如何获得图像位置？

Question

This is the code in the paint event of pictureBox1. I need to find the location of the variable mImage.

if (null != mImage)
{
    e.Graphics.DrawImage(mImage, theLocationOfImage);
}

mImage is Image type. Instead theLocationOfImage I need to put the mImage location. This is how I got the mImage:

private void pictureBox1_MouseWheel(object sender, MouseEventArgs e)
{
    Bitmap bmp = new Bitmap(pictureBox1.Image);
    Bitmap bmp1 = GetPartOfImageInRect(bmp, mRect);
    CalculateNewSizeFactor(e.Delta);
    Image img1 = ResizeImage(bmp1, 
        new Size((int)(bmp1.Width * currentfactor), 
           (int)(bmp1.Height * currentfactor)));
    mImage = img1;

    pictureBox1.Invalidate();
}

mRect is a rectangle I draw over the pictureBox1.

EDIT

This is how i draw the rectangle:

private void DrawRectangle(Graphics e)
        {
            using (Pen pen = new Pen(Color.Red, 2))
            {
                e.DrawRectangle(pen, mRect);
            }
        }

        private void pictureBox1_MouseDown(object sender, MouseEventArgs e)
        {
            mRect = new Rectangle(e.X, e.Y, 0, 0);
            pictureBox1.Invalidate();
        }

        private void pictureBox1_MouseMove(object sender, MouseEventArgs e)
        {
            if (e.Button == MouseButtons.Left)
            {
                mRect = new Rectangle(mRect.Left, mRect.Top, e.X - mRect.Left, e.Y - mRect.Top);
                pictureBox1.Invalidate();
            }
        }

This is the resize image method:

private Image ResizeImage(Image img, Size size)
        {
            return new Bitmap(img, size);
        }

And this is the pictureBox1 paint event:

if (null != mImage)
            {
                e.Graphics.DrawImage(mImage, theLocationOfImage);
            }
            DrawRectangle(e.Graphics);

And last the calculate new size factor method:

private void CalculateNewSizeFactor(int delta)
        {
            if (delta > 0 && factor < 2.5)
            {
                factor *= increment;
                currentfactor = factor;
            }
            else if (delta < 0 && factor > 0.25)
            {
                factor /= increment;
                currentfactor = factor;
            }
        }

I could resize zoom in out the whole image but i want to zoom in out only the area the rectangle is drawn over.

EDIT

Forgot to add this method:

private Bitmap GetPartOfImageInRect(Bitmap source, Rectangle rect)
        {
            return source.Clone(rect, source.PixelFormat);
        }

Answer 1

The problem when zooming is that the aspect ratio of the rectangle to be zoomed will probably be different from the aspect ratio of the whole image. Therefore you must consider two different cases.

// Calculate the size and position of the zoomed rectangle.
double zoomFactorX = picturBox1.Width / mRect.Width;
double zoomFactorY = picturBox1.Height / mRect.Height;
Size newSize;
Point newLocation;
if (zoomFactorX < zoomFactorY) { // Fit image portion horizontally.
    newSize = new Size(picturBox1.Width, (int)Math.Round(zoomFactorX * mRect.Height));

    // We have a top and a bottom padding.
    newLocation = new Point(0, (picturBox1.Height - newSize.Height) / 2);
} else {  // Fit image portion vertically.
    newSize = new Size((int)Math.Round(zoomFactorY * mRect.Width), picturBox1.Height);

    // We have a left and a right padding.
    newLocation = new Point((picturBox1.Width - newSize.Width) / 2, 0);
}