Added effects manager and two effects to test attached to the player

scene.

scripts/effects/flash_effect.gd

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+class_name FlashEffect
+extends BaseEffect
+
+## Shader applied to the target sprite during the flash.
+@export var flash_shader: Shader = preload("res://shaders/flash.gdshader")
+
+## Color of the flash overlay.
+@export var flash_color: Color = Color.WHITE
+
+## How many flash cycles per second.
+@export_range(0.0, 60.0) var flash_frequency: float = 10.0
+
+## Fraction of each cycle the flash is visible (0.0–1.0, i.e. duty cycle).
+@export_range(0.0, 1.0) var flash_length: float = 0.5
+
+## How the flash blends with the original sprite.
+@export_enum("Mix", "Additive", "Screen") var blend_mode: int = 0
+
+## Additional brightness added to the flash color (0.0 = none, 1.0 = double).
+@export_range(0.0, 1.0) var brightness_boost: float = 0.0
+
+## Duration of the fade-in at the start of the effect (seconds).
+@export_range(0.0, 5.0) var start_ease: float = 0.0
+
+## Easing curve for the fade-in.
+@export_enum("Linear", "Smooth", "Ease-In", "Ease-Out", "Ease-In-Out") var start_ease_mode: int = 1
+
+## Duration of the fade-out at the end of the effect (seconds).
+@export_range(0.0, 5.0) var end_ease: float = 0.0
+
+## Easing curve for the fade-out.
+@export_enum("Linear", "Smooth", "Ease-In", "Ease-Out", "Ease-In-Out") var end_ease_mode: int = 1
+
+var _original_material: Material
+
+
+func start(target: Node) -> void:
+    super.start(target)
+    if target is CanvasItem:
+        _original_material = target.material
+        var flash_material := ShaderMaterial.new()
+        flash_material.shader = flash_shader
+        flash_material.set_shader_parameter("flash_color", flash_color)
+        flash_material.set_shader_parameter("flash_intensity", 0.0)
+        flash_material.set_shader_parameter("blend_mode", blend_mode)
+        flash_material.set_shader_parameter("brightness_boost", brightness_boost)
+        target.material = flash_material
+
+
+func process(delta: float, target: Node) -> void:
+    super.process(delta, target)
+    if target.material is ShaderMaterial:
+        var intensity := _compute_intensity(_elapsed)
+        target.material.set_shader_parameter("flash_intensity", intensity)
+
+
+func stop(target: Node) -> void:
+    if target is CanvasItem:
+        target.material = _original_material
+
+
+## Compute the combined eased flash intensity for a given elapsed time.
+## Returns a value 0.0–1.0 where 1.0 means full flash visibility.
+func _compute_intensity(elapsed: float) -> float:
+    if duration <= 0.0:
+        return 0.0
+
+    # Clamp elapsed to duration to avoid overshoot on the final frame
+    var t: float = min(elapsed, duration)
+
+    # Overall envelope: fade in during start_ease, hold, fade out during end_ease
+    var envelope: float = 1.0
+    if t < start_ease and start_ease > 0.0:
+        envelope = _ease_value(t / start_ease, start_ease_mode)
+    elif t > duration - end_ease and end_ease > 0.0:
+        var fade_progress = (t - (duration - end_ease)) / end_ease
+        envelope = 1.0 - _ease_value(fade_progress, end_ease_mode)
+
+    # Flash pattern: on/off cycling at the given frequency and duty cycle
+    # Each flash pulse also eases in and out for a smoother look
+    var period := 1.0 / flash_frequency if flash_frequency > 0.0 else 1.0
+    var phase := fmod(t, period) / period  # 0.0–1.0 position within the current cycle
+
+    var pulse: float = 0.0
+    if phase < flash_length:
+        # Inside the "on" portion of this cycle — ease within the pulse itself
+        var pulse_progress = phase / flash_length if flash_length > 0.0 else 1.0
+        # Ease in for the first half of the pulse (build up), ease out for the second (fade down)
+        if pulse_progress < 0.5:
+            pulse = _ease_value(pulse_progress * 2.0, 2)  # Ease-In (build up)
+        else:
+            pulse = _ease_value((1.0 - pulse_progress) * 2.0, 3)  # Ease-Out (fade down)
+
+    return envelope * pulse
+
+
+## Apply easing to a 0.0–1.0 normalized value based on the selected mode.
+func _ease_value(value: float, mode: int) -> float:
+    match mode:
+        0: return value  # Linear
+        1: return smoothstep(0.0, 1.0, value)  # Smooth
+        2: return ease(value, -2.0)  # Ease-In (accelerating)
+        3: return ease(value, 2.0)  # Ease-Out (decelerating)
+        4: return ease(value, 3.0)  # Ease-In-Out (S-curve)
+    return value