Skinning is a very important step in the setup of a character for animation that will allow us to deform a mesh parented to a rig. It should be noted that the term skinning is not directly used in Blender. In Blender, you will generally find the term "Weight" designating the influence that a bone has on the geometry. It is often a long and delicate step, but fortunately, Blender allows us to perform an automatic skinning that is already very clean and quick. This is one of the most efficient skinning algorithms.
Before skinning our character, just as a reminder, we must determine which bones will deform the mesh and which not. This will be done as follows:
- We will verify whether the Deform option is unchecked for all deforming bones (Properties | Bone | Deform).
- In the Object Mode, we will select the mesh of the Rat Cowboy, then the Armature, and we will make them child and parent (press Ctrl + P and select With Automatic Weight).
A nice skinning has been done for us. You can make a few rotations on the rig in the Pose Mode to visualize the result.
However, we must do a few adjustments to improve this. Let's dive into the tools that we have at our disposal.
If we select our mesh and observe the Data menu of the Properties panel, we can see Vertex Groups that matches the bones of the Armature. This menu, in Weight Paint mode, allows us to select and view the influence of each bone. The Weight Paint mode could be activated directly on the object. If the armature is in the Pose Mode, it is possible to select the bones by a RMB click as well while we are in the Weight Paint mode of the object.
In the Weight Paint mode, we can view the influence that each bone has on the geometry with a color play. Blue means a 0% influence, a greenish-blue color means 25%, green means 50%, yellow means 75%, orange means 85%, and red means 100%.
In order to modify the influence, we have several brushes that can be used exactly in the same manner as Texture Paint and Sculpt Mode in the left panel of the 3D viewport. These brushes allow us to paint bones influence directly on the mesh. In our case, we will use only three brushes. The brushes that will serve us for sure will be the Add, Subtract, and Blur brushes.
- The Add brush allows us to increase the weights
- The Subtract brush allows us to reduce the weights
- The Blur brush allows us to soften and mix the weights
The options of the brushes are exactly the same as with Texture Paint and Sculpt Mode. We can change the radius of the brush by pressing F and moving the mouse. Also, we can change the strength of the brush that will completely modify the impact of the brush. You can change the curve, too.
We can paint the weight in symmetry. To do this, the mesh must be perfectly symmetrical. We will check the X-Mirror option in the Option tab of Left Panel (T).
There are also a few useful options in the Weight Tools menu. For example, Mirror, to make a symmetric skinning and Invert, to invert the influence of our bones.
Note
For more information, you can have a look at the official Blender manual at this address: https://www.blender.org/manual/modeling/meshes/vertex_groups/weight_paint_tools.html.
The weight paint of the Rat Cowboy (here the head influence is shown)
Weight Paint is a very useful technique, but sometimes it is not very accurate. It can be useful to assign weight precisely on some geometry components.
To do this, we must be in the Edit Mode and select the vertices to which we want to assign a weight. Then we can go in the Vertex Group menu (Properties | Data | Vertex Groups). There will be a Weight bar from which we must select the desired weight and click on Assign. If you don't have any group, you can click on the + icon.
Another nice feature is located in the Right Panel (N). There the Vertex Weight menu allows us to visualize the bones that influence the selected vertex and adjust the vertex directly. We will notice that the total weights assigned to a vertex group may exceed 1.000. In fact, Blender will add the total of influences and make an average.
Correcting the weight paint of the toes.
If you have used the With Automatic Weight option, you should have a very few things to change. The arms, legs, and head deformations should be quite good.
However, the toes aren't working well because there isn't a bone for each toe. So we will fix this as follows:
- We will check the X-Mirror option, and we will select Toe bone.
- Now, we can paint with Add Brush to add some weight to the toes until we get a red color (100%).
- Then, we will need to remove the influence that the foot bone has on the toes. To do this, we will use the subtract brush. Now the foot shouldn't affect the toes.
Let's do the skinning of the belt. It is not a particularly easy element to skin because of its thickness and possible interpenetration with the body, but do not be discouraged. In this case, we will manually assign the weight to the vertices. This is shown in the following steps:
- We will start by selecting the belt, then select the Armature, and we will make them child and parent (Ctrl + P and select With Automatic Weight).
- In the Vertex Groups menu (Properties | Data | Vertex Groups), we will remove all the vertex groups except these: Hips, Thigh.L, and Thigh.R with the - button.
- First, we will assign a weight of 1.000 to the Hips vertex group, so the hips bone deforms all the belt.
- Then, we will select the vertices on the right half of the belt in the Edit Mode, and we will assign a weight of 0.2 to the Thigh.R group.
- We will do the same thing for the vertices on the left half of the belt but with Thigh.L.
- Then we will check the rotations of the Belt bone to verify some of the potential problems of transition. We will adjust the weight of a few vertices. The goal here is to create a gradient of weight at the center according to each thigh bone so that the thigh "attracts" some part of the belt in a smooth manner.
The weight of the left-hand side of the belt