Surface Area, Volume, and Ratios

I’ve been considering the underlying game design philosophy of Thrive and have come to the conclusion that we might benefit from introducing another layer of simple detail for the player to consider in building their organism.

Right now, I think we have established our base mechanics well and have a very smooth and functional editor, with well-defined parts and an easy to understand editor. But in my opinion, I think editor gameplay - more specifically, player choices within the editor - might be a bit simple and lack depth. You place parts to boost stats, and besides making sure you have a net-bonus ATP production system, there isn’t much more of a decision to make. Of course, it is important not to overwhelm the player in tedium and details regarding the editor when, ideally, most of the gameplay will be happening outside of the editor. But at the same time, I think it is important that trips to the editor are not just thoughtlessly placing two parts down.

Many other good games which use an editor mechanic also have factors external to a placeable part for the player to consider; these factors are an important measure of progression, providing challenges and limitations for the players to creatively address. For example, alongside money, Kerbal Space Program also challenges the player to create an aerodynamically sound vehicle, accounting for factors such as center of mass, drag, and air flow. And though I personally don’t know much about it, the fun of a game like Factorio isn’t necessarily the action of placing a part down itself, but instead the relationship between parts: the challenge is in creating a functional system. And though the mechanic itself isn’t liked by many, even Spore introduced another factor external to a part itself for the player to grapple with in the complexity meter.


Design Philosophies and Progression

One of the most important decisions we’ve made regarding the design for Thrive is our reluctance to have anything reminiscent of “flat” upgrades to organelles - for example, spending MP to make mitochondria go from producing 6 ATP to 8 ATP, and so on. Rather, we’ve decided to go with a system of progression that involves “specialization” - changing aspects of your organism as a whole to become better suited at a specific function, at the potential detriment of other functions. This is because we want to emphasize the fact that no adaptation is necessarily better than another adaptation; rather, one adaptation is more capable in certain conditions than another adaptation which is more capable in its own conditions. And similarly, an adaptation is better than another adaptation within certain body plans, niches, and behaviors. There are no “levels” in Thrive when it comes to “parts,” only specializations and complexity levels.

This effectively means that we want the player to creatively alter the very nature of their organism to become better at something, asking them to be aware of what they are exchanging as a result of their decisions. For example, rather than flatly unlocking chloroplasts, players will alter their nature and morphology to become better-suited for photosynthesis.

The Problem

The “specialization” line of thought is a very cool way of thinking of progression that, if executed well, will result in an amazing sandbox simulation of evolution. The problem right now however is that I don’t think there are enough ways to “shape your organism” into becoming more ideal for a specific function to warrant much depth and strategy within the editor. For example, let’s say I want to “shape my organism” into becoming better suited for photosynthesis. This is what I can do in the editor to achieve that goal…

  1. Place more thylakoids and chloroplasts.

That’s it really. You do have to attach enough mitochondria/metabolosomes/whatever to become ATP sufficient, but besides placing more of the part, there isn’t really much for the player to do.

Now, that was a bit of a cherry-picked example in that photosynthesis is a pretty simple strategy. For example, if I want to make a successful predatory organism, I would consider…

  1. Placing more digestive enzymes to increase digestion.
  2. Placing more external parts to become better at catching/killing prey.
  3. Placing enough internal organelles to fuel these activities.

That is better, but I still feel that the line of thought is pretty simple, repetitive, and can be made to be more engaging. Because ultimately, the only thing you are really thinking in the editor is “should I place another part down”, and I think a good simulation game should have a bit more level of detail than that. Just look at the first verb of every option I’ve outlined in the two examples above. As games like factorio and KSP demonstrate, it’s not the parts themselves that create the engagement, but rather the way you use those parts in the face of constraints.

We do have some sort of constraint in the form of osmoregulation. But it is so tremendously easy to overcome osmoregulation by, you guessed it, placing more mitochondria. And of course, we do have the constraint of MP, which only serves to slow down the placing of parts.


Let me describe some of the thought process that goes on behind a trip to the editor of KSP in contrast…

  1. What part do I place?
  2. If I place that part, how is my center of gravity affected?
  3. Is the structure as a whole robust enough to withstand the force of propulsion?
  4. Am I generating enough lift to combat gravity?
  5. Am I effectively combating drag?
  6. Can my vessel withstand the heat of atmospheric re-entry?

The number of variables isn’t what I am trying to argue for here - there are so many factors to consider in evolution, that implementing everything would make this game very inaccessible. What is instead important to consider is the nature of these different challenges. For many of these questions, it isn’t as simple as identifying and placing a part - it’s orienting your parts in a way that makes the vehicle as a whole aerodynamic and successful in space-flight. Not every question requires a brainstorm - in some playthroughs I watched, players made their ships more robust by just placing more connections. It’s variety that is important.

For example, consider the answer to various questions in Thrive. How do I make a more efficient photosynthesizer? Place more thylakoids and chloroplasts. How do I make a more energy-productive organism? Place more mitochondria. How do I make a faster organism? Place more flagella. How do I make a more damaging organism? Place more pilus/toxins. How do I make a faster organism? Place more flagella. All the problems a player might have can be answered by the placement of a part, and to me, that indicates we are lacking a bit of depth and creativity.

I hope this clearly demonstrates my main point and convinces you. We don’t need more mechanics just to give the player more systems to micromanage. We need problems that cannot be solved by just placing down a part and thinking nothing more of the issue.


THE SOLUTION - SURFACE AREA AND VOLUME

I am arguing that we should implement a constraint for the player to wrestle with to make editor gameplay more engaging - like how variables such as drag and center of gravity are constraints in KSP. In my view, a good constraint for Thrive…

  1. Isn’t “flat” like the complexity meter of Spore, and instead is fluid. There isn’t an overbearing factor outright blocking the player from doing something, it just makes certain things require thought and deliberation to pull off. In KSP, there are various way to tackle constraints, and these constraints act differently depending on your craft.
  2. Isn’t solved by the mere act of placing a part like osmoregulation currently works in Thrive. We have enough of those types of constraints - we should now be asking the player to holistically access their organism.
  3. Isn’t merely a negative in that the player is constantly having to minimize an effect they are trying to avoid. There should be rewards for designing a solid organism, not just the minimizing of costs. For example, creating an aerodynamic spaceship in KSP doesn’t just give you more control over your ship, but can allow you to move at very fast speeds as well.
  4. Is scientifically accurate, an obvious mandate for this game.

My first thought was something along the lines of creating a “streamlined” cell which will allow you to move better. While I do think that will be a very engaging mechanic for the macroscopic stage, I don’t think it would be appropriate for the Microbe Stage. At the microscopic level, water acts less like the flowing fluid we are familiar with and more like a slush that cells push through. And besides, movement is pretty uniform across all cells - it’s a 2D stage.

As such, I believe surface area and volume are great constraints to implement for various reasons…

  1. Already Planned - We already are planning to involve surface area and volume for the macroscopic stages. The square-cube law, which we will use as a means of limiting the size of organisms, is entirely a result of surface area and volume ratios. Organ systems as a whole are also defined extensively by surface area and volume - certain skeletal and respiratory structures are more effective at certain sizes as a result of the square-cube law, for example. It would then be worthwhile to involve surface area and volume within the Microbe Stage to introduce the player to a phenomena they will have to be continuously mindful of.
  2. Important Biological Phenomenon - Cells especially need to be mindful of their surface area and volume. A cell’s surface area facilitates the exchange of resources, and a cell’s volume facilitates the various chemical reactions and processes within a cell.
  3. A “Fluid” Constraint - Although cells generally prefer a higher surface area to volume ratio, there are various factors and strategies life has undertaken. Some cells seek to maximize surface area, while others do benefit from a bit more balance.

THEORY

4.4: Studying Cells - Cell Size - Biology LibreTexts.

As briefly alluded to above, surface area and volume, and the ratio between them, are important physical characteristics to a cell. Cells need enough surface area to supply their cellular functions with enough resources. The issue is, however, that surface area and volume do not increase equally as an organism increases in size. As the radius of a cell increases, the surface area increases as a square of the radius, while the volume increases as a cube. As such, energy demands wrought on by increased volume with size might not be fueled by a similar increase of resources supplied, with surface area lagging behind.

As such, organisms generally prefer to maximize surface areas. Different cells might prioritize this ratio differently - for example, photosynthetic unicellular organisms might prioritize a greater surface area more than heterotrophic unicellular organisms since they depend a lot more on constantly capturing an environmental resource. However, greater surface area to volume ratios also come with some detriments. A greater surface area can mean a quicker loss of important resources, less resistance to temperatures, and a more delicate organism as a whole (think of a leaf - maximized surface area, but flimsy and delicate).


How Can We Implement Surface Area to Volume?

We can calculate surface area by counting the number of hexes along the membrane of a cell. Volume is a bit more complicated since the cellular stage is 2D, but perhaps it can increase at a higher rate in relation to the total number of hexes counted (to the power of three if we want to be maximally accurate, though we should be mindful of balancing issues). Here is an older thread with a related discussion regarding scaling osmoregulation non-linearly with total hex count:

We can also implement a slider or something in the membrane tab, indicating a cell that is more or less spherical/flat. Though that might now be necessary at all.

The important part then is the ratio between the surface area and the volume. A higher surface area to volume ratio (meaning much more surface area than volume) results in…

Positives

  • Faster compound intake
  • Boost to photosynthetic capabilities
  • Boosted toxin resistance (faster exchange with environment)
  • Increased chemoreception range (greater exchange with environment)
  • Decreased osmoregulation costs

Negatives

  • Decreased health
  • Decreased resistance to extreme environmental conditions
  • Decreased resistance to currents

And vice versa for a lower surface area to volume ratio, along with any other buffs and debuffs which we discover to be intuitive. If you feel that the benefits to more surface area outweigh the detriments too significantly, keep in mind that a benefit inherent to more volume is the part you’re adding itself.

With that balancing act, we will find two things…

  1. Players will be vigilant of their surface area, making sure their osmoregulation costs don’t scale up too dramatically.
  2. Players will also have to gauge just how much surface area they are willing to put on in the face of the listed detriments.
  3. Players will face some constraint in the face of size, encouraging a bit of prudence and incentivizing multicellularity and colonies.

This intersection creates a lot of interesting design questions. Do you value absorption more than your health? Should you maintain a general balance of things? As a photosynthesizing organism, are you willing to become a more efficient organism at the loss of durability? How should you address toxins? These aren’t immense tasks for the player to balance, but they do offer a good amount of depth for a relatively simple, scientific, and intuitive mechanic. A simple-enough introduction to a mechanic that will act as a constraint in potentially more nuanced ways with the macroscopic stages. A strengthening of our key design idea: there is only specialization, and no adaptation is outright better than another.

And this simple mechanic results in interesting gameplay down the line, even in the early multicellular stage. Imagine making a long high-surface area cell and attaching chemoreceptors on it, and the same for digestive cells. Imagine making large cells that act as armor. This will all organically affect your organism, creating a unique combination of cells working together.


Concluding Thoughts

By now I hopefully have conveyed the value of adding more variables for the player to address.

There are some design questions still remaining, especially around the idea of volume and the exact way to balance everything. As well as how exactly this mechanic could be expanded upon in the later stages I don’t think this is a feature that needs to be implemented soon, but I do think it is important to discuss. We need to encourage a bit more depth to editor gameplay in my opinion.

1 Like

So, I read through it, and I can only abide by the conclusion and thought process.

However I would argue against scaling osmoregulation with total hex count (linearly or not). As you actually highlighted it, the problem should not be merely deciding to place parts or not: a key, little-used mechanics is where you place parts. The denser the cell, the smaller osmoregulation costs should be. Of course, the real challenge here is to find the right formalisation of this latter sentence.


In addition, I would just point out 2 minor disagreements I have with some points.

  • I think you underestimate plant gameplay a bit. In fact, you also have to defend yourself from predators (gain speed and/or defensive abilities (pili, toxins)). It doesn’t invalidate you points, but it makes for alternative problems which we can leverage. Note that, in the case of pili, it is of the utmost importance to decide where to place them.
  • Isn’t greater surface supposed to incur higher osmoregulation costs? Since you have more points where energy flows away.

And finally, a link to a previous earlier comment of mine, which relates to the topic (dwarfism & gigantism) and you may, I hope, find of interest : Game Design Discussion - #3 by Maxonovien

2 Likes

Isn’t it volume which incurs greater costs on the organism to regulate itself and surface area which better increases an organism’s capacity to do so? The material which I read in writing this post and a quick conversation with @Bird seemed to confirm this. Unless I’m misunderstanding what you mean.

I thought that was the point of the square cube law and I would anticipate more large cells if it wasn’t so. Cells are so small because of this SA:V ratio rule, where after a certain point, they just don’t have enough surface area to supply their internal structure since costs associated with volume starts to outpace any gain onset by increased surface area. That was where multicellularity stepped in as such a valuable strategy; maintain your surface area and volume, but still get bigger.

I know eukaryotes broke a lot of size constraints prokaryotes face, but that’s because endosymbiosis/the mitochondria provided so much energy for such a small amount of additional costs that the prokaryotic “rules of the game” were broken for a while.


IMPORTANT NOTE: Once again, I’ve realized that I am not the smartest man alive and have been using my terms incorrectly, as I’ve been using “osmoregulation” as a catch-all term for metabolic costs. So Maxonovien is correct, osmoregulation costs do increase with increased surface area. It is the rate of diffusion which increases with surface area, which takes in important resources faster and therefore makes too much volume potentially dangerous - too big of a cell cannot get its resources fast enough without adequate surface area.

In light of this, I guess there are two things that can be a negative to excessive volume:

  1. We make compound absorption speed be heavily influenced by one’s surface area.
  2. We add an “inefficiency” debuff of some sorts applied to the organism as a whole, where ATP costs increase to represent the added amount of effort required for resources to flow into the cell. Players can reduce this debuff, or perhaps even mitigate ATP costs, by having a good surface area to volume ratio.

I’m in favor of option two since I feel like it could be a bit confusing for players if they have an organism that should be energetically economic, but still not be producing enough energy because you aren’t absorbing stuff fast enough. It could be hard for the player to determine if the rate of absorption is adequate considering it can already be hard enough to see exactly how much of a compound is at a spot. So I think a more general “inefficiency” debuff would be easier for the player to address.

3 Likes

Surface area has a substantial impact on osmoregulation. The more surface area exists in your body, the more of your body is exposed to outside elements for better and for worse. Volume is large but not the only contributing factor to surface area.
Surface area can be mitigated by less volume, or using coverings (cell walls, or other entire cells) that help reduce overall exposure. It can be increased by having thinner coverings, or folds that increase overall surface area without greater volume.

In the end, volume kind of introduces it’s own penalties to an organism (More nutrients required to reach such size, energy upkeep, resource transference, mass, pushing against gravity, etc) but it also contributes to surface area. Volume is just a single (albeit major) variable in the equation of surface area.

Optional ravings of a mad man

If you live in an environment with very high salinity, it is likely beneficial to have low surface area because it allows you to expend far less energy in pushing salt out of your body. Why? Because there’s far less area for salt to enter in. Think of it as kind of a war front. When you are in active conflict you don’t want your forces spread out across all borders, it will strain your military until it breaks. The less area of concern, the better.

On the other hand, having more surface area can be beneficial for the same reason. Your nose has sensory cilia designed to increase the total surface area of your chemoreceptors which helps pick up smells all the easier. Many plants have large surface area because it let’s them catch the sunlight better.

Oh yeah speaking of plants, that’s a significant reason behind why evergreen trees have nettles compared to deciduous trees. The significantly lowered surface areas of the leaves allows pine trees to handle the cold much better as there is far less surface area exposed to the elements. Elephants also have folded skin for similar reasons, allowing them to more effectively dissipate heat through the mud that collects on their skin. Having more surface area in your stomach allows you to more effectively digest harder meals, such as raw foods. But of course it also takes more energy upkeep. Humans have far less folds in their stomachs than many natural predators which is why raw food doesn’t do us much good. (Note that enzymes play a pretty large role in this too) Don’t get me started on herbivore stomachs, whew! And of course there’s the brain, with more surface area increasing the overall effectiveness of the brain’s functions without outright increasing size. I don’t really know the specifics of that but it’s important there or so I am told.

I’m getting a bit sidetracked here, but the point I’m making is surface area is HUGE like, really REALLY HUGE. The decision to go with more or less surface area is a very important decision to make almost everywhere in an organism. It all comes down to how much or little you want your assets to be exposed, and either choice has it’s ups and downs.
Now onto the subject of volume; It’s often rather synonymous with surface area as being bigger just adds more surface area as a consequence no matter what. That’s just the nature of being big. It’s volume that we mostly use to factor surface area in Thrive at this time just because it’s easy.

Anyway yeah sorry the spontaneous rant

Currently in Thrive we’ve implemented this as osmoregulation. Osmoregulation increases as you get bigger because you have more surface area. It’s reduced by cell walls because these walls help reduce (but don’t entirely prevent) exposure. In the future, this will become more impactful once environmental conditions are implemented. Being smaller will mean you are less affected by salinity, temperature, etc because there is less of you to be exposed to it. Of course, you can then have enzymes/proteins/contractile vacuoles to fight the good fight and give you more room to expand your surface area despite the conditions.


  1. sounds fine to me, it kind of already exists in a way with larger cells being able to just hoover up more compounds by virtue of having a bigger hitbox. Not really sure if we should expand it more than that, as it might not really be noticeable.

I agree with 2., though I would prefer we implement environmental conditions and their effects on the cell before we try adding the additional layer of transportation tax. Though maybe it would be better to implement the simpler method first…

Environmental conditions can help prevent a player from getting too big as larger size increases your exposure to the elements. More extreme conditions will have a sharper incline in osmoregulation. I see it as something like HexCount * (1+0.X) where X is the value of environmental condition outside of your range. EX: A 10 hex cell tolerant up to 45C existing in a 55C environment would have 10 * (1+0.10), or 11 osmoregulation cost. Probably not as sharp of an incline as we would want but it’s roughly what I’m looking for.

2 Likes

^Yeah see that’s what I’ve been trying to tell you guys all this time (sarcasm)

You think so? I feel like since this mechanic would have an impact on a lot more than just environmental tolerances, it would be fine if we implement the other facets of SA:V, then implement its effects on environmental conditions later with enzymes. I feel like this mechanic could fit in with the theme of 0.6.

Regardless, even though I think this would be a great addition for a (relatively) simple mechanic, I don’t think we should be in any rush to implement it quickly. We’d probably benefit from a quick brainstorm on how such a mechanic could carry over to the macroscopic stage - as illustrated in Buckly’s post above, there are soooo many ways to make this a cool feature that we should utilize, but the question is how. It also just would help to think things over to make sure we aren’t missing a glaring fault or addition.

1 Like

Woe is me for speed-reading, I’m sorry about that. Reading through the original post again I see that you’ve already gone over the importance of surface area and all that.

Fair enough.

Thinking on this more though, I feel it’s at risk of occupying the same niche as osmoregulation. It’s pretty much the exact same effect unless I am missing a key difference somewhere so correct me if I am wrong.

Instead, it might be more interesting to apply an efficiency factor to parts based on their exposure… More on that later in my reply.

I feel hexcount should impact osmoregulation since it flatly increases total volume, just maybe not so absolutely. But then again, surface area is unavoidably increased by hexcount no matter what you do so maybe it would be redundant?

You know what? Yeah. Let’s change things up a bit and use surface area proper.

I agree with density/surface area having a significant impact though, that’s a huge one and actually gives me an idea that I’ll elaborate on below.


A proposal of change.

I’m convinced now that part placement having more importance could go a long way in making for more engaging decision-making, so I’ll focus on that in particular. Factoring in surface area might be mechanically difficult, but the more I think about it, the more I realize that determining what is exposed and not could provide a great strategic layer to part placement.
We just need to be careful not to go overboard with it’s impact and depth as Thrive is already pretty mechanically broad. There’s alot for players to wrap their head around as is.

Surface Area is Osmoregulation Cost
As of now osmoregulation is simply increased by hexcount. This works well enough, but if we want to better emphasize part placement it may be more appealing to replace the hexcount variable in the original equation with Surface. Surface would be the total amount of exposed hexagonal faces present on an organism.
The initial hex of a player would have a Surface of 6, because they are a single hexagon which of course has 6 faces.
Six

Throw a couple hexes on there, and suddenly you have a Surface of 14.

Ten
This cell shape looks great for speed, as you could easily center a flagellum for maximal speed output. However, it also has more overall exposure…

Nine
A more frugal player could adjust their hex positions like this, which would reduce their total Surface by 2, resulting in 12. This may not be very impactful at their current size, but it certainly adds up later on!
You might see that this position compromises their ability to place a flagellum in a centered position though, so they wouldn’t be quite as fast as the more linear build.

This is the basics of surface area based osmoregulation cost, and ideally would be about as complex as it gets outside of dealing with environmental conditions. It’s easy to grasp, hopefully very easy to explain in a tutorial, and even if a player is unoptimal they would still be able to survive just fine.
We could stop here, and already have more engaging placement strategy than before, but there’s more potential here.

Part Specific Placement Strategies:
So as we know, surface area is exposure. So what if some parts want to be exposed? What if others shouldn’t ever be exposed? Instead of total surface area having a blanket effect on the efficiency of all processes, exposure could effect certain parts in specific ways.

Photosynthesizing parts for example could have increased output based on per-part exposure, encouraging players to keep such parts on the outside instead of just wherever suits them.
Thylakoidunoptimal
This fellow here has opted to put their thylakoid in the center of their cell. It’s got a Surface value of 4, which is better than nothing.

ThylakoidOptimal

Being more mindful of the mechanics at hand, this player decides to put their thylakoid on the end instead, thus leading to an exposure of 5. Not a huge difference, but it comes at no cost!

In a vacuum, this would obviously lead players to maximizing exposure of their photosynthesizing parts while being mindful of osmoregulation. But what if we added other parts that wanted exposure? Players would need to sacrifice the exposure of parts in favor of others. There’s plenty of possibilities!


I believe that an implementation as outlined above could significantly improve the impact of part placement without drastically changing how the game works. It’s easy to understand, it’s not too mechanically involved, and it leaves plenty of room for additional strategy without mandatory complexity.

In terms of impact, I feel that players should not be punished for an unoptimal organization of their cell, rather instead they be rewarded for good placement. parts won’t need to be exposed to function adequately, and the player will be able to survive just fine even if they need to eat a little more due to slightly higher osmoregulation.

I’ll need some help when it comes to the math though, haha.

2 Likes

Apologies for a rather abrupt late response, as things are a bit busy for me right now!

True.

My brain might be imploding, but aren’t there 14 exposed faces here? I like this method of counting surface area though.

This is really cool, I like it. It absolutely introduces a fun mechanic to make the player more mindful of their part placement.

  1. Wouldn’t basically every internal part benefit from close placement to the membrane? This isn’t necessarily a point against this mechanic, since the cost to placing a certain part would just be the missed gained efficiency of another part. I do agree that there really shouldn’t be a “punishment” applied to placement.

  2. I still do think we should introduce some costs and benefits of surface area to volume applied to the organism as a whole alongside this part-placement based mechanic, just to encourage mindfulness of the holistic layout of your organism. Surface-adjacency bonuses are a great way to encourage more thought behind placing parts, but I think we should also develop the ability to strategize regarding your general body plan as a cell. Of the ones I mentioned in the OP, boosts to certain processes would be covered by the part placement mechanic, but things like decreased health, boosted toxin resistance, decreased environmental tolerances, etc. could be interesting. It would also generally provide a way to control size so that players can’t just place more mitochondria and be fine. And also, it would prevent things like players just becoming straight lines to maximize surface exposure without having to balance out some negatives.

With that said, this has the chance of being a very exciting mechanic.

1 Like

You’re fine and good, apparently I just cannot count. I’m not sure what I did to end up with those numbers… I must of been too excited. Regardless, the idea is conveyed at least. I’ll go ahead and edit the original to fix that.

I always prefer simplicity over extensive amounts of tradeoffs as it can make it ever harder for players to understand the mechanic to it’s fullest. I feel we should at least start off with minimal tradeoffs to see how players fare with it before expanding it if we go down this route. I guess we’ll have to wait on things like environmental tolerance regardless haha.

Everything you propose seems good in my mind save for the impact on health, which I feel is a bit much and would rather do without.

Edit: Thinking on it a little more, it aught to be fine to throw it all in at once and then tweak it from there, it would save us the trouble. Still not so sure about it effecting health though

1 Like