Custom definitionsCustom definitions

A custom definition animates storage the catalog doesn’t cover. Pass delegates to Tweens.Property, or derive from TweenDefinition<TTarget, TValue> for setup and cleanup around each playback; both start like any built-in definition. Custom properties walks through both.

DelegatesSubclass

// Tweens a camera's zoom as one number, keeping X and Y equal.
var zoom = new Tweens.Property<Camera2D, float>(
    target => target.Zoom.X,
    (target, value) => target.Zoom = new Vector2(value, value),
    Interpolators.Float,
    to: 2, duration: 0.5, ease: InOut.SmootherStep);

camera.Tween(zoom);

UniformZoomTween.cs

// Tweens a camera's zoom as one number, keeping X and Y equal.
public sealed class UniformZoomTween : TweenDefinition<Camera2D, float>
{
    protected override float Read(Camera2D target) => target.Zoom.X;
    protected override void Write(Camera2D target, float value) => target.Zoom = new Vector2(value, value);
    protected override float Interpolate(float from, float to, float weight) => Interpolators.Float(from, to, weight);
}

camera.Tween(new UniformZoomTween { To = 2, Duration = 0.5, Ease = InOut.SmootherStep });

Delegates

Constructor	Arguments
new Tweens.Property<TTarget, TValue>(getter, setter, interpolate, to, duration, ease, delay)	The property operations, then the optional endpoint and timing
new PropertyTween<TTarget, TValue>(getter, setter, interpolate)	The same operations, as a mutable class definition

interpolate takes (from, to, weight); pass one of the Interpolators. Captured objects stay shared between playbacks.

Members to override

TweenDefinition<TTarget, TValue> is abstract; TTarget is a class and TValue a struct. Its public members, from From to OnFinally, match the built-in definitions. These are all protected:

Method	Returns	Purpose
Read(target)	TValue	Read the current value. Required
Write(target, value)	void	Write a value. Required
Interpolate(from, to, weight)	TValue	Blend two values; weight leaves 0 to 1 when an ease overshoots. Required
Prepare(target)	void	Set up this playback’s bindings
Restore(target, initial)	void	Undo the tween at a non-retaining end; writes initial unless overridden
Release()	void	Free this playback’s resources
ReadsWrittenValue	bool	Whether Read returns what Write stored; true unless overridden

Binding lifecycle

1. Copy. Each start works on a private, shallow copy of the definition, so per-playback state belongs in its fields. Reference-valued fields stay shared.
2. Prepare runs on that copy at activation, before the first read.
3. Read captures the start value.
4. Interpolate and Write run on every update.
5. Restore runs at a natural end whose fill doesn’t keep the final value. It can write initial back, or remove an override instead.
6. Release runs after the ending callbacks, and also after a failed Prepare. Release only what this copy owns.

Interpolators

Interpolators has one static method per built-in value type, each taking (from, to, weight). Pass one as the interpolate argument, or call it from your own Interpolate.

Method	Returns	Purpose
Float, Double	float, double	Linear blend; overshoot passes through
Int	int	Rounds half away from zero; overshoot saturates at the int limits
Vector2, Vector3, Vector4, Color, Rect2	the same type	Component-wise linear blend
Quaternion	Quaternion	Shortest-path spherical blend; endpoints must be nonzero

Builders

The class-based definitions, such as Position2DTween, and your own subclasses of TweenDefinition<TTarget, TValue> are mutable. They inherit TweenOptionsBuilder, the mutable form of TweenOptions, and each start snapshots them. IntelliSense hides the built-in classes and offers the Tweens.* structs instead.

A shorthand method’s configure callback receives one of these builders: TweenPosition on a Node2D passes a Position2DTween. Write reusable configure methods against TweenOptionsBuilder.

Rules

• By, factors, and deltas work with int, float, double, vector, Color, Quaternion, and Rect2 values.
• By reads the property back on every update. If Read doesn’t return what Write stored, override ReadsWrittenValue to return false, and By is added to the start value instead.
• Don’t change reference-valued configuration while playbacks share it.