Skinning the Avatar
This doc goes over skinning the custom Avatar for Roblox in Blender, or applying the skeleton rig to your character model.
Skinning is the term used for applying the mesh to the bones so that when you move the bones the model flexes to the bone.
A simple example would be applying vertex weight at the elbow to the upper arm 50%, and the lower arm 50%. When you rotate the lower arm, these vertices blend between the two.
Weights should be between 0-1 and all vertices should equal 1 in total, so in this example the upper arm would be 0.5 and the lower arm would be 0.5.
The process to do this is called Weight Painting, where you paint the percentages of bones to each vertex. Roblox allows a maximum of four bones per vertex, although it is rare to need more than three.
Requirements
Rig is positioned correctly.
All meshes have Transforms Applied.
Skinning the Character
Select all the body parts you would like to apply to the rig.
Use Shift in the Viewport or the Outliner to select multiple assets.
Select the Rig last. If the rig is not last it will not work.
Right click and select 'Parent / With Automatic Weights'.
The meshes are now rigged to the bone but only with basic weights that may not work as well as you'd hope.
Select only the rig and go to 'Pose' mode (at the top left).
Select any bone and rotate it (using 'R'). The mesh should move accordingly.
Custom Weight Painting
To improve Weight painting in Blender it is recommended to do the following :
Select the rig first, then select the assets you would like to paint the weights on.
This allows you to use 'Alt' to select bones for painting.
Switch to 'Weight Paint' Mode (at the top left).
If you have a symmetrical character :
If the asset is still mirrored, enable the X in the Symmetry tool at the top right of the viewport.
If the arm is not mirrored this will not work, one approach is to rig the model before splitting up the avatar into parts.
Turn symmetry off if the weight paints behave oddle like in the example above.
Enable 'Auto-Normalize' in the 'Options' pulldown at the top right of the viewport (to the right of the symmetry properties).
This makes sure that weights in your model always add up to 1 which improves managing the weights. It is possible to have weights higher than 1, but this makes things more complicated than they need to be.
This only applies to painting the weights, manually setting the weights may not take this into consideration.
As the parts are split up you will need to be very accurate on weight paints of vertices that overlap.
Draw Tool
The Draw tool is your main tool for Weight Painting in Blender. This allows you to basically paint the weights with a brush.
In 'Weight Paint' mode, select the 'Draw' tool at the top left of the viewport.
Set the properties of the brush as needed at the top of the viewport.
Weight is how strong the weight is applied to the bone .
1 makes the bone completely control the vertex.
0 makes this bone not control the vertex at all.
0.5 means that this bone controls the vertex 50%. Another bone, or bones, controls the other 50%.
Radius is how big the brush is.
You can also adjust this with the '[' and ']' keys.
Strength is how strong the brush is to apply the weight.
.5 strength of 1.0 weight means it will add 0.5 to the weight.
This allows you to blend weights as needed.
Select the bone you would like to edit the weights using 'Alt + left click'.
Paint the weights on the vertices.
Blur Tool
The Blur tool allows you to soften the weights between bones easily.
Select the 'Blur' tool under the Draw Tool.
This tool blurs the weight on vertices to the vertices around it.
Set the properties of the brush as needed at the top of the viewport.
Radius is how big the brush is.
You can also adjust this with the '[' and ']' keys.
Strength is how strong the brush is to apply the weight.
Paint Mask / Vertex Selection
The 'Paint Mask' and 'Vertex Selection' tools allow you to select only the faces or vertices you want to paint on.
Select the 'Paint Mask' or 'Vertex Selection' tool next to the Mode pulldown.
Select the 'Select Box' tool towards the bottom of the toolbar.
Select the faces or vertices you would like to limit weight painting to.
Continue with Draw/Blur tools to paint your weights.
This tool also allows you to easily hide elements of your model in Weight Painting mode.
Select the 'Vertex Selection' tool next to the Mode pulldown.
Select the 'Select Box' tool towards the bottom of the toolbar.
Select the vertices you would like to hide.
Use 'A' or 'Ctrl + L' to select the entire model or mesh element.
Use 'H' to hide the selected vertices.
Use 'Alt + H' to unhide all hidden vertices.
Testing in Roblox
It would be possible to test your character in Roblox after you have got your character this far.
To export your assets, use Exporting the Avatar.
To import your assets into the Roblox Avatar Test Space, use Importing the Avatar.
In this doc, we looked at setting up Weight Painting in Blender.
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