Draw symbols on the stretched image.

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Hi,

I need to draw symbols like 'O' and 'X' just with a mouse click on the stretched image. Am using PictureBox and windows form.
i tried something like this.

private void pictureBox1_MouseClick(object sender, MouseEventArgs e1)
        {
            if ((e1.Button & MouseButtons.Left) == MouseButtons.Left)
            {
                Bitmap b = (Bitmap)pictureBox1.Image;
                pictureBox1.Image = b;
                Graphics g = Graphics.FromImage(b);
                p = new Point(e1.X, e1.Y);
                Pen p3 = new Pen(Color.Red, 2);
                this.Text = p.ToString();
                g.DrawEllipse(p3, p.X, p.Y, 15, 15);
                pictureBox1.Invalidate();
            } 
}

Problem is the circle is drawn away from the mouse clicked point. I think its because of image stretch. Please help.

Posted 11-May-11 21:53pm

Deepurs

Updated 11-May-11 22:13pm

walterhevedeich

v2

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OriginalGriff · Accepted Answer · 2011-05-11T22:13:00

1) You need to declare "p":

Point p = new Point(e1.X, e1.Y);

2) You need to dispose of all the Graphics, and Pen objects you create - not doing that will cause problems later.
3) The start point for a Ellipse is always the top left corner: Try offseting them:

g.DrawEllipse(p3, p.X - 7, p.Y - 7, 15, 15);

From OP:
"pictureBox1.SizeMode = PictureBoxSizeMode.StretchImage;"

Now, that is relevant information!
When you use PictureBoxSizeMode.StretchImage you apply a transform too all graphics operations, to make them scale appropriatly into the re-sized image. You don't want that!

Instead use this:

//pictureBox1.SizeMode = PictureBoxSizeMode.StretchImage;
using (Image source = Image.FromFile(@"F:\Temp\BTC.jpg"))
    {
    Image resized = new Bitmap(source, pictureBox1.Size);
    pictureBox1.Image = resized;
    }

And modify your Mouse Click event as per the suggestions above:

private void pictureBox1_MouseClick(object sender, MouseEventArgs e)
    {
    if ((e.Button & MouseButtons.Left) == MouseButtons.Left)
        {
        Bitmap b = (Bitmap) pictureBox1.Image;
        pictureBox1.Image = b;
        using (Graphics g = Graphics.FromImage(b))
            {
            Point p = new Point(e.X, e.Y);
            using (Pen p3 = new Pen(Color.Red, 2))
                {
                this.Text = p.ToString();
                g.DrawEllipse(p3, p.X - 7, p.Y - 7, 15, 15);
                }
            }
        pictureBox1.Invalidate();
        }
    }

Seriously, not disposing of objects (particularly graphics related objects) causes unpredictable problems later on - it can be very hard to work out what the problem is if it doesn't occur until two weeks after you wrote and tested this code!