void DrawViewRect(ScrollViewDrawer contentsDrawer)
 {
     GUI.BeginGroup(viewRect);
     contentsRect.y -= viewRect.y;
     contentsRect.y -= position.y;
     GUI.BeginGroup(contentsRect);
     contentsDrawer(viewRect, position);
     GUI.EndGroup();
     GUI.EndGroup();
 }
 public void Draw(Rect viewRect, Rect contentsRect, ScrollViewDrawer contentsDrawer)
 {
     this.viewRect     = viewRect;
     this.contentsRect = contentsRect;
     HandleScrollWheel();
     DrawVerticalScrollBar();
     DrawViewRect(contentsDrawer);
     if (targetScrollTo.HasValue)
     {
         DoScrollToTarget();
     }
 }