Motivation

The trick behind a moving character

• a surface that looks like a person or creature
• an internal skeleton that gives it structure
• motion data that says how the body changes over time
• rendering choices that make the result readable

Four-Week Timeline

Week	Mode	Focus
Week 1	Individual	Implement and debug forward kinematics on a simple block character.
Week 2	Individual	Implement and compare one-hot skinning and linear blend skinning on SMPL.
Week 3	Pairs	Explore human motion clips and reconstruct group-member characters.
Week 4	Pairs	Refine the group animation scene and export the final video.

Assessment

Coursework	Due date	Marks	Mode
Interim report	Friday 29 May 2026 (4pm)	20	Individual
Interim animation results	Friday 29 May 2026 (4pm)	5	Individual
Final presentation	Tuesday 9 June 2026 (11-1)	10	Group
Final report	Friday 12 June 2026 (4pm)	30	50% individual, 50% group
Final animation results	Friday 12 June 2026 (4pm)	15	Group

The Project In One Sentence

Build a small character-animation pipeline, then use it to create an animated human-avatar scene.

The Pipeline

Build a small character-animation pipeline, then use it to create an animated human-avatar scene.

This project studies a simple version of the character-animation pipeline:

1. represent a character as a skeleton and a mesh
2. pose the skeleton with forward kinematics
3. attach a surface to that skeleton with skinning weights
4. turn a sequence of poses into a short animation

The emphasis is on understanding the mechanics of animation, not on learning a large authoring package.

Materials

• docs/: handouts, report requirements, and setup instructions
• viewer/: interactive viewer and scene tools
• viewer/student_submission/: files students edit
• assets/: block characters, motions, and SMPL assets
• slides/: browser presentation decks and local notes support

Week 1: Forward Kinematics

From skeleton hierarchy to motion

Why We Start With Blocks

The early parts use a blocky articulated character rather than a realistic human mesh.

That is deliberate. A block character makes the hierarchy easy to see:

• each body part is rigid
• each joint is easy to identify
• FK bugs are visually obvious

Once the skeleton logic is clear, we switch to SMPL and study mesh deformation.

Part 1: Forward Kinematics

• explain what a joint hierarchy or kinematic chain is
• distinguish local coordinates from world coordinates
• compute world-space joint rotations and positions from local transforms
• debug a broken articulated character by checking parent-child relationships
• create a short custom motion by placing key poses on a timeline

Output: one custom motion clip with at least 10 keyframes.

Demo: Show The Viewer

• skeleton overlay
• joint selection
• shoulder or hip rotation
• timeline keyframes
• exported motion video

Open local viewer

Viewer Controls

• Motion: choose a built-in or saved motion clip.
• Animate: play or pause the selected motion.
• Show Skeleton, Show Mesh, Show Skinning Weights: toggle visual layers.
• Selected Joint and Joint Editor: inspect and edit one joint.
• Timeline: capture keyframes for a custom sequence.
• Export Motion Video: render evidence from the current browser camera view.

Part 2: Skinning And SMPL

• explain what a skinning weight means
• derive one-hot skinning from a full weight matrix
• explain why one-hot attachment creates artifacts near elbows, shoulders, hips, and knees
• compare one-hot binding against linear blend skinning (LBS)
• reuse the same motion on both the toy character and SMPL

Same motion, different character surface.

One-Hot Skinning

One-hot skinning is the simplest baseline:

• find the joint with the largest weight for each vertex
• set that joint's weight to 1
• set all other weights to 0

This creates rigid piecewise motion. It is easy to implement and easy to interpret, which is why it is a good first baseline.

Linear Blend Skinning

In LBS, a posed vertex is a weighted sum of the transforms from several joints:

v'_i = sum_j w_ij T_j v_i

You do not need to derive the full production form of LBS in this part, but you do need to understand the idea: vertices near joints are shared across influences instead of being assigned to a single bone.

Interim Checkpoint

• your code
• your saved custom motion clip
• a short video of the toy-rig motion
• a short video of the same motion on SMPL
• one-hot versus LBS comparison figures
• the interim report PDF

Parts 3 And 4

Work in groups of two to create a coherent 30-second animated human-avatar scene.

• explore human motion sequences using a human body model
• understand how SMPL-compatible motions can drive a skinned character
• connect a reconstructed character mesh to the same 24-joint body skeleton
• choose, combine, and refine motion clips for a short scene
• produce a 30-second final animation video
• explain the strengths and limitations of your character-animation pipeline

Preview: Scene Composition

• preset human motion clips
• multiple character tracks
• root placement and facing
• draft preview before final export
• saved .scene.json files

How Students Should Work

• implement a small piece
• test it visually in the viewer
• save evidence immediately
• compare failure cases, not just final results
• ask for help with a specific screenshot or clip

AI Use Policy

• Parts 1 and 2: no AI-generated code, math derivations, or results.
• Parts 3 and 4: AI tools may support creative/production work.
• Final focus: a realistic, controllable 3D avatar rendering scene.
• Reports: no wholesale AI-written content; grammar help is allowed.
• Every report needs an AI Use Statement.

Where To Go Next

• Setup
• Part 1
• Part 2
• Interim report
• References
• Project repository