How good is the d20 engine for computer games?

[Anymage]

The d20 engine has a lot to recommend it for tabletop play. The math is fast and easy, and the variance of the die over the modifiers (moreso in 5e than earlier options, admittedly) allows for exciting highs and lows, while the DM can help mitigate the harshness on a night when a player's dice go cold. However, put all this on a computer and most of those advantages become a lot less applicable. Computers are good at doing much crunchier math quickly, and the dice will have to be programmed with a skew because it's fairly well known that real randomness does not match our intuitions about randomness at all. At which point you might as well go all in on an engine designed to play up what computers do best.

And yet when talking about the new OGL, VTTs and even whole new D&D branded video games are often mentioned. Which aside from name recognition for saying that you're running on the D&D rules engine, I'm not sure how good a draw that actually is.

So I'm curious. If you're playing a game on a VTT or a generally fantasy themed video game, what sorts of rules do you think are more or less suited towards those mediums. And how well does D&D match those expectations.

[Batcathat]

I imagine that the biggest upside is familiarity with not just the brand, but the specific rules, making it both easier to understand and potentially more interesting to a D&D-player.

For someone not already familiar with the d20 rules, a custom engine would probably be better, for the reasons you mention.

[NichG]

Well for one thing, computers let you work with percentage effects, which are very useful design but really obnoxious to do on tabletop. It's also easier to have a bunch of modifiers and adjustments that are dynamically and perfectly tracked.

No reason you can't have something like 'every pound of worn gear makes you 1% less stealthy, x5 effect for shoes', per-foot accuracy and detection modifiers, things that look at ambient light level or which raycast against 3d geometry of obstacles and body to determine cover.

On the other hand, things like reactive choices tend to be very awkward on computer. Something like 'any time you take damage, make a save, are targeted with an effect, during enemy moves, etc you could choose to use any immediate action power you have' end up being very awkward to implement - either the game gets bogged down or you don't really have the full time to make those choices you would on tabletop.

[DeMouse]

As someone who has GMed and played a wide spectrum of different systems I personally don't think the D20 system is even above average quality as far as systems go. However it does have the massive advantage that most people who play TTRPGs or CRPGs got into them via some kind of D&D derived game, so for one they are already familiar with it and for second they are expecting that style of system in their games.

As much as I hate to admit it D20 is probably the best pick since familiarity counts for far more than the actual quality of the system when it comes to actually enjoying a game.

[AvatarVecna]

The math is fast and easy

This is the big reason, IMO, why there's almost certainly other systems that are much much better for computer games than d20 is. The big advantage of the d20 system is that it's fairly simple - it's rare for mechanics to be anything more than simple addition and subtraction, giving it a very low barrier of entry. I personally started playing around 9 years old, and while I've gotten better at math, I feel like I've gotten worse at roleplaying, so 9 year old me is a better D&D player than I am now, probably.

But when you've got a computer doing all the math in the background, suddenly all the math is fast and easy. Every first person shooter in existence is an enormous pile of complicated equations that take your inputs and the current gamestate and figures out what happens next, and it does this fast enough to render the new result quick enough that you don't notice any delay in the delivery despite the fact that it's in 4k.

As a very straightforward example, anyone familiar with GURPS knows that the combat is absolute garbage because of all the calculations involved in getting a realistic (or realistic enough) result. Pick a gun and a target. Pick a body part on that target. Look up the range modifiers on the specific weapon you're using, and the specific kind of damage it's dealing. Look up how the ammo you're using affects the attack roll. Look up the size modifiers and damage reduction/resistance/mitigation modifiers of the body part you're aiming at. Check the tables for how cover and concealment affect the attack. Check the tables for how wind conditions and high/low ground affect the attack. Check the table for how lighting affects your attack. Check the table for how the position of the moon affects your attack. Check the table to see how both your and your target's birthdays affect your attack. Resolve your attack. Roll on several more tables to figure out exactly how debilitating that wound is going to be for your target. Roll on several more tables to figure out exactly how debilitating that recoil is going to be for you. I'm being a bit hyperbolic, but the point is that it's very tedious for what is, in-universe, a simple "point and shoot" mechanic, just because GURPS is trying to be so realistic that you have the option to factor in a thousand different modifiers for each attack. It's an agonizing process.

...or rather, it's agonizing if you're doing it all by hand.

Spoiler: Fallout V.A.T.S

Show

I will make two minor caveats in regards to the d20 system when it comes to computer games, but I'm not a game developer by any means so take it all with a grain of salt:

1) I've heard it said that most video games are built to just barely do whatever they're doing, and that's why most games are extremely exploitable. They're designed to work just well enough as long as you're not doing anything too weird. The more complicated your game mechanics are, the more likely there's going to be weird stuff that falls through the cracks that developers didn't think of. A game based on D&D 3.5 is going to have more weird edge cases come up than a game based on D&D 5e, for example. A video game based on GURPS or Shadowrun will likely be even worse in that regard.

2) I mentioned earlier that a computer makes the math of really complicated FPS games so quick and easy that it delivers it all in 60 fps/4k, but that's only sometimes true. That's dependent on the machine of the person running it. The more processing power that has to be spent calculating how to make that person's arm explode in 7 different directions, the less processing power their is for actually displaying that explosion. To that end, there is an argument for the value of simpler mechanics, in that it means more processing power for other things.

[Vahnavoi]

You do know there are both commercial and non-commercial d20-based computer games, right? Have been for 20 years or so.

For the former, play Icewind Dale 2 or something. For the latter, take a look at Incursion roguelike. The latter is especially instructive - despite being unfinished, it models a good chunk of d20 SRD content up to character level 10. It also documents whar kind of changes it made and why to make itself workable as a single player dungeon crawl.

For what it's worth, it's not particularly bad, but it's not particularly good either - computer games had been doing most things that are part of the d20 engine before it even existed. Some computer games loosely based on it (Knights of the Old Republic?) became classics of a sort, but mostly on virtues other than the cruse basics of how they crunch numbers.

[Kane0]

Icewind Dale II, Pool of Radiance (buyer beware, modding necessary), NWN 1 and 2, KotOR 1 and 2, Pathfinder Kingmaker and WotR and plenty more already that you can use to sample.

The core parts are pretty straightforward and somewhat flexible. You can get pretty thick into the sinulationist weeds or keep things relatively light and either can be pulled off just fine depending on execution. Its not amazing, but it works and is a well trodden path at this point.

[Batcathat]

I'm not sure how much the existing games proves one way or the other (except that basic fact that the d20 system can be used), since it's pretty much impossible to tell how much better/worse Baldur's Gate or NWN or whatever had been with a different system.

EDIT: Oh wait, Baldur's Gate isn't based on the d20 system, is it? Well, you get the point.

[Vahnavoi]

You kidding? There are hundreds of other computer roleplaying games that can be used as point of comparison. For a non-d20 example that can be analyzed for how much a system does or doesn't make a difference, there's the Exile / Avernum series by Spiderweb Software. Exiles 1 to 3 are the originals, using one system, old Avernums 1 to 3 are isometric remakes using a second system, Avernums 4 to 6 continue the series with a third, and finally, the new Avernums are remakes of Avernums 1 and 2 using a new engine and a fourth system.

So, using Exile: Escape from the Pit, Avernum and Avernum: Escape from the Pit, you have the same campaign implemented with three different engines and three different sets of game rules.

Similarly, Icewind Dale uses an older, 2nd Edition AD&D based system (the same as Baldur's Gate, if I recall right), while Icewind Dale 2 uses d20 3rd edition. It's about as straightforward as can be to review where the new system improves gameplay and where it does not.

[Batcathat]

Yes, where it's possible to play the same game with different rule systems, that would indeed be a very good comparison. However, I don't think comparing two different games with two different rule systems prove much about what difference the rules make (though they can obviously be used as a basis for discussion).

My point was basically just that saying "there are good games that uses d20 rules" doesn't equal "d20 rules are a good basis for a game" since we don't know what those game would've been like with a different set of rules.

[GloatingSwine]

Mu.

Computer games tend to hide the actual dice rolls and maths, which means that no matter what system you use you need an extra layer of communication about the value of different options for the player.

That means that the underlying rolls and maths are less important than how well that layer of communication helps the player make decisions.

[SpyOne]

Another big advantage of using the d20 system would be that the rules are already written.
I mean, you are designing a system from scratch you need to write rules for everything that comes up. How high can a character jump, how fast are ships, how much damage does a cannon do, how many punches can a martial artist do?
But if you use the d20 system and OGL Open Content, all those rules are out there. There are a ton of rules for weird circumstances, although admittedly the amount that has been thought through, playrested, and checked for balance against other mechanics is only a fraction of that.

Starting from scratch has a lot of advantages, and if you can put in the work will produce better results. But not everyone has the time to build the whole thing from scratch, and sometimes building the world or the story is more important than optimized rules.

[Rynjin]

The level of variance inherent in d20 systems is pretty terrible when mapped to a game, IME. I've played most of the big d20 based CRPGs out there and the one thing they all have in common is that they really encourage savescumming.

I don't feel nearly as much need to do so in other games (like Divinity: Original Sin 1 and 2) because the percentages are a bit more granular, stakes for failing a single check are lower, and the math is more hidden so I don't know that everything is just ticking up in 5% increments.

[warty goblin]

My guess is, in general, not very. I say this because, despite being free for 20 years, and there being a ton of cRPGs in that time, very few use d20 rules. If they were great for cRPGs, you'd expect them to be used.

There's probably a couple reasons for this. For starters a tabletop game is, at most, played with miniatures, while a cRPG is pretty much always animated to some degree. Knowing how far a character can jump by d20 rules isn't very useful there, because you need to animate the jump in the non-d20 game world. Much better to say "characters can jump X distance " so you can keep people from breaking the level or getting stuck in the scenery or whatever. Or you do like the Pathfinder adaptations do, and only let you jump at certain points via a dive roll and a super convincing fade to black oh look you're there now system.

This system is bad, and pretty much means there can't be a lot of jumping in the game.

But more broadly, the two are just good at different things. Look at, say, Divinity Original Sin 2. At first glance it seems quite tabletop like. You've got turn based combat and action points and abilities and spells. Now just try to imagine the nightmare of templates and rules and futzing it would take to deal with the surfaces in that game. Resolving a single fireball would be like you're got this dude who just gets damaged but this guy is out of the effect but is in the poison cloud which explodes but somebody cast rain of blood last turn so he's wet and oh look it's 1AM well good game everybody we got through a whole round of combat this week.

The computer version does all that in like a second, most of which is just animation.

Meanwhile most tabletop systems have a lot of interrupt type abilities you can use on somebody else's turn, often with vague triggers, or that could be used at any time. These are awful to do in a cRPG because you kinda have to ask every time they become relevant, which means you're mostly just clicking through a bunch of interface prompts. Makes the game about as much fun as clicking through the license agreement, and drags the turns out into super boring epics.

The ttRPG you just say "I'm using my X ability " when you want, and otherwise ignore it. No fuss.


There's other structural differences too. A lot of cRPGs are set up so you have fairly minimal choices early on. Maybe you start out totally generic, or pick between rogue/warrior/spellcaster or something. This lets you just start playing the game and more or less figure out what's fun as you go. Hemce the frequency of cRPGs having midgame respec options as well. To use Original Sin 2 again, you can just pick somebody who looks cool, and evdn if that first choice doesn't fit what you like to do, it's pretty easy to spec out of that and into something else.

D20 games are, by and large, not like that. If anything they frontload their choices. Sure you can pick Fighter and basically autopilot through leveling up for the next 20 levels, but you still have to pick Fighter out of the 12 or 40 or whatever choices right there before you've even started the game! If you find you like ranged combat or magic, but went sword and board, you are pretty much stuck.

[KorvinStarmast]

Mu.

Computer games tend to hide the actual dice rolls and maths, which means that no matter what system you use you need an extra layer of communication about the value of different options for the player.

Or you need a fellow like Jarulf and whomever first opened the door into .mpq files to get an idea for what the game engine was doing.
(I refer here to Diablo I, but also Diablo II, neither of which used the d20 system, thank goodnes, but I seem to recall that in D1 (and maybe in D II) there was always a 5% chance for a miss and a 5% chance for a crit.
Been years since I browsed the Phrozen Keep forums, so memory may not be serving well here.

[Vahnavoi]

Mu.

Computer games tend to hide the actual dice rolls and maths, which means that no matter what system you use you need an extra layer of communication about the value of different options for the player.

That means that the underlying rolls and maths are less important than how well that layer of communication helps the player make decisions.

This varies significantly by game. Some are outright tabletop rule ports, like aforementioned Icewind Dales and Incursion, and will display individual die roll results if so desired. Others, like old Areena gladiator management games, simply document their own rules to such degree that one could copy them to the tabletop by hand.

On the flipside, it isn't uncommon for tabletop games to omit or obscure information to the players. A casual player in a game where a game master does most of the math, probably will miss as much of the mechanics as a casual player of a computer game.

Another way to put it is that information design and presentation are parts of the system, both in computer games and on the tabletop.

[NichG]

Incursion is interesting to me as I feel it actually went well above and beyond the d20 rules and made a lot of choices interesting that are pretty boring in actual tabletop d20, like some of the scaling side-effects to other things from investing in skills which would normally be only relevant if the GM called for them. I wouldn't say that Incursion is just a straight port from the tabletop - its an adaptation and improvement, partially to the needs of a CRPG/Roguelike/single-character game, but also in some ways that would actually be nice if they were back-ported into tabletop play. Incursion's skills and feats feel a lot more meaningful than most 3.5e choices.

High enough Balance makes a character invisible to Tremorsense, you can identify magic items and potions with skills rather than needing the Identify spell, there are rules for creating a distraction with Bluff to make Hide checks easier and Bluff can supplement UMD in certain ways, dwarves can use the Craft skills in place of item crafting feats, Escape Artist can be used to remove the paralysis condition, ...

[PhoenixPhyre]

If all we're using is the concept of d20 + mods >= TN and the concepts of classes/races/feats/levels, not much. If you go with the full SRD, you get a little bit more (predefined values for various TNs, mostly).

But the core d20 system just doesn't give you much directly. It's too locked into DM + player + hard turn-based (with reactions, action economy, etc all designed around it).

I'd bet you'd be better most of the time doing combat as a (new) X-COM derivative, using "action points" and doing the accuracy calculations more directly/smoothly (ie faked[1] percentages). Basically keeping the skin but redoing all the core math.

[1] X-COM lies about percentages. And always has. In many different ways.

[sithlordnergal]

My point was basically just that saying "there are good games that uses d20 rules" doesn't equal "d20 rules are a good basis for a game" since we don't know what those game would've been like with a different set of rules.

While its true the statement "there are good games that uses d20 rules" doesn't equal "d20 rules are a good basis for a game", that doesn't mean d20 rules are a bad basis for a game. It just means that its a potentially useful basis for a game. I can name off quite a few computer games that make use of d20 rules, more or less. Hell, I'm currently playing a rather funny game I got on steam that makes use of Call of Cuthulu's system, to and including the d100 system.

I also disagree with the idea that you lose a lot of the advantages of the d20 system by using a computer. The biggest thing you lose is player agency when you turn a TTRPG into a computer game. Cause no matter how many options you program into a game, its really difficult to program everything a player could do at any given time. But as for the randomness, exciting highs and lows, and dice variance, that can all be emulated with a computer pretty easily. Baldur's Gate, KotOR, and a plethora of other games prove that. And you can hide or show as much as the math you want.

For example, KotOR doesn't really show you what was rolled from what I remember, it just tells you if it was a success or failure. On the other hand, Baldur's Gate does show you what you rolled, but does so pretty quickly in a small text box to prevent the pace of the game from slowing down. And then there's the Call of Cthulhu game I've been playing, which has a full on animation of dice rolling in order to emulate the anticipation of rolling the dice. Its a lot slower than Baldur's Gate, but you keep those few seconds where you "wait" to see what the dice lands on.

As for skewing things, computer games always skew the odds. That's never been anything new, and can be considered similar to a DM mitigating the harshness of a few bad rolls.

[Kane0]

I also disagree with the idea that you lose a lot of the advantages of the d20 system by using a computer. The biggest thing you lose is player agency when you turn a TTRPG into a computer game. Cause no matter how many options you program into a game, its really difficult to program everything a player could do at any given time. But as for the randomness, exciting highs and lows, and dice variance, that can all be emulated with a computer pretty easily. Baldur's Gate, KotOR, and a plethora of other games prove that. And you can hide or show as much as the math you want.

For example, KotOR doesn't really show you what was rolled from what I remember, it just tells you if it was a success or failure. On the other hand, Baldur's Gate does show you what you rolled, but does so pretty quickly in a small text box to prevent the pace of the game from slowing down.

NWN had a pretty good combat log along the bottom of the screen, you could split it in half and turn on/off which things you wanted to see in it. Showed you pretty much all the 3.0 workings as it happened, even telling you ACs, DCs and enemy bonuses. The way the engine handles turns isn't exactly true to the tabletop though, it's almost real-time with pause but not quite.

[Psyren]

I imagine that the biggest upside is familiarity with not just the brand, but the specific rules, making it both easier to understand and potentially more interesting to a D&D-player.

The reverse is equally important; there are number of folks who aren't D&D players but want to try out a facsimile of the tabletop ruleset at their own pace or without having an actual group to do so with. In fact, I recall several folks even on this forum - myself included - whose first experience with D&D was via a video game like Baldur's Gate or Neverwinter Nights.

[Kane0]

In fact, I recall several folks even on this forum - myself included - whose first experience with D&D was via a video game like Baldur's Gate or Neverwinter Nights.

*Raises hand* Specifically those, very much so the latter.

[Grod_The_Giant]

Take a look at Solasta: Crown of the Magister-- it's an insanely faithful adaptation of 5e D&D that also manages to be a pretty fun cRPG. And when I say faithful, I mean, like, down to the action economy.

[Tanarii]

NWN had a pretty good combat log along the bottom of the screen, you could split it in half and turn on/off which things you wanted to see in it. Showed you pretty much all the 3.0 workings as it happened, even telling you ACs, DCs and enemy bonuses. The way the engine handles turns isn't exactly true to the tabletop though, it's almost real-time with pause but not quite.

I played a lot of 3e and a lot of Neverwinter Nights. NWN delivered an experience that was almost, but not quite, entirely unlike 3e.

[PhoenixPhyre]

I played a lot of 3e and a lot of Neverwinter Nights. NWN delivered an experience that was almost, but not quite, entirely unlike 3e.

Yeah. NWN and 3e are like first cousins...in Alabama. Close enough to see a family resemblance, but very definitely not the same.

[TaiLiu]

One computer game that uses a d20 engine and hasn't been mentioned yet is Dungeons & Dragons Online (DDO). It's a real-time MMORPG. To my knowledge, the developers have been moving away from the d20 engine by adding all kinds of calculations that would be a real pain to do in a TTRPG. But the core is still technically the d20. I think they've been adding all that stuff cuz the d20 engine, along with things like binary AC and all that, is a poor fit for a MMORPG.

So... I guess it depends on yr goal. If you wanna make something super dedicated to TTRPG D&D, something like a AI-powered VTT, then the d20 engine is great. A MMORPG, not so much.

[GloatingSwine]

This varies significantly by game. Some are outright tabletop rule ports, like aforementioned Icewind Dales and Incursion, and will display individual die roll results if so desired. Others, like old Areena gladiator management games, simply document their own rules to such degree that one could copy them to the tabletop by hand.

They can show die rolls, but those older games don't generally give information in advance when you actually need it to make decisions.

So the roll log can show you why something happened, but not show the chances of two different things that are going to happen. eg. do you have a better chance of succeeding with Hold Person or Web? You don't know unless you use an external resource to look up their saves or trial and error it.

As an example of "presenting useful information" Pillars of Eternity in its default mode will show the chances of success of any given attack and which defence it is targeting. So even though its underlying mathematics are quite complicated you don't need to know them, you click an ability and mouse over a target and you know how likely you are to succeed with it. (It doesn't use randomness for out of combat actions, it uses either fixed thresholds, consequences or resources. eg. if your lockpicking skill is 1 lower than the level of a lock you can spend a lockpick, if it's 2 lower you can spend 3, if it's 3 or more lower it's impossible, or sometimes if you don't meet the threshold for a check you pass with a wound).

[Vahnavoi]

@GloatingSwine:

Of the given examples, Areena is completely transparent. It literally gives you all the numbers needed to figure out the information you say it doesn't.

Icewind Dales give about the same information as a tabletop game would. Under normal rules, D&D doesn't give players perfect information on enemy statistics either, so figuring out the odds empirically through trial and error is part of the game even on tabletop.

Incursion and other roguelikes have monster memory that can, with correct player resources or just killing the monster over and over again, give you the exact statistics of those monsters, again allowing the exact kind of inferences you say they don't.

So, again, lumping computer games on one side and tabletop games on the other makes no sense. How transparent and perfect information a game gives to the player is entirely game dependent. There are tabletop games that work like Pillars of Eternity and it would not surprise me if that design scheme originated from a tabletop game.

[Rynjin]

One computer game that uses a d20 engine and hasn't been mentioned yet is Dungeons & Dragons Online (DDO). It's a real-time MMORPG. To my knowledge, the developers have been moving away from the d20 engine by adding all kinds of calculations that would be a real pain to do in a TTRPG. But the core is still technically the d20. I think they've been adding all that stuff cuz the d20 engine, along with things like binary AC and all that, is a poor fit for a MMORPG.

So... I guess it depends on yr goal. If you wanna make something super dedicated to TTRPG D&D, something like a AI-powered VTT, then the d20 engine is great. A MMORPG, not so much.

Ehhh, a lot of the things they added that go against tabletop (like Grazing Hits) actually make it a worse game overall. They're just there to paper over the horrendous powercreep the game has experienced.

[Tanarii]

They can show die rolls, but those older games don't generally give information in advance when you actually need it to make decisions.

So the roll log can show you why something happened, but not show the chances of two different things that are going to happen. eg. do you have a better chance of succeeding with Hold Person or Web? You don't know unless you use an external resource to look up their saves or trial and error it.

That's no different from a d20 game. There's no assumption you will know the TN in advance of making the roll.

A rough estimate of difficultly (or even exact DC) is reasonable for a DM to provide in any case where the character has time to assess in advance. But it's not assumed.

In cases of AC and saves, it's very likely you won't know before choosing which form of attack / spell to use what your odds of success are.