So that's the general example, but where are the actual controls? They're in the Editing buttons (F9) in the Shapes panel. Figure 11-1 shows three different states for the Shapes panel. By default, it looks pretty innocent and empty with just the one Add Shape Key button. However, when you left-click that button, you get buttons to control the Basis shape, or the original shape that other shape keys relate to. Left-clicking the Add Shape Key button a second time gives you another set of controls that controls the change from the Basis shape to this one, named Key 1.

Figure 11-1. The three different sets of options that the Shapes panel can provide you.

The best way to see how all of this works is to go through a practical example. Staying with the "bug-eyed monkey" theme, use Suzanne as your test subject, and go through the following steps:

Figure 11-2. Creating a bug-eyed shape key for Suzanne.

This process creates two shape keys, the Basis and Eye Bulge. Using the slider in the Shapes panel, you can smoothly transition from the Basis shape to the Eye Bulge shape. A value of zero means that Eye Bulge has no influence and you just have the Basis, whereas a value of one means that you're fully at the Eye Bulge shape. But here's where things get really cool. Notice the Min and Max values to the left of the slider. The Min is set to 0.0 and the Max is set to 1.0. Just for kicks, change the Max value to 2.0 and pull the slider all the way to the right. Doing this pushes your bulged eyes larger than your actual shape key made them. Now change the Min value to −1.0 and pull the slider to the left. Now Suzanne's eyes pinch in to a point smaller than the Basis pose. Figure 11-3 shows the results of these changes. This is a great way to provide even more extreme shapes for your characters without having to do any additional shape key modeling. How's that for cool?

Figure 11-3. Suzanne with excessively bulged and pinched eyes, just by changing the minimum and maximum values for a single shape key.

From this point, you can create additional shape keys for the mesh. Say you want to have a shape key of Suzanne's mouth getting bigger, like she's screaming because her eyes have gotten so huge. If that's the case, the first thing you want to do is switch back to the Basis key. To do this, use the left/right arrows next to the key's name in the Shapes panel. You can also left-click the up/down arrow button and choose Basis from the list. The reason for doing this is because unless you're doing something special, it's a good idea to have most of your shapes based on the Basis. Otherwise, you may end up accidentally over-amplifying a shape key or nullifying it. When you're back at the Basis key, the process is about the same as before:

Figure 11-4. Creating a scream shape key.

Now that you have the Scream shape key, you can freely mix it with the Eye Bulge shape key or you can have Suzanne screaming with her regular, bulge-free eyes. The choice is yours. You have the flexibility here to mix and match your shape keys as it pleases you. And animating the mesh to use these keys is really easy. Split off an Ipo Curve Editor window from your 3D view and change the Ipo Type to Shape by left-clicking the drop-down button in the Ipo Curve Editor's header that says Object. You should notice that you have two animation channels here with the names you gave your shape keys. Scrub the timeline cursor forward in time and adjust the sliders in the Shapes panel. When you do this, new keys are added to the curves in the Ipo Curve Editor. Now you can freely scrub the timeline and watch Suzanne bulge and scream to your complete delight. Figure 11-5 shows a screenshot of me having exactly this kind of fun.

Figure 11-5. Animating shape keys with the Shapes panel and the Ipo Curve Editor.

Now, you could do an entire animation using shape keys. But do I recommend doing that? No. There are other ways to control your meshes that may give you more natural movement for things like animating arms and legs. That said, shape keys are the perfect choice for things that can't be done with these other means (or, at least, that are very difficult). One big one is facial animation. The way parts of the face wrinkle up and move around is pretty difficult to re-create without modeling those deformations in. Furrowed brows, squinty eyes, natural-looking smiles, and phonemes, or mouth shapes for lip-syncing, are where shape keys shine. You can also team them up with other controls discussed later in this chapter to achieve cool effects like cartoon stretchiness, muscle bulges, and morphing objects from one shape to another.

The workflow for adding a hook is pretty straightforward. You Tab into Edit mode and select one or more vertices or control points. Then you press Ctrl+H

Figure 11-6. Control options for the Hook modifier.

Tab back into object mode and transform the hook. When you do, all the vertices or control points that you assigned to the hook move with it. And with the options in the Hook modifier, you can control how much influence the hook has over these vertices or control points. The following example should give you a clearer understanding of this:

Figure 11-7. A cube smoothly deformed by a hook.

Figure 11-8. Moving the hook Empty and recentering the hook's location.

The best use for hooks is for large organic deformations. Like shape keys, they're nice for creating muscle bulges and cartoony stretching. You can even use them along with shape keys. Because shape keys always use the same shape as the basis for deformation, adding a hook can give it a little bit more variety. For example, in the bug-eyed Suzanne example that you did for shape keys, you could add a hook for one of the eyes so it bulges more than the other one. It's touches like these that can give more character to your 3D characters.

Now it's time to take that rather inauspicious single bone armature and do something more interesting with it. Like nearly every other object in Blender, you can edit it in more detail by selecting it (right-click) and Tabbing into Edit mode. In Edit mode, there are three things you can select: the sphere at the bone's head, the sphere at the bone's tail, and the bone itself. Selecting the bone body actually also selects both the head and tail spheres as well.

Figure 11-9. An armature object with a single bone. Woohoo!

There are four ways to add a new bone to the armature:

Figure 11-10. Using the Transform Properties floating panel to name your bones.

Blender has a pretty cool way of understanding symmetric rigs, or rigs that have a left side that's identical to the right. For cases like this, it's best to use a ".L" and ".R" suffix on your bone names. So in the previous example, if you are rigging a character with two arms, the bones in the left arm would be named "arm_upper.L" and "arm_lower.L". The right arm bones would be named "arm_upper.R" and "arm_lower.R". This gives you a couple of advantages, but the one that's most apparent when modeling is the X-Axis Mirror feature.

To understand this better, create a new armature at the origin (Shift+C

As you continue to build your armature, another pretty useful set of tools is in the Specials menu. You access it by pressing W in the 3D View. Two of the options in this menu are the Subdivide function and the Switch Direction function. As you may guess about the former, it takes the selected bones and creates more bones in their place, based on the number of subdivisions you would like to have. This is good if you've done something like make a character's spine a single bone and then later want to change that to two or three bones. The Switch Direction function is also pretty helpful. It prevents you from trying to do the same thing with an imprecise rotation.

Parenting bones

One of the important things that make armatures helpful is the notion of how its bones relate to one another. The most important of these relationships is the parent-child relationships between bones. The same hotkeys for parenting and unparenting objects also work with bones, but there are a couple additional features. To illustrate this, start a new scene (Ctrl+X), delete the default cube (X), add a new armature object (spacebar

1. Duplicate the single bone created and place it somewhere in space (Shift+D).

   After you confirm placement (left-click), this new bone should be selected.

2. Add the original bone to your selection (Shift+right-click).

3. Press Ctrl+P to make the original bone the parent of the duplicate. When you do this, you are given two options:

   • Connected: Choosing this option moves the head of the child bone to the same location as the tail of the parent. This creates a bone chain as if you'd created the second bone by extruding it from the first.

   • Keep Offset: Choosing this option leaves the child bone in place and draws a dashed relationship line between the two bones. They're not connected, but one still has an influence on the other.

4. After you've created the parent relationship, select the child bone.

5. Clear the parent relationship by pressing Alt+P.

   When you do this, you have another pair of options:

   • Clear Parent: Choosing this option removes any sort of parent-child relationship this bone has. This also means that if it was connected to the parent bone, it is now disconnected and can be moved around freely.

   • Disconnect Bone: This option doesn't actually clear the parent relationship. Instead, if you have bones that are connected, choosing this option maintains the parent-child relationship, but you can move the child bone independently of the parent. It would behave as if you made the parent by using the Keep Offset option.

Figure 11-11 shows two bones that are unparented, parented with an offset, and parented as a connected bone.

Figure 11-11. Bones that are unparented, with an offset parent, and parented with a connection.

Tip

You may notice that even with bones parented – connected or otherwise – if you rotate the parent bone, the child does not rotate with it as you might expect in a typical parent-child relationship. This is because you are still in Edit mode, which is designed mostly for building and modifying the armature's structure. The parent-child relationship actually works in a special mode for armatures called Pose mode. You access this mode by pressing Ctrl+Tab. When you're in pose mode, if you select individual bones and rotate them, their children rotate with them, as you might expect. From there, you can swap back out to Object mode by pressing Ctrl+Tab again, or you can jump back into Edit mode by just pressing Tab.

Armature panels in the Editing buttons

When working with armatures, the Editing buttons (F9) have some panels with options that are incredibly helpful. Select all the bones in your armature (A) and have a look at the Editing buttons. What you see should look like Figure 11-12.

Figure 11-12. Editing buttons for armatures.

Tip

Because the Armature Bones panel can display options for up to five bones at the same time, it may be a good idea to change your screen layout and put your Buttons window along the left or right side of the screen and display them vertically.

As you may have guessed, the Armature panel provides options for the Armature overall while the Armature Bones panel provides options for the currently selected bone or bones. Looking at the Armature Bones panel first, there are some options and controls that are immediately helpful. The first row of buttons lets you name your bone and define its parent. Rename the bone by left-clicking in the BO field and typing a new name. The drop-down menu to the right of the name field displays the selected bone's current parent, if it has one, and allows you to choose another existing bone as its parent. If you have a parent defined here, the Co button to the right of it allows you to tell Blender whether it's connected to its parent. These options change a bit between Edit mode (Tab) and Pose mode (Ctrl+Tab), so keep that in mind.

There are two other really important sets of buttons in the Armature Bones panel. The first is the Deform button. It's a simple toggle that tells Blender whether this bone will be used to directly deform geometry. A quick way of explaining it is that you can have bones that actually deform your mesh and bones whose purpose are to control the location of these deformer bones. Disabling the Deform button for those controller bones is how you prevent them from directly controlling your mesh's geometry.

The other really important buttons in the Armature Bones panel are those on the last row. These are bone layers. Just as you can place objects on layers in Object mode, Blender's armatures have a special set of layers to themselves. The reason for this is that character rigs with armatures can get pretty involved. Using bone layers is a good way to keep the rig logical and organized. Left-click on a layer button to assign the bone to it. If you would like the bone to live on more than one layer, you can Shift+left-click the layer button.

Notice that there's a corresponding row of layer buttons in the Armature panel. These buttons control which layers the armature is actually displaying. One thing to note is that unlike Blender's regular layers, these layers do not indicate whether they have anything in them, so you just have to keep track of where you place things.

Below the layer buttons in the Armature panel are a set of buttons for controlling how bones in the armature are displayed. A description of each bone follows:

• Bone types: Only one of these four buttons can be enabled at any point in time. Note, however, that even though the bone type may not be drawn in the 3D View, the things it influences are still valid. That is, even if you're displaying Stick bones, they still control the same vertices within the range of the Envelope bones. Figure 11-13 shows examples of each of these bone types.

  • Octahedron: The default bone type. These bones are great for building a rig because they show which way the bone points and if it's rotated.

  • Stick: Draws the bones as a thin stick. I like to animate with my bones in this draw type so they stay out of my way while I work.

  • B-Bone: Bones are drawn as boxes and can be treated as simple Bézier curves. To make them deform more smoothly, increase the individual bones' Segm, or segment value in the Armature Bones panel. One thing to note is that even if you don't use the B-Bone drawtype, Blender still pays attention to the Segm value. So if your character deforms in an expected way, this may be why.

  • Envelope: Draw the bones with a scalable sphere at each end and a tube for the bone. Vertices within the influence area of these bones will be affected by them. Alt+S increases the bone's range.

• Extra display options: All, one, or none of these controls can be enabled in any combination you desire.

  • Axes: Display the center axes of the bones. This is helpful for understanding their true position and orientation.

  • Names: Display the name of each bone in the 3D view. This can make selection and defining constraints much easier.

  • Shapes: To help communicate a bone's purpose to the animator, any bone in Blender can be replaced with any object in your scene. While in Pose mode, for a selected bone in the Armature Bones panel, you define the object you want by typing its name in the OB field. Enabling the Shapes button allows the replaced object to be seen in Pose mode.

  • Colors: To help organize bones in an armature for an animator, you can actually define custom colors for bones by using bone groups (explained later in this chapter in the section entitled "Making the rig more user-friendly"). Set all facial controls to blue, or the left side of the armature in red. Use whatever convention you care to and enable this button so you can make use of it.

Tip

Two other buttons I like to enable in this panel are X-Ray and Quaternion. The X-Ray button does the same thing that the X-Ray button in the Object buttons (F7) does. It allows you to see the bone in the 3D View, even if it's technically inside or behind another object. This makes your bones much easier to select when animating. The Quaternion button is more relevant after you begin animating with your rig, but enabling it makes the armature deform the mesh a lot more cleanly than if it's disabled.

Figure 11-13. The different drawtypes for bones in Blender from top to bottom: Octahedron, Stick, B-Bone, and Envelope.

Armatures and bones are pretty interesting, but they do you no good if they don't actually deform your mesh. If you've been using the last section as a guide for the tools to create your own rig, you might notice that when you Ctrl+Tab to Pose mode, you can Grab, Rotate, and Scale bones, but the moving bones have no influence whatsoever on your mesh. What you need to do is bind the vertices of the mesh to specific bones in your mesh. This binding process is commonly referred to as skinning. Blender has two primary ways of going about this: Envelopes and Vertex Groups.

Quick and dirty skinning with envelopes

Envelopes are the quickest way to get the mesh's vertices to be controlled by the armature. Nothing extra has to be created: It's just a simple parenting operation that seals the deal. To use envelopes to control your mesh, use the following steps:

1. In Object mode or Pose mode, select the mesh by right-clicking it and then add the armature to your selection by Shift+right-clicking.

2. Press Ctrl+P to make the armature the parent of the mesh.

   A set of options appears: You want to choose Armature. Immediately after you select the type of armature, you are prompted with a question about whether to make vertex groups. For this example, choose Don't Create Groups.

3. After you do this, when you Ctrl+Tab into Pose mode, the mesh should be under the influence of your armature.

   To see this better, go to the Armature panel in the Editing buttons and enable the Envelope drawtype for the bones. This lets you see exactly where the influence of your envelopes really lie. And if some part of your mesh is not under the influence of an envelope, you can Tab into Edit mode and edit its size and influence.

That's the basic workflow for envelopes. Figure 11-14 illustrates this in action.

Now, envelopes are great for quickly roughing out a rig and testing it on your mesh, but for detailed deformations, they aren't ideal. Where the influence of multiple envelopes overlap can be particularly problematic, and there's a good tendency for envelope-based rigs to have characters pinch a bit at their joints. For these cases, a more detailed approach is necessary.

Tip

That said, using envelopes in your armature does give you one distinct control that you can't have with armatures otherwise. You can actually use an armature with envelopes to control the deformation of curves and surfaces. So long as a control point is within the influence space of a bone's envelope, it can be modified and therefore be animated with the armature.

Figure 11-14. Using envelopes to control your armature's influence over the mesh.

Assigning weights to vertices

So if envelopes are the imprecise way of controlling your mesh, what's the precise way? The answer is vertex groups. Chapter 10 briefly touches on vertex groups in reference to the use of the Child Of constraint. A vertex group is basically what it sounds like: a set of vertices that have been assigned to a named group. In many ways, it's a lot like a material index, as discussed in Chapter 7. Besides the fact that vertex groups don't deal with materials, there are a couple of distinctions between them and material indices. First of all, vertex groups are not mutually exclusive. Any vertex may belong to any number of vertex groups that you define. The other distinction is that a vertices can be given a weight, or a numerical value that indicates how much that particular vertex is influenced or dedicated to the vertex group. A weight of 1.0 means that the vertex is fully dedicated to that group, whereas a weight of zero means that the vertex may as well not even be part of the group.

To use vertex groups with armatures, you need to do two things first. First of all, like with envelopes, it's best that the mesh object is a child of the armature object.

Secondly, vertex groups need to have the exact name of the bones that control them. So if you have a bone called "pelvis," there should be a corresponding vertex group with the same name. The vertices assigned to that group then have their position influenced by the location, rotation, and scale of the pelvic bone. That influence is tempered by the vertices' weights.

To adjust the assignments and weights of vertices in their respective vertex groups, you can use the Link and Materials panel in the Editing buttons (F9). All of the vertex group controls are on the left side of the panel, as shown in Figure 11-15. You create a new group with the New button and select the vertices that you wish to assign to the group. With the vertices selected, you can adjust the value in the Weight field and then assign them by left-clicking the Assign button.

Figure 11-15. The Link and Materials panel gives you control over vertex groups.

Note

Something to note about vertex weights is that they are normalized to 1.0. That is, a vertex can be a member of two vertex groups and have a weight of 1.0 for both. In cases like this, Blender adjusts the weights internally so they add up to 1.0. So in my example, that double-grouped vertex behaves like it has a weight of 0.5 on both groups.

Of course, on a complex armature, this process of creating vertex groups and painstakingly assigning weights to each vertex can get excessively tedious. Fortunately, Blender has a couple tools to make things less painful. First of all, you don't have to create all of the vertex groups by yourself. Recall the process of skinning with envelopes. You have to parent the mesh to the armature there and, in doing so, you're presented with a few options, as shown in Figure 11-16. For using envelopes only, you choose Ctrl+P

Figure 11-16. The vertex group options you get when parenting a mesh to an armature.

• Don't Create Groups: As the name says, this option does not create any vertex groups, thereby ensuring that the mesh is only influenced by the bone envelopes.

• Name Groups: This option creates vertex groups for you using all of the bones that have the Deform button enabled in the Armature Bones panel. However, it doesn't automatically assign any vertices to any of the groups. Use this option if you want to handle assigning weights on your own. Without assigning any weights, the default behavior is to be controlled just by bone envelopes.

• Create from Envelopes: This option is a bit of a compromise. It first creates the vertex groups based on the bones with their Deform option turned on. Then it looks at the influence area of the bone envelope and uses that to assign vertices to the group, with their weights varied accordingly. The advantage of this option is that it gets you weighted vertices. The downside, though, is that if the influence area of your envelopes isn't set up well, the weight assignment can look messy.

• Create from Bone Heat: This is my favorite option to use. It works like the Create from Envelopes option, but instead of using the influence area of the bone envelopes to determine weights, it uses a more complex process that generally results in better vertex assignments and weights.

Regardless of which option you choose, you'll likely have to go in and manually tweak the weights of the vertices. And as you've noticed, trying to do that just from the Link and Materials panel can be pretty painful. Fortunately, there's a solution for that as well called Weight Paint mode. This mode is almost exactly like Vertex Paint mode, as described in Chapter 7, except that rather than painting color on the mesh, you're painting the weight assignment to a vertex group. To access Weight Paint mode, select the mesh (right-click) and press Ctrl+Tab. Even if you don't intend to paint weights, this is a great way to see how the weights were assigned by Blender if you used the Create from Envelopes or Create from Bone Heat options.

The way that weights are visualized is kind of like a thermal map where red is the hottest value and blue is the coldest value. Extending this logic to work with bone weights, vertices that are painted red have a weight of 1.0, whereas vertices painted blue are either not assigned to the vertex group or have a weight of zero. The 50% weight color is bright green.

After you're in Weight Paint mode, you get a new Paint panel in the Editing buttons (F9), as shown in Figure 11-17. Also like with Vertex Paint, if you have the Transform Properties floating panel visible in the 3D View (N), it changes to a Weight Paint Properties floating panel. This panel shares the same content as the Paint panel in the Editing buttons.

Figure 11-17. The Paint panel in the Editing buttons when Weight Paint mode is activated.

Some buttons in this panel are more interesting and helpful than others. The first of the useful buttons is the Wire button. Enabling this button overlays the mesh's wireframe on it. This is actually really helpful when weight painting because it helps you see where the actual vertices on the mesh are. That way, you're not just painting in empty space where no vertices exist.

The next button that's pretty helpful is the Vgroup button. This limits your paintable vertices to the ones that are already part of the vertex group you're working on. This way, you don't accidentally add a set of vertices on the other side of the mesh to the group you're working on while you try to tweak their weights. This is especially useful if you're trying to paint weights with a mouse, which can be a bit harder to control for painting than a drawing tablet.

I also love the X-Mirror button. It can literally cut your weight painting time in half. When you enable this button, Blender takes advantage of the left/right naming convention discussed earlier in this chapter and allows you to paint symmetrically. So if you're tweaking the vertex weights on the left leg, Blender automatically updates the weights for the corresponding bone on the right leg so that they match. If that ain't cool, I don't know what is.

The actual process of weight painting is nearly identical to painting colors with vertex paint. However, there is one other thing with weight painting, and that's the need to tell Blender which vertex group you're painting. There are two ways to do this. The slow way, you already know: Select the group from the Vertex Groups menu in the Link and Materials panel in the Editing buttons (F9). Of course, though, there's a faster way. That is to simply right-click the bone that you want to paint weights for. Doing that selects the bone and automatically switches to the corresponding vertex group in the mesh and allows you to paint it. Figure 11-18 shows a mesh in Weight Paint mode with some painting done on it. Because weight paint relies so much on color, I highly recommend you look at the corresponding full-color version of this image in this book's color insert.

Tip

If you choose to use vertex groups, you have something else to decide. Refer back to the Armature panel in Figure 11-12. At the bottom of the panel is a block of buttons under the heading of Deform Options. With both of the first two buttons, Vertex Groups and Envelopes, enabled, the mesh is influenced by both vertex groups as well as the bone envelopes. This can be useful in some instances, but I tend to prefer to work with just one or the other. And if I've created vertex groups and assigned weights to vertices, I generally disable the Envelopes button. Your rigging needs may be different, but this works for me because this way I know that the only reason a vertex is deforming improperly is that I didn't assign its weight properly. I don't have to concern myself with the influence of the bone's envelope.

Figure 11-18. Painting vertex weights.

What you currently have in place is the basic structure of the rig's armature. The primary function of these bones is to deform the character mesh. Technically, you could animate with just these bones after you skin them to the mesh. However, there are some additional bones that you can (and should) add to the armature to make it easier to animate. They work by taking advantage of the parenting set up by the bone chains and combining them with some reasonable constraints.

For example, you currently have a structured skeleton in place, but what happens if you Ctrl+Tab into Pose mode and Grab the body.1 bone and move it (G)? Because the entire upper body is directly or indirectly a child of this bone, the upper torso, arms, and head move with the body.1 bone. Unfortunately, the lower half of the body doesn't share this relationship, so as Figure 11-23 shows, you end up tearing Stickman's skeleton in half. Ouch!

To compensate for this, you need a bone that both the hip and body.1 relate to, binding the upper half of the body to the lower half. This is what you call the root bone. Moving this bone should move the entire armature. Adding this bone to the rig is pretty simple:

Figure 11-23. There's nothing relating the upper body to the lower body, so you can accidentally tear Stickman in half.

This bone is intended purely to control the other bones. You don't want any of the mesh's vertices assigned to it. Your Stickman rig should now look something like Figure 11-24.

Figure 11-24. Adding a root bone to the rig prevents the top of the body from unnecessarily leaving the bottom.

Another convenient control bone that you may want to add is a head control. Sure, you can rotate the head bone as you wish, but often it's easier to use a bone as the head's (or eyes') target. That way, when you want the character to look at something, you just move the target bone to that something's location. An added benefit of this is that by doing it this way, you can successfully create complex moves, such as keeping the character looking at an object as he walks by it. Again, you could do this by animating the rotation of the head bone by itself, but this control certainly simplifies things for the animator. To do this, you just use a Track To constraint:

Figure 11-25. The Stickman rig, now with head control!

Your Stickman is mostly functional now. However, there's another constraint that is a staple of nearly all character rigs and is monumentally helpful to animators. It's called an inverse kinematics, or IK, constraint. The next section goes into what this constraint does, how it works, and how to give your rig its benefits.

When it comes to animating characters in 3D with an armature, you have two ways to move limbs around: inverse kinematics and forward kinematics, or IK and FK. Kinematic is just a fancy way of saying motion. By default, your rig is set up to use FK. Say you have a bone chain and you want to place the tip of the last bone to a specific location in 3D space. In order to achieve this, you have to rotate the first bone in the chain, and then the next, and then the next, and so on until you can get that last bone's tip properly placed. You're working your way forward down the bone chain. Because of the parenting relationships between the bones, you can currently do this with your Stickman rig right now.

That's FK. It gets the job done, but it can be awfully difficult and tedious to try and get the tip of that last bone exactly where you want it. It would be nice if you could just grab that tip, put it in place, and let the computer figure out how all the other bones have to bend to compensate for that. This, basically, is the essence of IK. You move the tip of the last bone and Blender works backwards up the chain to get the other bones properly placed.

To see what this is like, select your Stickman armature and Ctrl+Tab into Pose mode. Now, select the body.2 bone and press G to Grab and move it. Notice that all it does is rotate. It doesn't actually change its location. Now go to the Armature panel of the Editing buttons (F9) and left-click the button that says Auto IK. This isn't a real IK constraint, but it will help you understand how IK works. Now Grab and move the body.2 bone. Notice that now, it moves around, and the body.1 bone rotates to compensate for the locations that you try to put body.2. Selecting the head bone or one of the arm_lower bones results in similar behavior. Click around and play with it. It's pretty cool. When you're done, disable the Auto IK button.

IK is really awesome stuff and it's very powerful, but it's not the ultimate solution for animating. See, one of the core principles of animation is movement that happens in arcs. Generally speaking, arcing movement is move believable and natural-looking. Things that move in a straight line tend to look stiff and robotic. Think about how a person's arms swing when they walk. It doesn't necessarily matter exactly where the hand is. The entire arm rotates and swings back and forth. That is FK movement. If you're animating, you can recreate that motion by keying the upper arm bone at the extreme ends of the rotation.

In contrast, IK movement tends to happen in a straight line. You're just keying the tip of the chain, so that tip moves directly from one location to the next. To recreate a swinging arm in IK, you'd need at least three keyframes: one at each extreme and one in the middle to keep the hand from going in a straight line. And even then you might need even more intermediary keys to try to get that smooth arc that you get automatically with FK.

Where IK shines is when the tip of the bone chain needs to be precisely positioned. A perfect example of this are feet. When a person walks, the feet must touch the ground. Trying to achieve this with just FK usually ends up with feet that look "floaty" and not locked into place as the character moves. Another example is if the character is holding on to something and doesn't want to let go of it. You want to keep the hand in place and let the elbow bend naturally. In instances like these, IK is really helpful. The biggest use, though, is for foot/leg rigs on characters. And to that end, you're going to use the following steps to add IK controls to the Stickman rig:

Figure 11-26. A basic IK rig for the legs of Stickman.

Test your rig out by selecting the root and moving it around, particularly up and down the Z-axis. The leg bones in your Stickman rig should bend all by themselves to compensate for the location of the root bone relative to the IK bones. You can also select each of the leg_IK bones and move them around to control the bending of each leg independent of the other.

In doing this, however, you may notice that there are occasions where the legs don't quite know how to bend. They may randomly flip backward or roll out in odd angles. This is because, aside from slightly bending the rig at the knees when you created the leg bones, you haven't provided the legs with much of a clue as to how exactly they should bend. Fortunately, the solution to this is pretty simple. It's called a pole target. To define it, you need to create two more bones, one for each leg:

Figure 11-27. A completely working Stickman rig.

At this point, it should be pretty safe to skin the Stickman mesh to your armature. Using the bone heat method should give you the best results, so select the mesh (right-click), select the armature (Shift+right-click) and press Ctrl+P

At this point, you've got a great basic rig that you can start animating with immediately. However, you can make a few tweaks that make it even more usable. The first thing you can do is change the way the bones display in the 3D View. Now that you're done with the bulk of rigging, knowing which end of a bone is the head or the tail is a bit less important. Go to the Armature panel in the Editing buttons (F9) and change from Octahedron to Stick. Stick bones are the least obtrusive bones that are immediately available to you. Now you can see more of your mesh while you're animating and there's not as much clutter and geometry in the way. Figure 11-28 shows the Stickman rig with stick bones.

Figure 11-28. Stickman ... rigged with sticks!

Another relatively new feature to Blender that is quite helpful for organizing your rigs is the ability to create bone groups. To do this, select the bones you would like to group together and press Ctrl+G. When you do this, you get four options:

I used the bone groups feature to create groups for my main bone chains: left arm, right arm, left leg, right leg, and body. I left root, head, and head_target groupless. Create your own groups as you see fit.

Beyond organization, there's an additional benefit to using bone groups. You can define custom bone colors based on the bone groups you have. The control for this is in the Editing buttons. First, in the Armature panel, enable the Colors button under display options. Then, in the Link and Materials panel, left-click the button that says Default Colors and choose a Theme Color Set from the menu that pops up. I used this feature to make all of my left-side bones green and my right-side bones red. It's a good visual trick to let you or another animator quickly identify which bones are being used. Figure 11-29 shows what the bone groups and bone colors options look like in the Link and Materials panel.

Figure 11-29. The Link and Materials panel with controls for bone groups and bone colors for those groups.

Besides groups, another organizational tool for making your rig more usable are bone layers. Bone groups make it easy to visualize bones and even select them. However, bone layers are a faster, more reasonable way of showing and hiding the bones in your rig. As an example, have a look at Stickman's legs. They're entirely controlled by the IK and knee bones. Because you can see the Stickman mesh, you really don't need to see these leg bones. In some ways, they just get in the way of seeing your character's acting. In that case, it makes plenty of sense to move them to a different layer and hide that layer. To do this, use Shift+right-click, Border Select (B), or press L with your mouse over the leg bones to select the entire leg chain and then press M to move them to a different layer. I moved the bones to the first layer in the second block of layers. Now, if you ever want to see those bones, just go to the Armature panel and enable the layer there. In the meantime, though, as Figure 11-30 shows, your Stickman rig is much cleaner and now you're really ready to start animating.

Figure 11-30. Stickman, reporting for duty!