Animating Quadruped Characters in The Flame in The Flood

[Music] uh my name is Gwen I'm a tech artist I'm an animator and I'm a studio founder I've been an animator for about eight years now yeah why thank you two years ago I actually went Indie I left triaa and I started a small Indie studio in Boston with five other people we just shipped our first title the flame in the flood [Applause] this is really good you should just do this the whole time I feel really good about this anyway so the flame of the flood was very unique this was a this was a game where most of the characters I was animating were not humanoids they're not bipeds most of the characters I was working on were quadrupeds they're animals with four legs uh to worry about and I found that traditional biped animation techniques just didn't work very well for quadruped characters I found that there was uh the quadrupeds present unique problems that

we needed to solve uh when working on a quadruped character I want to kind of go through my process I kind of want to go through my process I uh mostly try to solve three problems before I dive down into actually animating the character or polishing any animation the three problems I want to solve are moving forward through the world you know your forward Locomotion I want to solve I want to figure out how I'm going to get the character to turn which is extremely difficult for quadrupeds and I want to figure out how I'm going to transition between moving and idle and back again and I found if you can solve these three problems then after that it's mostly polishing up your animations and adding on whatever your gameplay layer is so for this talk I'm going to be demonstrating my solutions for these problems using two characters the first character I'm going to show you is the boore this is a uh kind of cartoony Stumpy little character with short little leg

it's a character that kind of idles for a while and then charges the player really quickly like a battering ram and then it returns to idle um I streamed the entire development process for the boore so all the footage you're going to see in this talk is from when I was actually working on it developing the boore uh and I'm supposed to tell you we used Unreal Engine 4 for development so a lot of the footage you're going to see is actually using the uh the in-game animation Blueprints and such all right so let's get started the first thing I work on when I'm doing Locomotion for a quadraped is forward Locomotion uh this is just moving forward through the world I think everyone here is probably familiar with um how you make a a bipad move forward through the world usually you animate a walk and then you animate a jog and you animate a run and you do like a linear blend between these animations you keep the foot phasing roughly similar between these animations so that you know your linear blend will work properly

um for quadrupeds a lot of people uh if if you're looking at a quadruped they generally have like a trot and a Gallop so a linear blend like that wouldn't work what I decided to do for the boore because the boore pretty much always moves at roughly the same rate I decided to make it a linear blend and actually use that biped style linear blend and just go between having a slow Trot a slightly faster Trot and a super fast Trot for the boore I thought I could get away with this because his character is really cartoony and here you can see the final result um I'm slowing this down quite a bit for the slowest animation for the boore and the fastest animation for the boore and you can see it's it's the feet are hitting the ground at roughly the same time the footfalls happen at roughly the same percentage of the animation for both of these animations so if you're familiar with biped this should seem pretty uh pretty standard to you here you can see actually all four animations for Locomotion for the boore and you'll notice that each animation the footfall

uh line up pretty closely with the next slowest and the next fastest animation and you this helps you really visualize and know that your animations are going to uh blend together properly when you set up your blend space all right and this is the actual blend space for the boore in game um what you see here on the the line are the little the dots are those animations that I demoed a minute ago um and you what I'm doing is I drag the cursor from left to right I'm manipula this speed variable this is the speed at which the character is moving through the world uh and I'm just simulating what would happen if the character moves faster through the world and you can see I'm blending through these animations again this is probably really familiar to you you will notice that I have more animations when the character is moving slowly I find when a character is moving slowly they um foot sliding and glitches are way more obvious than if a character's moving quickly they you can get away with a lot more when uh flailing around when a character is moving quickly through the world

all right so that was the boore I think this is a a good setup if you have a character that's maybe more cartoony like the bore was I think this is a setup that you're all familiar with so you can do it pretty quickly it's really easy to generate uh animations off of existing animations like it's it's easy to take a slow Trot and make it a fast Trot versus having a walk and a Gallop which will be totally different animations so I think this is a really fast setup but it is extremely unrealistic it's this is not what happens in the natural world all right the other character I want to demonstrate today is this wolf this is a character that always stays on a perimeter near the player this is a character that modulates its speed this is a character with a a long spine and these really lanky Limbs and I really really wanted to differentiate the motion between these two characters um because this is a character that that uh has much more Dynamic motion and moves through the world in

uh it it slows to a stop rather than stopping suddenly it tends to run around the player at any given time because this is a character that does this I really wanted to uh have it properly transitioned between having a walk and a gallop and so forth so when I started for the wolf I went ahead and I animated a walk and a trot and a Gallop just like you would expect and the foot phasing for these is not the same they don't line up at all really if I was going to try to do a linear blend like here's a trot and a Gallop if I try to blend between them that's obviously not going to work you're going to get into some kind of funky dance right so instead what I'm going to do is I'm going to take and I'm going to scale the play rate of those animations based on the speed of the character so if the character is moving twice as fast as the animation was authored at then I play the animation twice as fast if the character is moving half as fast as the animation was offered at then I move then I play uh the animation at half speed I what what I want to what I want

to do is when I move at a certain speed I want to transition from the walk to the Trot to the gallop this way you never actually see the walk playing at 2x speed you only ever see the walk playing at uh maybe 20% faster or 20% slower I transition quickly between these animations and each of these animations has the play rate uh scaled based on the velocity of the pawn or I'm sorry the velocity of the character for this you will actually notice there is a uh uh some foot slidding when I go between the Trot and the gallop if you look closely because they obviously don't line up in any way but because the character is moving so quickly through the World by the time that transition happens you really don't notice that it's basically imperceptible so what should you take away from this I think both characters were successful I think the wolf feels more like a quadrip I was actually pleasantly surprised that I could just do a quick transition and I didn't have to offer an animation to transition between TR and Galloping it actually

worked pretty well to just do a quick blend I think the the boore was successful because it it mostly ever only ever moves at one speed um so I was pretty happy with both characters so after forward Locomotion you tackle your next problem which is turning this is extremely difficult for quadrip heads quadrupeds tend to have multiple points of the contact with the ground at any given time I can demonstrate just looking around being incredibly difficult for quadrupeds I mean imagine like it I'm here if I look around or if this biped character looks around it's pretty simple it's pretty straight forward you can manip uh you can look behind you and you can twist your spine in order to look behind you whereas for a quadrip if you try to do the same thing if you try to twist the spine you get some really ugly deformation you get a pose where the the front limbs feel like they're they're unnatural they they should be moving just to even look around

so I knew that turning would be very difficult and I decided to break down turning into three steps I decided that the first thing a character does when they turn is they a quadraped should look in the direction that it's going to turn and then I felt like the front legs should move in that direction and the spine should kind of Arc and then as the quadrip continues to move in that direction I wanted the spine to straighten out and I wanted the back legs to catch up so here's a prototype early on this is after I had already had the forward Locomotion happening so the the character is walking forward obviously I haven't had a turning solution yet here uh and what I'm done is I've slowed the turn rate of the character in engine so that you can see the this wolf is not snapping to turn in the direction it's moving it's moving a little bit slowly what I'm going to do now is every frame I'm going to query the direction that the wolf is moving and and I'm going to query the direction that the wolf is facing I'm going to find the Ang that's the difference between those two

directions if I take that angle and I apply it to the spine I can get the front legs to kind of follow uh or to I can get the front legs to point in the direction that the wolf is moving so here's a really early example of this all I'm doing is I'm taking that angle that I'm getting every frame I'm dividing it by three because there's three joints in my Wolf's spine and I'm adding that as a world space rotation to the spine and what I get now is I get a character that has its front limbs always moving in the direction that the wolf is is or always pointing in the direction that the wolf is facing and I get the back limbs to kind of catch up as the wolf moves forward because the pill is turning slowly um I did this using skeletal controls but you can imagine once you get that angle you could solve this in many ways you could use that angle to drive an additive animation that that off that curves the spine you could drive a blend space that has a spine um arked in different directions there's

any number of things you can do once you have that angle I mean obviously there's a lot of foot slidding in this video it was still pretty early on what we ended up doing finally in game was I I worked with my programmer at this point to manipulate the path of the wolf slightly uh we we decided to take the turn rate of the character of the pill of the character and we set that to Scale based on the speed of the character so if the wolf was ever stationary it couldn't twist its spine but as the wolf moved faster it could twist its spine more um my programmer Damon also went ahead and uh set the wolf to never turn directly in place the wolf always moves forward just a little bit in order to turn similar to a car like a car has to kind of be moving forward a little bit in order to turn and that's how we got the result that you see here so I like that result a lot I thought it worked really well for the wolf

uh I didn't think it would work very well for the boar for the boar I wanted this to be a character that I I didn't want to have a separate looking with the head and looking with the spine I didn't want the separation there I wanted this to be one mass that was always focused on either uh looking in the direction it's moving or looking at the player I also wanted to experiment with different solutions uh I knew that the boore would mostly be moving in a straight line and not arcs so for the boore I decided to try using a blend space instead I'm going to take that same angle and I'm going to use it to drive a blend space here you can see I have my fastest Trot my my medium Trot and at the top my slowest Trot and for each one I authored a variant one where I'm looking 180° to the left and one where I'm looking 180° to the right in order to do this I actually in each of these animations the board is facing forward but I'm kind of creating a strafing motion at these extremes when you're looking completely behind you because I I didn't want the bore to look like a u I wanted the bore

to kind of strafe if it was looking completely behind it and here's the result of applying those animations to this blend space this is the same thing you saw earlier where I had when I was moving between left and right I was manipulating the speed of the character I'm still doing that now I've also added this turn direction for the up and down Vector here right so whenever I move the cursor are up or down I'm simulating if that angle is 180° or if that angle is 180°. and I've created this blend space where just by getting the angle between the the direction the character is moving and the direction the character is facing and by getting the speed I can uh completely blend between these different animations to get a final result that'll work for the character all right so now we've handled turning we've handled forward local motion and we get the hardest part about

quadrupeds which is stopping and starting again I find like I said earlier that a character glitches and foot sliding is way more obvious when a character is moving slowly your character is never moving slower than when it's about to stop so this is where you really need to focus your attention on trying to make this look good for a bipad stopping and starting again is pretty trivial bipeds pretty much only ever have one foot on the ground at a time you can see here I'm showing anytime the left or the right foot is hitting the ground um and they're they're never both planted so if you really wanted to you you could do what most of you is do where you actually animate the transition between idle and or between Locomotion and idle and back again uh you would only have to make two animations one when the left foot is planted one when the right foot is planted and I think a lot of Studios do this and I think this is a complete non-starter for quadrupeds quadrupeds could have two feet on the ground at any given time they could have three feet on the ground um the the the feet could be

in different positions relative to each other if they're in a Gallop versus if they're in a trot so offering animations to transition between Locomotion and Idol seemed like a complete nightmare it seemed like a complete non-starter to me you could always do what many games do which is just blend directly from Locomotion to Idol I think this looks really bad I I think it it's uh it just didn't hit my personal Quality Bar um um the when you animate your idol and you assume that the feet are going to be in certain positions and then you're your blending from a Locomotion where the feet could be in completely different positions then when you do that blend the feet will probably slide along the ground you'll get something that looks really wonky what I'm going to recommend instead is what you see here on the right where you assume with your idle that you don't know where the feet are going to be you just pull them right down to the ground and you idle wherever you are here's how I accomplished that with the wolf so for the wolf I had this walking

forward animation and what I did was I authored a second animation which is the same thing it has the feet in the same place but I any feet that were off the ground I just pull it to the ground on that at that point in the animation so I get this animation where the feet are just kind of sliding around around on the ground right I also lowered the center of gravity for the wolf slightly if you recall from earlier for the wolf I'm scaling the play of the animation based on the velocity of the character so if the wolf is moving at half the speed that the walk was ather at then the walk is playing at half speed if the wolf is not moving at all if velocity is zero then that walk freezes because the play rate is zero at that moment I all I have a a blend on my tree so I blend from a walk to an idle State this idle State uh is that grounded animation that ground animation is set to sink with The Walking

animation so what happens now is anytime the wolf stops moving the walk freezes we blend the idle which is uh the same frame uh it's just that that the same Frozen animation but with the feet down and uh the wolf will kind of freeze there in place it'll lower its body and it'll kind of be Frozen with its feet on the ground when the wolf starts moving again when velocity increases the wolf will blend back to walking it'll pick up right where it was before just picking up any foot that it just put down on the ground and it'll just resume walking I thought that was pretty cool so I decided to do the same thing for the boar however if you recall the boar is set up a little bit differently there's three walking animations for the boar so in order to do this for the boar I had to offer three feet planted animations and I had to create a blend space I would mirror what I was doing with the walk and that's what you can see here

and here's an earlier prototype when I was working in the boore this is where I was at this moment I had the boore moving forward through space um using its trotting blend space I had the boore turning in this case pretty much always to face the player rather than facing move Direction and I have the boore stopping so anytime the B stops it pulls its feet it freezes and it pulls its feet down to the ground this is all well and good but now your character is frozen anytime it stops moving and we're animators so that's not okay so the next thing I did was I authored an additive Idol for these characters and I'm going to play this anytime the character is frozen this was the first additive Idol I made for the boar you can see here it's a very basic keep alive I'm mostly only animating the Torso and the head and the tail I'm very careful not to animate the feet because I don't know

exactly where the feet are going to be they could be in any position and the legs could be at any rotation when the character stops and this is the result of applying that additive animation to that idle state so now whenever the bore stops moving it freezes in place it lowers its legs and it in that Frozen poses it plays this additive Idol you'll notice here that the feet are kind of swimming around on the ground a little bit this is especially a apparent when the boore turns because its hips are turned and its torso is also turned so I'm going to zoom in in a second here and you'll see there's a lot of foot swimming they're kind of drifting around on the ground they don't quite feel planted and grounded I think anybody that's worked with additive animation is familiar with this uh this is a result of the way a computer sees additive animations when you create an additive animation you give uh your engine a finished result and it breaks it down to a pose and an

and uh an animation if you take that same animation and you apply it to a pose where the the Bas is is turned or moved in any way or I'm sorry if you apply that to a pose where the hips or your base is rotated then what you're going to get is a something that's mathematically correct but doesn't quite look right the feeder is going to be swimming around on the ground so the way I fixed this for the boore was a little unorthodox I just went ahead and I parented the Hooves directly underneath the root of the character and I reversed the joint chain so that the knees are underneath the ankles and the hips are underneath the knees I did this rather than use ik in order to kind of save some performance because we couldn't run for ik at all times on all quadrupeds um but what this is going to do because I did not move the Hooves during the additive idle there's no translation data on the Hooves so when I play the additive Idol the hoves are going to be locked down to

the ground and you can see that here so now the hopes are locked down to the ground and technically there is still joint swimming but it's occurring at the shoulders and at the hips which is very difficult to detect especially with this particular character this is a character with a massive torso and our camera is top down so you you never see what's going on in the chest or in the hip region of this character I can get away with this cuz I am you know the rigger and the animator and everything in my studio but I know most Studios you probably can't re parent up your joints if you're in the middle of production that's probably a non-starter for most people so I think a more typical response would be to run ik on each leg if you can afford it for your game and I'm going to demonstrate that now this is the additive Idol that I made for the wolf it's just kind of like an an aggressive motion I am definitely moving the hips and the I'm

definitely changing the rotation on the hips and on the Torso for this character and this is that additive applied in Engen and what I'm doing here is I'm going to or what I'm doing is I'm taking the world space position of the Paw before the additive is applied and I'm running an in-game ik on each paw that will end at that position and so this is just doing a bit of fix up to keep the feet completely planted in place while that additive [Music] runs all right so what should you take away from this I think there's three main things you should look into when you're animating a quadruped I think the first thing you do is you figure out how this specific character is going to look moving forward through space you solve that because that's a lot of that's a lot of the character and the feeling behind whatever it is you're animating the next thing you do is you figure out the technical problem of how you're going to turn because that is a huge challenge quadrupeds and then you figure

out how you're going to transition between moving and stopping and starting again what I did for this talk was I showed the boar using a linear blend for its forward Locomotion I showed the wolf doing a kind of gated approach for its Locomotion and I showed how I solved turning and how I personally solved transitioning to idle and back again I recommend when you transition to idle I I think it's wise to not assume that the feet need to be in any specific place but to find a way in your engine or in your game to pull the feet down directly to the ground and animate wherever they are I think that's an elegant solution and it's one I I've personally enjoyed doing quite a bit all right so that was my talk I am on Twitter and on YouTube I do two minute technique videos two minute animation technique videos on YouTube that just show off whatever Tech animation stuff I'm working on at any given time so definitely you know check that out I hope you enjoyed the talk

thank you for coming I did just ship my first title as an indie the flame in the flood so if you get a chance to I don't know maybe Google it or something that would be cool it's kind of a big deal to me um what else was I supposed to remind them oh if you have any questions please come up to the mic and please say your name and uh I'm going to repeat the question back at you thank you [Applause] no questions that's cool that makes this way easy one question uh hi Garrett um okay so I have a couple questions you talked about your process but how does your process fit in with everybody else so like did you have ai behavior for the for the enemies before you started prototyping your animation blending and

how that worked or was it kind of Al together or did you do that okay so there I feel like there was two questions there you asked first I think you you asked how what I'm doing here is different from how other people approach quadrupeds uh no um within your studio um how did you work with the people prototyping the actual enemy Behavior or did you do that like as far as gameplay gotcha okay so our studio is six people uh I do all the protot typing everything you saw up there up until until I said my programmer stepped in here was literally me I just used blueprint to script the pond to move from one location to another uh we're we're a very small outfit so there isn't I don't have to worry too much about working with other people uh clearly um yeah so I I guess that would be me um so you said with the bore that you couldn't afford to apply ik to all fourt with you know potentially multiple

creatures and then you said with the wolf that you then did that yeah I was playing around sorry yeah I was playing around I to be honest I did the the wolf before the boar um and for the the wolf I wasn't sure if I could afford to have those 4 ik running at all times it was at that moment we had not yet done our profiling and we were unclear on exactly what platforms we would be on at that point the wolf was the very first AI we worked on so when I came time to do the boore I was going I decided to use the boore as a chance to experiment with other solutions that would be maybe save us some performance because it was something I was personally a little bit worried about I was looking at the time at this and I'm like that's 12 I is running at all times plus the dog so that's another four so I guess I'm not that good at math uh and I I was concerned that that might be EXP expensive I didn't actually know yet sure so the for the wolves that

stayed in and then for the BS you found another solution or did you then retrofit the wolf as well I have not yet retrofitted the wolf I've decided to tackle that when it becomes a problem because it's a huge pain to change if you're going to change the rig to and reverse the joint order that's that's a and then reexport all the animations and then like check it to make sure that everything looks right that's a significant chunk of work and I'm one person so if we end up hitting a performance problem on the CPU I I will definitely look into that and see if that's a place we could uh we could make some savings um sorry uh oh sorry go yeah hi um so this might be a bit more of a technical question in terms of like how you doing specific things in unreal but um you said you mentioned you're getting the the turn uh the AI characters actually doing how how are you actually get in that cuz we don't seem to be able to have access to that to get access to

the turn rate of the character to the not not the rate but the actual turn that is going to actually be making oh manipulating the path finding to AR yeah that's why I got a program invol oh right yeah that was uh I tried scripting solutions for that it did I I did not succeed in finding a scripting solution for that quite yet maybe uh sorry um I can answer that a little bit there was a talk yesterday if you go look at the vault um and it was on quadruped motion involving a dog yeah and so it was a very similar solution so you can go look that up on the vault which will answer that question okay thank you cool that that's do my job for me I appreciate that hi um so it seems like you basically had two kinds of creatures the wolf were had a discret spine and you wanted to separate the motion of the front and back legs versus the bore which didn't really have a spine you wanted the whole body to move as as one object uh would you foresee like a third

kind of creature we have to do something in between them or do you think that you could pretty much separate all quadrupeds into these two categories um every time I do a character I do a completely different solution because I can so these aren't the only two characters these are the just the two I focused on cuz I only have half an hour so there's also a bear that rears up on its H legs and that moves in a way that's very different it's actually like kind of like a rabbit for the bear I tried to I experimented with idea that the front legs and the back legs actually move completely differently and independently and I kind of solved in between um that was not the best solution so it didn't make this talk uh the dog I believe is the dog is actually a pretty good hybrid between the two uh between my solution for the wolf and my solution for the boar uh the rabbit's obviously a totally different creature entirely okay thanks cool so you're showing a lot of flat terrain and I don't I don't know if you guys build the levels with this in mind but how do you

handle inclines and the change in slope how would I handle that oh I'm sorry the question was how I would handle inclines or a change of slope we don't have too much of that in our game we do have subtle inclines at times and that did come online a little bit late if I was working at a tripa studio or somewhere where I had to worry about that generally what you would do is you would take the pill and you would adjust the pill to kind of rotate to be um uh perpendicular to the to the whatever ground that it's over and then you would probably update the feet using ik Solutions so that they're always on the [Music] ground all right that's our time thank you everybody [Applause]