Implemented TweenChannel.

util/TweenChannel.gd

@@ -0,0 +1,62 @@
+class_name TweenChannel extends RefCounted
+## Arbitrates between concurrent tweens, e.g. of the same property.
+
+## Emitted when a tween finishes or is killed.
+signal terminated(what: Tween)
+
+## How to arbitrate between a tween request and an already running tween.
+enum ArbitrationMode {
+	YIELD, ## Request yields until there is no longer any current tween.
+	REPLACE, ## Rather than request yielding, current tween is killed.
+	IGNORE ## Rather than request yielding, request is denied (returns null).
+}
+
+## How to arbitrate between a tween request and an already running tween.
+var arbitration_mode := ArbitrationMode.YIELD
+## Tween currently running if any, else null.
+var current_tween: Tween = null
+
+## Returns target.create_tween() if and when arbitration_mode allows.
+##
+## "If:" if arbitration_mode is IGNORE and there is a current tween,
+## then null is returned.
+## "When:" if arbitration_mode is YIELD and there is a current tween,
+## then this function yields until there is not.
+## (If arbitration_mode is REPLACE and there is a current tween,
+## then this function returns target.create_tween() immediately,
+## and the preexisting current tween is killed.)
+func create_tween(target: Variant) -> Tween:
+	assert(target is Node or target is SceneTree)
+	match arbitration_mode:
+		ArbitrationMode.YIELD:
+			while current_tween:
+				await terminated
+		ArbitrationMode.REPLACE:
+			if current_tween and current_tween.is_valid():
+				current_tween.kill()
+		ArbitrationMode.IGNORE:
+			if current_tween:
+				return null
+	current_tween = target.create_tween()
+	_cleanup_later(current_tween)
+	return current_tween
+
+## Yields until the given tween has terminated.
+##
+## The given tween must have been created with self.create_tween.
+func sync(what: Tween) -> void:
+	var last_terminated: Tween = null
+	while last_terminated != what:
+		last_terminated = await terminated
+
+## Yields until the given tween is invalid and then cleans up bookkeeping.
+##
+## Bookkeeping cleanup entails the following:
+##	-	if the given tween is the current tween, clears the current tween;
+##	-	terminated is emitted with the given tween as the argument.
+func _cleanup_later(what: Tween) -> void:
+	while what.is_valid():
+		await Wait.tick()
+	if current_tween == what:
+		current_tween = null
+	terminated.emit(what)