networking model this week, though, and my hope is to have some early versions of that next week internally, and then fully ready by the time we hit alpha.

Of course, with any new networking model, we’re going to run into unexpected problems and places where we have to optimize when a variety of players get into the game on a variety of kinds of networks. That will all shake out in alpha. My tentative goal is to support at least 16 players per world, but in reality it will be limited by whatever your network supports, I think — so it could be more or less than that, depending on where you put the server. The game itself will be able to be run in sort of a headless server mode, and then the other instances of the game can connect to it. You’ll be able to run both a server instance and a client instance on one computer, if you want.

All of that networking stuff is subject to change, of course — it’s new territory for us, some I’m cautious about promising too much for sure. But it’s looking promising, and we should have some early working versions pretty soon to raise our confidence levels that this is definitely viable. I think it will turn out well, I’m just not sure how much bloodshed will be involved in getting it there!

RPS: If you look at what you guys have done with AI War, with near constant updates, and really huge expansions, there’s a really deep level of interaction between you and the community of the game that isn’t typical in game development. Has AVWW been developed with that kind of involvement in mind?

Absolutely! And actually, this game is designed to make that a tighter connection than even we’ve had in the past. Players are always wanting to help us out with direct content creation, but in AI War that’s tricky because of balance concerns being that it’s a strategy game. Even so, we’ve had donations of player art and sound effects for that game, and literally hundreds of design ideas, ship or feature concepts, etc, that we’ve implemented. With AVWW, we’ll be doing all that, but also trying to take it to the next level for the core community.

There is a pretty cool component of custom procedural-content-script creation that advanced players can partake in (and then get their creations added to the official builds of the game, potentially, or just release them as unofficial mods). Part of the problem with having huge spaces in the game is that you don’t want to be exploring Office Buildings A, B, and C hundreds of times. That’s boring and feels stale.

The goal is that with AVWW we hope to hit an unprecedented number of unique places. We’ve already developed out techniques for a hybridized model of procedural and hand-crafted elements, all tied together with procedural seeding. Instead of literally designing “Office Building A” by hand, we instead make a “chunk script” that defines the overall design of that office building, and then which components of it can be randomized and in what way. That alone makes for dozens or hundreds of possible office building variants from just a single script. But by having lots and lots of scripts, that gets multiplied into the thousands or tens of thousands even for just a concept as discrete as “office building.”

When you start adding in other concepts like scripts for “suburban house” and “rich person house” and “old shack” and so forth, and even “types of clumps of trees,” the number of possible emergent designs quickly gets ridiculous. My goal is for Arcen to create a few hundred of these sorts of scripts by the time 1.0 hits (and numerous dozens by the time we even reach public alpha), and then my hope is that we’ll hit many more hundreds of scripts that are player-created. The end result is hopefully worlds that are orders of magnitude more unique than in any other game ever seen.

RPS: Something like Spore? One of the problems that seems to plague procedurally-generated content is that while each building or level is unique in general, there are recognisable parts that pop up again and again. The same table, the same rock, the same colour palette. How are you setting about adding unique flair to the world, where the threat is just creating the same building in a million different ways?

Park: That’s fair enough — and to some extent, is unavoidable, for sure. Yes, you’ll be seeing the same chairs and tables and rocks, the same pieces of wall, repeatedly. That’s absolutely unavoidable and I wouldn’t want to pretend otherwise. That said, AVWW is going to have the same advantage over Spore that AI War has over other RTS games: it’s 2D. That means that the RAM cost, and the production-time cost per item, is vastly lower than in 3D. So if we want to have 10 different variations of trash can, we can and it’s not that hard. If we want to have thirty different types of brick wall: also possible.

I think that Minecraft is a really good example of how many different things can be constructed out of even a simple toolset, though. How many blocks are in Minecraft that people commonly use for construction. A dozen? Yet the end product is often really more than the sum of its parts. With AVWW, we have less “atomic” parts compared to Minecraft, so the variations won’t be so endless for each individual part. But given our 2D nature, and general art pipeline flow, one of my personal goals for the game is just having an enormous amount of possible parts to use.

Does that mean that, at some point, you’re still exploring the same house with windows in a different place, stairs shuffled around, different tables and chairs in slightly different spots, and a different texture for the walls, door, and roof? Absolutely. But that’s true of real life, too, I think. Our homes are not all that unique except in the details. You and I might have the same TV, or the same armchair, or both.

The cool thing about a randomized procedural scripting system, though, is that it can take broad hand-designed outlines — such as a split level home, a duplex, or even a duplex with these general features or eaves or whatever — and then it can randomize selected components such that you wind up with a surprising number of combination. Even how you design a duplex and how I design one would be different, if we each make a script for it. If you have all that variance in designs just for houses alone, and a suitably large number of props and textures to fill in the blanks with… that complexity is multiplicative. There’s obviously a lot more structures for the game than just houses, anyway, right?

The result won’t match real life any more than any other game does, but if we wind up with enough content and enough scripts, we will be able to push this further than most games. I think that some games that have come before, like Graal, Minecraft, and even Spore do show what’s possible going in that sort of direction. The proof is in the pudding, and our pudding isn’t done yet, so I’ll be as interested as anyone to see how far we can really push this. But seeing what we’ve been able to accomplish with AI War, in as barren and blank a place as outer space, I’m really encouraged. I really think that we can do for procedural adventure games what AI War did for strategy games.

RPS: Right, so the players will be almost as important as the developers, ideally.

Park: Yeah, and how far we’re really able to push that procedural generation is largely based on player support and involvement, but past experience is that this is the sort of thing players will be all over. Worst case is that the game will be larger than most, but given our past experience with AI War in making one of the most (if not the most) content-rich strategy games around, I think we’re well suited to this job.

In terms of why we’re doing an early alpha, it’s all about the players: we’re wanting to let the core fanbase (and anyone else who wants to join in) get at the game early either by preordering or demoing it. The larger gameplay elements will still be very much in the process of being added at that time, but there will be enough to be exciting and for players to help with content scripting if that’s their thing. That way we get lots of testing, and hopefully lots of player-created content to make the world feel even more huge and varied than we can do on our own.

Our past experience has been that some players really love getting into our games as early as humanly possible. Most likely, their ideas and suggestions will take the higher-level game mechanics in directions that I can’t currently foresee, as happened with AI War. What we have presently designed on paper is really solid and already really huge, but new ideas will be occurring to us as we go, and players always come up with really innovative stuff we’d never have thought of.

And given that we’re self-funded for all this, we need the support of those preorders in order to fully realize this game. We’re able to coast on our recent releases like the latest AI War expansion up to alpha and a bit beyond, but to make it all the way to 1.0 in the way that I’ve laid out here, it’s going to take player support. Our job is to make even the early alpha versions so compelling that folks want to get involved right from the start, and just can’t resist playing it even before some of our cooler world-persistence ideas are in there. It’s worked for Minecraft, Dwarf Fortress, and in a lot of senses AI War as well, so we’ll see what happens.

Right now we’re focused on making the art as amazing as possible and something that will get folks excited to play the game, and then it’s on to packing in as much content and functionality as humanly possible before we get to alpha. Given the early response on our forums and other sites, the future looks bright for AVWW. But time will tell!

RPS: Thanks for your time, and your many, many words.

Expect an alpha release in March!


  1. CMaster says:

    Going to the second to last question – I think that to some extent, when you’ve seen one massive tower or one castle in Minecraft, for the moment, you really have seen most of them.

  2. adonf says:

    I didn’t like the art at first but it’s true that it looks much better in full resolution.

    Also this makes me think of a pop-up book. Wouldn’t it be great if the ground rotated on the Y-axis depending on the movement speed while the sprites stay parallel to the screen ? Come on Arcen, time to bring back the old SNES Mode 7 !

  3. tomeoftom says:

    It’s hard to overstate how much I appreciate these really eloquent interviews. Great article!

    • Mr_Hands says:

      The dude just dropped “multiplicative” like it wasn’t no thang. In the parlance of our times, “That dude a eloquent motherfucker.”

  4. J. says:

    Great interview! I still have serious doubts about AVWW’s current art style. Of course it’s going to look better in the final release, but I would prefer a bit more cartoony/SNESsy style.

  5. Schaulustiger says:

    The concept sounds incredibly amazing and since this is Arcen Games we’re talking about, I will pre-order this as soon as it’s possible.

    BUT, I absolutely do not like the art style. Chris Park said that it resembles the old SNES style games, and that is true from a viewpoint perspective, but the high-res graphics don’t match very well with the clunky character animation and the strange white outlining. A pixel-art style would’ve been much more nicer to look at, me thinks.

    • Mad Hamish says:

      It would be easier to make a load of cute looking pixel art alright. But they seem to have a strong enough idea for the art direction. Takes balls to do hi res sprites. At first glance, looking at the video and the small screen shots the game looks ugly. But looking at the hi res shots and the art assets on the page, it looks a lot better. The trees have a really nice style to them.

      It’s still early too. There seems to be a lot of white boarders on the sprites, especially on the trees. Lighting is also something that I’m wondering about. Remove the lighting from any game and it’ll look pretty shit. I hope they use some kind of lighting to get the mood right. Post apocalyptic wastelands need good lighting. Oh and as an animator, that dude needs a proper run cycle, it looks like half a cycle and then they reversed it.

      If the only holes you can poke in a games design are graphical though, you’re flying. Looking forward to checking this out, sounds really interesting. That video gave me flashbacks of the forest section on that Shadowrun RPG for the mega drive all those years ago.

  6. MuscleHorse says:

    This instantly became my most wanted after just skimming the press release.

    Hopefuly the art-direction will be tweaked somewhat through alpha, but then Gameplay < Graphics.

    • thebigJ_A says:

      I hope you meant ‘>’. Because gameplay is certainly NOT “less than” graphics.

  7. brulleks says:

    ‘ “What’s left,” right? ‘

    aargh. reality breakdown.

  8. icupnimpn2 says:

    If a tower defense game has turned into this in the space of a few months then I am all sorts of confident that the finished product will make some different design choices, so I won’t harsh on the art style too much.

    I will say one thing, though. Graphical polish is not Arcen’s strong point. I’ve only played a little bit of AI War… the images were nice, but the game itself seems fairly sparse and the sprites static. I think a lack of a certain shiny, iconic simplicity was part of why Tidalis didn’t draw the casual crowds. The tiles looked like flat images, not blocks. And this current game certainly has issues with flatness and perspective. Here’s to believing they can tighten it up.

  9. malkav11 says:

    I’m still a bit skeptical about procedural generation, myself. AI War does all right with it, but AI War just has to plop a few structures into empty space, not create interesting places to explore. And other games that have relied heavily on procedural content generation in the past (say, Daggerfall, or Diablo) have tended to be boringly repetitious, environmentally. It’s especially notable how much more interesting to explore Daggerfall’s followup, Morrowind, is – because there’s a much higher level of hand-crafting.

    • Mattressi says:

      On the flip side there’s Minecraft and Oblivion. Minecraft has some amazingly beautiful procedurally generated landscapes that always seem very unique to me. Oblivion, however is boring. Certainly the world terrain was okay, but bloody hell those dungeons/caves/ruins were all exactly the same! Hand crafted, but oh so repetitive.

      I guess what I’m trying to say is that it’s less about the method by which the content is made (i.e. procedural or hand made) and more about how (i.e. lazily or lovingly) the content is made. With that said, I’ll always favour procedural simply because it makes the game so unique and replayable.

    • Mr_Hands says:

      I’m a minority in this, but I preferred the first Diablo’s atmosphere to the second.

      As for Daggerfall, I don’t think the problem was necessarily repetition, it was largely that the randomized dungeons were often unplayable. Even something as significant as that didn’t stop me from playing the everloving holy fuck out of that game.

      I certainly have my reservations, and I’m sceptical that this game will be a quantum leap forward in terms of graphics for Arcen, but when they say they’re going to craft a meaningful, content-rich experience, I’m inclined to believe them.

    • malkav11 says:

      Well, certainly, Daggerfall’s procedural generation tech was broken in ways that Arcen will presumably be able to avoid – none of this random placement without respect to balance or indeed possibility (quest objectives that cannot be reached by any means, etc). But it also completely failed to create interesting environments to explore, and the less said about the cities full of identical people with no character or personality the better.

      As far as Oblivion goes, I actually found many of the dungeons reasonably engaging as -spaces-, they just stuffed random assortments of critters and loot in them, that respawned and levelled with you, and failed to give any context or story to 95% of them. The dungeon right outside the Imperial City is a good example of the sort of coolness a handcrafted dungeon can offer if any effort is put in. I don’t see anything like that happening from procedural generation.

      I’m not really qualified to comment on Minecraft. I purchased it on speculation and am still waiting for it to transition from sandbox to game.

    • Mattressi says:

      That’s funny; I’m still waiting for Oblivion to go from ‘choose your own adventure’ book to a game. Perhaps people have different definitions of what makes a game a game. For me, I like to be able to do whatever I want, rather than play through a flow chart (or worse, a movie).

  10. misterk says:

    I get really excited about this. I really like the developers honesty in this interview, so while he’s hopeful that the game is going to include x y and z features he’s also being cautious. I’m not bothered by the graphics, mainly because my sad old laptop can’t handle anything terribly intensive anyhow.

  11. 7rigger says:

    This looks, and sounds, fantastic. I`ll be keeping an eye on their site for the March alpha release :)

    But I know that RPS will remind me.

  12. Jp1138 says:

    Well, having been able to see higher resolution images now, I must say the graphics don´t look so ugly, but the animatios really do look very bad – the guy seems to be walking backwards or something. The screen scroll doesn´t look right, either: it seems you have to walk too near the border to “activate” it: I think it might work better to keep the character more centered in the screen.
    Anyway, don´t take this as a very serious comment (I think you felt a little attacked in the other part of the article with so many coments talking about graphics) – I love what you are trying to do and will buy the game ASAP! Just hoping you polish some little things that, seeing the support you are giving to AI, I´m sure you´ll do :)

    • keith.lamothe says:

      “The screen scroll doesn´t look right, either: it seems you have to walk too near the border to “activate” it: I think it might work better to keep the character more centered in the screen.”

      Haha, I had it lockstep-centered since the initial implementation, and then we decided that was too much scrolling fatigue and changed it to what it is now. We might tighten it up a bit more, we’ll see.

      “I think you felt a little attacked in the other part of the article with so many coments talking about graphics”

      Not so much attacked as fatigued. We’ve been in a pretty rapid feedback loop with our players on AI War since September (CoN/4.0, and then LotS/5.0) and while it’s exceedingly helpful we do eventually develop a sort of “feedback fatigue” where even well-meant and helpful feedback starts to slowly sap away energy. The AIW players were probably feeling “change fatigue” from the game getting so much reinvention, too, so it was a good time to take a break. Anyway, personally I was looking forward to AVWW’s early development as a time to let all that cool down. I didn’t make the connection that releasing this early info would rather defeat that purpose ;)

      So not attacked, really, but we’re human and can only stand so much drinking from the wide-open fire hydrant ;)

      Things are coming along well, in any event.

    • Jp1138 says:

      “Haha, I had it lockstep-centered since the initial implementation, and then we decided that was too much scrolling fatigue and changed it to what it is now. We might tighten it up a bit more, we’ll see.”

      Yep, that may be a problem, but right now I think you may find a nasty creature without time to react because you are too close to the border of the screen. The scroll may need to be more “elastic”, recentering you while you walk, perhaps?

      Anyway, thanks for showing your work in such early stage :)

    • icupnimpn2 says:

      We criticize because we care!

    • squidlarkin says:

      You might want to try a predictive camera: calculate a point some ways ahead of the character in the direction he’s moving, and then have the camera converge on that point (say, every frame you move the camera to the average of its current location and the target point). That way you mostly see what’s ahead of you, and the camera moves around naturally.

    • Reapy says:

      Was glad people said to look at the graphics full screen, and it did make a huge difference. I’m still not sure what the big glass brick thing is though :)

      I was thinking the same thing watching the video that if something ran at you, you would eat it before you could see it coming for sure.

      I’m still not super keen on the chosen perspective, but honestly it will all come down to how the combat/action is going to play out. That is really what will make or break the game because you’ll be going through the action motions so much, they should receive the most TLC.

      Anyway, really interested in the game and also think it’s great you guys put your money where your mouth is by releasing early screen shots and even a video, most people would leave us with an intriguing wall of text and nothing else to go along with it.

  13. Bassism says:

    You guys have my money as soon as Alpha hits. And I’ll be all over whatever content creation areas you give us!

  14. Ex Lion Tamer says:

    I’m with you there. I really appreciated AI War without fully loving it – I tend to think that was more my fault than the game’s. This, on the other hand, seems right up my alley. Keep up the fine work, Arcen, and I will continue to throw (my minuscule) piles of money at you.

  15. Consumatopia says:

    I was critical of the art in the other part, but after reading this I’m pretty sure I’ll be pre-ordering no matter what it looks like.

  16. cyrenic says:

    If you guys can, you should add high res links to all the pictures. The game looks much much better in high resolutions.