Image function zoom and rotate

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C#

image

picturebox

Hey guys,
I originally posted this on Stack Overflow but after a few minutes realized the whole community is pretty much toxic, unhelpful and unwelcoming. So I thought id try posting my question here instead :)

So here is the issue, I have found 2 different code snippets on the internet related to what I need to do but I cannot successfully merge the snippets in the way I need.

So essentially I have this as my base: Rotate a picture in C# - C# HelperC# Helper[^] this code works great for my rotation and even has zooming, however the zoom will only work from the top left corner which doesnt work for my situation.

What I want to be able to do is to keep the rotation function but to be able to zoom in and out of a specified point on the image. When it comes to matrix operations it just goes all over my head tbh.

What I have tried:

  // Display the image at the current rotation and scale.
private void DisplayImage()
{
    if (OriginalImage == null) return;
    RotatedImage = null;
    picRotatedImage.Visible = false;

    float angle;
    if (!float.TryParse(txtAngle.Text, out angle)) return;

    // Find the size of the image's rotated bounding box.
    Matrix rotation = new Matrix();
    rotation.Rotate(angle);
    int old_wid = OriginalImage.Width;
    int old_hgt = OriginalImage.Height;
    PointF[] points =
    {
        new PointF(0, 0),
        new PointF(old_wid, 0),
        new PointF(0, old_hgt),
        new PointF(old_wid, old_hgt),
    };
    rotation.TransformPoints(points);
    float[] xs =
        { points[0].X, points[1].X, points[2].X, points[3].X };
    float[] ys =
        { points[0].Y, points[1].Y, points[2].Y, points[3].Y };
    int new_wid = (int)(xs.Max() - xs.Min());
    int new_hgt = (int)(ys.Max() - ys.Min());

    // Make the rotated image.
    RotatedImage = new Bitmap(new_wid, new_hgt);
    using (Graphics gr = Graphics.FromImage(RotatedImage))
    {
        gr.TranslateTransform(-old_wid / 2, -old_hgt / 2,
            MatrixOrder.Append);
        gr.RotateTransform(angle, MatrixOrder.Append);
        gr.TranslateTransform(new_wid / 2, new_hgt / 2,
            MatrixOrder.Append);
       // MY ATTEMPT AT SCALING
       float newScale = Math.Min(Math.Max(m_dZoomscale + (zoomIn ? s_dScrollValue : -s_dScrollValue), 0.1f), 10);
       float adjust = newScale / m_dZoomscale;
       m_dZoomscale = newScale;
    ///HERE
    gr.ScaleTransform(adjust, adjust, MatrixOrder.Append);
    ////

        RectangleF source_rect = new RectangleF(0, 0,
            OriginalImage.Width, OriginalImage.Height);
        PointF[] dest_points =
        {
            new PointF(0, 0),
            new PointF(OriginalImage.Width, 0),
            new PointF(0, OriginalImage.Height),
        };
        gr.DrawImage(OriginalImage, dest_points, source_rect,
            GraphicsUnit.Pixel);
    }

    // Scale the output PictureBox.
    SetPictureBoxSize();

    // Display the result.
    picRotatedImage.Image = RotatedImage;
    picRotatedImage.Visible = true;
}