added simple sleep state for elements

refactoring

Scripts/Elements/Liquid.cs

@@ -1,9 +1,33 @@
-using System;
-using Godot;
+using Godot;
 
 namespace FOU.Scripts.Elements;
 
 public abstract class Liquid : Element {
+    public const int MAX_VERTICAL_SPREAD = 3;
+
     protected Liquid(int x, int y, ref Level level) : base(x, y, level) { }
 
+    public override bool Update(int currentFrame) {
+        if (!base.Update(currentFrame)) return false;
+        if (LastMove + STEPS_UNTIL_INACTIVE < currentFrame) Active = false;
+
+        Tick();
+
+        return true; // not necessarily end, subclasses could do some more things
+    }
+
+    protected override void Tick() {
+        Vector2I randomDirection = RandomDirectionDown();
+        if (randomDirection.Y != 0)
+            randomDirection *= Vector2I.Left * (int)(GD.Randi() % MAX_VERTICAL_SPREAD);
+
+        if (Level.IsEmpty(Position + Vector2I.Down))
+            Level.Swap(this, Position + Vector2I.Down);
+
+        else if (Level.IsEmpty(Position + randomDirection))
+            Level.Swap(this, Position + Vector2I.Right * randomDirection);
+
+        else if (Level.IsEmpty(Position + randomDirection))
+            Level.Swap(this, Position + Vector2I.Right * randomDirection * VERTICAL_OPPOSITE);
+    }
 }