Preparation and Binding | Game Character Development with Maya

Before we can test our completed characters' deformations, we need to prepare the geometry and bind it to the skeleton. If you followed the joint-based facial setup in Chapter 13, your geometry is already bound to the skeleton, so feel free to skip along to the next section. If, on the other hand, you are using the blend shape method, follow the instructions here for attaching the mesh to the base skeleton. This will drive the characters' movement, deforming the mesh so that the character can achieve poses and, ultimately, animate.

Load the file called Kila_FaceRig_BS.mb, (or Grae_FaceRig_BS.mb if you are working on him). The geometry for the first LOD is already preparedin Chapter 13 we combined it into a single mesh and cleaned it up, so it is ready for final weighting. The face and body must remain separate because blend shapes manipulate iterations of all the vertices of Kila's face, allowing her to talk.

1.	In the Outliner, navigate to the first joint of the base skeleton, called Root. Select it and open up the hierarchy.
2.	Go to Edit > Select Hierarchy to select all the objects beneath Root.
3.	Although we have the skeleton hierarchy selected, there are some joints we don't want to bind. Scroll down the Outliner and, holding Ctrl/Cmd, deselect all the joints that end with _Tip. These are only here as visual aids; they do not deform the character. Also, make sure no icons or other nodes are selected, we want only the joints to deform the mesh when moved.
4.	With the correct joints selected, hold Shift and add the KilaBody mesh to the selection.
5.	Go to Skin > Bind Skin > Smooth Bind and open the options. For Bind To, choose Selected Joints; for Bind Method, choose Closest Joint; and set Max Influences to 3 and Dropoff Rate to 4.
6.	Click on Bind Skin; the body geometry is now attached to the base skeleton.

NOTE

Alternatively, you can select just the body geometry and press the Bind button on the GCDM shelf. Provided that the base joint is called Root, this button will automatically select the proper joints and bind the mesh to them.

We now have to attach her face in a slightly different way. Because in this case the vertices of her face are controlled via blend shapes, certain game engines will have trouble if the vertices are also controlled by a number of joints. As far as I am aware, this conflict is due to the game engine's having to handle two types of deformation at the same time: It can be quite processor intensive, so using just one method is preferred. However, we still need the head to move with the skeleton, so it will have to be affected by one joint (the head joint). Sometimes simply parenting the face geometry to the head joint will suffice, but you can also bind it, and making sure it is only influenced by the head joint will certainly please the programmers.

For either method, binding or linking, all of the face vertices will essentially be controlled 100 percent by the head joint alone. With that in mind, it's crucial to also make sure that all vertices bordering the face mesh are also 100 percent bound to this same joint. If not, the mesh will break apart at those seams during posing and animation.

NOTE

It's a good idea to talk through this issue with your team's lead programmer, who may have specific ideas on how it should be handled.

1.	Select the main head joint, called Head.
2.	Holding Shift, select the face geometry.
3.	Go to Skin > Bind Skin > Smooth Bind, and set Bind To to Selected Joints, and Bind Method to Closest Joint. Set both Max Influences and Dropoff Rate to 1, which will fully weight the face to the Head joint. We don't need to do any more work on it.
4.	Save the file as Kila_Bound_BS.mb.

Both the blend-shapes and joint-based versions of our characters are now at exactly the same stage. This means we only need to edit the weighting information on their bodies, because the joint-based faces were completed in Chapter 13. So we will just look at the joint-based version. The same weight-painting techniques can easily be applied to the blend-shapes version if need be.