Weight Paint Mode
The Weight Paint mode is used to create and modify vertex groups. A vertex may not only be a member of one or more vertex groups, but also may have a certain weight in each group. The weight symbolizes its influence on the result.
Mode: Weight Paint mode
Hotkey: Ctrl⇆ Tab
Menu: Mode menu (Image 1)
When you change to Weight Paint mode you see the selected object (if you have not created any groups yet), in a slightly shaded, blue color (Image 2).
The color visualizes the weight of each vertex of the currently active group. A vertex drawn in blue indicates either: a weight of zero, not in the active group, or not in any group at all.
You assign the weight of each vertex by painting on the mesh with a certain color. Starting to paint on a mesh will automatically creates a new vertex weight group (when no group existed or is active). If a vertex doesn’t belong to the active group it is automatically added (if the option Vgroup is not set), even if you paint with a weight of “0”. The used color spectrum is shown in (Image 3).
You paint on the mesh with a brush. The color only influences the vertices, neither the faces nor the edges. So don’t try and paint these. There is a tool panel for the brush in the Editing context (F9) as well as in the 3D Window (press N to open it).
The tools in the Paint panel are sophisticated, and you can apply weight in the finest nuances. But normally you won’t need all these options, and you will apply weight using a few techniques. The most used and important settings are drawn in bold.
- Weight: The weight (color) that is used to paint. The button row below contains five weight presets to paint. By default, painting works with an absolute fixed amount (like Gimp or Photoshop defaults), so you can set for example “0.2 weight” to vertices while keeping the mouse button pressed, whatever their original weight was.
- Opacity: The extent to which the vertex color changes while you are painting.
- Size: The size of the brush, which is drawn as a circle during painting.
- Spray: The Spray option accumulates weights on every mouse move.
- Mix/Add/…: The manner in which the new color replaces the old when painting.
- Mix: The new color replaces the old color. Applying more and more of the new color will eventually turn it the new color.
- Add: The new color is added to the old. Note that you must think in weight here (not in RGB colors): adding blue (0.0) to something won’t modify it, adding green (0.5) to green will give red (1.0), …
- Sub: The new color is subtracted from existing. Here again you have to think in terms of “weight”, and not “RGB colors”.
- Mul: The new color is multiplied by the old.
- Filter: Paint based on alpha value.
- Lighter: Only paints vertices “darker” (lower weight) than the current “color”, “lightening” them.
- Darker: Only paints vertices “lighter” (higher weight) than the current “color”, “darkening” them.
- All faces: If this is turned off, you will only paint vertices which belong to a face on which the cursor is. This is useful if you have a complicated mesh and you would paint on visually near faces that are actually quite distant in the mesh.
- Vertex Dist: Paints only on vertices which are actually under the brush. If you switch this off, all vertices belonging to faces touched by the brush are painted. If you have a sparse mesh and use subsurfaces you want to keep this on.
- Soft: This specifies that the extent to which the vertices lie within the brush also determine the brush’s effect. It’s extremely difficult to paint with zero then. You want to turn this off in all normal situations.
- Normals: The vertex normal (helps) determine the extent of painting. This causes an effect as if painting with light.
- Vgroup: Only vertices which belong to the active vertex group are painted. Very useful for clearing up and refining vertex groups without messing other groups up.
- X-mirror: Use the X-mirror option for mirrored painting on groups that have symmetrical names, like with extension
_L. If a group has no mirrored counterpart, it will paint symmetrical on the active group itself. You can read more about the naming convention in Editing Armatures: Naming conventions. The convention for armatures/bones apply here as well.
- Wire: Show additionally the wireframe of the objects. Since it shows the subsurfaced wire it’s quite useless. It’s better to use the Select mode (see below).
- Clear: Removes all vertices from the active group.
If you have a complex mesh it is nearly impossible to reach all vertices in Weight Paint mode. And it is quite difficult to tell where the vertices are exactly. But there’s a very good and easy solution: the Select mode.
Mode: Weight Paint mode
Select mode has many advantages over the normal Weight Paint mode:
- The original mesh is drawn, even when subsurface is active. You can see the vertices you have to paint over.
- You can select faces, only the vertices of selected faces are painted on.
- Selecting tools include:
- You may hide selected faces with H and show them again with AltH (Image 6).
- To constraint the paint area further you may use the Clipping Border. Press AltB and LMB -drag a rectangular area. The rest of the 3D window is hidden. To show everything again, just hit another time AltB.
- If you want to know which groups a vertex belongs use ⇧ ShiftLMB . You can change between the groups in the appearing pop-up menu (Image 7).
- N in the 3D window opens a Weight Paint Properties panel instead of the Transform Properties panel (Image 8).
Scripts in Paint Menu
- Weight Gradient
- This script is used to fill the selected faces with a gradient (Image 3 & Image 9). To use the script, select the faces you wish to apply the gradient to. Click twice on the mesh to set the start and end points of the gradient. The color under the mouse will be used for the start and end blend colors, so you have to weight paint first. Holding ⇧ Shift or clicking outside the mesh on the second click will blend the first color to nothing.
- Normalize/Scale Weight
- Maximizes weights to a user set peak and optionally scales other groups too to keep the proportion of the weights even.
- Grow/Shrink Weight
- Uses the mesh topology to expand/contract the vertex weights (works like color bleeding).
- Clean Weight
- Removes vertices with low weights from the current group.
Weight Painting for Bones
This is probably the most often used application of weight painting. When a bone moves, vertices around the joint should move as well, but just a little, to mimic the stretching of the skin around the joint. Use a “light” weight (10-40%) paint on the vertices around the joint so that they move a little when the bone rotates. While there are ways to automatically assign weights to an armature (see the Armature section), you can do this manually. To do this from scratch, refer to the process below. To modify automatically assigned weights, jump into the middle of the process where noted:
- Create an armature.
- Create a mesh that will be deformed when the armature’s bone(s) move.
- With the mesh selected, create an Armature modifier for your mesh (located in the Editing context, Modifiers panel). Enter the name of the armature.
Pick up here for modifying automatically assigned weights.
- Select the armature in 3D View, and bring the armature to Pose mode (Ctrl⇆ Tab, or the 3D View window header mode selector).
- Select a desired bone in the armature.
- Select your mesh (using RMB ) and change immediately to Weight Paint mode. The mesh will be colored according to the weight (degree) that the selected bone movement affects the mesh. Initially, it will be all blue (no effect).
- Weight paint to your heart’s content. The mesh around the bone itself should be red (generally) and fade out through the rainbow to blue for vertices farther away from the bone.
You may select a different bone with RMB . If the mesh skins the bones, you will not be able to see the bones because the mesh is painted. If so, turn on X-Ray view (Buttons window, Editing context, Armature panel). While there on that panel, you can also change how the bones are displayed (Octahedron, Stick, B-Bone, or Envelope) and enable Draw Names to ensure the name of the selected bone matches up to the vertex group.
If you paint on the mesh, a vertex group is created for the bone. If you paint on vertices outside the group, the painted vertices are automatically added to the vertex group.
If you have a symmetrical mesh and a symmetrical armature you can use the option X-Mirror. Then the mirrored groups with the mirrored weights are automatically created.
Weight Painting for Particles
Faces or vertices with zero weight generate no particles. A weight of 0.1 will result in 10% of the amounts of particles. This option “conserves” the total indicated number of particles, adjusting the distributions so that the proper weights are achieved while using the actual number of particles called for. Use this to make portions of your mesh hairier than others by weight painting a vertex group, and then calling out the name of the vertex group in the VGroup: field (Particles panel, Object context).