private Decal getFreeDecal() {
      long min=Long.MAX_VALUE;
      Decal decal=null;
      for (int i=0; i<MAX_DECALS; i++) {
         if (!decals[i].getVisibility()) {
            return decals[i];
         }

         if (decals[i].getDecalID()<min) {
            min=decals[i].getDecalID();
            decal=decals[i];
         }
      }
      return decal;
   }