Character Animation Starter Kit: From Blocking to Splines—Refinement Without Losing Clarity

From Stepped to Splines: What “Refinement Without Losing Clarity” Means

Stepped blocking is your “pose statement.” Spline refinement is your “how it moves.” The risk is that interpolation starts inventing motion you didn’t intend: drifting feet, mushy holds, softened accents, and arcs that no longer match the original idea. The goal of this chapter is to switch to splines only after the shot is logically solved, then control interpolation so the original pose intent stays readable while motion becomes fluid.

1) When to Switch to Splines (and What Must Be Solved First)

Switch criteria: you’re done making story decisions

Move to splines when you can watch the stepped version and answer “yes” to these questions without excuses:

• Contacts are correct and intentional: every plant, touch, grab, sit, or lean happens on the frame you mean, on the surface you mean, with no ambiguity.
• Timing is approved: the rhythm of actions, holds, and accents feels right. You’re not still debating “should this beat be earlier/later?”
• Storytelling reads in stepped: the audience can understand what the character is doing and why, even without in-betweens.

What to lock down before splines

Before converting, make these practical preparations so splines don’t create chaos:

• Key pose integrity: ensure the key poses you care about are on clean, whole frames (no accidental sub-frame offsets).
• Contact keys are explicit: for feet/hands that must stick, set keys on the contact frame and at least one frame before/after (so the contact is “bookended”).
• Holds are real: if a pose should hold, it needs at least two identical keys spanning the hold (not just one key and hope).
• Scene scale and constraints are stable: if you use constraints (IK/FK, parent switches), confirm they don’t pop in stepped.

Step-by-step: a safe “switch to splines” procedure

1. Duplicate your shot (new version file). Keep a stepped “golden master.”
2. Identify critical frames: contacts, reversals, accents, and story beats. Mark them (timeline markers or notes).
3. Convert in stages: start with one body area (often feet/legs), then expand. Avoid converting everything at once if your rig is complex.
4. Immediately check contacts after conversion: scrub frame-by-frame around each contact.

2) Managing Interpolation: Fixing Floatiness with Tangents and Intentional Breakdowns

Why floatiness happens

Stepped blocking has “instant” transitions; splines create continuous curves. If tangents are too smooth, the character eases into and out of everything, which can remove weight, blur accents, and create unintended hovering. Floatiness is usually one (or more) of these:

• Over-eased spacing near contacts (the foot slows too early and never “commits”).
• Missing breakdowns that define the path and timing of a limb.
• Auto tangents rounding corners that should be sharper (direction changes, impacts, stops).

Tangent control: practical rules

Different software names vary, but the principles are consistent:

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• Use spline tangents intentionally: auto/smooth is a starting point, not a final.
• Flatten tangents to hold: if something should pause, flatten the curve (or use plateau) so the value stays stable.
• Break tangents at accents: if a motion should change direction sharply, break tangents so incoming and outgoing slopes can differ.
• Linear segments for “commit” moments: short linear sections can remove mush and restore crispness (common around foot plants or quick hand placements).

Add intentional breakdowns (don’t let the computer invent them)

A breakdown is not “more keys everywhere.” It’s a purposeful in-between that defines: (a) the path, (b) the spacing, or (c) the overlap. Add breakdowns when you see any of these symptoms:

• The limb takes the wrong route (cuts through the body, arcs outward, or drifts off the intended plane).
• The motion loses its accent (impact feels soft, stop feels like a slow fade).
• Contacts slide because the curve is easing through a planted frame.

Step-by-step: de-float a planted foot

1. Isolate the problem: temporarily hide upper-body controls or mute their curves so you only judge the foot/ankle/knee and root.
2. Pin the plant: on the contact frame, key the foot control (and any relevant toe/heel attributes). Add a second key 1–2 frames later with the same values to enforce the hold.
3. Fix the approach: adjust tangents on the translate/rotate curves so the foot arrives decisively. If it “eases forever,” shorten the ease by steepening the curve into contact.
4. Fix the departure: if the foot should stay planted, keep tangents flat through the plant window. If it should roll, add a breakdown for heel/toe roll rather than letting interpolation guess.
5. Re-check in world space: view the foot trajectory (motion trail) and confirm it’s stable during the plant.

3) Maintaining Arcs and Preventing Ease-Related Drift

Arcs: keep the original intent, not just “smoothness”

When you spline, arcs can become “pretty” but wrong: wrists may balloon outward, the head may bob in unintended loops, and the hips may drift off the line that sold the pose. Treat arcs as designed paths.

Tools and habits that protect arcs

• Motion trails/ghosting: use them to see the path of wrists, ankles, head, and root. You’re looking for clean, purposeful curves, not wobbles.
• Planar checks: many actions live on a plane (walks, reaches, turns). Check from side/front/top views to ensure the arc doesn’t drift in depth accidentally.
• Key the arc, not the noise: if the path is wrong, add a breakdown at the point where the arc should change, rather than adding many tiny fixes.

Preventing ease-related drift

“Ease drift” is when a control slowly creeps during what should feel like a stable moment (a hold, a plant, a settled stance). It often comes from shallow tangents around a key.

• For holds: flatten tangents and ensure at least two identical keys across the hold.
• For planted contacts: keep the contacting control’s translation stable; let motion come from upstream controls (toe roll, heel lift, knee, hips) only when intended.
• For body settles: if the torso should settle after an impact, define the settle with one clear breakdown and a clean ease-out, rather than a long, vague drift.

Step-by-step: clean a wrist arc that “balloons” in splines

1. Show the wrist motion trail across the problematic frames.
2. Find the frame where it deviates from the intended path (often mid-transition).
3. Add one breakdown at the deviation frame and place the wrist on the desired arc.
4. Adjust tangents so the curve passes through the breakdown cleanly (avoid overshoot by reducing tangent length or breaking tangents).
5. Re-check from camera view to ensure the arc supports the shot’s staging, not just the orthographic view.

4) Polishing Passes in Order (So Fixes Don’t Fight Each Other)

Polish works best when you stabilize the foundation first. If you polish arms before feet and hips are solid, you’ll redo the arms repeatedly because the body’s base keeps changing. Use this order:

Pass 1: Feet (and any primary contacts)

• Goal: no sliding, no unintended penetration, clear heel/toe behavior, consistent plant duration.
• What to edit: foot controls, toe/heel attributes, ankle rotation, contact constraints if used.
• Checks: scrub around every plant and lift; verify the foot’s world position is stable during plants.

Pass 2: Hips/Root (center of motion and weight)

• Goal: the root supports the feet and sells weight changes without creating drift.
• What to edit: root translate/rotate, hip control, up/down and side-to-side shifts.
• Checks: root path should be clean; avoid unwanted figure-eight loops unless motivated.

Pass 3: Torso (spine, chest, shoulders)

• Goal: clear body orientation changes, controlled overlap, no “rubber spine.”
• What to edit: spine controls, chest rotation, shoulder girdle.
• Checks: watch for counter-rotation that becomes too smooth and erases accents; keep holds readable.

Pass 4: Arms and Hands

• Goal: clean arcs, purposeful spacing, stable hand placements when needed.
• What to edit: IK/FK arms, wrist rotations, finger poses if visible.
• Checks: avoid wrist “swim” during holds; ensure hand contacts (touching a prop/body) are locked and not easing through.

Pass 5: Head and Neck (final clarity and intent)

• Goal: head leads/supports attention without jitter; clean settles; no micro-bobbing from spline noise.
• What to edit: neck/head rotations, subtle translations if rig allows, eye/aim controls if present.
• Checks: verify the head doesn’t unintentionally drift during held beats; keep directional changes crisp where needed.

5) Final Review Checklist (Clarity Tests Before You Call It Done)

Silhouette readability

• In the camera view, does each key moment read instantly if you pause on it?
• Do spline in-betweens preserve the same readable shapes, or did they collapse into tangles?

Balance

• Does the character look supported by the feet during plants and settles?
• Any frames where the pose feels like it would topple unintentionally?

Consistent spacing

• Do accents still hit with the same punch as in stepped?
• Any sections where everything eases too much and feels slow or floaty?

Clean contacts

• Feet: no sliding during plants; toe/heel behavior matches intent.
• Hands/props/body touches: no penetration, no hovering, no “magnet” drift.

Stable camera and staging

• From the actual render camera, do arcs and overlaps support the shot, not distract?
• Any camera-relative pops (limbs crossing tangents, silhouette flicker) that weren’t noticeable in orthographic views?

Practical playback routine

• Playblast at speed to judge overall flow.
• Half-speed playback to catch drift and unintended easing.
• Frame-step contacts (1–2 frames before/after) to confirm stability.
• Flip between stepped master and spline version to verify the spline did not change the original pose intent.