How to display a control which (transparent) BackColor doesn't cover below controls?

Question

I have a custom Control:

public class Temp : Control
{
    public Temp(Color col, int x, int y)
    {
        Size = new Size(x + 10, y + 10);
        this.x = x;
        this.y = y;

        SetStyle(ControlStyles.SupportsTransparentBackColor, true);
        BackColor = col;
    }

    int x, y;

    protected override void OnPaint(PaintEventArgs e)
    {
        base.OnPaint(e);

        using (var p = new Pen(Color.Black, 3))
        {
            e.Graphics.DrawLine(p, new Point(10, 10), new Point(x, y));
        }
    }

}

And from the Load event of my Form I add two of these control to the Controls of a Panel I added as the only control of my Form:

panel1.Controls.Add(new Temp(Color.Red, 50, 50));
panel1.Controls.Add(new Temp(Color.Violet, 10, 100));

This is the output:

As you can see the first control cover the second one, while I'd want to display only the two lines, where the controls background color is transparent.

Note that using a transparent BackColor doesn't work:

panel1.Controls.Add(new Temp(Color.Transparent, 50, 50));
panel1.Controls.Add(new Temp(Color.Violet, 10, 100));

And this is the output:

How can I solve this problem? That is, display only (and completely) both my lines?

Answer 1

Instead of Inheriting from Control, create two points in your custom class. Sample code given below

using System;
using System.Collections.Generic;
using System.Drawing;
using System.Windows.Forms;

namespace SOWinForm
{
    public partial class Form1 : Form
    {
        List<Line> lines;
        public Form1()
        {
            InitializeComponent();
        }
        private void Form1_Load(object sender, EventArgs e)
        {
            lines = new List<Line>();
            lines.Add(new Line(){ StartPoint = new Point(10,10), EndPoint = new Point(10,100)});
            lines.Add(new Line() { StartPoint = new Point(10, 10), EndPoint = new Point(50, 50) });
        }

        protected override void OnPaint(PaintEventArgs e)
        {
            foreach (var line in lines)
            {
                using (var p = new Pen(Color.Black, 3))
                {
                    e.Graphics.DrawLine(p, line.StartPoint, line.EndPoint);
                }
            }
        }
    }

    public class Line
    {
        public Point StartPoint {get;set;}
        public Point EndPoint { get; set; }

        //Add Custom Properties
    }
}