Refine movement, water recovery, and UI baseline

ui/screen_fade.gd

@@ -0,0 +1,65 @@
+class_name ScreenFade
+extends ColorRect
+
+signal transition_completed(generation: int, faded_to_black: bool)
+
+@export_range(0.01, 3.0, 0.01) var fade_out_duration: float = 0.4
+@export_range(0.01, 3.0, 0.01) var fade_in_duration: float = 0.45
+
+var _fade_tween: Tween
+
+
+func _ready() -> void:
+	modulate.a = 0.0
+	visible = false
+
+
+func fade_to_black(generation: int) -> void:
+	_start_fade(1.0, fade_out_duration, generation, true)
+
+
+func fade_from_black(generation: int) -> void:
+	visible = true
+	modulate.a = 1.0
+	_start_fade(0.0, fade_in_duration, generation, false)
+
+
+func reset_immediately() -> void:
+	if _fade_tween != null and _fade_tween.is_valid():
+		_fade_tween.kill()
+	_fade_tween = null
+	modulate.a = 0.0
+	visible = false
+
+
+func _start_fade(
+	target_alpha: float,
+	duration: float,
+	generation: int,
+	faded_to_black: bool,
+) -> void:
+	if _fade_tween != null and _fade_tween.is_valid():
+		_fade_tween.kill()
+	visible = true
+	_fade_tween = create_tween()
+	_fade_tween.set_trans(Tween.TRANS_QUAD)
+	_fade_tween.set_ease(
+		Tween.EASE_IN if faded_to_black else Tween.EASE_OUT
+	)
+	_fade_tween.tween_property(
+		self,
+		"modulate:a",
+		target_alpha,
+		maxf(duration, 0.01)
+	)
+	_fade_tween.finished.connect(
+		_on_fade_finished.bind(generation, faded_to_black),
+		CONNECT_ONE_SHOT
+	)
+
+
+func _on_fade_finished(generation: int, faded_to_black: bool) -> void:
+	_fade_tween = null
+	if not faded_to_black:
+		visible = false
+	transition_completed.emit(generation, faded_to_black)