Set up framework for more advance pickup behaviours.

resources/pickups/drift_diagonal.tres

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+[gd_resource type="Resource" script_class="PickupDriftBehavior" format=3 uid="uid://cdiglwsw46g4y"]
+
+[ext_resource type="Script" uid="uid://b4lar4f3526b1" path="res://resources/pickups/pickup_drift_behavior.gd" id="1_drift"]
+
+[resource]
+script = ExtResource("1_drift")
+drift_type = 3
+wave_amplitude = 100.0
+wave_frequency = 2.0
+drift_speed = 30.0
+diagonal_forward = true
+drift_along_x = true
+reverse_direction = false
+randomize_origin = false

resources/pickups/drift_leaf_fall.tres

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+[gd_resource type="Resource" script_class="PickupDriftBehavior" format=3 uid="uid://pickup_drift_leaf"]
+
+[ext_resource type="Script" uid="uid://pickup_drift_uid" path="res://resources/pickups/pickup_drift_behavior.gd" id="1_drift"]
+
+[resource]
+script = ExtResource("1_drift")
+drift_type = 2
+drift_speed = 30.0
+fall_speed = 15.0
+wave_amplitude = 40.0
+wave_frequency = 1.0
+drift_along_x = true
+reverse_direction = false
+randomize_origin = false

resources/pickups/drift_sine_wave.tres

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+[gd_resource type="Resource" script_class="PickupDriftBehavior" format=3 uid="uid://cr7lye10sx1q6"]
+
+[ext_resource type="Script" uid="uid://b4lar4f3526b1" path="res://resources/pickups/pickup_drift_behavior.gd" id="1_drift"]
+
+[resource]
+script = ExtResource("1_drift")
+drift_type = 1
+drift_speed = 30.0
+wave_amplitude = 40.0
+wave_frequency = 1.0
+drift_along_x = true
+reverse_direction = false
+randomize_origin = false

resources/pickups/pickup_behavior.gd

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+class_name PickupBehavior extends Resource
+
+## Base resource that defines how a pickup moves and looks on screen.
+## Assign to [member pickup_behavior] on a PickupBehaviorController.
+
+@export_group("Animation")
+## Whether the pickup bobs up and down in place.
+@export var bob_enabled: bool = true
+## Bob oscillation frequency in cycles per second.
+@export var bob_frequency: float = 2.0
+## Bob vertical amplitude in pixels (peak-to-center).
+@export var bob_amplitude: float = 4.0
+
+## Whether the pickup subtly shakes (jitter) in place.
+@export var shake_enabled: bool = false
+## Shake frequency in Hz (how fast the jitter oscillates).
+@export var shake_frequency: float = 8.0
+## Shake amplitude in pixels (peak-to-center).
+@export var shake_amplitude: float = 1.5
+
+## Optional fade-in duration (0 = no fade).
+@export var fade_in_duration: float = 0.0
+## Optional fade-out duration when the pickup is about to be collected
+## (used by controller; 0 = no fade).
+@export var fade_out_duration: float = 0.0
+
+var _elapsed: float = 0.0
+
+
+func start() -> void:
+    _elapsed = 0.0
+
+
+func process(delta: float) -> float:
+    # Returns the current opacity factor (0..1) based on fade timers.
+    _elapsed += delta
+
+    var target_alpha: float = 1.0
+
+    if fade_in_duration > 0 and _elapsed < fade_in_duration:
+        target_alpha = clampf(_elapsed / fade_in_duration, 0.0, 1.0)
+
+    return target_alpha

resources/pickups/pickup_behavior.gd.uid

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+uid://d0l8e2ymk0lx1

resources/pickups/pickup_drift_behavior.gd

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+class_name PickupDriftBehavior extends Resource
+
+## Base resource that defines the global travel pattern of a pickup across
+## the screen. Assign to [member drift_behavior] on a PickupBehaviorController.
+
+enum DriftType {
+	STATIONARY, ## Does not move (aside from bob/shake).
+	SINE_WAVE, ## Travels in a sine curve.
+	LEAF_FALL, ## Drifts downward with gentle horizontal sway.
+	DIAGONAL, ## Moves diagonally in one direction.
+}
+
+@export_group("Drift")
+## The drift pattern to apply.
+@export var drift_type: DriftType = DriftType.STATIONARY
+
+## Horizontal speed in pixels per second (applies to SINE_WAVE, LEAF_FALL).
+@export var drift_speed: float = 30.0
+## Vertical fall speed in pixels per second (applies to LEAF_FALL).
+@export var fall_speed: float = 15.0
+
+## Horizontal wave amplitude in pixels (applies to SINE_WAVE, LEAF_FALL).
+@export var wave_amplitude: float = 40.0
+## Wave frequency in cycles per second (applies to SINE_WAVE, LEAF_FALL).
+@export var wave_frequency: float = 1.0
+
+## Diagonal direction: +X forward, -X backward (applies to DIAGONAL).
+@export var diagonal_forward: bool = true
+
+## Main drift axis for SINE_WAVE and LEAF_FALL.
+## true = horizontal travel (x), false = vertical travel (y).
+@export var drift_along_x: bool = true
+
+## Reverse the primary direction (left/right or up/down).
+@export var reverse_direction: bool = false
+
+## Randomize the perpendicular axis origin (y if horizontal, x if vertical).
+@export var randomize_origin: bool = false
+
+## Phase offset in radians — randomize per-instance for variety.
+@export var phase_offset: float = 0.0
+
+var _initial_x: float = 0.0
+
+
+func reset(initial_position: Vector2) -> void:
+	_initial_x = initial_position.x

resources/pickups/pickup_drift_behavior.gd.uid

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+uid://b4lar4f3526b1

resources/pickups/rare_powerup.tres

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+[gd_resource type="Resource" script_class="PickupBehavior" format=3 uid="uid://pickup_rare_powerup"]
+
+[ext_resource type="Script" uid="uid://pickup_behavior_uid" path="res://resources/pickups/pickup_behavior.gd" id="1_behavior"]
+
+[resource]
+script = ExtResource("1_behavior")
+bob_enabled = true
+bob_frequency = 3.5
+bob_amplitude = 6.0
+shake_enabled = true
+shake_frequency = 12.0
+shake_amplitude = 1.5
+fade_in_duration = 0.5

resources/pickups/std_powerup.tres

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+[gd_resource type="Resource" script_class="PickupBehavior" format=3 uid="uid://dflj31qle75ol"]
+
+[ext_resource type="Script" uid="uid://d0l8e2ymk0lx1" path="res://resources/pickups/pickup_behavior.gd" id="1_behavior"]
+
+[resource]
+script = ExtResource("1_behavior")
+shake_enabled = true
+fade_in_duration = 0.3