Rig a quadruped from one image

A quadruped is the most common non-human subject people bring to Bake3D: a fox, a dog, a horse, a dragon on four legs. The rig has to put a pivot in each hip, knee and ankle, run a spine from hips to head, give the tail its own chain and assign every surface to the right joints. Bake3D does that automatically, then measures the result. This guide explains what it checks, what the numbers mean and what to do when one of them is wrong.

What happens when you press Rig

The mesh is rendered into orthographic views, and a vision model places a joint plan on them: each joint is named by a role such as thigh.L, shin.R, spine.1, neck, head or tail.2, and is located in at least two views so its position can be triangulated. The plan is checked against the geometry: joints that fall outside the surface are pulled inside their intended part, bilateral pairs are compared for symmetry, and each chain is checked so that its joints lie on one parent-child path.

Skin weights are then solved for the creature’s own shape, not a template. Finally the rig is posed through four diagnostic stress poses and the surface is measured for stretching and compression. Each of these stages produces a report you can read in the studio’s Rig tab.

The Faces control tells the planner which way the creature looks (+Z by default). The optional Hints field lets you describe moving parts or intended pivots in a sentence before the plan is made. Both matter more for quadrupeds than for humans, because a side-on animal has front and back legs that look similar in a single view.

Read the reports

Joint placement summarises the plan: how many joints were placed, how many views constrained each one, and which joints were under-constrained. The Rig check card lists problems by category. Outside mesh means a joint started outside the surface and was corrected, or could not be corrected; Symmetry means a left/right pair disagrees in position more than expected; No influence means a joint moves no surface; Weight errors means a vertex ended up with invalid or missing weights.

The deformation report is the most useful number for a quadruped. It shows the percentage of the original surface area that exceeds 3× extension or falls below 0.1× compression across the diagnostic poses, together with the joint and triangle counts tested. It weights by area, so a dense patch of small triangles does not dominate. Above 0.5% the server can revisit the joint plan within its attempt limit before returning the rig. The saved comparison image shows the most affected pose, and the report names the skin influences involved.

A placement score of 100 does not prove good deformation, and a deformation percentage below the threshold can still hide a visibly poor bend in a paw or ear. Use the numbers as pointers, then look at the actual surface.

Common quadruped problems and fixes

Front and back legs confused. The hips and shoulders of a side-on animal can be swapped if the planner misreads which way it faces. Set Faces to match the image, then re-rig. Adding a hint such as “four legs, the tail is at the back, head faces +Z” removes the ambiguity.

A joint pulled into the body instead of the leg. On thin legs a knee or ankle can start just outside the surface; the correction step pulls it into the nearest part, which is usually right but can be the torso when the legs touch it. The Rig check card flags this as Outside mesh. Re-rig with a hint that names the appendage (“place the knee inside the lower rear leg”), or regenerate the mesh with the legs more separated in the source image.

Legs fused in the mesh. If two legs were generated as one shell, no joint plan can separate them. The Source geometry panel compares the image with seven mesh views and, for a high-confidence finding, can trigger one recovery candidate within the same generation job without another charge. If recovery does not help, return to the image: a three-quarter view with daylight between the legs reconstructs better than a side view with the legs overlapping.

Stretching across the belly or chest. A high deformation percentage with the hips or shoulders listed as involved influences usually means a leg root sits too close to the spine, so the torso surface follows the leg. Re-rigging with a hint about the leg roots (“hips at the top of the rear legs, not in the belly”) commonly moves them. Compare the before-and-after deformation percentages; a single re-rig costs the rig price shown on the pricing page, charged on accept and refunded on failure.

Tail or ears do not move. No influence in the Rig check, or a motion that addresses tail and produces nothing, means the chain received no surface. Check that the part exists as geometry rather than as texture. A painted tail on a flat surface cannot be rigged.

Feet slide in the walk. Use Walk · fit to this rig (preset adaptive-walk in the API and MCP), which measures stride from limb reach and staggers footfalls across every resolved leg. Review the cycle with travel enabled: a planted paw should stay in place while the body advances. Sliding after that points at a knee or ankle placed too high or low; re-rig rather than editing the motion.

When to regenerate instead of re-rig

A rig cannot add anatomy the mesh lacks. Missing paws, a tail merged with a leg, or a head fused to the chest are generation problems, and the fastest fix is a better source image or another generation. Save the assets you want to keep; both the original and a recovery candidate stay downloadable in the project.

Re-rig when the mesh is right and the joints are wrong. Regenerate when the mesh itself is incomplete. Hints and the forward axis are free to change between attempts; the rig charge applies to each accepted rig job.

Verify in the target editor

Export a rigged GLB and import it into Blender, Godot or Unity, then bend each leg and the spine with the same isolated-movement test described in the rig checklist. Shading and skinning implementations differ between viewers, so a joint that looks acceptable in the studio deserves a second look where the creature will actually be used. The Blender import guide shows what to expect from a native glTF import.

What the tests cover

Bake3D’s regression fixtures include four-legged bodies at different proportions and scales, creatures with repeated limbs, non-standing rest poses and rigid assemblies, and the homepage fox gaits were fitted from measured paw surfaces. These establish the behaviour on those cases; they do not prove every generated quadruped will rig cleanly. The Khronos glTF 2.0 specification defines how the exported skin, joints and inverse bind matrices are stored, and the Blender manual’s armature pages are a good reference for inspecting the result.