Character Rigging - Shoulders are the Pits
by Brian Immel
Smooth Without Influence Objects and Editing Vertices Weights
1. Select the geometry.
2. Shift-select the root joint.
3. Go to Skin > Bind Skin > Smooth Bind > option box. Make sure the following is set to Maya’s default:
- Bind to = Complete Skeleton. Or you can choose Selected Joints that does just as it says.
- Bind Method = Closest Joint. This option tells Maya to bind the vertices by proximity of the joint or distance from each joint. The latter usually involves lots of painting weights later on.
- Max Influences = 5. The number of influence limits to how many joints can share the weight of any given vertex.
- Dropoff Rate = 4.0. Dropoff rate tells Maya how much to decrease the influence of each vertex from each joint.
4. Click on Bind Skin.
5. Now that we have the geometry skinned, you need to test the rotation of each joint to see where we need to prune or edit the vertex weights. Here are some tips for searching for identifying errant vertex weights.
- Misbehaving vertex weights can be anywhere on the geometry. Use wireframe view instead of shaded view to see the through the geometry as you rotate the joints. You could also use X-Ray view as well.
- Rotate each and every joint! This sounds silly and can be time consuming but sometimes, Maya will put vertex weights in the odds places (toe vertices get weighted to finger joints, etc.).
- Name each joint. This will save a lot of headache and time later down the pipeline when you’re pruning or painting the weights.
- Use the Component Editor to see if you
need to prune any vertex weights away from needless joints.
1. Select all the vertices of the geometry and go to Window > General Editors > Component Editor.
2. Select the Smooth Skins tab.
3. Scan the window for tiny weight on vertices. Chances are, those tiny weights are on the wrong joint. I don’t have any particular rule of thumb for how much weight is too little but I usually prune anything that is below the value of 0.05.
4. You can remove/adjust these weights in the Component Editor by simply typing in a new value. Note: If you type if a value of 0, Maya will average that weight to the next one or more joints near it that already has weight. It won’t add weight to any joint that does not have weight to that particular vertex. If you type in a value more than what was originally there (lets say from 0.1 to 0.2), Maya will subtract an average weight from all the other joints listed under the vertices under their influence. Example: If vertex 130 (vtx130) is weighted evenly between three joints (weight = 0.333) and you want to take away all the weight from one joint, the remaining joints will equally share the removed value to both the joints (weight now equals 0.5).
Pruning
- Pruning allows you to remove, and redistribute, weights under a specified value that you can set.
- Select the geometry you have smooth bound.
- Go to Skin > Edit Smooth Bind > Prune Small Weights > option box.
- Type in the value you will wish to prune. Again, you will have to determine what is a good value to trim.
Painting Weights
1. The last and best way to edit vertex weights is to use the Paint Skin Weight Tool.
2. Select the geometry that has been smooth bound.
3. Go to Skin > Edit Smooth Bind > Paint Skin Weights Tools > option box.
4. In the Tool Setting window for Paint Skin Weights, change the Paint Operation to Add. I use the technique of ‘painting away’. Using this technique works best with a wacom tablet but works well with just a normal mouse. What I do with painting away is that I will add more weight to a joint if I want to lessen weight from another joint. This is best done by lowering the Opacity to 0.1 to 0.25 and leave the Paint Weights Value at 1. Figure 26 illustrates how weight is being added to the Spine03 joint while taking away from Shoulder_L joint.
5. Go back to the rotate tool and rotate the joint in question until you see the offending vertices popping/dropping.
6. Flip back to the Paint Weight Tool and paint the vertices up/down until the surface is nice and rounded again.
7. Repeat steps 5-6 until you've covered the entire character. This could take some time. Figure 28 displays a well-weighted armpit.
Here are some notes to consider:
- If you overpaint/add to much weight to a joint, simply select the joint you were taking weight away from and paint a little weight back into it and/or switch the Paint Operation to Smooth.
- Never paint a weight that is lower than the weight value that is already there (when in Replace mode). If you are in Add mode, you cannot paint down to a lower value. Maya will seemingly randomly dissipate the removed weights when painting with a lower weight value. This causes many first time smooth skinners many hours of headaches.