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Question

I have a form where I place a panel. In this panel I add some pictureboxes. My problem is that I want to draw lines inside this panel that can overlay the other controls (pictureboxes). The lines must be at the panel bounds

I tried to draw on form above controls overriding WS_CLIPCHILDREN value with the code below.

const int WS_CLIPCHILDREN = 0x02000000;


    protected override CreateParams CreateParams
    {
        get
        {
            CreateParams cp = base.CreateParams;
            cp.Style &= ~WS_CLIPCHILDREN;
            //cp.Style &= ~0x04000000; //WS_CLIPSIBLINGS
            //cp.ExStyle |= 0x00000020; //WS_EX_TRANSPARENT  
            //cp.Style &= 0x7DFFFFFF;

            return cp;
        }
    }

The problem is occured when the panel scrollbars appear. The code where i draw is on Form1_Paint event and when I scroll the panel, all of the lines spread in the whole form.

   private void panel3_Paint(object sender, PaintEventArgs e)
    {
        for (int i = 0; i < from.Count; i++)
        {
            AdjustableArrowCap bigarrow = new AdjustableArrowCap(5, 5);
            Pen pen = new Pen(Color.Black, 3);
            pen.StartCap = System.Drawing.Drawing2D.LineCap.Round;
            pen.CustomEndCap = bigarrow;
            Graphics g;
            g = this.CreateGraphics();
            g.DrawLine(pen, from[i].X - panel3.HorizontalScroll.Value, from[i].Y - panel3.VerticalScroll.Value, to[i].X - panel3.HorizontalScroll.Value, to[i].Y - panel3.VerticalScroll.Value);
        }
    }

The from & to arrays are two List variables where i save the position where the line should start and end. See the pictures below:

I don't want those lines in the red circle to show any idea?

Answer 1

Try to use the Graphics object that comes with arguments of the Paint event rather than creating own graphics.

so that you'd have:

private void panel3_Paint(object sender, PaintEventArgs e)
{
    for (int i = 0; i < from.Count; i++)
    {
        AdjustableArrowCap bigarrow = new AdjustableArrowCap(5, 5);
        Pen pen = new Pen(Color.Black, 3);
        pen.StartCap = System.Drawing.Drawing2D.LineCap.Round;
        pen.CustomEndCap = bigarrow;

        var g = e.Graphics;
        g.DrawLine(pen, from[i].X - panel3.HorizontalScroll.Value, from[i].Y - panel3.VerticalScroll.Value, to[i].X - panel3.HorizontalScroll.Value, to[i].Y - panel3.VerticalScroll.Value);
    }
}