Added FPS=5 limit when the game window is not active.

Game/Assets/HUD/Performance.gd

@@ -39,4 +39,6 @@ func _process(delta):
 
 
 	text += "\nFPS: " + str(Engine.get_frames_per_second())
+	if Engine.target_fps != 0:
+		text += " (capped at " + str(Engine.target_fps) + ")"
 	text += "\n" + version + " · https://git.gieszer.link/unfa/liblast"

Game/Main.gd

@@ -77,6 +77,14 @@ var game_score_limit = 10 #15
 
 const destroy_free_player_crash_workaround = true
 
+func _notification(what: int) -> void:
+	match what:
+		NOTIFICATION_APPLICATION_FOCUS_OUT:
+			Engine.target_fps = 5
+		NOTIFICATION_APPLICATION_FOCUS_IN:
+			# `0` means "unlimited".
+			Engine.target_fps = 0
+
 func _process(delta):
 	uptime += delta