/// <summary>
 /// Initializes a new instance of the <see cref="Animation"/> class,
 /// using the specified <see cref="SpriteSheet"/> as source.
 /// </summary>
 /// <param name="source">The <see cref="SpriteSheet"/> containing the
 /// animation's frames.</param>
 public Animation(SpriteSheet source)
 {
     spriteSheet = source;
 }
 /// <summary>
 /// Optionally releases all managed resources used by this <see 
 /// cref="Animation"/>.
 /// </summary>
 /// <param name="disposing"><c>true</c> to release managed resources.
 /// </param>
 protected virtual void Dispose(bool disposing)
 {
     if (disposing)
     {
         if (spriteSheet != null)
         {
             spriteSheet.Dispose();
             spriteSheet = null;
         }
     }
 }