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Introduction to Character Rigging

Using Spline IK

 

Autodesk 3ds Max Tutorials > Character Animation Tutorials > Character Animation without Biped > Introduction to Character Rigging > 

Skinning

In this lesson, you will associate the bones with the character mesh so the bones will deform the mesh. This process is called skinning. In 3ds Max, you skin a character with the Skin modifier.

Prepare the scene:

1. Continue from the previous lesson, or open the file tut_introrig_spinebend.max.

   

2. If you are continuing from the previous lesson, go to frame 0.
3. Unhide all the objects in the scene.
4. If you have not changed the rig on frame 0, the bones should fit perfectly inside the mesh. If they do not, make adjustments to the rig to fit the bones inside the mesh.
5. Select Pluggo_Body, and press Alt-X to make it solid.

   

Apply the Skin modifier:

You apply the Skin modifier the mesh that you want to deform with bones.

1. Select Pluggo_Body.
2. On the Modify panel, click Editable Poly on the modifier stack to highlight it.

   If MeshSmooth has been applied to the character, as it has in this case, it is usually better to apply the Skin modifier below MeshSmooth on the stack. With this technique, you will have fewer vertices to control with the Skin modifier, and the character will still deform smoothly at the MeshSmooth level of the stack.

3. On the Modify panel, turn on the Show End Result On/Off Toggle if it's not already turned on.

   This will show you the results of the MeshSmooth modifier as you work, even though it is higher on the stack than the current level.

4. Apply the Skin modifier to the mesh.

   The Skin modifier is applied above Editable Poly, but below MeshSmooth. Now you will associate the bones with the mesh.

5. On the Parameters rollout, click Add. On the Select Bones dialog, select all the bones except BoneHeadTip and BoneToeTip. The selected bones appear on the Parameters rollout.

   There is no need to select the control objects, as they will not deform the mesh. The control objects move the bones, which in turn deform the mesh. The bones at the tip of the head and toe are not inside the mesh, and so should have no influence on the mesh deformation.

Adjust the scene to help you see the skinning results:

It will be easier to use the animation between frames 0 and 10 to test the skinning if the active time segment is shorter.

1. Click Time Configuration, and change the Length to 100. Click OK to close the dialog.
2. Scrub the time slider between frames 0 and 10.

   

   The mesh follows the bones, but the eyes are left behind. The eyes must be linked to the head bone to animate correctly.

3. Select Pluggo_EyeLeft and Pluggo_EyeRight, and link them to BoneHead.

   Now, when you scrub the time slider, the eyes go with the head.

   

   You could have applied the Skin modifier to the eyes as well as the body, but this is not necessary unless the head will deform. In this character rig, the head will always be rigid, so it is easier to link the eyes to the head bone.

   Now that you have applied the Skin modifier, you no longer need the bones in the scene, and it will be easier to adjust the Skin modifier with the bones and controls hidden.

4. Click Select to turn it on and turn off Select And Link.
5. Select all the bones, IK chains, and control objects. Right-click any viewport and choose Hide Selection from the quad menu.

Look at the envelopes:

When you apply the Skin modifier, each bone is assigned a pair of envelopes that determine how much the bone affects the vertices within it:

1. Select the mesh, and highlight the Skin modifier in the stack.
2. On the Parameters rollout, click the Edit Envelopes button to turn it on.
3. On the Parameters rollout, highlight different bones on the list, and look at their envelopes in any viewport.

   Each envelope pair is defined by two distinct splines:

   • The inner envelope, where vertices receive the fullest influence from the bone. This envelope is displayed as a red spline.
   • The outer envelope, where vertices between the inner and outer envelopes receive less influence from the bone. The farther the vertex is from the inner envelope, the less the bone's influence on the vertex. This envelope is displayed as a brown spline.

   Any vertices that are not inside the outer envelope are not influenced by the bone. Where two envelopes overlap, the bones share influence over the vertices.

   Ideally, the inner envelope surrounds the non-bending part of the skin, such as the main part of the thigh or calf. Outer envelopes from adjoining bones should overlap somewhat to provide influence over joints, such as the knee and ankle.

   The initial size of the envelopes is determined by the size of the bone at the time the Skin modifier is applied. In shaded viewports, the selected envelope's influence is shown as a color on the mesh. Red areas are the most influenced, while yellow and orange areas receive some influence. Blue areas receive no influence at all from the selected envelope.

   

   Envelope for BoneSpine01 with colors showing influence

4. Scrub the time slider and watch the animation again.

   The mesh goes with the bones, but the joints are not well defined. For example, the crease at the top of the thigh does not bend cleanly. Instead, the entire thigh bends. This is because the envelope around BoneSpine01 is too large, and it encompasses half of the thigh. In addition, the head envelope is very large, and it encompasses the body.

   

Adjust the envelopes:

Now you will adjust the head and lower spine envelopes so they encompass more appropriate parts of the mesh. You can adjust envelopes by moving their handles. Handles appears as round shapes on the envelope spline.

1. Go to frame 0.
2. On the Parameters rollout, highlight BoneSpine01.
3. In the Front viewport, select one of the handles near the bottom of the outer envelope. The handle and its cross section turn purple when they are selected.
4. Move the handle in toward the character's body until the outer envelope overlaps about half the thigh.

   

5. Move one of the handles near the top of the outer envelope to make the envelope overlap the area where the top spine bone will have its influence.

   

6. On the Parameters rollout, select BoneHead.
7. Adjust the head envelopes in the same manner, so the envelopes overlap the neck area slightly. Also, move the inner handles along the length of the bone to reduce the size of the envelope. (The outer handles along the length of the bone don't move.)

   

   NoteWhen you move the handle for an outer envelope past its inner envelope, the inner envelope is automatically reduced in size so it is always inside the outer envelope.

Test the skinning:

1. Turn off Edit Envelopes.
2. Scrub the time slider to frame 10.

   There is now a definite crease at the thigh, and the thigh itself is no longer bending.

   

   If you continue to see problems after you adjust a skin's envelopes, one way to fix these is to adjust vertex weights. That technique is shown in the lesson, Applying Skin to the Alien .

3. Save the scene as my_introrig_skin.max.

   You can find a version of this scene in the file tut_introrig_skin.max.

   In this case, you applied the Skin modifier to just one object. You can also apply it to multiple objects at the same time.

   There are many more adjustments you could make to the envelopes and vertex weights to make the mesh deform more realistically. There are several sample files you can look at to learn more about rigging:

   • You can find this character and rig structure with completed skinning and a little animation in the file tut_introrig_complete.max.
   • You can find fully skinned and animated example of this character with slightly different rigging in the file tut_introrig_sample.max. You can also view the animation from this scene in the file tut_introrig_sample.avi.