Stand in front of the camera and a rigged 3D character copies your pose in real time.
Fig.1: Example 1
Fig.2: Example 2
Model
Two models, no training:
YOLO pose (models/yolo26s-pose.pt) returns 17 body keypoints per person
(shoulders, elbows, wrists, hips, knees, ankles, face), tracked across frames and
smoothed with a one euro filter.
Rigged glTF characters (models/characters/*.glb) carry their own skeletons:
Michelle (Mixamo), Rigged Figure and Cesium Man (Khronos samples). Switch with
M / N. The .glb files are read directly - meshes, skinning weights, bones and
embedded textures - and drawn by a small software rasterizer, so there is no
game engine and no GPU requirement.
Logic
Each bone is aimed at the direction its keypoints describe. A bone points along
parent.rotation @ child_offset, so making that equal the target gives its local
rotation:
R = animated_parent.rotation^-1 @ swing(rest -> target) @ bind_parent.rotation
Both accumulated rotations are needed, animated and bind. Using the animated one on
both sides only works when the bind rotation is identity, which is never true once a rig
has an axis-conversion root, and it misaims every limb by up to 20 degrees.
The rest of it:
Depth. One camera sees no depth, so a limb shorter than its own reference length
must be angled toward or away from the lens; that missing length is recovered as a
damped Z component.
Turning. Shoulders narrower than the body's proportions mean the torso is turned.
That yaw is folded into every bone's swing, because each driven bone's orientation is
absolute - spinning one alone is undone by the next one down.
Mirroring. The camera image is flipped, so left and right chains swap and the
horizontal axis flips: raise your right arm and the character raises its right arm,
facing you.
Speed. All per-triangle work - projection, culling, lighting, colour - is batched
in numpy, leaving one OpenCV polygon fill per triangle, and dense meshes are thinned
at load to a triangle budget. Roughly 30-70 FPS depending on the character.
Views cycle with K: character only, character with a camera inset, or camera with a
character inset. Keypoints and the skeleton are drawn on the camera image.
Keys: K view, M / N model, F detail, L keypoint names, Y / P rotate view,
R reset view, D debug, H help, Q quit.
