Auto Rig

Auto Rig turns a static character into one a game engine can animate. You mark nine spots on the character (chin, neck base, groin, wrists, elbows and knees), and the node builds a skeleton inside it and binds the surface to the bones. The skeleton uses the same joint names and bone directions as Mixamo’s, so Mixamo animations play on it as they are. Use it for a character you modeled, bought or generated, right before you export it.

What it does

The mesh comes out exactly as it went in: same points, faces, UVs and materials. What Auto Rig adds is a rig that travels with the mesh:

a skeleton of 25 joints (hips, spine, neck, head, shoulders, arms, hands, legs, feet and toes), or 65 with finger joints (see Fingers);
skin weights, which say for every point of the surface which bones move it and by how much (up to four bones per point).

The weights come from bone heat, the method Blender’s automatic weights use. Each point is warmed by the bone it is nearest to and can see from where it sits, and that warmth spreads along the surface. A point’s weight for a bone is how warm the bone leaves it. Because the warmth travels over the skin and not through the air, an arm resting against the torso does not pull the torso with it. Near a joint, the warmth from the two bones that meet there overlaps, so an elbow or a knee bends over a short stretch and does not crease along a line.

Smoothing relaxes the weights across the surface after the solve. At 0 you get the solve as it is. Raise it to soften the bend at every joint and spread it over more of the limb.

Export writes the rig into the .glb as a skinned mesh in its rest pose. Open the file in your game engine, or in Blender, and play a Mixamo animation on it. To ship the character with ready-made clips such as Idle, put Add Animation after Auto Rig: Export then writes each clip as a named animation in the same file.

Preparing the character

Auto Rig expects a humanoid that:

stands upright, feet on the ground;
faces +Z (towards the front view). The character’s left hand is then on the +X side;
holds an A-pose (arms angled down) or a T-pose (arms straight out).

If the character faces another way, turn it with a Transform before Auto Rig. A model with holes, loose fragments or cracks rigs better after Clean and Fill Holes.

Bone heat needs every part of the surface to see a bone. A loose part that sits outside the body, such as a floating accessory or a stray fragment, sees none, because the bones are inside the body. Auto Rig binds such a part to its closest bone instead and shows an amber note saying how many points it bound that way. The node always cooks. To bind everything by heat, remove or join the loose parts with Clean.

Placing the markers

Each marker has an X and a Y, read on the character seen from the front, as a share of its bounding box: X runs from 0 at the box’s −X side to 1 at its +X side, and Y from 0 at the ground to 1 at the top of the head. You do not set a depth. The node finds the middle of the body at each marker by itself, so every joint ends up inside the limb. Hair or a cape hanging behind the neck or shoulders doesn’t pull a joint back: the node tells the body from anything separate that lies behind it.

Because the markers are shares of the bounding box, they stay on the character when you move it or change its size earlier in the graph.

The markers start at a guess for an A-pose. While Auto Rig is the selected node, the viewport shows them on the character, each with its name, and the skeleton they make beneath them. Move each one onto its spot:

Chin: the tip of the chin. It places only the head.
Neck base: the bottom of the neck, between the collarbones, at the height of the shoulders. It places the neck and the shoulders, so a long or short neck fits: move the chin and the shoulders stay where they are.
Groin: where the legs meet.
Wrists, Elbows, Knees: the middle of each joint. Left means the character’s own left, which is on your right when you look at its face.

To move a marker, drag it. Selecting Auto Rig turns the view to the front, and markers can only be dragged there: a marker only has an X and a Y. The skeleton follows as you drag, and the skin weights are worked out again when you let go. Click a marker to put the move arrows on it, and drag an arrow to move it only left and right, or only up and down.

Mirror (on at first) keeps the two sides matched: moving a left marker moves its right partner the same way on the other side of the groin, and back. The chin and the neck base stay on the line through the groin and only move up and down. Turn it off with the Mirror button or X for a character whose two sides differ. Reset markers (the button beside it) puts every marker back on its starting guess. Ctrl+Z and Ctrl+Shift+Z undo and redo marker moves. You can also type the numbers into the parameters below; the markers in the viewport follow.

To check the skeleton from another side, pick Left, Right or Perspective in the camera view menu above the viewport. The markers and skeleton stay on screen there, so you can see whether each joint sits in the middle of the limb, but you can’t drag them; switch back to Front to move them again. Hold the right mouse button to fly and scroll to zoom in any view. In the front view, a drag that starts on a marker always moves the marker.

For a T-pose, raise the wrists and elbows to shoulder height (Y around 0.8) and spread them (wrists X around 0.06 and 0.94, elbows around 0.27 and 0.73).

Every other joint is worked out from these nine: the spine between the groin and the neck base, the shoulders from the neck base and the elbows, and the ankles and toes from the shape of the feet.

Fingers

Fingers chooses the skeleton:

None (the default): 25 joints. Each hand is one joint, and the fingers move with it.
Full: 65 joints. Each hand gets a thumb and four fingers, each with three joints and a tip, named as Mixamo names them, so the finger motion in an animation plays too.

With Full, Auto Rig finds the fingers from the shape of the hand past each wrist marker. It follows the surface out from the wrist, and wherever the hand splits into separate fingers it lays a chain of joints down the middle of each one: the knuckle just behind where the finger leaves the hand, then the two finger joints, then the tip. The thumb is the finger that leaves the hand nearest the wrist, on the front of the hand. There are no finger markers to place; the wrist markers are enough.

The fingers have to be separate on the mesh: five of them, with a gap between each. A hand modeled as a mitten, or with the fingers joined together, has no fingers to follow. Auto Rig then spreads the finger joints out in a fan inside the hand and shows an amber note saying which hand. Those joints won’t line up with real fingers, so set Fingers back to None for such a hand.

Switching Fingers never moves any of the 25 body joints. With fingers each hand points at the middle of its knuckles, as Mixamo’s does, so a hand’s own orientation is slightly different between the two.

Checking the rig

While the displayed mesh carries a rig, the viewport’s view menu offers Rig next to Mesh, Textures and UVs. It draws the skeleton through the surface and colours the surface by the binding:

With no joint selected, each part of the surface takes the colour of the bone that moves it most, so you can see at a glance where each bone’s reach ends.
Click a joint to see its own weights: red where it moves the surface fully, through yellow and green to blue where it barely does, and the plain surface where it does not move it at all. Click empty space to go back to the overview.
Weights over chooses whether the colours sit on the plain surface or tint the textured one.

If the arm’s colours run into the torso, or a knee’s into the other leg, move the markers until they stop doing so.

The test motion

Colours show where each bone reaches; the test motion shows how the surface bends. In the Rig view, the Motion picker beside Weights over starts on Test motion; press the play button next to it. The character runs through a short loop: it raises its arms and lowers them against its sides, bends its elbows, bends forward and twists its torso, turns its head, and steps with each leg. The skeleton and the weight colours move with it. Drag the scrub bar to stop at any moment and look closely at a shoulder, an elbow, a hip or a knee. The start of the bar is the rest pose.

The test motion is only for looking. It is not saved with the project, it does not change the node’s output, and the exported file and an Unreal push are the same whether or not you played it. Leaving the Rig view puts the character back in its rest pose.

The motion bends each joint the way a Mixamo animation does. If a limb bends the wrong way here, it would bend the same wrong way in a clip, which usually means a marker is off.

Once Add Animation has added clips to the rig, the Motion picker lists them after the test motion (Idle, …). Displaying an Add Animation node starts the picker on its own clip; displaying any other node starts it on the test motion. Play, pause and scrub work the same for a clip, and the clip plays exactly as Export writes it.

Where to put it

Put Auto Rig at the end of the chain, with only Add Animation and Export after it. The paint nodes and Selection keep the rig. Any node that reshapes the mesh after Auto Rig, such as Transform, Subdivide, Bevel or Boolean, drops the rig, and shows an amber note saying so. Do the modeling first and rig last.

Limits for now

The weights come from the surface’s shape alone. A garment modeled as a separate shell over the body is a loose part and follows its closest bones.
Fingers: Full needs five separate fingers. A four-fingered cartoon hand, a mitten or joined fingers gets the fanned guess and a note.
The Unreal Engine Output node sends the mesh without its rig and clips, as a static mesh, and says so. To bring a rigged character into Unreal, export a .glb and import that.

Inputs

Mesh

The character to rig: upright, facing +Z, in an A- or T-pose.

Outputs