/// <summary>
        /// Adds a new sprite animation.
        /// </summary>
        /// <param name="key">The animation key.</param>
        /// <param name="texture">The animation texture.</param>
        /// <param name="frameTime">The frame time.</param>
        /// <param name="nextAnimationKey">The key of the next animation.</param>
        /// <param name="loopAnimation">Whether the animatin is looped or not.</param>
        private void addAnimation(string key, Texture2D texture, float frameTime, string nextAnimationKey, bool loopAnimation)
        {
            var animation = new AnimationStrip(
                texture,
                SourceWidth,
                SourceHeight,
                frameTime);

            animation.NextAnimationKey = nextAnimationKey;
            animation.LoopAnimation    = loopAnimation;

            animations.Add(key, animation);
        }
        /// <summary>
        /// Creates a new multi sprite instance.
        /// </summary>
        /// <param name="texture">The texture of the base animation.</param>
        /// <param name="frameWidth">The frame width.</param>
        /// <param name="frameHeight">The frame height.</param>
        /// <param name="frameTime">The time for each frame.</param>
        public StoryboardSprite(Texture2D texture, int frameWidth, int frameHeight, float frameTime)
            : base(texture, frameWidth, frameHeight)
        {
            var baseAnimation = new AnimationStrip(
                texture,
                frameWidth,
                frameHeight,
                frameTime);

            baseAnimation.LoopAnimation = true;
            this.animations.Add(
                BASE_ANIMATION,
                baseAnimation);
            this.currentAnimationKey = BASE_ANIMATION;
        }
 /// <summary>
 /// Creates a new sprite instance.
 /// </summary>
 public AnimatedSprite(Texture2D texture, int frameWidth, int frameHeight, float frameTime)
     : base(texture, frameWidth, frameHeight)
 {
     this.baseAnimation = new AnimationStrip(texture, frameWidth, frameHeight, frameTime);
     this.baseAnimation.LoopAnimation = true;
 }