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Motion

Motion provides generic, sampleable motion functions for procedural "juice": continuous idle motion (floating, wobble, breathing) that you read every frame and add to a node.

Use it where a Tween does not fit: a Tween animates a punctual A → B move, while Motion gives you a value to sample forever in _process.

It is inspired by the motion functions of 2D BOY's Boy framework (the engine behind World of Goo): SmoothTransitionFunction and SinFunction2D.

Usage

Sample a function each frame with an accumulating time t and add it to a base value:

var basePosition: Vector2
var t := 0.0

func _ready():
  basePosition = position

func _process(delta):
  t += delta
  position = basePosition + Motion.bob(t, 8.0, 0.5)
  scale    = Vector2.ONE * Motion.breathe(t, 0.05, 0.8)
  rotation = deg_to_rad(Motion.wobbleDeg(t, 4.0, 1.2))

frequency is in Hz (cycles per second), phase in radians. Offsetting the phase per node desynchronizes a crowd of objects so they do not pulse in unison.

API

Oscillators

  • Motion.oscillate(t, amplitude, frequency, phase = 0.0) -> float 1D sine oscillation around 0, within [-amplitude, amplitude].
  • Motion.oscillate2D(t, amplitude: Vector2, frequency: Vector2, phase = Vector2.ZERO) -> Vector2 Independent oscillation per axis (Boy's SinFunction2D). Combine axes for circular / figure-eight motion.

Ready-made offsets

  • Motion.bob(t, amplitude, frequency, phase = 0.0) -> Vector2 Vertical floating offset (idle bob).
  • Motion.sway(t, amplitude, frequency, phase = 0.0) -> Vector2 Horizontal swaying offset.
  • Motion.breathe(t, amplitude, frequency, base = 1.0, phase = 0.0) -> float Pulsing scalar around base (breathing scale): base ± amplitude.
  • Motion.wobbleDeg(t, amplitudeDeg, frequency, phase = 0.0) -> float Rotation wobble in degrees, within [-amplitudeDeg, amplitudeDeg].

Smooth transition

  • Motion.smooth(x, x0, x1, y0, y1) -> float Smooth cosine transition from y0 to y1 as x goes from x0 to x1 (Boy's SmoothTransitionFunction). x is clamped to [x0, x1], so it is a handy ease for mapping any input range to an eased output:

    # fade an alpha as a value crosses [0, 100]
modulate.a = Motion.smooth(distance, 0.0, 100.0, 1.0, 0.0)