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You can use the Skin, Edit Smooth Skin, Paint Skin Weights tool on a per-vertex level as well as an entire object level. Many people are not aware that you actually can use the Paint Weights tool on a per-vertex level by selecting the vertices and loading the paint weights tool. This is extremely useful when you first start painting the weights on your character and you are trying to lay out your initial weights, or when you are trying to "point-tweak" certain vertices and leave others alone. Select the vertices whose weights you want to change, and use the Flood button to flood those vertices in Replace mode with a value of 1; this is a great first step at very quickly roughing in your character's weights. You can then go in and use low opacity in Replace mode with a value of 1, as well as Smooth mode with flooding, to really disperse the gradual fall-offs of your joints' weighting.
Sometimes it is difficult to paint or select the correct vertices on a character that you are trying to change the weights on because those areas are in little crevices, such as under the armpits, in folds of skin, between the legs, or between crevices in fingers. These most difficult areas to paint the weights on also end up becoming the most crucial areas for making the best-looking deformations on your character. So, having a quick and easy way of selecting and editing these areas ends up being crucial as well. A great tip for selecting these difficult vertices of your polygon character is to use the UV Texture Editor, but still select it using Vertex Component Selection mode. The geometry is literally unwrapped in UV space. If your modeling and texturing departments have done a good job laying out your UVs, the process of selecting vertices using this unwrapped representation of your character becomes an extremely quick and easy trick to use.
Figure 17.73 shows difficult vertices to select in 3D space and the exact same vertices selected in UV space. This is an example of how much easier and quicker it can be if you have the right UV layout at hand.
Figure 17.73
Using the UV layout to quickly select vertices.
The smooth binding in Maya works quite nicely because it enables you to use multiple influence objects. It even allows geometry to become an influence object that you can paint weights for.
Although it wasn't necessary to use influence objects for our character rig, I highly recommend using them to achieve complex deformations. Check them out in the Maya documentation. You create an influence object from any transform node in Maya by selecting the smooth bound mesh and then the object that you want to become an influence. Then you choose Skin, Edit Smooth Skin, Add Influence (see Figure 17.74).
Figure 17.74
The Add Influence menu command.
When you have finished painting weights and you have done all the other steps necessary to finish setting up your character, such as parenting low-res geometry and creating control boxes (as explained in earlier sections of this chapter), you are ready to hand off your file to the animator.
Character rigging can be a very fun and interesting process. The one thing to remember about this entire process, though, is that it will always be a collaboration between you and other teams. The way that the file is set up, as well as the controls there, will ultimately be used by the animator; thus, they need to be easily understood and controllable. The deformations of the character will ultimately change the shape and nature of the character's model and must therefore stay true to the design and style in which the character was originally modeled. The character that you set up must eventually be textured, lit, and rendered, so it absolutely must not have geometric problems such as bad normals or bad UVs when you bind it to the skeleton. The difficult part in setting up a character is being able to systematically take all of this into consideration, with the final goal being a stable character whose transformation space has been manipulated to offer full control to the animator.
Character animation is a long and difficult process, and the capability to have the character react in a desirable and predictable way is the most valuable thing that can be achieved. To make the character's controls and deformations predictable, and to give the character the capability to be textured, lit, and rendered are all vital in their own ways. The process of character animation will continue to become more simplified—and, therefore, capable of more sophistication—as time goes by. The same can be said of the techniques to rig a good character that is capable of achieving more types of motion. Always remember that, much like a puppet, there is a human behind the controls of your character breathing the appeal of artificial life into its computer-generated soul.
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Created: March 11, 2003
Revised: November 7, 2003
URL: http://webreference.com/3d/insidemaya/2
