EasingEasing

Easing maps each leg’s progress to a weight between its endpoints. Pick one In and one Out curve and join them with |. The easing playground draws every combination.

Tweens.play(sprite, Tweens.position_2d_x(300.0, 1.2, In.SINE | Out.CUBIC))

Members

Field	Type	Default	Meaning
ease	int	LINEAR	An In curve, an Out curve, both joined with |, an InOut pair, or a legacy ease
blend_type	int	BlendType.MAKIMA	How mixed pairs join
blend	float	0.1	Width of the centered join window, in [0, 1]
skew	float	0.5	Where the outward leg splits between In and Out; see pacing
weks	float	0.5	Where the ping-pong return splits
ease_function	Callable	Callable()	Custom function of progress; overrides ease
curve	Curve	null	Godot curve sampled over progress; overrides ease

Each has a with_*() copy method, such as with_ease() or with_blend_type().

Families

• LINEARt

  In

  Out

  InOut

• SINE1 − cos(πt/2)

  In

  Out

  InOut

• QUADt²

  In

  Out

  InOut

• CUBICt³

  In

  Out

  InOut

• QUARTt⁴

  In

  Out

  InOut

• QUINTt⁵

  In

  Out

  InOut

• EXPO2^(10t − 10)

  In

  Out

  InOut

• CIRC1 − √(1 − t²)

  In

  Out

  InOut

• SMOOTH_STEP3t² − 2t³

  In

  Out

  InOut

• SMOOTHER_STEPso soft

  In

  Out

  InOut

• BACKovershoots

  In

  Out

  InOut

• ELASTICsprings

  In

  Out

  InOut

• BOUNCErebounds

  In

  Out

  InOut

• JUMPhops

  In

  Out

  InOut

• Every family is available as In.X, Out.X, and InOut.X; InOut.SINE is exactly In.SINE | Out.SINE.
• SMOOTH_STEP and SMOOTHER_STEP are symmetric, so their In and Out legs match.
• Weights aren’t clamped: Back, Elastic, and Jump overshoot. Native property setters still apply their own limits.

Composing

• A single leg, such as Out.CUBIC, runs over the whole duration.
• In.SINE | Out.CUBIC eases in with one family and out with another. Choose at most one of each side; two different In or two different Out flags are rejected.
• In.NONE and Out.NONE omit a leg. In.LINEAR and Out.LINEAR select a straight line for that side of a mixed pair; no selection at all is linear.
• In, Out, and InOut are global classes of integer constants, so flags from either side compose. Pass them as a helper’s third argument, assign them to ease, or sample them with Tweens.Easing.evaluate().

Numbered variants

Back, Elastic, Bounce, and Jump come in five strengths, 10 to 50, such as Out.ELASTIC40 or InOut.BACK20. The plain name is the 30 variant. The number is a percentage of the full tween range:

Family	The number sets	Out.X30 from 0 to 100
BACK	Peak overshoot	Peaks at 130, then settles at 100
ELASTIC	Peak overshoot	Swings to 130, then oscillates into 100
BOUNCE	Depth of the first rebound	Reaches 100, falls back to 70, then rebounds a quarter and a sixteenth as deep
JUMP	Height of the first hop above the target	Rises to 130, lands, then hops to 107.5 and 101.875

• An In leg mirrors its motion: In.ELASTIC30 dips to −30 before leaving.
• A matching InOut pair keeps the percentage in each half: InOut.ELASTIC30 reaches both extremes, and InOut.BOUNCE30 rebounds 30 units in each half.
• A single Elastic leg relaxes its damping after the main swing, so it settles at about 90% of the duration; a paired curve settles within each half. Both keep the named peak.
• Jump stays above the target once it first reaches it.
• In a mixed pair, the join can reshape overshoot or rebounds inside its window.

Mixed pairs

At the neutral split, the In leg covers the first half of progress and of the value range, and the Out leg the second; every pair passes through (0.5, 0.5). Where two different families meet, a centered window of width blend joins them:

BlendType	Join
MAKIMA	The default. Two cubics with matched velocity at the window’s edges, sharing a midpoint velocity from modified Akima weights
HERMITE	Two cubics with matched velocity at the edges and equal acceleration at the midpoint
SMOOTH_STEP	Crossfades the two families’ InOut profiles with u²(3 − 2u)
LINEAR	Crossfades the profiles with u; velocity may jump at the window’s edges

• With the default width 0.1, progress up to 0.45 follows the In half exactly, and from 0.55 the Out half. A wider window reshapes more of each leg; zero splices the halves directly and may jump in velocity.
• blend must be finite and within [0, 1].
• All methods preserve the midpoint. For monotone families, Makima and Hermite add no reversals or overshoot; the crossfades can inherit steep midpoint slopes from a family such as Circ.
• Matching families skip the join and use their paired profile.
• Join settings don’t affect a single leg, a matching pair, a legacy ease, ease_function, or curve.

The join, in detail

Each half is the family’s InOut half profile: for Sine, 0.5 * SineIn(2 * t) and 0.5 + 0.5 * SineOut(2 * t - 1). Back, Elastic, and Jump are calibrated to their named overshoot, and Bounce to its first rebound depth.

Makima sets the midpoint velocity with the modified Akima weights of MATLAB’s makima: a weighted mean of the slopes on either side, favoring the half whose slope is steadier and closer to zero, so the result stays between them. Hermite solves the midpoint velocity from equal acceleration between the cubics, then limits it to prevent new reversals in monotone families. For a window half-width h, edge values y0, y1, and edge velocities v0, v1:

d0 = (0.5 - y0) / h
d1 = (y1 - 0.5) / h
Makima:  w0 = |v1 - d1| + |v1 + d1| / 2
         w1 = |d0 - v0| + |d0 + v0| / 2
         midVelocity = (w0 * d0 + w1 * d1) / (w0 + w1)
Hermite: midVelocity = clamp((3 * (d0 + d1) - v0 - v1) / 4,
                             0, 3 * max(0, min(d0, d1)))
left cubic:  (0.5 - h, y0, v0) -> (0.5, 0.5, midVelocity)
right cubic: (0.5, 0.5, midVelocity) -> (0.5 + h, y1, v1)

The edge velocities stand in for the outer slopes that makima takes from neighboring samples. Both methods give a continuous velocity across the join at regular points of the source curves; acceleration can change at the window’s edges, and with Makima also at the midpoint.

Pacing

skew moves the outward leg’s In/Out split; weks moves the ping-pong return’s.

• At 0.5, the default, the pair stays balanced. At 0 the Out curve fills the whole leg; at 1 the In curve does. Values between move the split in both time and value, and the join window follows it, shrinking near either end.
• weks = 1 - skew makes the return retrace the outward curve.
• Duration, intervals, and the handle’s raw progress stay unchanged.
• Both apply to In/Out pairs. A single leg, a legacy ease, ease_function, and curve keep their shape.
• Moving the split redistributes the legs’ value ranges, so the numbered percentages describe the balanced pair.
• Both must be finite and within [0, 1], even without ping-pong.

Custom functions and curves

• ease_function maps normalized progress, from 0 to 1, to a weight. Return 0 at the start and 1 at the end for an ordinary arrival.
• A Godot Curve is sampled over the same 0 to 1 domain. Each start samples its own duplicate, so later edits reach only later starts.
• Either one overrides ease; setting both is rejected.
• The Callable runs synchronously on every update. If it becomes invalid or returns anything but a finite number, the tween ends with FAILED. A script error inside it stays an ordinary Godot script error.
• Effects builds functions for punch, shake, and breathing; Functions and Curves show each in use.

Sampling

Method	Returns	Meaning
Tweens.Easing.evaluate(ease, progress, blend_type, blend, skew)	float	The weight at progress, without starting playback; the last three default to MAKIMA, 0.1, and 0.5