Animation Bootcamp: An Indie Approach to Procedural Animation

[Music] all right can you hear me so I'm David from Wolfire games I've been making games in my spare time for about 20 years and recently we're probably best known for starting a distribution platform called Humble Bundle but I'm not going to talk about that today right now I'm working on a game called overgrowth and we have a pretty small team it's just myself and an artist that's twice as big as any team that I've worked in before but I'm still doing all the animation and the programming so I really had to try to use my time very efficiently when making this game so I tried to abstract whatever animation tasks they could from keyframe work into curves and other overlapping systems so I'll talk about how I did that for movement with movement we've always had kind of a trade-off between responsive movement and detailed animation like on one

extreme we have a game like Mario where a controller input is mapped directly onto acceleration of the character and the animation is very simple like you probably has like two frames running one frame for jumping down the other extreme we have like rotoscoped animation like in prince of persia where all of the animations transitions smoothly from one to another and during these transitions controller input is more or less ignored so it looks really smooth but it adds a bit of latency for a controller input so nice thinking of trying to get both responsive and detailed controls one thing i looked at is vehicle movement like the warthog and halo when it does have stopped there it's still responding very quickly to all the controller input but it also has all this fancy animation like the shocks on the wheels secondary movement on the antenna and so on so I want to think about how to apply

this to a human character so it seems like a human would be a very complicated vehicle because we have like 40 animation bones moving around and twisting but really if we think about it if you look at his center of mass it's moving in a very simple way it's just making these simple curves around the ice and not moving up and down very much at all except when he jumps it goes in a little gravity parabola there are only a few rules he has to always follow like he always has to keep his center of mass over his skates so he doesn't fall over and he has to tilt into acceleration so that that'll be true in the next second so then I second to the center of mass will still be over his skates if he has to conserve his angular momentum whenever he wants to spin please can start spinning and then he'll compact into a line to spin really fast or I'll spread out to spin more slowly the same is true with this gymnast doing floor exercises like she seems very complicated but she's really just like

animation 101 just a bouncing ball she's bouncing once once and then a big one and then she compresses a little bit on the landing with some squash and stretch and there's always a constant gravity like she's always accelerating downwards at nine point one eight or nine point eight one meters per second squared whenever she's not in contact with the ground that's true if she's jumping flipping running or in the air in any way so the overgrowth I wanted to start by focusing on the basics physics movement like start with and Mario like controller input equals acceleration and wrap everything around there and never interfere with it so I had this one green sphere as a bumper sphere it lets him fly it off objects that he runs into you hit a weightlifters sphere which moves up over small obstacles and this by using this as a foundation for all the animation we always had really consistent controls like whenever the player presses forwards are right it

does something predictable so if they fall off a cliff they know about it's their fault and not the game's fault and whatever it's so predictable they describe it using words like intuitive and responsive which is a much better thing to see in reviews of your game than like awkward or sluggish or floaty so I kind of feel like there should be a Hippocratic oath for game animation which is at first you do no harm to the game play so by making sure we have the movement in first and we do the animation on top of that we can make sure that that's the case so the first step was just to drape an idle pose onto our physics fear so here he just floats around and he rotates towards his velocity and his rotation is reactive to the velocity it's not the direction the controller is pushing it's the direction he's actually going so if he moves along the wall he kind of slides to face in the direction he's going instead of kind

of running into the wall the next step was to add some acceleration tilt to it so when you whenever he accelerates it tilts in that direction that already makes it kind of fun to move around like he starts to move around a bit like a Segway or some other simple vehicle but I'm not making an ice skating game so I wanted him to actually move on the ground so I just added these two keyframes there's the pass pose and the reach pose where his legs are passing and then the extreme position and it just kind of he's the surveyor wheel-like technique just to figure out how much distance he's moved on the ground and that kind of takes off the keyframes in the animation so no matter how fast or how slow he's moving he never floats and his footsteps it destroys and sync with the ground then I tried adding another speed for walking the walk has much smaller stride so it has to have a much smaller wheel just to

take off each one and it's a bit jarring to suddenly transition from one to the other so I added a synchronized blend between them so at any intermediate speed it was blend between the two keyframes and also blend between their stride size so I can go at fast slow or any intermediate level and since I was just keyframing the shape the shape of his limbs around the center of mass I had to add in a bit of a bounce so you could have a bouncy jog when he's moving slowly and it gets flatter the faster he goes just because gravity is always constant if you have half as half as much time between each you can only fall a quarter as much distance just by doing out the integration two keyframes is not nearly enough to just work from one to the next so I had to start interpolating from one angle to the next just by doing a weighted average between the two nearest

frames and that helps preserve spatial continuity so it goes from one frame to the next but there's a sudden velocity jar at the end his arms reach forwards and suddenly start going backwards so I've created that to by cubic interpolation which makes sure there's spatial and velocity continuity and that made the I thought the run even in slow motion looked pretty acceptable even with only two keyframes then I needed some squash for the compression like we saw with a gymnast decided a Crouch frame we can interpolate linearly linearly there but organic creatures almost always like that with linear interpolation and now animator whatever use linear interpolation just for their own internal animation but it's also important to avoid it when transitioning from one to another so I tried using a spring damper system to interpolate

between these two keyframes which just has these two parameters the stiffness of the spring and the damping factor I just tweaked that into a looked right and that adds a lot of the nice easing in and follow-through that I would have animated if I wanted to do like a transition animation by hand but since the curve is separated from the transition itself it can work with any standing pose in any crouching pose or even with a standing animation and a crouching animation so decided another synchronized locomotion for Crouch walking so now we have our six locomotion keyframes and our two standing keyframes and since we're using a spring damper system I could use the existing Crouch to handle absorbing landings it just adds some downwards force to the crouching spring so we don't really need to land animation at all and since this transition is separated also it will

work while he's running or while he's standing still next I wanted to add some ways for players to express themselves while they're in the air so they could flip in any direction by just pressing a controller direction and pressing the flip button with the linear rotation as always it looks pretty bad especially at the end there we certainly like where this is angular momentum go just kind of disappears where does it come from in the first place for that matter so I tried to dressing that a little bit by changing the curve this is a little bit of acceleration or anticipation at the beginning so he's still kind of manufacturing momentum from nowhere but it looks a lot more plausible and then at the end the he is out is synchronized with his transition back into his jump pose so it works more like it works for the figure skater like he's rotating really fast boys balled up and then he slows down as he expands outwards and he

used the same system for a roll we just rotates around the center of mass with a rolling pose but he has the different tuck pose for rolling forwards and rolling to the side and interpolates between them for any intermediate angle so he's always kind of rolling over his shoulders instead of rolling over his spine or his head those are all really simple systems but when you put them all together it gets pretty compelling results I think even with only 13 keyframes pretty it transitions between every possible thing you might do pretty well like we have a simple system for all standing and crouching transitions using that spring damper system we have an acceleration tilt for all horizontal movement and we have all these rolling and flipping systems with controlled curves and the nice thing about using so few keyframes is that it's not that hard to add a whole new variation like if I want to make a variation where he's carrying a spear I don't have to like

layer a spear pose on top I could just make 13 new poses that take this beer into account so he'll roll nicely without like trading the ground once we have as animations we're happy with there are a lot of procedural ways to refine them like we've already gone over in risk kinematics a little bit where you just move the foot or the hand and automatically calculate the angles for the joints we don't really need a library for that like it's kind of pretty simple trigonometry just to figure out that angle for a2 to bone I K there can take that a little bit farther for really tricky situations like this ledge climb I just had the one keyframe for grabbing onto a ledge and then constructed all his movement using in brisk and medics so you can shimmy along using big shimmies or small ones or whatever angle you can go up and down so

I just couldn't it seemed easier than making a hundred different variations in blender which is what I'm using for animation in this case we can all see you semi K for just look targets so I use the multiple joint I K for the hands and feet to make sure that all the contexts are preserved but this helps with more like social contacts so enemies your characters always looking at their targets are looking in the direction of the camera or facing they can face their torso one way and their head another way it just helps make the characters look a lot more alive and aware of what's going on it's pretty common now also to add secondary physics to the character somehow like by adding a cape or by adding like wobbly scabbard or in this case is wall blue ears but I wanted to try bringing that a little bit deeper into the character so every animation has sort of a softness softness

parameter for each bone in this case his arms are a little bit soft she kind of wobbles when he runs around and secondary physics are nice to bring as much of that in as possible because it helps transition not only between different animations but different rotations and different velocities and any kind of change and finally for refinement I tried to address it kind of like a profiling problem like I just tried different things find what looks the stupidest so in this case it kind of like stupid to slide along the wall on this face like that because it kind of exposes this like invisible collision sphere so I tried just using my locomotion system to replace that with a simple wall run animation and I found that took one of the stupidest looking situations and made it one of the cooler ones that everyone likes to post screenshots have on Steam in almost every game now uses

rag dolls for destroyed characters they first saw them and Carmageddon to where they just use simple box physics to allow you to collide with pedestrians and pile drives them into walls or like knock one pedestrian into another one and make them both fall over but I didn't see articulated ragdolls until hitman codename 47 which kind of blew my mind at the time because you could drag on the bodies by any limb that you want to you or you could bless them up against walls and they kind of slide down in a dramatic way and since he wrote a paper about it the guy who did this immediately wanted to try it for a game jam project series one where you're a psychic bodyguard where you have to protect the VIP and the white outfit by shooting all these guys so the instant ragdoll transition worked well for extreme situations like you blow their limbs off with a grenade or something

but in movies they're often different kinds of death animations that are more dramatic and drawn out like this guy is kind of following slowly like a tree or someone's clutching their shoulder when they get shot or even sometimes they just acted out by standing up for a while so the hero can just shoot them dramatically and satisfyingly many times like this poor guy here so I try just delaying the ragdoll a little bit to allow the characters to have a bit more time to react to what's going on it's like if you shoot them in the leg they might grab there like and if you shoot them again then they'll go into an immediate rag doll or they'll stay up for a little while she can just unload your machine gun into them and it even added a little bit to the gameplay because sometimes you'll shoot someone and they're dying but they're still about to kill your VIP so you have to keep shooting them which is very violent now that I think about it okay it did

add to the game I think the next big thing in rag dolls Rockstar announced they're using this technology for eeeh Ted active ragdolls so it's some kind of AI for the joint forces so not totally limp they're still trying to do something like grab onto things or sort of keep their balance so try doing something like that in over go and started with pose matching so he'll just try and preserve whatever pose he was in by applying joint constraints and that was pretty fun to do the next step was to add animation matching so now he's playing is his walk animation but he's not really walking very well and finally I extended that to like an actual useful system so when he's far

away from a surface he'll flail with these three flailing keyframes and when he gets close to the surface will kind of curl up and try and protect himself and if there's a surface coming to the front he'll put his arms out forwards it doesn't help very much but it makes him look a lot more alive unless like he is just unplugged from the matrix a lot of the time when you punch someone they'll fall over and I don't want them to keep looking like they're dying getting resurrected the same kind of techniques can be applied to anything any kind of animation not just third-person characters like in this case I made a game jam project called receiver which is all about really detailed gun manipulation it's instead of our for reload it's like our is rack the slide and he is like eject magazine so I did the fight divide it all up into little stages like this and linear interpolation continues to look bad so I

tried using the spring interpolation again and that already I thought looked pretty natural like even with just two or three keyframes like that's more like how someone's arm might move around I still reacts instantly at any controls like you can interrupt any any of those transitions at any time but we still only need three keyframes for that it's a similar kind of rotational spring for the gun which I use for any kind of sudden impacts like there's a gun recoil of course but I also used it for footsteps and even for like taking out a magazine and slamming it back in just helped accent the movements a little bit and receiver I had to decompose everything into little movements like this because that was just part of the gameplay design but I feel like I would do it even if you just press Start to reload like usual because it made it really easy to make variations each time

like when you eject the bullets one of them might get stuck so you have to do it multiple times or you might not fill it completely or you could spin it a little bit while putting it back and having it in little pieces like that could make it really easy to randomly add variety to all reloads every time there a bunch of good examples of games that I didn't work on that do a pretty cool job with procedural animation like Shadow of the Colossus had a remarkable animation problem because they had one skin character climbing around on the bigger skin character which i think has not really been attempted since then so usually that has just handled by rotating the character and using inverse kinematics to make sure the hands and feet lined up but in extreme cases he'll lose his grip entirely then he's simulated with a sort of two part pendulum like one part from his hand to his chest one part from his chest to his legs so it kind of flaps around and that simulation is applies to the pre-made flopping around animation just to make

sure it all lines up a 2d example is this upcoming game called reign world which has this really cool little slug cat character which i think is what they call it whenever he runs he tilts in the direction he's going kind of like the figure skater or what I did for overgrowth always crawling like even seeing a little window on the left he moves like the character and snake-like has his front part is kind of dragging his rear part behind it and he's inverse kinematics to make sure his limbs all hooked up to the nearest surface and he always has secondary motion on the tail the tail is always physically simulated so it has nice smooth transitions between every state the more extreme examples this game called gang beasts which is always in an active ragdoll state so you can have these crazy situations like little guy trying to climb on the big guy and pummel him in the head and they didn't have to simulate it in great detail they use an

invisible sphere to kind of prop the guy up but it's really neat how it allowed for such difficult situations environment interaction you don't have to take it quite this far you could always do like a hybrid so sometimes they're active rag doll and sometimes they're moving around normally I saw this is a great case study so in the future I think we really need animation and code to work more closely together so that we can use the code to like help offload repeated tasks from the animators like if you keep on having to animate it like an overshoot for your punch you could just add a new curve for that we could add a little overshoot curve and then for each of those overshoots you just do the one keyframe you apply that curve and just cut down on your work a lot so if you keep on identifying any repeated animation tasks and extracting them out and making good

tools for the animators to use while doing that I think that could save a lot of time it would also allow animators to focus a lot more on the performance and less on the like busy work like transition animations and repetitive things and thanks for watching it's on my contact info if you'd like to talk afterwards I rather than use your tools because it's way cool it well I think it's a lot easier to program yourself then it

probably seems like for the pose matching I'll just make sure I'll just read the relative matrices from the animation and then I just apply a joint constraint to enforce its relative positions in bullet and things like that well so I don't really have like specific user-friendly tools that I can sell but I could tell you how it works thank you is that can you think of good ways of like one of the main problems with using just physics to move between keyframes is you lose intentional in-betweens which is something that animators really like having control over is can you think of a good way of biasing the in-betweens towards certain performance focus in betweens rather than just submitting to what physics dictates well it's so kind of animating in the same way as you normally would but you would take the transition that you would normally animate with the intentional in-betweens and then kind of

trying to abstract that out a little bit so can apply to multiple transitions which is mostly what I'm trying to do trying to like avoid the combinatorial explosion of trying to transition from every stand to every crouch so we can kind of make it more of a linear not explosion it's possible yeah so you were talking about you you coded in basic to bone I K for your wall hanging for instance how is there like a resource that you used to to maybe learn more about that or I mean could you point me in the right direction maybe because I'm not it's something I'm unfamiliar with and I'd like to figure out as well I can't think of a specific resource for that but you could talk about it on email oh sure it's basically just it's like the right triangle problem like you have just bone in this bone now you have two right triangles so you find this angle here okay yeah they did so you mentioned the case of

like having the character to hold like a ball or something like that and you said that the approach for that would be just to have you know make all those key frames except with him holding a ball did you try doing like putting AI K so you put his hands onto the ball and then so you wouldn't have to make those all those frames again I'll try and answer one minute yeah I think you can definitely do a lot of that with AI K I try not to I try to only use AI K when it's like super needed because usually I'll find better results by having it like hold a very small ball and hold a very large bar while and then interpolate because then we have animation control of the extremes or do that with an animation layer that gets layered on top because otherwise you're animating with very awkward tools so you're like animating in a text editor which is not ideal okay well thanks I don't think [Applause]