How do I prevent clipping when rotating an image in C#?

Question

I just went through a bunch of stuff trying to figure out how to get the image to even rotate. That works but now it\'s clipping and I\'m not really sure how to make it stop

Answer 1

A rotated image may require a larger bitmap to be contained without clipping. A fairly simple way to compute the bounds is to apply the transformation matrix to the corners of the original bounding rectangle. Since the new bitmap is larger, the original image must be drawn such that it is centered, rather than at (0,0).

This is demonstrated in the following revision to your code:

public static Image RotateImage(Image img, float rotationAngle)
{
    int minx = int.MaxValue, maxx = int.MinValue, miny = int.MaxValue, maxy = int.MinValue;

    using (Bitmap bmp = new Bitmap(1, 1)) // Dummy bitmap, so we can use TransformPoints to figure out the correct size.
    {
        using (Graphics g = Graphics.FromImage(bmp))
        {
            g.TranslateTransform((float)img.Width / 2, (float)img.Height / 2);
            g.RotateTransform(rotationAngle);
            g.TranslateTransform(-(float)img.Width / 2, -(float)img.Height / 2);

            Point[] pts = new Point[4];
            pts[0] = new Point(0, 0);
            pts[1] = new Point(img.Width, 0);
            pts[2] = new Point(img.Width, img.Height);
            pts[3] = new Point(0, img.Height);
            g.TransformPoints(CoordinateSpace.Device, CoordinateSpace.World, pts);

            foreach (Point pt in pts)
            {
                minx = Math.Min(minx, pt.X);
                maxx = Math.Max(maxx, pt.X);
                miny = Math.Min(miny, pt.Y);
                maxy = Math.Max(maxy, pt.Y);
            }
        }
    }

    Bitmap bmp2 = new Bitmap(maxx - minx, maxy - miny);
    using (Graphics g = Graphics.FromImage(bmp2))
    {
        g.TranslateTransform((float)bmp2.Width / 2, (float)bmp2.Height / 2);
        g.RotateTransform(rotationAngle);
        g.TranslateTransform(-(float)bmp2.Width / 2, -(float)bmp2.Height / 2);
        g.InterpolationMode = InterpolationMode.HighQualityBicubic;
        g.DrawImage(img, bmp2.Width / 2 - img.Width / 2, bmp2.Height / 2 - img.Height / 2);
    }

    return bmp2;
}