Example Windower IPC implementation in C#. To use, load the `Eval` addon and simply register the IPC event with `//eval windower.register_event('ipc message', print)`.

Program.cs

using System;
using System.Diagnostics;
using System.IO.MemoryMappedFiles;
using System.Linq;
using System.Text;
using System.Threading;
using static System.Console;

namespace WindowerIpc;

internal class Program {
	private const String Character = "Arcon";
	private const String Addon = "eval";
	private const String Text = "Test";

	private static void Main() {
		if (Addon.Length >= 0x20) {
			WriteLine("Addon name too long.");
			return;
		}

		if (Text.Length >= 0x1000 - 0x20 - 0x20) {
			WriteLine("Text too long.");
			return;
		}

		var pol = Process.GetProcessesByName("pol").FirstOrDefault(process => process.MainWindowTitle == Character);
		if (pol == null) {
			WriteLine("Target process not found.");
			return;
		}

		using var mutex = new Mutex(false, $@"Local\Windower Mutex IPC");
		using var ev = EventWaitHandle.OpenExisting($@"Local\Windower Event {pol.Id}");
		using var processesMmf = MemoryMappedFile.OpenExisting(@"Local\Windower MMF Instances", MemoryMappedFileRights.ReadWrite);
		using var messagesMmf = MemoryMappedFile.OpenExisting($@"Local\Windower MMF {pol.Id}", MemoryMappedFileRights.Write);

		mutex.WaitOne();

		var processes = processesMmf.CreateViewAccessor(0, 12 * 100, MemoryMappedFileAccess.ReadWrite);
		var (processOffset, processId, processIndex) = Enumerable.Range(0, 100)
			.Select(index => index * 12)
			.Select(offset => (offset, ProcessId: processes.ReadUInt32(offset), processes.ReadUInt32(offset + 0x08)))
			.First(process => process.ProcessId == pol.Id);

		var messages = messagesMmf.CreateViewAccessor(0, 0, MemoryMappedFileAccess.Write);
		var messageOffset = 0x1000 * (processIndex % 0x10);

		var utf8 = Encoding.UTF8;
		var addon = utf8.GetBytes(Addon);
		var text = utf8.GetBytes(Text);
		messages.WriteArray(messageOffset + 0x00, addon, 0, addon.Length);
		messages.WriteArray(messageOffset + 0x20, addon, 0, addon.Length);
		messages.WriteArray(messageOffset + 0x40, text, 0, text.Length);

		processes.Write(processOffset + 0x08, processIndex + 1);

		ev.Set();

		mutex.ReleaseMutex();
	}
}