Intro to Skeletons, Skinning, and Weights
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Everything below represents notes for Sepha to finish the YouTube vid and article with.
We're going to skin and weight paint a character in this chapter.
So don't worry. But first, SOME THEORY!
A brief history
In the past, characters were 2d, and individual sprites were flipped between to create the illusion of motion.
Then characters became 3d, and their individual verts were animated frame by frame to create the illusion of motion.
Then as characters became more complex, and polycounts and Vert counts bolooned - animators needed a better way to animate their characters.
This "better way" is via Skeletons, Bones, Weights, and Rigging.
The Skeleton and Bones
Instead of animating individual vertices, we bind verts to bones, and animate the bones instead. Blender stores bones inside of "Armature" objects.
A collection of bones within a single object, a single armature, are referred to as a Skeleton.
We can then either create, or take an existing mesh that matches this skeleton, like so:
and then Bind them together, by parenting the Mesh, to the Skeleton:
And once correctly bound with a valid and artistic set of Weights, the character or prop can now be animated:
Weights
If I select my character, and move into weight paint mode:
I can visualize and edit the "Strength" (aka Weight or aka Bone Influence) that each bone has over the whole mesh:
Full Influence (1.0) is shown as Red, and No influence (0.0) is shown as Blue.
Blender Stores Weights as Vertex Groups. which can be viewed from the Meshes Data Properties panel:
And selecting any individual Vert in Edit Mode, will list the weights currently applied to this vert:
The Bind Pose
If I enter Edit Mode, you will see that the character returns to their non animated position:
Skeletal Meshes are said therefore to have a Bind Pose.
This Bind Pose represents the meshes true and natural position as we molded it. All deformations are therefore relative to this initial position.
The Skeleton itself, is also said to have a Bind Pose.
If I select the Skeleton that is currently posed:
And enter Edit Mode:
The skeleton returns to its initial pose, as we created it initially, before animating it.
Key Insight: Both Skeletal Meshes, AND skeletons themselves are said to have a Bind Pose. The Bind Pose acts as our default position prior to any animation or deformation, and all motion will be relative to this pose.
Skinning
This process of creating Bones, and creating their Weights is reffered to as Skinning.
The process of using the Weight Paint mode to assign weights:
... is reffered to as Weight Painting.
Rigging is a more complicated concept we will cover later, that is related to skinning and weight painting, but distinct and separate.
Technical Requirements:
In order for our Skeletons and Weights to function correctly and be easy to work with, we have a few technical requirements to keep in mind:
Our Armature (skeleton)'s pivot point must be centered at the world origin, or at another common sense location.
An origin like so is unacceptable:
The Meshes that we Bind should have scales of 1.0, and if possible, rotations of 0.0.
Scales beyond 1.0 lead to undefined behavior, and can cause errors in rendering as the engine struggles to calculate the meshes bounding volume.
Our total weights on any given vertex must always sum to 1.0.
It is undefined behavior for vertices to not sum their total weight to 1.0.
Some engines will fill in the blanks as best they can, others will simply glue these verts to the middle of players screen, or leave them un-animating, floating in space.
There must be no more than four bones influencing any one vertex.
This is a performance consideration. The more influences, the more expensive the mesh.
More importantly, most engines will allow only between 1 and 4 influences by default, and how they handle the 5th and above is undefined.
Some attempt to make it work, but others simply delete the influences.
Our Bone Names and our Weight Names must always match.
Blender will "loose track" of which Bones correspond to which Weight Influences if their names fall out of Sync. Keep this in mind at all times. If you rename any bone, and blender fails to rename the vertex groups, they must be manually re-named to match.
Our Bone Names must always have common sense human readable names.
Do not leave bones named Bone, Bone.001, Bone.002 in your Skeletons.
Symettric bones must be identified with either an R or an L, and designated with either a . or a _
.L and .R are fine
as are _L and _R
You are free to use either, but do not mix and match them within the same skeleton.
This makes our rig more readable, but also allows blender to short cut our workload by mirroring constraints when rigging, and mirroring weights when painting and using mirror modifiers.
Some of these requirements are not negotiable, others are subjective, but in general, I want you to follow every rule on this list.
Keep this chapter simple and introductory, you want to highlight the fact that meshes need to be parented to bones and the weights need to match the bone names - highlight importance of correct naming etc and symettry.
Include a simple youtube vid showcasing all of this and the weight binding process.
Key begginer point - the weights linearly fall off, try and communicate this.
— CREATE A YOUTUBE VIDEO SHOWCASING THE BASICS OF ARMATURES, AND WEIGHT PAINTING.
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