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MotionAtelier

Motion Stack

The Motion Stack adds effects on top of the current shape (an Ease curve or a generated shape) without changing it. Each effect is a layer you can mix, reorder, bypass and remove at any time. The result is committed as a small set of keys, never one key per frame.

A Spring effect on a fast easeThe base curve is a sharp ease in and out. With the Spring layer, the value lags at first, overshoots the end by about 15 percent, swings back, and settles exactly on the end value.
  • With a Spring layer (Damping 0.10)
  • Base curve
Spring on the Exponential S-Curve recipe: the value follows the base curve like a weight on a spring. Plotted from MotionAtelier 0.4.2's own curve code, outside Houdini. An illustration of the curve, not a screen capture.
The Motion Stack tab in Houdini with a Contrast layer expanded and a Jiggle layer collapsed. The graph shows the output curve and the dashed base curve.
Open full screenScreenshot from Houdini. Try it live swaps in a simulation: the shipped MotionAtelier engine running in your browser (about 13 MB, loaded once), with an HTML copy of the panel and a simulated Houdini scene.

Add and edit layers

Section titled “Add and edit layers”
  1. Open the Motion Stack tab (the first tab on the right).
  2. Press Add Effect and choose an effect. It is added at the end of the stack.
  3. Expand the card and adjust its parameters. The graph shows the result live.

Each layer card has, left to right:

Control What it does
Expand arrow Shows the layer’s parameters and actions. Double-clicking the card also expands it.
Check box Enables or bypasses the layer.
Grip Drag to reorder layers.
Name The layer name. Right-click to rename.
Mix % Layer strength, 0–100 %. At 0 % the layer has no effect.

An expanded card adds the parameters and four buttons: Move Up, Move Down, Duplicate and Delete. The card’s right-click menu offers Rename, Duplicate, Reset Parameters and Delete.

A stack holds up to 16 layers. Every change is a local undo step; the scene is not changed.

How the stack is evaluated

Section titled “How the stack is evaluated”
  • Top to bottom. Each layer processes the output of the layer above it, so order matters: Noise followed by Gaussian Smooth is softer than the reverse.
  • Mix blends a layer’s result with its input. For Contrast and Arc Bias, mix scales the effect’s strength.
  • Ends are kept. Every effect keeps the start and end values of the curve, so committed boundary keys never move (Boundary: Preserve Ends on each card).
  • Per-shape stacks. Each shape keeps its own stack. Switching SHAPE does not carry effects over. Recipes save the stack with the shape.
  • Viewing one layer. Click a card to view the stack only up to that layer; the Base overlay shows the curve before effects. This changes only the display: Commit Keys always uses every enabled layer.

Committing effects

Section titled “Committing effects”
  • Contrast and Arc Bias transform the curve exactly and are committed key for key.
  • All other effects produce a dense result that is fitted with a small number of Bezier keys within 0.5 % of the value range, then verified. If no such fit exists, the commit is refused (the effect result could not be fitted with fewer keys within the tolerance …) and nothing is written. The panel has no control for this tolerance; lower the effect’s mix, amplitude or frequency and try again. See Known limitations.

See Effects and key count.

Effects

Section titled “Effects”

Ranges and defaults are the values shown in the panel. Each figure applies the effect, at its default settings unless stated, to the dashed base curve.

Contrast

Section titled “Contrast”

Steepens or relaxes the curve’s tangents without moving its knots: positive values exaggerate the ease, negative values straighten it.

ControlRangeDefaultWhat it changes
Amount-100% to 200%50%-100% straightens tangents, 0% is unchanged, positive exaggerates.
Contrast at 50 percentThe S-curve becomes steeper in the middle and flatter at the ends.
Contrast, Amount 50 %.

Arc Bias

Section titled “Arc Bias”

Bends every rise and fall towards one of its ends, keeping peaks, dips and key times: positive values bow each arc towards its lower value, negative towards its upper value.

ControlRangeDefaultWhat it changes
Bias-100% to 100%40%Bends each rise and fall: positive bows it towards its lower value, negative towards its upper value.
Arc Bias at 40 percentThe curve bows below the base S-curve.
Bias 40 %
Arc Bias at minus 40 percentThe curve bows above the base S-curve.
Bias −40 %

Noise

Section titled “Noise”

Adds smooth random variation, tapered to zero at both ends. Unlike the Noise shape, it works on top of any curve.

ControlRangeDefaultWhat it changes
Amplitude0.000 to 0.5000.050Noise size relative to the curve's value range. A fraction of the curve’s value range.
Frequency1 to 64
slider to 40; type larger values		12Number of noise cells across the motion.
Seed0 to 2147483647
slider to 999; type larger values		7Pattern number; the same seed always gives the same noise.
Noise effectSmall irregular wiggles along the S-curve, none at the ends.
Noise, default settings.

Gaussian Smooth

Section titled “Gaussian Smooth”

Softens sharp corners and fast changes by averaging over a time window.

ControlRangeDefaultWhat it changes
Width0.0% to 25.0%5.0%Smoothing width as a percentage of the duration.
Passes1 to 41How many times the smoothing is applied.
Gaussian Smooth on a bounceThe bounce contacts are rounded and the small rebounds are softened.
Gaussian Smooth on Bounce, default settings.

Sharpen

Section titled “Sharpen”

The opposite of smoothing: exaggerates detail of about the chosen width.

ControlRangeDefaultWhat it changes
Amount0.0% to 400.0%100.0%Strength of the sharpening.
Width0.5% to 25.0%4.0%Width of detail to emphasise, as a percentage of the duration.

Jiggle

Section titled “Jiggle”

Adds a bounded wobble that follows the motion, like loose secondary motion. Limit caps how far it can stray.

ControlRangeDefaultWhat it changes
Frequency0.5 to 30.0
slider to 20.0; type larger values		8.0Wobble oscillations per duration.
Damping0.02 to 1.000.12Damping ratio of the wobble.
Limit0.01 to 1.000.15Largest deviation from the motion, as a fraction of its range.
Jiggle at default settingsA slight wobble where the base curve changes fastest.
Default settings
Jiggle with low damping and a higher limitA clearer wobble that overshoots the end slightly before settling.
Damping 0.04, Limit 0.30

Spring

Section titled “Spring”

Makes the value follow the curve like a mass on a spring: it trails, overshoots and settles. Frequency is the number of spring oscillations per duration; Damping 1 settles without overshoot.

ControlRangeDefaultWhat it changes
Frequency0.5 to 30.0
slider to 15.0; type larger values		4.0Spring oscillations per duration.
Damping0.05 to 2.000.35Damping ratio; 1 settles without overshoot.
Spring at default settingsThe value trails the base curve and overshoots very slightly.
Default settings
Spring with damping 0.1A clear overshoot past the end value and a swing back before settling.
Damping 0.10

Lag

Section titled “Lag”

Makes the value trail the curve smoothly, without overshoot. 90% Response is how long the value takes to cover 90 % of a sudden change.

ControlRangeDefaultWhat it changes
90% Response0.0% to 115.1%11.5%Time to reach 90% of a step, as a percentage of the duration.
LagThe value rises a little later and more gently than the base curve.
Lag, default settings.

Delay

Section titled “Delay”

Starts the motion later by a share of the duration. The end value is still reached at the last key.

ControlRangeDefaultWhat it changes
Delay0.0% to 50.0%10.0%Delay as a percentage of the duration.
DelayThe S-curve starts later and catches up towards the end.
Delay 10 %.

Effect figures are plotted from MotionAtelier’s own effect code, outside Houdini. They are illustrations, not screen captures.

Section titled “Related”