c# - Convert PictureBox Selection Rectangle according to SizeMode

Question

I have two PictureBoxes pbOriginal and pbFace. After Selecting a "face" from an image in pbOriginal I clone the rectangle selection and place it into pbFace. However, Because pbOriginal is using SelectionMode=Stretch the actual area being copied is not the same as the area being selected.

How do I convert the coordinates of the Rectangle so that they truly reflect the coordinates of the Stretched Image?

Answer 1

Here is an example that draws the second rectangle right along as you draw the first one..:

Point mDown = Point.Empty;
Point mCurr = Point.Empty;

private void pictureBox1_MouseDown(object sender, MouseEventArgs e)
{   mDown = e.Location;  }

private void pictureBox1_MouseMove(object sender, MouseEventArgs e)
{
    if (e.Button == System.Windows.Forms.MouseButtons.Left)
       { mCurr = e.Location; pictureBox1.Invalidate(); }
}

private void pictureBox1_Paint(object sender, PaintEventArgs e)
{
    Rectangle r = new Rectangle(mDown.X, mDown.Y, mCurr.X - mDown.X, mCurr.Y - mDown.Y);
    e.Graphics.DrawRectangle(Pens.Orange, r);
    pictureBox2.Invalidate();
}

private void pictureBox2_Paint(object sender, PaintEventArgs e)
{
    if (pictureBox2.Image == null) return;

    float stretch1X = 1f * pictureBox1.Image.Width / pictureBox1.ClientSize.Width;
    float stretch1Y = 1f * pictureBox1.Image.Height / pictureBox1.ClientSize.Height;

    int x = (int)(mDown.X * stretch1X);
    int y = (int)(mDown.Y * stretch1Y);
    int x2 = (int)(mCurr.X * stretch1X);
    int y2 = (int)(mCurr.Y * stretch1Y);

    Rectangle r = new Rectangle(x, y, x2 - x, y2 - y);
    e.Graphics.DrawRectangle(Pens.Orange, r);
}

Note that it assumes that you are drawing top-left to bottom-right..

If you want to copy the selection you can use the same factors and the same Rectangle as the source for a DrawImage call:

float stretch1X = 1f * pictureBox1.Image.Width / pictureBox1.ClientSize.Width;
float stretch1Y = 1f * pictureBox1.Image.Height / pictureBox1.ClientSize.Height;

Point pt = new Point((int)(mDown.X * stretch1X), (int)(mDown.Y * stretch1Y));
Size sz = new Size((int)((mCurr.X - mDown.X) * stretch1X), 
                   (int)((mCurr.Y - mDown.Y) * stretch1Y));


Rectangle rSrc = new Rectangle(pt, sz);
Rectangle rDest= new Rectangle(Point.Empty, sz);

Bitmap bmp = new Bitmap(sz.Width, sz.Height);
using (Graphics G = Graphics.FromImage(bmp))
    G.DrawImage(pictureBox1.Image, rDest, rSrc , GraphicsUnit.Pixel);
pictureBox2.Image = bmp;

You may want to code the MouseUp event to store the finla mCurr position and trgger the copying..