Paint Certain Areas inside of a Picture Box C#

Question

I'm using WinForms. In my form i have a picturebox with an image. How can i paint the picturebox but not the area inside the expanding square. Here is my code. Currently i could create the expanding square but i don't know how to paint the picturebox white outside of that square.

    int _cropX, _cropY, _cropWidth, _cropHeight;
    private State _currentState;

    private void pictureBox1_MouseMove(object sender, MouseEventArgs e)
    {
        if (Crop_Checkbox.Checked == true)
        {
            if (_currentState == State.Crop)
            {
                Cursor = Cursors.Cross;
                if (e.Button == System.Windows.Forms.MouseButtons.Left)
                {
                    //X and Y are the coordinates of Crop
                    pictureBox1.Refresh();
                    _cropWidth = e.X - _cropX;
                    _cropHeight = e.Y - _cropY;
                    pictureBox1.CreateGraphics().DrawRectangle(_cropPen, _cropX, _cropY, _cropWidth, _cropHeight);
                }

            }
        }
        else
        {
            Cursor = Cursors.Default;
        }
    }

    private void Crop_Checkbox_CheckedChanged(object sender, EventArgs e)
    {
        if (Crop_Checkbox.Checked == true)
        {
            this.Cursor = Cursors.Cross;
        }
    }

    private void pictureBox1_MouseDown(object sender, MouseEventArgs e)
    {
        if (Crop_Checkbox.Checked == true)
        {
            if (_currentState == State.Crop)
            {
                if (e.Button == System.Windows.Forms.MouseButtons.Left)
                {
                    Cursor = Cursors.Cross;
                    _cropX = e.X;
                    _cropY = e.Y;

                    _cropPen = new Pen(Color.FromArgb(153, 180, 209), 3); //2 is Thickness of line

                    _cropPen.DashStyle = DashStyle.DashDotDot;
                    pictureBox1.Refresh();
                }
            }
        }
        else
        {
            Cursor = Cursors.Default;
        }
    }

    public Pen _cropPen;

    private enum State
    {
        Crop
    }

    private void pictureBox1_MouseUp(object sender, MouseEventArgs e)
    {

        if (Crop_Checkbox.Checked == true)
        {
          //Paint picturebox...

        }
        else
        {
            Cursor = Cursors.Default;
        }

   }

score 1 · Accepted Answer · edited May 23 '17 at 12:30

This is best done with a GraphicsPath:

using System.Drawing.Drawing2D;
..

private void pictureBox1_Paint(object sender, PaintEventArgs e)
{
    Rectangle r1 = pictureBox1.ClientRectangle;  // note I don't use width or height!
    Rectangle r2 = new Rectangle(50, 30, 80, 40);
    GraphicsPath gp = new GraphicsPath(FillMode.Alternate);
    gp.AddRectangle(r1);  // first the big one
    gp.AddRectangle(r2);  // now the one to exclude
    e.Graphics.FillPath( Brushes.Gold, gp);
}

Note that I..

..use the Paint event for persistent grphics
..only paint onto the surface of the PictureBox, not into its image. See here for the difference!
You can add more rectangles or other shapes to exclude.

If you want image and surface combined, either draw into the image or ask the PictureBox to DrawToBitmap..

Thank you Taw, for always explaining things : ) – taji01 Feb 10 '16 at 09:26 — taji01, Feb 10 '16 at 09:26

Paint Certain Areas inside of a Picture Box C#

1 Answers1