:tada: Add ability to go to previous slide

godot/projector/show/Show.gd

@@ -33,6 +33,10 @@ func go_fast_to_next_slide() -> void:
 	next_slide(Focus.Transit.BEAM)
 
 
+func go_fast_to_previous_slide() -> void:
+	next_slide_at(_previous_id(), Focus.Transit.BEAM)
+
+
 func next_slide(trans: Focus.Transit) -> void:
 	next_slide_at(_next_id(), trans)
 
@@ -96,6 +100,15 @@ func _next_id() -> int:
 	return next_id
 
 
+func _previous_id() -> int:
+	var next_id: int = current_id - 1
+
+	if next_id < 0:
+		return slides.size() - 1
+
+	return next_id
+
+
 func _reset_id() -> void:
 		current_id = VOID_SLIDE_ID
 
@@ -107,6 +120,9 @@ func _unhandled_key_input(event: InputEvent) -> void:
 	if event.is_action("ui_right"):
 		get_viewport().set_input_as_handled()
 		go_fast_to_next_slide()
+	elif event.is_action("ui_left"):
+		get_viewport().set_input_as_handled()
+		go_fast_to_previous_slide()
 	elif event.is_action("ui_cancel"):
 		get_viewport().set_input_as_handled()
 		_reset_id()