public Rectangle MinDistanceRegion(Rectangle sourceRect, Drawable drawable, SelectionMask selectionMask)
        {
            Debug.Assert(sourceRect.Width == sourceRect.Height);

            var windowSize = sourceRect.Width;
            var windowDelta = windowSize/2;
            Rectangle minRegionRect = null;

            var minDistance = 0.0;

            var sourceRgn = new PixelRgn(drawable, sourceRect.AdjustedToImageEdges(drawable.Bounds), false, false);
            var sourceArray = sourceRgn.ToArrayWithoutSelection(selectionMask);

            var currentCoordinate = new IntCoordinate(0, 0);
            for (int i = windowDelta; i < drawable.Width - windowDelta; i++)
            {
                for (int j = windowDelta; j < drawable.Height - windowDelta; j++)
                {
                    if (j == sourceRect.Y1 + windowDelta && i == sourceRect.X1 + windowDelta)
                    {
                        continue;
                    }
                    currentCoordinate.X = i;
                    currentCoordinate.Y = j;
                    var currentRgnRect = currentCoordinate.PointCenteredRectangle(windowSize);
                    var dist = RegionDistance(sourceArray, currentRgnRect, drawable, selectionMask);
                    if (dist == null)
                    {
                        continue;
                    }
                    if (dist == 0)
                    {
                        return currentRgnRect;
                    }
                    if ((minDistance > dist || minRegionRect == null))
                    {
                        minDistance = (double) dist;
                        minRegionRect = currentRgnRect;
                    }
                }
            }

            return minRegionRect;
        }
        public Rectangle MinDistanceRegion(Rectangle sourceRect, ImgGradient gradient, Pixel[,] layerPixels, SelectionMask selectionMask)
        {
            Debug.Assert(sourceRect.Width == sourceRect.Height);

            var windowSize = sourceRect.Width;
            var windowDelta = windowSize/2;
            var layerWidth = layerPixels.GetLength(0);
            var layerHeight = layerPixels.GetLength(1);

            Rectangle minRegionRect = null;
            var minDistance = 0.0;
            var adjustedSourceRect = sourceRect.AdjustedToImageEdges(new Rectangle(new IntCoordinate(0, 0),
                                                                                   layerWidth, layerHeight));
            var currentCoordinate = new IntCoordinate(0, 0);
            var orthoGradient = new Coordinate<double>(-gradient.YMagnitude*windowDelta,
                                                       gradient.XMagnitude*windowDelta);
            for (int i = windowDelta; i < layerWidth - windowDelta; i++)
            {
                for (int j = windowDelta; j < layerHeight - windowDelta; j++)
                {
                    if (j == sourceRect.Y1 + windowDelta && i == sourceRect.X1 + windowDelta)
                    {
                        continue;
                    }
                    currentCoordinate.X = i;
                    currentCoordinate.Y = j;
                    var currentRgnRect = currentCoordinate.PointCenteredRectangle(windowSize);
                    var dist = RegionDistance(adjustedSourceRect, currentRgnRect, layerPixels, selectionMask);
                    if (dist == null)
                    {
                        continue;
                    }
                    if (dist == 0)
                    {
                        return currentRgnRect;
                    }
                    if ((minDistance > dist || minRegionRect == null))
                    {
                        minDistance = (double) dist;
                        minRegionRect = currentRgnRect;
                    }
                }
            }

            return minRegionRect;
        }