Skinning

Skinning

Working with the Angle Deformers

 

Autodesk 3ds Max Tutorials > Character Animation Tutorials > Character Animation without Biped > Skinning > 

Applying Skin to the Alien

In this lesson, you will apply the Skin modifier to the alien model. You will adjust envelopes and vertex weights for the model's left side, then mirror the settings to the right side. In doing so, you'll learn the following techniques:

• Changing the envelope start or end point
• Copying and pasting multiple envelopes
• Painting vertex weights
• Using the weight table
• Mirroring vertex weights

Set up the lesson:

• Load the file tut_skinalien_start.max.

  The character rig is in the scene, but it is currently hidden because it isn't needed for the skinning process.

  

  Reference pose in user view, with visible bones

Apply the Skin modifier:

1. Select MeshBody.
2. On the Modify panel, apply the Skin modifier to MeshBody.
   NoteIn this case, you applied the Skin modifier to just one object. You can also apply it to multiple objects at the same time.
3. On the Parameters rollout, click Add, and select all the objects on the list.

   There are other bones in this scene, but the ones not being used for skinning have been hidden.

4. Choose Edit > Select Invert.

   This selects everything except MeshBody: that is, all the bones in the scene.

5. Hide the bones by right-clicking a viewport and choosing Hide Selection from the quad menu.

Display and adjust the shoulder envelope:

1. Select MeshBody.
2. In the Front viewport, zoom in on the shoulder area of the model.
3. On the Parameters rollout, click Edit Envelopes to turn it on.

   

   Selectable bones, with handles on each end

   Each envelope selector displays over its corresponding bone as a dark gray line with circular handles on each end.

   TipWhile Edit Envelopes is active, the Select button is disabled. If you have a mouse with a wheel, you can zoom and pan without trouble. If you don't have a wheel mouse, after you zoom and pan, toggle Edit Envelopes off and then on again, so you can select envelopes once more.
4. Click the left shoulder envelope line to display the corresponding envelope.

   

   Left shoulder envelope selected

   NoteIn this lesson the “left shoulder” means the character’s left side, not your own left.

   Each envelope consists of an inner envelope (bright red) and an outer envelope (dark red).

   The vertices inside the inner envelope receive the most influence from the bone, while vertices between the inner and outer envelopes receive less influence. The farther the vertex is from the inner envelope, the less it is influenced by the bone.

   For a smooth skin, outer envelopes for adjacent bones should overlap slightly. This will cause the skin in a joint area (knee, shoulder, elbow, hip) to be influenced partially by each bone, making a smooth skin transition at joints.

   As you adjust an envelope, the vertices inside the envelopes change color to show the degree of influence from the envelope. Red vertices receive the most influence, while blue vertices receive the least.

5. Move one of the outer envelope handles to decrease the size of the envelope.

   

   Adjusting the outer envelope

Change the envelope’s length and direction:

The shoulder envelope sits a little too far into the arm. You can change the length and direction of an envelope by moving one of its end handles.

1. In the Front viewport, notice the two handles within the inner envelope. These control the envelope length. Select the right handle. When selected, it turns purple.
2. Move the handle to the left to shorten the envelope.

   

   Shortening the envelope

3. Make adjustments to the inner and outer envelopes and the envelope length until it looks like the following image.

   

   Size and shape of the shoulder envelope corrected

4. In the Front viewport, adjust the arm envelopes to look like the pictures below.

   

   Envelope for the upper arm

   

   Envelope for the lower arm

Paste to multiple hand envelopes:

1. In the Top viewport, zoom in on the left hand.
2. Select one finger bone, and adjust its envelope so it just encompasses the finger mesh, and overlaps the next bone a little bit.

   

   Finger joint envelope adjusted

3. In the Envelope Properties group, click Copy.
4. From the Paste flyout, choose Paste to multiple bones. This is the last button on the flyout.
5. In the Paste Dialog, choose all bones that contain the word “finger”, “thumb” and “hand”. Click OK to paste the envelope settings to these bones.
6. Check the envelopes at the fingertips and make sure they cover the entire mesh fingertip. Adjust if necessary.
7. Adjust the main left hand envelope as shown in the following image.

   

   Main hand envelope adjusted

8. In the Envelope Properties group, click Copy.
9. Choose Paste to multiple bones. Paste the selected envelope onto the HandRBONE envelope.

   Later in this lesson, you will learn how to mirror envelopes and vertex weights from one side of the character to another.

Adjust the body envelopes:

1. In the Front viewport, adjust the top chest/spine envelope (spine05BONE) so the outer envelope is not huge (as it is by default), but make sure each envelope encompasses the torso from side to side.

   

   Spine envelope adjusted

2. Repeat the previous step for the other spine bones: spine04BONE through spine01BONE. The envelopes for all the spine bones should be similar. You can also use the copy/paste to multiple bones combination to that effect.

Adjust the head envelopes:

1. In the Left viewport, adjust the neck envelopes so they encompass the mesh and overlap slightly.

   

   Neck envelopes adjusted

2. Adjust the main head bone's envelope so it encloses the head, but is not too much larger.

   

   Main head envelope adjusted

3. The bone just above the main head bone (hair1BONE) appears to be a single dot because it is aligned perpendicular to the left view. Leave it to its default settings and move to the next bone in the chain.
4. Adjust the envelopes for the alien's “topknot” so they follow the contours of the mesh.

   

   Adjusted topknot envelopes for the alien

Adjust the legs:

• In the Front viewport, adjust the envelopes for the character's left leg. You will have to move the thigh's top handle downward. Leave the left foot for the next procedure.

  

  Adjusted leg envelopes

Adjust foot envelopes:

1. In the modify panel, select the footLBONE. You can also select that envelope in the User view where it is easier to locate.
2. In the Left viewport, zoom in on the foot.
3. Adjust the character's upper foot envelope so the outer envelope is just outside the foot. You will need to move the handles to make the foot envelope parallel to the foot.

   

   Upper foot envelope aligned and adjusted

4. Adjust the left toe envelope so it is similar to the upper one.

   

   Adjusted toe envelope

   You can find a scene with the envelopes adjusted in the file tut_skinalien_envadjust.max.

View envelope influence:

1. Select the left toe envelope, and zoom in on the left foot in the User viewport.

   

   Shaded user view of the toe envelope

   In a shaded viewport, the model is shaded in red, yellow and blue to show the influence of inner and outer envelopes, with red indicating the strongest influence and blue a weak influence or no influence at all.

   The toe is mostly red, fading to yellow, then blue where the toe meets the foot. This indicates that the toe is influenced strongly by its bone. These envelopes will work well with the bone structure and mesh.

2. Select the top chest envelope (spine04BONE), and look at the colors.

   

   Shaded view of chest envelope

   The colors on the chest area indicate that the chest is barely influenced by the bone. This presents a problem. The envelope is too small to include the chest vertices. But if you increase the size of the envelopes, they will encompass the arms and neck.

   You can solve this problem by painting weights.

Set painting options:

Envelopes assign weights to each vertex to define how strongly the envelope influences the vertex. A vertex weight can range from 0 to 1. A weight of 0 means the bone doesn’t affect the vertex at all. At 0.5, the vertex is 50% affected by the bone, and 50% affected by one or more other bones. At a weight of 1, the vertex is 100% influenced by that bone alone.

Each vertex can have weights from several different bones, but all the weights must add up to 1.

In an envelope, red vertices have a weight closer to a value of 1, while blue vertices have a weight closer to a value of 0.

The Skin modifier allows you to “paint” weights onto vertices with the cursor, so vertices outside an envelope can still be influenced by the bone.

1. In the User viewport, select the spine04BONE chest envelopes and zoom in on the area.
2. In the Parameters rollout > Weight Properties group, click Paint Weights.
3. In the User viewport, move the cursor over the chest area. Don't click or drag just yet.

   

   The default paint gizmo is too large for this model.

   A large paint gizmo appears. As you move the gizmo over each polygon, the line pointing out from the gizmo shows the polygon's normal direction.

   This gizmo is too big for painting this character.

4. Click the Painter Options button next to Paint Weights.
5. On the Painter Options dialog, change Max Size to 6 and press Enter. Leave the dialog open.
6. Move the cursor over the chest again. Now the gizmo is a more manageable size.

Paint vertex weights:

1. In the Front viewport, click and drag over the chest area.

   As you drag over areas, the vertices in the area turn red. In the User view, you can see that the mesh in these areas is also red.

   

   Painting chest envelope weights

2. Change the User view to a Perspective view, and then use Arc Rotate to rotate the view so you can see the back of the model.

   While you’ve been painting the front of the model, the back hasn’t been getting painted.

3. In the Painter Options dialog, turn on Mirror, and set the axis to Y.
4. Click Paint Weights again. In the Front viewport, click and drag the cursor over the chest again.

   In the Perspective viewport, you can see two gizmos moving simultaneously, one on the front of the mesh and the other on the back. The Mirror option on the Paint Options dialog causes the paint strokes on one side the mesh to be duplicated on the other side.

   

   Mirroring the paint tool to affect both the front and back of the model

5. Select another spine envelope from the list of bones on the Parameters rollout, and paint weights for it. Perform this step for each of the spine bones (1 through 5) except spine06BONE.
6. Close the Painter Options dialog, and turn off Paint Weights.
7. Exit Edit Envelopes mode.

Test the skin setup:

After adjusting envelopes and vertex weights for the left side, test the setup before you mirror it.

1. Continue working on your file or open tut_skinalien_vertex_weighting.max
2. Unhide footLCTRL.
3. Turn on Auto Key.
4. Go to frame 10, and then move footLCTRL in front of the character to lift the left foot into the air as if to take a step.
   NoteIt is common practice, and generally a good idea, to reserve frame 0 for the reference pose of the character.

   

   Some problems with deforming or “wandering” vertices

   You might see some deforming as the foot moves, especially at the joint between the thigh and the hips. The steps that follow show ways to correct these problems. These steps show what to do if any part of the body mesh is deforming too much as it follows the bones, or is following a bone that it shouldn't.

   NoteIn versions of 3ds Max prior to version 8, vertices could wind up unassigned, and stay in position when the nearest bone is moved. That problem has been fixed: in version 8, each vertex is assigned to a bone; however, the envelope shapes and vertex weighting may still need adjustment.
5. Turn off Auto Key.

Adjust vertex weights using the Weight Tool:

The Weight Tool is handy for quickly adjusting weights for several vertices. For example, take a look at the joint between the thigh and the hips. The area is crumpled, and the skin isn't stretching correctly with the leg. Fixing this problem with envelopes alone would be extremely difficult, if not impossible.

1. In the User viewport, zoom in on the hip area. Press F4 to turn Edge Faces Mode on.
2. On the Modify panel > Parameters rollout, turn on Edit Envelopes, and then, in the Select group, turn on Vertices. Make sure the Backface Cull Vertices option is off.
3. Scrub the animation to see the problem with the weighting. The vertices are behaving erratically around the joint.

   

   Problems with vertices around the joint area.

4. Go back to frame 0. From the main tool bar choose the Lasso Selection tool.
5. In the Web Properties group, click Weight Tool to turn it on.

   The Weight Tool dialog appears.

   The Weight Tool provides some convenient ways to select vertices and adjust weights.

6. Zoom in on the hips in the Front viewport. Select a couple of vertices right below the joint.

   

   Two vertices selected around the thigh ring.

7. In the Weight Tool window, click the Loop button to select the vertices connecting the loop around the thigh.

   

   Vertices selected around the thigh.

   Notice that the selected vertices are shown as 100% weighted (1.000) to the upperLegLBONE in the Weight Tool window.

   

8. Using the lasso tool, select the ring of vertices surrounding the joint.

   

   Notice how these vertices are currently assigned to the upperLegLBONE at full value (100%). Some of the strength applied to these vertices should be assigned to the lower spine envelope.

   

9. With the vertices still selected, select the lower envelope (spine01BONE) in the User viewport. You can also select that envelope from the envelope list in the Modify panel.
10. In the Weight Tool dialog, click the .25 button. This changes the selected vertices weighting so that they are 75% weighted to the bone and 25% weighted to the lower spine.
11. Scrub the animation. The vertices starting from the joint and running down the leg are now reacting nicely, but the vertices above the joint line still need some work.

    

    Problem with vertices above the thigh.

12. Select another ring of vertices above the joint line. Use a combination of different viewports to make your selection. It would also help to arc rotate around the user viewport to help with the selection.

    

    Vertices selected above the joint line.

13. With the vertices and the lower spine envelope still selected, click the .5 button on the weight Tool window.
14. Adjust the weights in the Weight Tool window by selecting an envelope in the list and clicking a weight button. Set the weights so that the spine has about 50% control, the left leg about 40%, and the right leg about 10%.

    

15. Select a few vertices situated above the previous selection.

    

    Vertices selected on one side of the belly area.

16. Adjust the weights so that the spine is 75% active and the left leg 25% active. Set the right leg to 0% strength for these vertices.
17. Scrub the animation. the joint area is getting better but you still need to fine-tune the weighting of some vertices.

    

    Individual vertices need adjustments.

18. Alternate between frames 0 and 10 to identify the problem areas. select vertices individually or as a group and adjust their weighting in the Weight Tool window. If you want to use a percentage value other than the preset buttons, you can use the Set Weight button after entering the appropriate value.

    

    Using Set Weight to apply custom weight values

19. Adjust the vertices so that the mesh deforms nicely around the joint.

    

    Appropriate deformation around the joint area.

20. Close the Weight Tool window and exit Edit Envelope mode when done.

At this point, the envelopes and vertex weights on the left side of the mesh are as they should be. The next and final step is to apply them to the right side of the mesh, as well.

Mirror the vertex weights:

In 3ds Max, you can mirror the vertex weights from one side of the character to the other. This process mirrors all envelope settings as well as manual vertex settings.

1. Continue working on your file or open tut_skinalien_mirror.max
2. Make sure the alien mesh is selected and that Edit Envelopes is on.
3. In the Mirror Parameters rollout, turn on Mirror Mode.
   NoteMirror Mode is available only when Edit Envelopes is turned on.

   The character's vertices turn red. In the Front and User or Perspective viewports, you can see the mirror plane down the center of the character.

   

   Vertices in mirror mode, with mirror plane through the model's center

4. Increase the Mirror Threshold value until the character's vertices turn blue and green. A value of 6 should be sufficient; you might want to choose a greater Threshold value.

   

   Mirror Threshold value increased

   The Mirror Threshold value changes the distance from the mirror plane that Mirror mode will look for left and right vertices. Blue vertices indicate the left side if the mirror plane, while green vertices indicate the right.

5. Adjust the Mirror Offset value until the mirror plane sits at the center of the character mesh. If necessary, zoom into the Front viewport to help you accomplish this. A Mirror Offset value of 1 should be adequate.
6. In the Front viewport, check the character carefully to make sure all the vertices on the character's left side are colored blue, and those on its right are colored green.
7. Click Paste Blue To Green Bones.

   This pastes the envelope lengths and sizes from the left side to the right.

8. Click Paste Blue To Green Verts.

   This pastes vertex weights from the left side to the right.

9. Turn off Mirror mode.

   The envelope and vertex weight settings on the right now match the settings on the left.

   You might have to make some additional adjustments to vertex weights around areas that are affected by both sides of the body, such as the back of the hips.

   Adjusting the Skin settings is as much an art as a science. Because a working skin setup is essential to the animation process, it's not uncommon for an animator to spend hours or days testing simple motions and adjusting the skin settings accordingly. Gaining skill with the Skin modifier takes practice, but the results are well worth it.

   To see a working skin setup for this character, open the file tut_skinalien_finished.max.