Painting Smooth Skin Weights

Painting weights is one of the single most important stages for your character's deformations to look believable and appealing. The process of painting weights basically involves using the Artisan paint brush architecture in Maya to paint on a value somewhere between 0 and 1. This will tell your skin cluster which joints will have an influence on the movement of which vertices.

The following text describes the process I use to paint weights on a smooth bound character. Then following exercise elaborates on the specifics involved to achieve good character weighting.

First, just as if you were doing a painting, rough in your general values by blocking out your weights, going through groups of vertices as well as each joint, and flooding them with either 0 or 1 values. Next, paint with a medium-size brush around the edges of your weights so that all the influences are at a value of 0 or 1. When you are finished and you have painted every single joint at either 1 or 0, you set the Artisan value to 1 but turn the opacity down to about .33.

Then go through and lightly soften the edges of all your weights by painting with this partially opaque brush. Every once in a while, use the smooth brush at this stage to also soften the edges. The last stage is to go through and use the smooth brush exclusively to really soften the weights on the joints that you want to have a lot of fall-off to their weighting. During this entire process, you should be testing your character's deformations by bending the joints and testing the controls. When you get things looking pretty good, you should do major motion and extreme poses for your character; test the weighting on an animated character that is hitting really exaggerated poses (with hands way up in the air, bending over and touching the head to the toes, and so on). At this point, you can go back and paint in the weights to fix any problems you see.

As a general workflow process, painting weights can seem somewhat repetitive, tedious, and often frustrating. It can feel like as soon as you change one joint's weights to look good in one pose, the other pose no longer works. It is important to note that sometimes it is simply a process of finding an acceptable state in between. Usually, though, if you follow the workflow outlined in the steps ahead, the painting of your character's weights should end up being a very smooth process (no pun intended!).

Exercise 17.13 Common Workflow for Effectively Painting Smooth Skin Weights

1. Select the smooth-bound polygon mesh and begin to paint weights using the Artisan options found under the Skin, Edit Smooth Skin, Paint Skin Weights Tool options box (see Figure 17.68).

2. Select the bound character. Under Skin, Edit Smooth Skin, Prune Small Weights (with a setting of about .4), get rid of all traces of pointlessly weighted vertices before you begin your weight painting. This enables you to see exactly which joints are the major influences deforming the geometry of your character. You will have a better idea of which joints you need to paint weights for the most (see Figure 17.69).

   

   Figure 17.68
   The Paint Skin Weights menu.

   

   Figure 17.69
   Painting weights with Artisan.

3. Deform the character by placing it into several extreme poses and setting keys across the timeline.

   A common sequence of poses during this phase would be a "jumping-jack" sequence, with the character's legs and arms reaching their full upward and downward extensions. This is known as range-of-motion testing. You want to paint the weights for your character so that they look decent even at the most extreme poses. This way, you will be sure that they will look good when the animators pose the character in a more normal, expected pose (see Figure 17.70).

   

   Figure 17.70
   Testing deformations while painting weights.

4. Paint the weights for only half of the mesh, until deformations are acceptable on that half. I almost exclusively use Replace mode and Smooth mode in Artisan to paint skin weights. These modes are set in the Paint Weights section of the Paint Skin Weights tool options.

5. When you have the weights painted for half of the character, select the skin and use the Mirror Weights feature under the Skin, Edit Smooth Skin, Mirror Skin Weights options box (see Figure 17.71). Be sure to use the correct axis settings that you want to mirror across.

   

   Figure 17.71
   Use the Mirror Weights feature to create your mirrored weights.

6. Now you can clean up your mirrored weights (they never come out perfect) by checking all the deformations and going through the same steps that you did previously to make sure all your weights are perfect on both sides. Painting precise and sparing brush strokes with the Smooth mode of the Paint Weights tool only where it's needed is crucial at this stage for really well-painted smooth skin weight deformations.

Tip - Use the Toggle Hold Weights on Selected button in the Paint Weights window to keep a joint's weights from changing after you have painted them (see Figure 17.72).

Figure 17.72
Using Toggle Hold Weights.