C# - Windows Form Game Overlay 8/19/2019

using System;
using System.Collections.Generic;
using System.ComponentModel;
using System.Data;
using System.Drawing;
using System.Text;
using System.Windows.Forms;
using System.Runtime.InteropServices;
using System.Threading;

namespace diwifgc
{
    public partial class Form1 : Form
    {



        public const string gamename = "Subnautica"; // Change this to your game's window name!!!

        //Including WINApi functions. You can find those on PInvoke.net
        [DllImport("user32.dll", EntryPoint = "FindWindow", SetLastError = true)]
        static extern IntPtr FindWindowByCaption(IntPtr ZeroOnly, string lpWindowName);

        [DllImport("user32.dll")]
        static extern int SetWindowLong(IntPtr hWnd, int nIndex, int dwNewLong);

        [DllImport("user32.dll", SetLastError = true)]
        static extern int GetWindowLong(IntPtr window, int index);
        IntPtr handle = FindWindowByCaption(IntPtr.Zero, gamename);

        [DllImport("user32.dll")]
        static extern IntPtr GetForegroundWindow();

        [DllImport("user32.dll", SetLastError = true)]
        static extern bool GetWindowRect(IntPtr hwnd, out RECT lpRect);

        // Making basic RECT struct for GetWindowRect function.
        public struct RECT
        {
            public int left, top, right, bottom;
        }

        // Making the graphics object.
        System.Drawing.Graphics g;

        RECT outrect;


        public Form1()
        {
            InitializeComponent();
        }

        private void Form1_Load(object sender, EventArgs e)
        {

            this.SetStyle(
            ControlStyles.AllPaintingInWmPaint |
            ControlStyles.UserPaint |
            ControlStyles.DoubleBuffer,
            true);

            this.FormBorderStyle = FormBorderStyle.None;
            this.BackColor = System.Drawing.Color.Black;
            this.TransparencyKey = System.Drawing.Color.Black;
            this.TopMost = true;

            /* Making the RECT object that will handle info from WINApi function. */

            /* Saving data to that object */
            GetWindowRect(handle, out outrect);

            /* Change the size of the form to the size of the Game window. */
            this.Size = new Size(outrect.right - outrect.left, outrect.bottom - outrect.top);

            this.Top = outrect.top;
            this.Left = outrect.left;

            /* Change the position of the form to the position of the Game window. */


            /* Change form's style to make it transparent and to remove the border */
            this.FormBorderStyle = FormBorderStyle.None;
            this.BackColor = System.Drawing.Color.Black;
            this.TransparencyKey = System.Drawing.Color.Black;

            /* Using WINApi function GetWindowLong and SetWindowLong to be able to click throught the form */
            int initialStyle = GetWindowLong(this.Handle, -20);
            SetWindowLong(this.Handle, -20, initialStyle | 0x80000 | 0x20);

            /* Make the form on top of other windows */
            this.TopMost = true;

            /* Change Form1 to your form's name if you have different.
            This is actually bad thing to do, but this will allow you to skip writing much code for our threading */
            Form1.CheckForIllegalCrossThreadCalls = false;

            Thread PrePaintThread = new Thread(new ThreadStart(prepaint));
            PrePaintThread.Start();



            //Thread stickThread = new Thread(new ThreadStart(stick));
            //stickThread.Start();

        }


        private void prepaint()
        {
            while (true)
            {

                this.Refresh();

                /* Refresh rate is 50ms */
                System.Threading.Thread.Sleep(50);

            }
        }
         /*
        public void stick()
        {
            while (true)
            {
                this.Top = outrect.top;
                this.Left = outrect.left;
            }
        }
        */


        private void Form1_Paint(object sender, PaintEventArgs e)
        {
            g = e.Graphics;
            painttext(g);
        }

        private void painttext(System.Drawing.Graphics g)
        {
            /* Make a new font object for drawing */
            Font bigFont = new Font("Arial", 20);
            /* Make a colored brush for drawing text */
            Brush mybrush = new SolidBrush(Color.White);
            /* Draw 'Hello, World' at position 50, 50 of the game window */
            g.DrawString("Hello, World!", bigFont, mybrush, 50, 50);
        }
    }
}