simple gui question

hello, i have this code for a vertical gui progress bar which works pretty well. however the progress bar fills up from top to bottom. can someone help me to change it to the opposite - namely filling from bottom to top?

here is the code :

 #pragma strict
 var barDisplay : float = 0;
 var pos : Vector2 = new Vector2(20,40);
 var size : Vector2 = new Vector2(20,60);
 var progressBarEmpty : Texture2D;
 var progressBarFull : Texture2D;
 var scalemax : float = 100;
  
 function OnGUI()
 {
     GUI.BeginGroup (new Rect (pos.x, pos.y, size.x, size.y));
         GUI.DrawTexture (Rect (0,0, size.x, size.y),progressBarEmpty);
         GUI.BeginGroup (new Rect (0, 0, size.x, size.y * barDisplay));
             GUI.DrawTexture (Rect (0,0, size.x, size.y),progressBarFull);
         GUI.EndGroup ();
  
     GUI.EndGroup ();
  
 } 
  
 function Update()
 {
     barDisplay = score.gameScore/scalemax;
 }