What are inverse kinematics and rigging?

- [Instructor] I'm in chapter two 01, What is IK Rigging? First things first, what the heck is Inverse Kinematics? How is it used in character rigging? Why bother using Inverse Kinematics for character rigging in the first place? And while we're at it, what is this character rigging thing I'm going on and on about anyway? Well, let's start with character rigging. Character rigging is basically setting up how you control and animate the different pieces of your character, like the arms or legs, or how the head rotates.

This setup is known as a rig. Traditionally in After Effects you would parent different layers of your character to other layers of that character and set the anchor point, so it rotates around the joints or other natural rotation points on a character, like the elbow or the wrist. You'd then parent these parented layers to other layers and begin setting up a hierarchy. So everything will eventually be moved by a single layer, often referred to as a control layer. This process is called Forward Kinematics, or FK.

For example, the rig I have here on my left side is using Forward Kinematics. If we take a look, I'm gonna hit Command + plus to zoom in, and I'm gonna just hold the Spacebar to move this over a little, so we get a closer look. These top layers I have here I have the Right Upper Arm, anchor point is set over here at the shoulder, if I hit R to bring up my Rotation and I rotate it you can see that it rotates both the Lower Arm and the Hand, which are both parented in a chain, or hierarchy to the next one.

So the Lower Arm is parented to the Upper Arm, the Hand to the Lower Arm. That way if I bring up Rotation on any of these and move them around they'll rotate around those joints and they'll move and be parented to the next, and that is Forward Kinematics rigging. Now this is really good, 'cause it gives you control over a lot of different pieces, but it's really annoying, because if you wanna do an animation, like if I want my character to go ahead and scratch his behind, then I have to set a whole lot of keyframes.

Like I'll have to rotate the Upper Arm to move it down, like so. I'll have to set keyframes for the Lower Arm to move it, and you know what? I don't even like how that Upper Arm is positioned right now, change that, uh, it's so much work. All these rotations. Then I'll have to go ahead and rotate the Hand to do a little bit of butt scratching.

Rotate it up, rotate it down, rotate it up, and if I want this to look a little more natural, I mean, our character should be looking at the behind in which he is scratching. So let's go to his Head. This layer here, and the Neck, I'll just Shift + select, hit R for both of them, come back here to as he's moving his arm down, I'll make keyframes for both of them, and let's move the Neck, so it's kind of pointing down, and the Head, so it's kind of looking back a little bit.

Uh, boy this is taking forever. If I preview, uh, it's not even going fast enough. I've gotta select all of these, and I'm gonna hold down Option, OK, you guys get the point. This is taking a long time just to get a single little behind scratch. I mean, there has got to be a better way. Well, better or not, there is a more streamlined way. And that's by using a little something called Inverse Kinematics. Let me go ahead and zoom back out briefly here.

With Inverse Kinematics there are a few set control layers for different sections of the body, and instead of animation being created by rotating several parented layers, those layers are all attached to these controllers. And simply animating the position of the controllers will adjust the rotation of several layers at once. So the character rig on the right side of my Composition window is using Duik's Inverse Kinematics, or IK. I'm gonna go ahead and Command + plus to zoom in a little bit. And I'm gonna move down in my timeline all the way below this pink dividing line that says Inverse Kinematics, and you can see that I have several control layers here.

These controllers, which are IK_C, that underscore stands for controller, are also guide layers. You'll see this little tic-tac-toe mark here, that means that these exist and we can see them, but they won't render out with our final animation. So I can actually just grab onto these and move their position and as you can see, it's moving the position of several different Arm layers. I can grab onto the Pelvis one and I can rock them back and forth a little bit, so they wiggle.

So if I wanna animate something like a little behind scratch I can do it much faster and much more streamlined using these controllers. I'm gonna hit P for the Position, I'm gonna go ahead and make a Position keyframe here, I'll move it over, so he moves his little behind over, I'll come up over here, select the Hand controller, hit P for Position, I'll move this down, and because it's attached to this controller I can also hit R on that for the Rotation, make a Rotation keyframe, I'm gonna hit U to bring up all my keyframes, and I can rotate the hand using this same single controller and I can do a little bit of behind scratch action, and it's a lot quicker, and I'm moving a lot more layers all together.

Yeah. I'll even give them a little bit of wiggle on their body to help make that more accented of a behind scratch. That's a much better looking behind scratch with a lot more character and a lot more attitude thanks to a little of Inverse Kinematics. So if you note really quickly, I have all these same layers in the Inverse Kinematics as the first one, make sure that my shy guy is unchecked, and we can see all of these different layers for the Head, Neck, Torso, there's all these zero layers too that get created automatically by Duik, but I like to lock those off and hide them with the little shy guy right here, and clicking that there, so all I'm looking at are these few simple controllers.

And by doing that I only have to worry about, let's say, five or six different layers, instead of 20 some different layers, to do a little bit of animation. I'm gonna go ahead and click over on the Duik Rigging toolbox right here, which is where we have all our tools to do all of this rigging. It has loads of fantastic tools to do all that heavy expression and rigging work for you, you just need to design your characters, do a little setup, and press a few buttons, and you're on your way to easy street when it comes to character animation.