void CreateFormShadow()
        {
            if (borderImageCacheManager == null)
            {
                borderImageCacheManager = new ShadowImageCacheManager();
            }

            if (dropShadowManager == null)
            {
                dropShadowManager = new DropShadowManager(this);
                UpdateShadowColor();
            }
        }
        void ReleaseShadow()
        {
            if (dropShadowManager != null)
            {
                dropShadowManager.Dispose();
                dropShadowManager = null;
            }

            if (borderImageCacheManager != null)
            {
                borderImageCacheManager.Dispose();
                borderImageCacheManager = null;
            }
        }