Program.cs

using System;
using System.Diagnostics;
using System.IO;
using Microsoft.Win32;

class Program
{
    // The name of the configuration file.
    const string ConfigFileName = "config.txt";

    static void Main()
    {
        // Get the directory where the launcher executable is located.
        string launcherDirectory = AppDomain.CurrentDomain.BaseDirectory;

        // Combine the directory with the config file name to get the full path.
        string configFilePath = Path.Combine(launcherDirectory, ConfigFileName);

        // Check if the config file exists. If not, inform the user and exit.
        if (!File.Exists(configFilePath))
        {
            Console.WriteLine($"Error: The configuration file '{ConfigFileName}' was not found at '{configFilePath}'.");
            Console.WriteLine("Please ensure the config.txt file is in the same directory as the launcher.");
            Console.ReadKey(); // Wait for user input before closing.
            return;
        }

        try
        {
            // Read all lines from the configuration file.
            string[] configLines = File.ReadAllLines(configFilePath);
            string gamePath = null;
            string gpuValue = null;

            // Parse the configuration lines to find the game path and GPU value.
            foreach (string line in configLines)
            {
                // Clean up the line by trimming whitespace.
                string trimmedLine = line.Trim();

                // Skip empty or comment lines.
                if (string.IsNullOrEmpty(trimmedLine) || trimmedLine.StartsWith("#"))
                {
                    continue;
                }

                // Split the line at the first '=' to separate the key and value.
                int separatorIndex = trimmedLine.IndexOf('=');
                if (separatorIndex > 0)
                {
                    string key = trimmedLine.Substring(0, separatorIndex).Trim();
                    string value = trimmedLine.Substring(separatorIndex + 1).Trim();

                    if (key.Equals("path", StringComparison.OrdinalIgnoreCase))
                    {
                        gamePath = value;
                    }
                    else if (key.Equals("gpu", StringComparison.OrdinalIgnoreCase))
                    {
                        gpuValue = value;
                    }
                }
            }

            // Check if both the game path and GPU value were found.
            if (string.IsNullOrEmpty(gamePath) || string.IsNullOrEmpty(gpuValue))
            {
                Console.WriteLine("Error: The config.txt file is missing 'path' or 'gpu' values.");
                Console.ReadKey();
                return;
            }

            // Construct the full path to the game executable.
            string fullGamePath = Path.Combine(launcherDirectory, gamePath);

            // Check if the game executable exists.
            if (!File.Exists(fullGamePath))
            {
                Console.WriteLine($"Error: The game executable '{fullGamePath}' was not found.");
                Console.WriteLine("Please check the 'path' value in your config.txt file.");
                Console.ReadKey();
                return;
            }

            // This is the correct registry key for all GPU preferences.
            string registryKey = @"Software\Microsoft\DirectX\UserGpuPreferences";

            // This is the correct value name, which is the full path to the executable.
            string registryValueName = fullGamePath;

            // This is the correct value data string.
            string registryValueData = $"GpuPreference={gpuValue};";

            // Use the correct key and value to set the preference.
            // CreateSubKey will create the key if it does not exist.
            using (RegistryKey userKey = Registry.CurrentUser.CreateSubKey(registryKey, true))
            {
                // Set the value with the full path as the name and the preference string as the data.
                userKey.SetValue(registryValueName, registryValueData, RegistryValueKind.String);
            }

            Console.WriteLine($"Successfully set GPU preference for '{fullGamePath}'.");

            // Start the game process.
            Process.Start(fullGamePath);

        }
        catch (FileNotFoundException ex)
        {
            Console.WriteLine($"Error: File not found. Details: {ex.Message}");
            Console.ReadKey();
        }
        catch (FormatException ex)
        {
            Console.WriteLine($"Error: The 'gpu' value in config.txt is not a valid number. Details: {ex.Message}");
            Console.ReadKey();
        }
        catch (Exception ex)
        {
            Console.WriteLine($"An unexpected error occurred: {ex.Message}");
            Console.WriteLine("Please ensure you have the necessary permissions to modify the Windows Registry.");
            Console.ReadKey();
        }
    }
}