If I rotate a bitmap and want to keep track of a point on the original image as translated on the new image, how would I achieve this. I essentially want to know where the top right corner of the original image is on the new rotated and expanded image, so I can draw to a graphics surface in the correct location. I’m using the following code to rotate the bitmap (originally taken from another post).

      public static Bitmap RotateImage(Bitmap origBmp, float angle)
      {
         Matrix matrix = new Matrix();
         matrix.Translate(origBmp.Width / -2, origBmp.Height / -2, MatrixOrder.Append);
         matrix.RotateAt(angle, new Point(0, 0), MatrixOrder.Append);

         using (GraphicsPath graphicsPath = new GraphicsPath())
         {
            // Transform image points by rotation matrix
            graphicsPath.AddPolygon(new Point[]
            {
               new Point(0, 0),
               new Point(origBmp.Width, 0),
               new Point(0, origBmp.Height)
            });

            graphicsPath.Transform(matrix);
            PointF[] pts = graphicsPath.PathPoints;

            Rectangle boundingBox = BoundingBox(origBmp, matrix);
            Bitmap bmpDest = new Bitmap(boundingBox.Width, boundingBox.Height);

            using (Graphics graphicsDest = Graphics.FromImage(bmpDest))
            {
               Matrix matrixDest = new Matrix();
               matrixDest.Translate(bmpDest.Width / 2, bmpDest.Height / 2, MatrixOrder.Append);
               graphicsDest.Transform = matrixDest;
               graphicsDest.DrawImage(origBmp, pts);
            }

            return bmpDest;
         }
      }

      private static Rectangle BoundingBox(
         Image img,
         Matrix matrix)
      {
         GraphicsUnit gu = new GraphicsUnit();
         Rectangle imgRect = Rectangle.Round(img.GetBounds(ref gu));

         // Transform the four points of the image, to get the resized bounding box.
         Point topLeft = new Point(imgRect.Left, imgRect.Top);
         Point topRight = new Point(imgRect.Right, imgRect.Top);
         Point bottomRight = new Point(imgRect.Right, imgRect.Bottom);
         Point bottomLeft = new Point(imgRect.Left, imgRect.Bottom);

         Point[] points = new Point[]
         {
            topLeft,
            topRight,
            bottomRight,
            bottomLeft
         };

         GraphicsPath graphicsPath = new GraphicsPath(
            points,
            new byte[]
            {
               (byte)PathPointType.Start,
               (byte)PathPointType.Line,
               (byte)PathPointType.Line,
               (byte)PathPointType.Line
            });

         graphicsPath.Transform(matrix);
         return Rectangle.Round(graphicsPath.GetBounds());
      }

I’ve attempted to use the same translation approach to translate the point on the original image, but with no luck.