niveau/transitions: shader de transition

Entre les niveaux et à la mort il y a maintenant un fondu au noir qui se
met en place pour éviter d'avoir la gerbe sur les mouvements de caméra.
la physique est en pause pendant la transition.

HUD/hud.gd

@@ -4,7 +4,11 @@ class_name HUD extends CanvasLayer
 @onready var gauge2 := $FartGauge2 as FartGauge
 @onready var gauge3 := $FartGauge3 as FartGauge
 
+@onready var shader := $TransitionShader
+
 signal fart_reloaded()
+signal screen_is_black()
+signal screen_is_ready()
 
 var cheese_number = 0
 var gauges = []
@@ -15,7 +19,6 @@ func _ready() -> void:
     gauge3.connect("reload_done", cheese_loaded)
     gauges = [gauge1, gauge2, gauge3]
 
-
 func reset():
     cheese_number = 0
     for gauge in gauges:
@@ -34,3 +37,17 @@ func dash_fart():
 
 func cheese_loaded():
     fart_reloaded.emit()
+
+func begin_scene_transition():
+    print("start scene transition")
+    shader.fade_out()
+
+func end_scene_transition():
+    print("end scene transition")
+    shader.fade_in()
+
+func _on_transition_shader_fade_in_done() -> void:
+    screen_is_ready.emit()
+
+func _on_transition_shader_fade_out_done() -> void:
+    screen_is_black.emit()