C#

Daniel Weschke

November 20, 2019

1 Desktop application - transparent, click-throgh, always on top, graphics

Visual Studio 2019 File / New / Project… / C# - Windows Forms-App (.NET Framework)

Note: .exe created with a “Windows Forms App (.NET Core)” project are not standalone, see also https://stackoverflow.com/a/44201386.

WindowsFormsApp1/WindowsFormsApp1/Form1.cs

using System.Drawing;
using System.Windows.Forms;

namespace WindowsFormsApp1
{
    public partial class Form1 : Form
    {
        public Form1()
        {
            // https://stackoverflow.com/a/11152884
            this.TopMost = true;                                               // make the form always on top
            this.FormBorderStyle = System.Windows.Forms.FormBorderStyle.None;  // hidden border
            this.WindowState = FormWindowState.Maximized;                      // maximized (fullscreen; overflows the taskbar)
            this.MinimizeBox = this.MaximizeBox = false;                       // not allowed to be minimized
            //this.MinimumSize = this.MaximumSize = this.Size;                   // not allowed to be resized. this. size is not full size (e. g. 800x450) therefore see below
            this.MinimumSize = this.MaximumSize;                               // not allowed to be resized
            this.TransparencyKey = this.BackColor = Color.Red;                 // the color key to be transparent, choose a color that you do not use
        }

        // override CreateParams to set the Window Form click-through
        protected override CreateParams CreateParams
        {
            get
            {
                CreateParams cp = base.CreateParams;
                // Set the form click-through
                cp.ExStyle |= 0x80000 /* WS_EX_LAYERED */ | 0x20 /* WS_EX_TRANSPARENT */;
                return cp;
            }
        }

        // draw on the Windows Form
        protected override void OnPaint(PaintEventArgs e)
        {
            base.OnPaint(e);
            // draw what you want
            Pen p = new Pen(Brushes.Blue, 2);
            int x = 1143;
            int y = 623;
            int w = 20;
            e.Graphics.FillEllipse(Brushes.Blue, x - 4 / 2, y - 4 / 2, 4, 4);
            e.Graphics.DrawEllipse(p, x - w / 2, y - w / 2, w, w);
        }
    }
}

Create .exe file by changing from Debug to Release and click start. The .exe can be found in WindowsFormsApp1/WindowsFormsApp1/bin/Release/WindowsFormsApp1.exe.