protected virtual void OnRenderCompleted(RenderResult result)
        {
            if (result.IsSuccess)
            {
                completedRequest  = result.Request;
                completedBitmap   = result.CreateBitmap();
                bitmapInvalidated = false;

                InvalidateVisual();
                BackgroundRenderer.RaiseRenderingFinished(this);
            }
        }
        protected virtual void OnRenderCompleted(RenderResult result)
        {
            if (result.IsSuccess)
            {
                completedRequest = result.Request;
                completedBitmap = result.CreateBitmap();
                bitmapInvalidated = false;

                InvalidateVisual();
                BackgroundRenderer.RaiseRenderingFinished(this);
            }
        }