In Chapters 4, 5, and 6, we learned how to create character rigs using Bones, Bipeds, and CAT rigs. In the Bones chapter, we also looked at using wire parameters and reaction managers to create varied animations of human body. We also learned to drive the bones using IK and FK tools. In this chapter, we look at binding our rigs that we created in earlier chapters to the character model. This way, any animation done to the rig will deform the mesh accordingly. This technique is called skinning. In the following sections, you will not only learn how to skin your bones, bipeds, and CAT rigs, but also how to weigh them to get the right deformations.
Skinning
The process of binding the bones, bipeds, or CAT rigs to a mesh so that it deforms accordingly is called skinning. We will be looking at two modifiers that allow us bind our character mesh to the rigs we created in earlier chapters. The modifiers are Skin and Physique. Note that there are other third-party modifiers available as well and there are a lot of third-party plugins that ease the process of skinning.
Skinning Bones
- 1.Load Human_Rigged_Bones.max from the scene files folder of Chapter 7. This rig was created from the techniques we learned in Chapter 4. At this point, I would like you to take some time and analyze the rig to see how it was created. I summarized a few points just to recap:
IK chain for arms and legs
Helpers for leg to get heel and tip toe animations: Orientation and position constraints and knee controller for knee orientation
Helpers for arm to get wrist rotation and position: Orientation and position constraints.
Fingers set with orientation constraint and wire parameters with reaction manager for curl animation.
Spine to head: Orientation and position constraints.
All the controllers have freeze transform applied so that they can be reset using transform to zero in the Alt+right-click menu. Experiment by moving the controls and see how the bones have been set up.
- 2.Open the Layer Explorer by going to Tools ➤ All Global Explorers ➤ Layer Explorer. Alternatively, you can load the Scene Explorer from Tools ➤ All Global Explorer ➤ Scene Explorer and the toggle Sort by Layers in the Scene Explorer.
We have three layers—the default, bones, and the meshes layers.
Enable the visibility flag and unfreeze the mesh so that it can be selected from the Scene Explorer or Layer Explorer.
- Selecting the character model in viewport and pressing Alt+X will show textures, but for now let’s work in see through mode. If you can see textures/color on the model, press Alt+X. You should see something like Figure 7-1.
Figure 7-1Character in see through mode with the Bones rig
- 3.Unfreeze the character from the Layer Explorer or Scene Explorer and add the Skin Modifier from the Modifier panel. Be sure to add the Skin Modifier to the character mesh and not the bones or controllers. See Figure 7-2.
Figure 7-2Character with Skin Modifier applied
- 4.
Select the character’s Skin Modifier. You should see that its parameters have a lot of options. We need to add our bones to the Skin Modifier.
- 5.
If you look at the Skin Modifier, there is a Bones ➤ Add option.
- 6.
Clicking on the Add option brings up a dialog box that shows all our controllers and bones. We need to select our bones alone from the list. It’s not impossible but it’s tedious to sort through the hierarchy and toggle the visibility flags to get the bones alone. Refer to Figure 7-3.
- 7.
You can choose bones this way, but I will show you an alternative way. Close the Select Bones dialog box.
- 8.
Select the hip_bone and double-click on it. This will select all the bones. At this point, you should deselect the end bones of the arms, legs, and head, because we don’t want the end bones to influence the mesh.
- 9.In the main toolbar you should see a Create Selection Set combo box (see Figure 7-3). Select it and give it a name. I named it Bones_Selection for this example.
Figure 7-3Select Bones dialog
- 10.Once you give a name and press Enter, you can deselect the bones by clicking anywhere in the viewport.
Figure 7-4Selection set, empty list
Selection set with a selection list
- 11.Now with the selection set created, let’s select our character mesh and go to the Skin Modifier and click the Add button again. This time in the toolbar of the Select Bones dialog, you can choose Bones_Selection that we just created. Refer to Figure 7-6.
Figure 7-6Select Bones from the selection list
- 12.
Choosing Bones_Selection will cause all the bones in your selection set to be selected. Click on Select.
- 13.Note how the Skin Modifier lists all the bones and the Remove button is available now. If you want to remove an end bone you can select it from the list and click on Remove. Or if you missed any bone earlier, you can add it using the Add option. In this example, the end bones are still in the list, so we can select them and click the Remove button to remove them.7
Figure 7-7Adding and removing bones
- 14.
With these steps done, the character mesh is bound to all our bones that we selected.
- 15.
Play around by moving and rotating the hand and leg controllers to see how the character moves. You might notice that our mesh is not moving naturally in places like the pelvis area and shoulder joints. Also, the elbows do not match inside the mesh. It’s important to be sure your bones are inside the mesh and perfectly aligned and then apply the Skin Modifier.
- 16.If you try to lift the left/right feet controller, you see an unwanted bulge near the hip area. Those are not the only mesh glitches; see the foot ankle area, shoulder clavicle, and neck areas as well. Figure 7-8 shows the potential problem areas.
Figure 7-8A mesh error near the hip when lifting the left leg
- 17.
A checkpoint file has been created called Human_Rigged_Bones01.max.
Skin Envelopes
In the previous section, we noticed that our character mesh has weird deformations near the hip area when the leg lifts up. This is because the bone envelopes need to be set correctly. The position of the bone and bone fins greatly influence how the software applies skinning.
- 1.
Fire up 3ds Max and load Human_Rigged_Bones02.max.
- 2.
Select the character model and right-click in any viewport. Choose Properties and disable see through in the Object Properties dialog.
- 3.
Select L_Leg_Control and move it a bit up and forward until you see the mesh overlaps, as seen earlier.
- 4.With the character mesh still selected, go into the Skin Modifier and click on Edit Envelopes. Once Edit Envelopes is clicked, you should see something like Figure 7-9. In this mode, instead of bones, you see lines in place of bones.
Figure 7-9Edit envelopes
- 5.
Now select the L_thighbone from the bones list in the Skin Modifier or click the corresponding line of the bone in the viewport.
- 6.Once the bone is selected, you should see the red influences, as shown in Figure 7-10.
Figure 7-10Edit Envelopes influence range
- 7.
The influence area includes a core influence (an inner capsule) and an outer capsule that’s bigger and covers the inner one. It’s used as a influence fall off.
- 8.
You can select the points of the influence capsules and move them to increase or decrease the bone’s influence area. Experiment by selecting the inner and outer points of both the top and bottom areas of the selected bone envelope. We can go the long way from here or the short way. Let’s use the short way and speed up things by editing how 3ds Max creates these envelopes.
- 9.
3ds Max’s default skin solution is called the voxel solver solution. We will tweak the solution to get better results.
- 10.Scroll in the Skin Modifier until you come to a section called Weight Properties. Currently it is set to Voxel. Click on the dotted button, as shown in Figure 7-11.
Figure 7-11Envelope Weight Properties
- 11.Once you click on the button, you should see the popup dialog shown in Figure 7-12.
Figure 7-12Envelope Voxel Solver options
Let’s discuss the options:Falloff: This determines how smooth the falloff is. The bigger the number, the harsher the blend between the two bones. The default value of 0.2 should be enough.
Max Influence: This determines how many bones the current envelope can influence.
Max Resolution: The higher the resolution, the slower the calculation and the better the result. It’s advisable to start with the lowest and gradually increase the number.
Use Winding Numbers: If you check this box, a more accurate solution will be given but it will be slower. It’s advisable to leave it off, unless you have a very powerful computer.
Turn Off Envelope Gizmos: Once you enable this, the solution is baked and you lose the ability to edit envelopes.
- 12.
Select the character and go to the Weight Properties. Choose the button to configure the solution, as shown in Figure 7-12.
- 13.
Change the max resolution to 64 and leave the other data to the defaults. Press Apply.
- 14.
Once you’re done, choose Enable Envelope. You can see the solution in Figure 7-13. Notice how the envelopes eases in. The closer the color is to red, the more influence the selected bone has in that area. Blue denotes that it is not influenced by the selected bone.
Envelope Voxel Solver with a value of 1
Envelope Voxel Solver with a value of 0.2
Try adjusting the Curl attributes of the finger controller that the rig has from the Modifier panel with a resolution of 64 and then 512 for the Voxel solution. You should notice the influence it has and the difference it makes.
Paint Weights
Now let’s look at the longer procedure that we talked about and avoided in the previous steps. You might be wondering why we will now examine the longer route when the Voxel method worked. The answer is that sometimes you might need to paint weights for a particular set of edge loops or vertices in your model. This can be achieved by choosing a set of vertex and painting the weights manually.
- 1.
Load Human_Rigged_Bones02.max.
- 2.
Select your character mesh. Go into the Modifier and select the Skin Modifier. Then, click on Edit Envelopes and ensure that Select Vertices is checked below the Edit Envelopes button (this allows us to select vertices to paint weights).
- 3.To better demonstrate this, select the L_Ankle_Bone and choose the Weight tool from the weight properties. See Figure 7-15.
Figure 7-15Paint Weight tool in the Weight properties
- 4.Clicking on the Weight tool opens the Weight Tool dialog, through which we will be painting weights. See Figure 7-16.
Figure 7-16Paint Weight tool options
- 5.
Note that all the options in the Weight tool are grayed out and no operation of any kind can be performed. This is because we have not selected any vertex or vertices.
- 6.
Switch to a wireframe by pressing F3 or changing the viewport shading mode. It will be easier to select the vertices in wireframe mode.
- 7.In Figure 7-17, I have posed the character’s legs in a running pose. Note the mess near the knee joints and ankle.
Figure 7-17Paint Weight: leg mess
- 8.Do a lasso selection (using the selection modes in the ribbon toolbar) around the knee area, as depicted in Figure 7-18.
Figure 7-18Paint Weight: vertex selection of the knee
- 9.
You don’t need to be accurate in terms of selection. Just select vertices around that position.
- 10.With these points selected, now you should notice that the Weight tool has all the options available. Let’s discuss a few options in the Paint Weight tools before we go any further:
Shrink: Contracts your current selection of vertices
Grow: Increases your selection area by adding adjacent loops
Ring: Selects all vertices parallel to the selected vertices
Loop: Selects the adjacent points that are in the continuous edge
These numbers will determine the weights for the selected vertices. If you select 1 for a set of vertices the bones will influence it 100%. Setting it to .5 will cause the bones influence to be 50%.
- 11.Now with the selection of the vertices mentioned in Figure 7-19, set the weight to .5 using the Weight tool.
Figure 7-19Paint Weight: Vertex selection and weightage applied
- 12.
Don’t panic if it looks like a mess, even more than before. We need to do one more tweak to fix it.
- 13.
With the vertex still selected, click on Blend a couple of times to ease the weightage.
- 14.You might need to select adjacent vertices loops that are still not controlled. For example, the blue loop of vertices below the knee are not controlled, and the red loop of vertices above the knee are over influenced. We need to give a weight so that the influence is smoother (by increasing the weight value for blue and decreasing the weight value for red). See Figure 7-20.
Figure 7-20Paint Weight: Vertex selection, knee fixed
- 15.
The yellowish-orange vertex areas need to be blended a little more with the red and blue loops. When you select the yellow loops and click on Blend, notice how the adjacent loops change color and the mesh eases in.
There are more techniques and plugins available for skinning, but a solid understanding of this should be enough to step into the world of 3D character animation.
Skinning Bipeds
In the previous sections, we learned how to skin our character rig using the Skin Modifier. The same Skin Modifier can be applied to bipeds as well. But the 3ds Max native skinning tool for bipeds is called Physique, so let’s look at how to skin a biped rig with the Physique modifier. I recommend you try skinning with the Skin Modifier as well.
- 1.
Load Human_Rigged_Biped.max.
- 2.
In this file I aligned a biped to our character mesh in Figure mode. Take the time to align the biped parts to the corresponding positions according to your mesh. The better the alignment, the easier the skinning process is going to be.
- 3.Select the character mesh node in the Scene or Layer Explorer. Once the character mesh is selected in the modifiers, choose Physique from the list. See Figure 7-21.
Figure 7-21Physique modifier`
- 4.
In the Physique section of the Modifier tab, click on the Attach to Node, as shown in Figure 7-21.
- 5.When you click it, nothing will appear to happen. In reality, the software is expecting you to choose the biped, so press H and pick bip001, as shown in Figure 7-22.
Figure 7-22The Pick Object dialog
- 6.
A Physique Initialization dialog box will pop up. Leave everything set to the defaults and click Initialize. Depending on your computer’s speed, this may take a moment.
- 7.
Once it has completed, you should see a faint yellow/orange line running across the biped structure. This denotes that the Physique Modifier has created the connection between your character mesh and the biped. If you want to see the line clearly, just select the parts of the biped and hide them.
- 8.
At this point, you can turn off Figure mode and rotate and move the biped parts to see how the mesh moves.
- 9.
In this case, there is a lot of work to be done. If we had scaled the biped part to enclose the mesh that it needs to influence, our work would be easier. I left it as such to show how to fix it.
- 10.
Select all the biped parts in the Layer or Scene Manager and hide them.
- 11.
With the character mesh selected, in the Physique Modifier tab, expand the modifier. You should see Envelope, Links, Bulge, Tendons, and Vertex. These are the submodes you can use to skin the biped to mesh. Let’s look at Envelopes.
- 12.Click on the left thigh area to see the envelope. See Figure 7-23.
Figure 7-23Physique Envelope: left thigh
- 13.
The envelope works the same way here as in the Skin Modifier, except it lacks the interactive tweak control.
- 14.Be sure the envelope is selected in the Physique Modifier section. Set the options as shown in Figure 7-24.
Figure 7-24Physique Blending Envelope
Strength: Determines how strong the influence is going to be.
Falloff: Determines the strength decrease rate.
Inner/Outer/Both: Choosing inner will only tweak the inner parameters. Choosing both will affect both the inner and outer parts of the envelope.
Radial Scale: This increases the size of the influence area. Note we have to be cautious with this, as increasing this value too much will start pulling mesh from the other side or from unwanted parts.
Parent Overlap: The influence area will be influenced by and pulled toward any parent bone structure (biped structure).
Child Overlap: The influence area will be influenced by and pulled towards toward any child bone structure (biped structure).
By playing around with these values, you can make adjustments when the mesh is not conforming to the biped. We will not be covering bulges and tendons, as they are an add-on to the skinning process and not a prerequisite. Bulges are used to emulate muscle bulge, and tendons are used to create links between bones that deform and twist along.
- 1.Once you select the Vertex mode for the Physique Modifier, you should see something like Figure 7-25.
Figure 7-25Physique vertex mode
- 2.To make sense of how this works, press Ctrl+A to select all the vertices. You should see something like Figure 7-26.
Figure 7-26Physique vertex mode: all selected
- 3.Okay, let’s discuss what is happening here. On the right in the Modifier panel, there are color codes for red, green, and blue. The icons in the modifier work as toggles. When the red cross is turned off, you can’t select the red vertices.
Red: Deforming vertex
Green: Rigid vertex
Blue: Rooted vertex
- 4.
We see shades of red (maroon/brown, red, and blue). Green won’t be visible unless you set it to rigid.
- 5.
You can select individual envelopes of biped sections only to see the vertex color for that section. In our case, choose Select from the modifier and select the blue vertex for the specific part of the biped rig. For example, let’s focus on the Bip001 L Calf area. Select all the blue vertex using a lasso selection and choose Assign to Link.
- 6.
Click on the yellow line area near the Bip001 L Calf to link the vertex. You need to work section by section on each biped part and link the vertices.
Physique Vertex Operations
Select: Allows you to lasso selected vertices.
Select by Link: Choosing this and clicking on a link allows you to select all vertices influenced by it.
Assign to Link: Select a group of vertices and choose Assign to Link. Click on a envelope link to assign the selection.
Remove from Link: Select a group of vertices from a link and click on Remove from Link, then choose the link. This removes the selected vertices from that link.
Lock Assignments: If you made an assignment and do not want it to be changed later when doing a selection, you can lock your assignment. Locked assignments are represented as bigger squares.
Unlock Assignments: If you want to change an assignment, you can unlock the link.
Type in Weights: Allows you to select the locked assignments and input weight values without unlocking them.
Hide: Hides the current selection of vertices.
Unhide All: Unhides all hidden vertices.
A word of note—the Physique Modifier is a legacy modifier. Even though it has changed a lot, it’s rarely used and is used only for bipeds. Most of the riggers use and rely on CAT rigs or custom bone rigs for character animations.
Skinning: CAT Rig
Load CAT_CharacterAnimation_Start.max in the 3ds Max scene source folder. This is the same file that we used to create a custom CAT Rig. Now let’s animate the rig and use it to animate our character.
- 1.Remember we froze the character so that we can set up the bones in the previous section, so right-click on the viewport and a click on Unfreeze All, as shown in Figure 7-28. This makes the character model selectable.
Figure 7-28CAT rig aligned to the character mesh
- 2.Select your character model and go to the Modifier panel. In the Modifier list, choose Skin Modifier. Your modifier stack for the character mesh should look like Figure 7-29.
Figure 7-29Skin Modifier
- 3.Select your Skin Modifier to populate the rollout and choose Add. See Figure 7-30.
Figure 7-30Skin Modifier, adding bones
- 4.In the Select bones popup box, choose CustomRigPelvis and press Ctrl+C to select all its children. Click on Select. See Figure 7-31.
Figure 7-31Skin Modifier, selecting bones
- 5.
A reference file has been created called CAT_CharacterAnimation_Start1.max.
- 6.
At this point, try selecting parts of the character rig and move and rotate them to see the deformation. As you see results where deformations are not happening, scale the appropriate parts of the CAT rig.
- 7.Select your character model by selecting it in the viewport. Then go into the Modifier panel and choose Edit Envelopes. See Figure 7-32.
Figure 7-32Skin Modifier, edit envelopes
- 8.You can see the bones as lines. Note that there is a heat map around the mesh for the selected rig part. In this case, the head rig part is selected. See Figure 7-33.
Figure 7-33Skin Modifier, envelope range
- 9.
The warmer the tone of a vertex, the more it is influenced by the selected part and the bluer it is, the less it’s influenced. (Follow the steps from the beginning of this section in 3ds Max and look at the visual feedback we get of the influence based on the heat map.)
- 10.We can change the influence by selecting the outer capsule wireframe shown in Figure 7-34 and resizing it by moving the capsule points. Refer to Figures 7-34 and 7-35.
Figure 7-34Skin Modifier, envelope original
Note the influence in these two images. They show how the influence range is tweaked by increasing the capsule size. Also notice that the heat map is stronger near the elbow.
Figure 7-35Skin Modifier, envelope altered
- 11.
The influence can be modified by tweaking the inner and outer radius of the influence envelope, as shown in Figure 7-35. The start and end tip can be repositioned too.
- 12.
At this point, feel free to move and rotate biped parts and see how the deformation happens. Lift the legs up and see how the knee area is holding up and deforming and tweak the envelopes as needed.
This process of skinning is time consuming but worth the effort for a polished animation.
- 13.
For the purpose of this section, let’s move on and select the CustomRig (Root Triangle base) and go to motion options.
- 14.
Create a CAT Motion Layer and turn on animation mode.
- 15.
You should see that the 3D model is deforming according to our CAT rig movement.
Skinning is an iterative process that requires you to set envelopes and test deformations. Think about how the bone parts in your body influence the flesh around it and set the envelopes accordingly. Refer back to the bones section for a detailed, step-by -step process of the envelope editing process and apply the same to CAT rigs. As a quick example: we could use the Voxel solver to handle the weight of biped parts as we did in the bones section.
Summary
In this chapter, we learned how to attach character rigs (bones, bipeds, and CAT rig) to a character mesh and bind them for proper deformation using modifiers such as Skin and Physique. In the next chapter, we look at creating walk and run cycles of the skinned characters. We will learn new techniques that will help us create a refined and polished animation.