Add Blender motion state inspection skill

Adds the Blender motion state inspection skill with maintainer refinements for tools metadata, usage guidance, meter-scale threshold assumptions, and Blender interpreter notes.
2026-05-19 07:13:07 +08:00 · 2026-05-18 01:11:31 -07:00
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+---
+name: blender-motion-state-inspection
+description: Use this skill when inspecting Blender characters, rigs, poses, animation retargeting, ground contact, facing direction, or model-vs-motion alignment where screenshots alone are not enough.
+origin: ECC
+tools: Read, Write, Edit, Bash, Grep, Glob
+---
+
+# Blender Motion State Inspection
+
+## When to Use
+
+- A Blender character looks twisted, mirrored, flattened, offset, or foot-sliding in an animation.
+- A user asks whether an imported avatar, armature, or retargeted motion matches an expected pose.
+- You need to compare rendered evidence with structured facts such as bones, bounding boxes, contacts, and facing vectors.
+- A workflow depends on deciding whether a model is a character, prop, proxy mesh, control rig, or broken import.
+
+## Core Principle
+
+Do not judge animated 3D assets only from screenshots. Screenshots are review evidence, but they hide axis conventions, bone names, object scale, local transforms, parented meshes, material slots, and frame-by-frame contact state.
+
+First extract structured Blender state, then use viewport screenshots or renders to confirm what the facts imply.
+
+## How It Works
+
+1. Establish the clean scene and asset baseline before judging motion.
+2. Extract structured facts from Blender using an exporter or Blender Python run inside Blender's own interpreter.
+3. Sample the frames most likely to expose contact, orientation, scale, and retargeting errors.
+4. Compare the measured facts against the user's expected pose, direction, ground plane, and render goal.
+5. Return a concise report that separates confirmed facts, likely causes, and required fixes.
+
+## Inspection Workflow
+
+1. Inventory the scene.
+   - List meshes, armatures, empties, cameras, lights, modifiers, parent relationships, and hidden objects.
+   - Separate character meshes from helper/proxy geometry before judging the avatar.
+   - Record object-space and world-space bounding boxes.
+
+2. Identify the skeleton.
+   - Capture armature names, pose bones, bone heads/tails, roll, parent chains, constraints, and rest-pose axes.
+   - Map semantic bones such as hips, spine, neck, head, shoulders, elbows, hands, thighs, knees, ankles, and feet.
+   - Flag missing left/right pairs and unusual naming schemes.
+
+3. Determine forward, up, and side axes.
+   - Use the pelvis, spine, shoulders, hips, head, and feet together; do not rely on a single mesh normal.
+   - Compare local armature axes with world axes and imported file conventions such as glTF Y-up vs Blender Z-up.
+   - Mark likely mirrored or backwards imports when face/head/feet direction conflicts with root motion.
+
+4. Sample animation frames.
+   - Inspect first, middle, contact, airborne, and extreme frames.
+   - Record root location, root heading, pelvis height, torso lean, limb directions, foot clearance, and mesh bounds.
+   - For long or fast motion, sample more densely around flips, landings, turns, collisions, and floor contacts.
+
+5. Check model integrity before retargeting blame.
+   - Confirm the clean baseline shape before applying animation.
+   - Preserve original mesh, materials, armature, and skinning unless the user explicitly asks for repair.
+   - Treat unexplained sphere-like blobs, giant proxy meshes, or crushed bodies as import/selection issues until proven otherwise.
+
+6. Diagnose contact and motion issues.
+   - Ground penetration: compare lowest foot or shoe vertices with floor height per frame.
+   - Foot sliding: compare foot world positions across planted frames.
+   - Leg crossover: compare left/right thigh, knee, ankle, and foot side ordering.
+   - Twist damage: compare bone swing direction separately from roll/twist around the limb axis.
+   - Scale drift: compare animated mesh bounds against the clean baseline bounds.
+
+7. Report facts before opinions.
+   - Include frame numbers, object names, bone names, world coordinates, and thresholds.
+   - Separate confirmed failures from visual suspicions.
+   - Attach screenshots only after the structured state explains what to look for.
+
+## Recommended Report Shape
+
+```markdown
+## Blender Motion Inspection
+
+### Scene Inventory
+- Character candidates:
+- Armatures:
+- Helper/proxy objects:
+- Cameras/lights:
+
+### Orientation
+- World up:
+- Character forward:
+- Root heading:
+- Mirrored/backwards risk:
+
+### Baseline Integrity
+- Clean mesh bounds:
+- Animated mesh bounds:
+- Materials/skin preserved:
+- Suspicious non-character meshes:
+
+### Frame Findings
+| Frame | Finding | Evidence |
+| --- | --- | --- |
+| 1 | Clean baseline pose | hips/spine/feet aligned |
+| 96 | Foot penetrates floor | left_foot min_z = -0.04 |
+
+### Verdict
+- Pass/fail:
+- Required fix:
+- Render readiness:
+```
+
+## Examples
+
+### Walk Cycle With Foot Sliding
+
+Scenario: a retargeted character appears to skate during a walk cycle, but the front camera angle makes the foot contact hard to judge.
+
+Apply the workflow:
+- Inventory the scene: character mesh `HeroBody`, armature `HeroRig`, ground plane `Floor`, no hidden proxy meshes.
+- Identify the skeleton: semantic feet are `foot.L` and `foot.R`; hips are `pelvis`; root bone is `root`.
+- Sample animation frames: inspect frames 1, 18, 24, 30, 42, and 48 around planted-foot moments.
+- Diagnose contact and motion issues: compare world-space foot locations during planted frames.
+
+Extracted facts:
+
+| Frame | Fact | Evidence |
+| --- | --- | --- |
+| 18 | Left foot is planted | `foot.L min_z = 0.004`, toe and heel both near floor |
+| 24 | Left foot slides while planted | `foot.L x = 0.21 -> 0.28` over six frames |
+| 30 | Pelvis keeps moving forward | `pelvis y = 1.14 -> 1.31` |
+
+Verdict: fail for render readiness. The motion needs foot-lock cleanup or retargeting constraint review; the body mesh does not need proportion changes.
+
+### Backwards Imported Character
+
+Scenario: a character looks correct in a still frame, but the animation moves opposite the expected travel direction.
+
+Apply the workflow:
+- Determine forward, up, and side axes: compare head, chest, feet, and root motion.
+- Sample animation frames: inspect frame 1 and the midpoint of the travel path.
+- Report facts before opinions: include the root heading and model-facing direction separately.
+
+Extracted facts:
+
+| Frame | Fact | Evidence |
+| --- | --- | --- |
+| 1 | Character face points toward world `-Y` | head/chest vector from `neck` to `head` resolves to `-Y` |
+| 72 | Root motion travels toward world `+Y` | `root y = 0.0 -> 2.8` |
+| 72 | Feet remain visually forward-facing opposite travel | toe bones point `-Y` while displacement is `+Y` |
+
+Verdict: likely backwards import or retargeting forward-axis mismatch. Fix the import/retarget axis mapping before editing animation curves.
+
+## Practical Thresholds
+
+- Assume Blender's default meter-scale units unless the scene unit scale says otherwise.
+- Treat ground penetration above 1-2 cm as visible unless the floor is soft or intentionally stylized.
+- Treat a sudden scale change above 5% as a likely rig, constraint, or transform inheritance problem.
+- Treat left/right ankle side-order flips during airborne inverted motion as leg crossover risk even if it recovers later.
+- Treat root heading jumps above 30 degrees per frame as suspicious unless the source motion includes a snap turn.
+
+## Anti-Patterns
+
+- Do not modify body proportions to force pose matching unless the task is explicitly mesh repair.
+- Do not bake away the clean baseline before recording it.
+- Do not use one rendered camera angle as proof that a pose is correct.
+- Do not delete helper objects until you have recorded why they are not part of the character.
+- Do not assume an avatar faces +Y, -Y, +X, or -X without checking head, feet, torso, and root motion together.
+
+## Tooling Notes
+
+If a Blender state exporter is available, prefer JSON that includes meshes, armatures, pose bones, materials, contacts, bounding boxes, and sampled animation frames. If no exporter exists, run a small Blender Python script through Blender itself, for example `blender --background scene.blend --python collect_motion_state.py`, because `bpy` is not available in a normal system Python interpreter.