Easing (Data Type)

A String naming an interpolation curve: how a value travels from its start to its end over time, instead of jumping straight there.

Names ignore case and separators, so ease_in_out, easeInOut and EASE-IN-OUT are the same curve.

Special curves

Value	Description
`linear`	A constant rate. The default everywhere an easing is optional.
`step`	No interpolation. It holds the starting value and snaps to the end value at the very end. Use it for on and off properties like `visible`.
`catmullrom`	A smooth spline through the surrounding keyframes instead of a straight line between two of them. It only means something between keyframes, and behaves as `linear` for a fade. Alias: `smooth`.
`smoothstep`	The classic `3t² − 2t³` S-curve, a gentle ease in and out.
`smootherstep`	Perlin's `6t⁵ − 15t⁴ + 10t³`. Like `smoothstep`, but flatter at both ends.

Standard curves

Each family comes in three forms: ease_in_* starts slow, ease_out_* ends slow, and ease_in_out_* does both. They are ordered from gentlest to sharpest:

Family	Values	Feel
Sine	`ease_in_sine`, `ease_out_sine`, `ease_in_out_sine`	Barely there. Good for subtle idle motion.
Quadratic	`ease_in_quad`, `ease_out_quad`, `ease_in_out_quad`	The safe default for poses.
Cubic	`ease_in_cubic`, `ease_out_cubic`, `ease_in_out_cubic`	Noticeably snappier.
Quartic	`ease_in_quart`, `ease_out_quart`, `ease_in_out_quart`	Sharp.
Quintic	`ease_in_quint`, `ease_out_quint`, `ease_in_out_quint`	Very sharp.
Exponential	`ease_in_expo`, `ease_out_expo`, `ease_in_out_expo`	Almost instant at one end.
Circular	`ease_in_circ`, `ease_out_circ`, `ease_in_out_circ`	Flat, then abrupt, like a quarter circle.
Back	`ease_in_back`, `ease_out_back`, `ease_in_out_back`	Overshoots the target and settles back, like anticipation.
Elastic	`ease_in_elastic`, `ease_out_elastic`, `ease_in_out_elastic`	Springs past the target and oscillates.
Bounce	`ease_in_bounce`, `ease_out_bounce`, `ease_in_out_bounce`	Hits the target and bounces off it.

warning

back and elastic leave the 0 to 1 range partway through the curve on purpose, so the animated value overshoots its keyframe. That is what they are for, but it means a visible or hidden transformation shouldn't use them.

Aliases

Alias	Resolves to
`ease_in`	`ease_in_quad`
`ease_out`	`ease_out_quad`
`ease_in_out`	`ease_in_out_quad`
`smooth`	`catmullrom`
`hold`	`step`
`constant`	`step`
`none`	`linear`

Example

{
  "model_part": "right_arm",
  "type": "pitch",
  "value": -1.5708,
  "override_animation": true,
  "easing": "ease_out_back",
  "duration": 6
}

The arm swings up over 6 ticks, overshoots slightly and settles.