Making the Most of Animation Blueprints | Unreal Fest Europe 2019 | Unreal Engine

>>Jeremiah Grant: The title of this talk is Making the Most of Animation Blueprints, and kind of sub-title it with Dynamic Motion in Fortnite First off, who am I? I am a Senior Tech Animator at Epic I have been working on Fortnite for about the last year, year and a half Previously I worked on Paragon, and a few movies and other games Either way, I have been doing rigging, simulation, Character work Gone by many titles; Rigger, Creature TD, Technical Animator, Character TD Technical Artist They are all kind of the same thing; creating simulation, attaching verts to bones, and making them move good Specifically, on Fortnite, Tech Animator is creating the Skeletal Mesh, doing the rigging, and adding the simulation on top Fortnite has been in development for many years, and there is a kind of a standard motion set on the Characters already, so the Skeleton is pretty fixed for the biped We have six body types, but they are all retargeted on the same Skeleton That is fixed All other bones that we want to add in, we do that later on individual Skeletons, and I will go over that in a bit This talk is kind of broken up into two parts; the first, I am just going to go over, what is a Character in Fortnite? How do they all combine and get assembled? Then I am going to go over more of the dynamics and individual nodes, how we assemble those and some specific settings, that might help you out, hopefully What is a Character? In this case we are looking at a constructor, one of our Save the World Characters You see a body and a head, some hair, an extra little robotic arm and a backpack Every Character is going to have a head and a body, that is kind of how we define our Characters That can be kind of weird; for instance, we had a banana Character recently Where is the head defined on a banana? I do not know But we got creative, and it worked out In this case, the beard and hair, which we call face accessories, those will have their own Animation Blueprint, their own Skeleton All of these will have their own Skeleton Animation Blueprint, and will be combined in right along Diving in a little deeper, I kind of feel like our job is moving just files around These are all the files that might make up the Character We would probably consolidate some of these, but again, every Character is going to have hair, which hair, Skeleton, Animation Blueprints and a data item, or a data Asset That data Asset, which we call Character parts, contains references to the Skel Mesh, the Animation Blueprints, the master Skeleton — which everything is targeted on — and a few other things You can do Material overrides and such on that That is a whole other talk, just about those data Assets as well Zooming out a little further, we see what makes up a Character in its completion There is a Character item definition, Hero Item Definition, and Hero Specialization, and multiple Character parts All of those are data Assets, and all of those contain some amount of information about what the Character is Once we get into Character parts, that is where as a Technical Animator, we start working We start adding in references to our Animation Blueprints, or Skel Meshes, Skeletons, and any other number of things This can get quite complex, especially on something like a progressive Character We have a Viking Character or a pirate Character, and those may have five or ten different tiers — all of those with individual Skel Meshes, Skeletons, Animation Blueprints, Character parts — that gets quite unwieldy, and so carrying those all the way across the finish line can be a bit of a challenge How do we do that? Copy Pose from Mesh is probably our go-to node, and in this case, that is what gets all the animation from that invis Skeleton or that base Skeleton onto our Characters Every Skel Mesh that you see is an attachment onto that base Skeleton That way, we get the performance of just running one Skeleton Everything gets attached on, so on the servers you will just see invisible Skeletons running around, and everything is propagated locally Some of the settings here on the Copy Pose from Mesh is the Use Attached Parent, and that is actually what gets the motion from that base Skeleton That is what we use on nearly every Animation Blueprint; this is how we start, except for a few exceptions

where we just attach to a bone or a socket That would be using probably a sub-graph input, or something like that, just for performance reasons Copy Pose from Mesh essentially does just bone mapping, direct bone mapping, so the bone exists in the base Skeleton or the parent Skeleton, and it exists in the attachment Skeleton, then it will just drive those directly That way, in your child Skeleton, you can add as many bones as you need, drive those individually with Anim Graph, and then you can get layers of motion That is really where the work comes in On a Character, again, we can have tons of different things Backpacks can take on various shapes, sizes, motion sets — all kinds of random things Hair and beards can practically be an entire Character of their own Clothing can be everything from a giant skirt or dress to whatever we can — to a banana, if you want Danglies are just anything that is hanging off, and danglies can be on a pickaxe, it can be on here — her hair would represent some of that The wings can have dynamic simulation that would just kind of be dangling We layer all of those on This gets really tricky when we are talking about putting a Character across a dozen different platforms, and still having them feel like they are the same Character If you spend real money on a Character, you want to be able to play that Character, whether it is on your phone, or on the Switch, Xbox, PC That becomes really trick as a Technical Animator, to make that work The way we approached it is, you start from the bottom You start with the lowest common denominator If you are doing a dress, how can that dress, when everything gets LOD down, still feel and react like it is part of that Character? When you are on a mobile device, we are not actually using some of the simulation libraries, like Rigid Bodies and AnimDynamics, and a couple of others But we still have a few other tools that we will get into later, to get some of that motion The key thing to think about is, peeling off these layers of simulation, and still making it work, like maybe just skinny two legs and adding some corrective bones or some corrective shapes, and then adding a simulation layer on top of that, which might be another Skeleton — not an actual Skeleton, but more bones that can be LOD’d off and still pad the skinning back up The key of this, of course, is test every LOD all the way through, because you will see it On some of our gameplay modes, you can have 20 Characters, 50 Characters all in one place, and you may only have three Characters that are LOD 1 The next tier — LOD 2, the next tier — LOD 3, and those can all be on screen at the same time They all have to look pretty good, hopefully With the most complex graphs, if we are doing a lot of complex evaluations in the event graph, then we would try and nativize that into code after the art has been complete, and that gives us a lot of performance Let us dive into a node here We are going to dive into the Rigid Body a little bit In this case, we have it on a pickaxe, on this floppy shark Here, I would not really call this a dangly, though I think we do have a dangle there on the rope But we need to just kind of have that rubbery feel, and we want the Rigid Bodies here I do not know if we can quite see those numbers on there, but starting at the top, that is where our physics Asset would be; though I think in this case we would put the physics Asset on the Skel Mesh Going into the gravity settings, we are not using it here, but on most of our Characters, we actually explicitly set the gravity That allows us to control the weight of the Asset Kind of an odd legacy thing that happened on Fortnite is, years ago, just as people were messing around and kind of game jamming the whole game, gravity got set to about three times gravity That is just now how gravity is in Fortnite, so we are countering all that back on our animation nodes, back to real-world gravity, just to make things work That was actually a real challenge for us, because we could not figure out why our Rigid Bodies were breaking all the time;

things were jittering all the time I have gone online and I have read a lot of people have had these same type of issues, and hopefully I can dive into how to help that out a little But setting gravity explicitly helped a lot Setting your simulation space helps a lot When you have a Character that is running around in World Space, which here we do have it set to World Space — though we should probably change that — when you are in a vehicle and moving at what unknown speed, everything is going to be pulled away from your Character You are not able to control it Usually we simulate either in component space, root bone space, or if you have a bunch of dynamics on the shoulders, you might just do Spine 4, Spine 5 space, and the infuse more motion using that component linear acceleration scale and component velocity scale Those, essentially infuse world velocities back into the Asset Danglies — that is what we are calling them here, because I do not know what else to call them We are looking at a couple of different nodes here We have the Trail Controller, the AnimDynamics nodes and Constraints I think Constraints are a little newer in the Engine — has anyone used them at all? Excellent! I will talk about Constraints All they are is, you enter in kind of a parent’s constraints, or a barnacle, or rivets, if you are familiar with any of those terms It attaches an Object to the surface, or wherever you place a bone, and then rides along based off the percentages of the bones listed there In this case we have a ring and a skull, so a skull on the hip, which is weighted 100 percent to the skirt and 0 percent to the pelvis It is parented to the skirt, I suppose You can drive those live If you wanted to swap out the kind of space switch, that skull, whenever a Character does some specific motion, you could absolutely do that This has been crucial for us to get bullets sitting on the chest, or some sort of layers of simulation, and then something that sits on top of that, and that thing on top can have its own simulation Since this is all a linear process, you can layer these in very specific ways to get the type of motion that you want Trail Controller is not in the simulation library, which means that we can use that on mobile That has kind of been our saving grace for everything, for capes and for various Objects I think in here we are using a little bit of Trail Controller for — the sword has some of it, I think That way, we can still get some of that life in the Character as we peel away those layers, and get down onto mobile A Trail Controller is a lag-based, positional-based node where as you pull the — it just comes right back to Ref Pose over a period of time You can define how quickly that is You can define a curve as it finds its children, to how quickly it returns draft pose But the downside to that is, you do not get any overlap, you do not get that secondary motion that you need You can combine that with things like the Spring Controller, which is also not in the simulation library, which works on mobile for us, and get that secondary motion kind of layering on these We also see AnimDynamics here AnimDynamics, some people love it, some people hate it I love it. AnimDynamics is essentially a pendulum; you are hanging a pendulum off of a bone The bigger you make the body, the slower it will move You can make it kind of like a pancake, and it will just wobble You can alpha it on, you can do all kinds of tricky things with this I have a little bit in here, where we talk about kind of being sneaky and driving simulation, using different simulation nodes to get exactly what we want Let us dive into specific Asset type, Backblings Backblings encompass anything that attaches to the back In this case, we have four different types We have just kind of a static backpack, a dynamic backpack, cape, and some wings They attach to a socket, so they will not be using that Copy Pose from Mesh They will probably be using a sub-graph input That means that they do not know where the shoulders are; they cannot react to how the spine bends But we still needed to attach

and feel like it is grounded to the Character, and still r react to the Character That goes back to selling that fantasy, being consistent across all platforms The backpack on the right, the static one — that is just geometry and a bone There is nothing fancy about it The next one, we are seeing some Rigid Bodies in action Having it just kind of move with the Character, we are able to simulate in component space, and that just gives it that feeling that it is part of the Character Since it is — I think we are driving in some of those forces; that component linear scale and velocity scale, to make it so when you move and run and twist, you can get specific motion Since you have each access available in those component scalers, you can say, only when I twist, feed in more motion, or only when I move on a vertical axis, feed in more motion You can get very specific about the type of motion you want in there The cape is — I think here we are seeing it as cloth solution, though we do use both cloth and Trail Controller — and I will go into that a little bit more here next The cloth solution is a little tricky, because back in the Character parts, we define what we call cape colliders A cape collider is a base set of physics bodies that that cape can collide against, and it just moves to wherever those bones are That allows us to collide against a Character, but it is a little tricky to get going at the first place The wings are kind of the most complex here, because they have an entire state machine They have specific poses that we are driving based off what the Character is doing, and we will get into that a little bit more here The capes — it was a pretty tricky thing, just trying to figure out how we were going to get that to work on mobile How do we get that to work on PC? How do we get it to still look good, feel like it is this cloth just draped from a Character? Characters can take on any size and shape, but again, how do you put a cape on a banana? Well, you can In this case, we are seeing the Trail Controller in motion, and you can see it kind of just return to that Ref Pose as he moves sideways But it gives it that kind of secondary motion In this case, we do have three chains; so there is a first chain and then two forks That way we can control the stiffness of the upper versus the bottom of the cape We standardized the Skeleton and the simulation Mesh, so that any cape that you create gets put onto that Skeleton, and then you automatically get all this behavior that we worked so hard to get, kind of for free That makes it so now we can create a cape in about five minutes For the cloth, you can just use the same simulation Mesh, even if it is long or short We have standardized that so it just makes it really quick to get the behavior Again, we are going into peeling off layers, so at lower LODs, we can manipulate the Trail Controller, LOD out bones, and still get some of the simulation that we need But I think at the lowest LOD, stiff as a board, just sticking off your back Diving in a little into wings, here we are seeing the animation play on the wings, based off the Character’s performance Whenever the Character aims down sites, the wings pull back Primary reason for that is, when you aim down sites, the camera zooms right over the shoulder, and you do not want wings blocking that, so we are getting those out of the way, and it kind of gives it a cool behavior We also have, when you start sprinting, those wings kind of fold back a little bit; when you skydive, the wings come out All those are just individual poses, and we are blending in to each pose You can see down at the bottom here, we are doing a little bit here in the Anim Graph to pull the Pawn speed, so the faster you go, blend in the wings between a sprint and a base kind of idle pose, that is just one place where we layer that on top of the state machine All right, hair Cannot really say this is how we do all our hair, but this is how we do — I mean, every hair gets its own treatment In this case, we are using AnimDynamics, and trying to be a little clever with it

In AnimDynamics, you are able to define collision spheres, and that is what is allowing us to get those little ponytails to react to the shoulder when the shoulders come up We are also able to feed in our alpha Has anyone used AnimDynamics or FInterp, or anything like that to get some of the behavior? In this case, basically, based upon speed, we are using the FInterp abilities of the alpha parameter on AnimDynamics to change the way that that hair bounces The Art Director said it is bouncing too much when running, tone that down, and this allows us to do that dynamically Since you can also change the way that alpha is on and off, you can use the interp speed also on that parameter, to make it so it can blend on really quick, and then settle again when you stop running, so you do not get this jump, start shaking, stop immediately, what you usually get with that type of alpha All right, so cloth We might spend a little time here We never know what animation is going to play on a Character They have a base traverse set that has been set for years, but at the end of the day, new emotes, dances and behaviors are being created, and there is always stress test the setups that we have created In this case, I created a dress out of Rigid Bodies and tried to — the front leg straps kind of flung up way too much, that are way too active When you are running from a third person, all you see are these leg straps kind of come in over the body I treated that a little differently, which you see in that graph there Diving into Rigid Body first to describe what I am doing, usually if you do a setup like this, you get a lot of jitter I am sure some of you have experienced that before The first thing that I learned was controlling my mass per body is extremely important I start kind of with a power of 2 mentality On the lowest child, I always start the body a mass of 1, and do mass 1, 2, 4, 8, 16 — you always want the sum of the children to be less than the parent That kind of takes — anywhere you do Rigid Bodies, that is true If you wanted to be more extreme, so the lower bodies move a lot more, then you could do 1, 5, 10 — I do not know, you can kind of fuss from there Another thing that we are doing here is, we are creating cross constraints You can create your own constraints between bodies First we get just — what do I have, like, 5, 10 chains there? Then I will create a cross-constraint between two You do not want to do it between every single one; that just does not give the bodies anywhere to go You want to give some flexibility, so I will do every two or every three That way, your leg does not just slip between the dress, rather it will move it out of the way, because those bodies will still stick together and kind of give you a cloth approach Then I think I pretty much always have some spring on here, some level, just to try and pull those back together For the cross constraints, those springs are pretty high I really do not want those bodies to pull apart too much, I want them to go along for the ride But if you go too high, again you get jitter, and that is kind of a balancing point That all describes this first dress node But there is a lot more going on in this Character In order to kind of prevent those cloth strips from flying out of nowhere and really screwing up everything, we went ahead and added these AnimDynamics nodes Where I am doing that — you see on this kind of danglies Rigid Body, there are two sets of blocks on the bottom are the Rigid Bodies that are colliding with the shins But the only way they are doing that is they are being — oh, sorry, they are not actually colliding there It appears that they are colliding I am driving the upper part of the legs with AnimDynamics,

because I can really control that motion, and I can control the way that it flies out Instead of hitting a body and bouncing out like I was getting with Rigid Bodies, I can just say, just kind of dangle between here Then I used those as kinematic bodies to then drive the simulation of the lower part I do this type of thing all the time, and it really allows me to art direct the simulation That can be one of the hardest parts, as when the Art Director says, hey, tweak this one little thing, and then it breaks your entire setup You may have noticed that these are all Rigid Bodies in AnimDynamics, so how does any of this work on mobile? That is a good question I am glad you asked What I am doing for mobile is, I am adding a Trail Controller for all of the skirts Now one of the key problems of Trail Controller, since it is lag-based, it does not care where it goes If she ran backwards, that skirt would just go straight through the body Based off the direction of the Character, I blend on and off Trail Controller, and I try to do that slowly so you do not pop back into position I also have spring controllers for all the fur around her neck, so I have basic simulation happening for that, which you see in those Rigid Bodies But then once we go into mobile, I am using Spring Controller just to get a little bounce As far as those leg cloth things, those, I think, just deform with the legs They look pretty good enough at a lower LOD Beyond simulation, we have to make everything look good all the time In this case, with this guy just crouching, and it does not really look like much, but that little llama on his hip normally would just pierce right through his thigh We have pouches and grenades and all kinds of things that always get attached there, and that always ends up being an issue Our approach to correct is generally — let us go back here — is to use this Get Delta Transform from Ref Pose Again, this is a newer node that I worked with the Anim Engineers to create We were normally doing the math; I do not want to do the math This makes it really easy to get a bone and get it in a specific space We use these all over the place On the backpacks and the capes and everything, if you have a really long backpack and you look up, it goes right through the chest, right through the stomach We will get a reference to the body or to the end of his Skeleton, and I like to get the head in Spine 5 space, and that just gives me kind of a drastic angle If you just said look up, well, he can do this, and it does not have any effect If you say, well, whenever the Spine 5 goes up, well, you could lay down and theoretically rotate it in root space or component space, and that still does not give you what you need But the head and the spine or pelvis space, that was giving me exactly what I wanted But in this case, I am taking a look at the left thigh, and whenever I crouch, I kind of define my angles here, and was able to generate an alpha, so I just would map that 0 to 1, and I feed that in my Anim Graph there at the top, into that Transform Modify Bone It is not the most performance way to do that, I will admit, but it gives us exactly what we need Then whenever our director says, hey, can we tweak this out a little bit more, you do not have to go all the way back into your DCC Maya or Blender and create a pose or animate it; you can just do it right there in the Engine Pose Driver — has anyone used Pose Driver before? Awesome, a couple Pose Driver is, in Maya we will create a set of poses for the Character I usually record these straight out of game, because I want those angles to be exact If I am aiming and I look up, I want the shoulder pads to react to that motion; I do not want it to guess If I just create an animation of this type of thing, and then adjust my shoulder pads to react to those,

I may never hit those angles in Engine, unless I create an animation that looks exactly like that But that is not a good way to validate it In this case, the Pose Driver allows me to create a set of animations for bone sets I will be watching, and then a set of animations, or a set of poses for the bones that I will be driving You see those big old cages over the shoulder pads — those are all being driven based off of the clavicle and the upper arm There are a few rules with Pose Drivers, or some guidelines with Pose Drivers The fewer bones that you are watching, the better You try and watch all of your clavicle upper arm, and maybe your spine — all of those bones have to line up to that exact, right place for you to hit that pose You want there to be some wiggle room You may hit it, and then that corrective pose will just pop on Then you wonder, why am I never getting this look? I like to narrow it down to just that shoulder-upper arm pose, if I can If I am not quite getting that, then I will add in a clavicle You also see here in the middle picture that I have it split out into four That is because I get poses that may be very similar when I am skydiving to aiming a specific weapon, but I do not want those skydiving poses to muddy up my weapon poses I create new Pose Drivers I detect if my Character is skydiving, and if it is, then I swap over to that other graph I spent a long time using quaternions, and that made it very difficult, because any time you do a little twist or something in your pose, you may completely lose — that kind of invalidates all other spaces that your arm could be in In this case, I am using swing angle I should have had a graphic for all the settings, but in this case, on the right we are seeing, I think, 12 or 15 poses I do recommend the fewer poses, the better if you can Otherwise, let us say, if you try and do poses all the way up the arm, like five different poses, then it will just pop between them, where you get this kind of jitter effects, which is not at all what you want Another thing is, I break out per shoulder, again, because I do not want to be watching both right clavicle-left clavicle, right shoulder-left shoulder I break each arm into its own In some cases I will have eight different Pose Drivers looking at all different things, because I really want to isolate the problem I went through that really quick Thank you! [Laughter] [Applause] ♫ Unreal logo music ♫