A simple, direct, ultra-thin CLR library for high-performance Win32 Native Interop
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prasannavl Merge pull request #20 from mpolicki/fix/GetButton
Fixed MouseButtonPacket.GetButton() returning Middle instead of X
Latest commit 7404816 Jul 16, 2018



A simple, direct, ultra-thin CLR library for high-performance Win32 Native Interop

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    static int Main(string[] args)
        using (var win = Window.Create(text: "Hello"))
            return new EventLoop().Run(win);


Install-Package WinApi

Fully supports the CoreCLR. Uses C# 7 features like ref returns to achieve performance without losing semantic value.


TL;DR: WinForms Comparison

Direct message loop performance: 20-35% faster.
Heap allocation: 0MB vs. roughly, 0.75GB / 100k messages.
Memory page faults (Soft): 0.005% - A mere 5k vs. roughly 1 million faults/100k messages)


  • WinApi - The core package that contains all the methods, helpers, and the tiny WinApi.Windows namespace.
  • WinApi.Desktop - Desktop-only helpers.
  • WinApi.Utils - Provides utilities like NativePixelBuffer, DwmWindow etc.
  • WinApi.DxUtils - Provides DirectX utilities that ease the version management of SharpDX factories, and provides cohesive automatic device management to write DirectX application with just a few lines of code automatically managing device loss, device errors, etc.
  • WinApi.Windows.Controls [Incomplete] - A small library that implements the EventedWindowCore for standard classes like Static, Edit and also provides Window, which is just a helper to ease direct derivation of EventedWindowCore. This library is currently incomplete and just provides the implementations to serve as an example.

Note: - Starting from v4, all packages are of minimum netstandard 1.4, and Source nuget packages are no more. Desktop package is netstandard 2.0.


  • Ultra-light weight, extremely simple and tiny wrappers that can be used to create, manipulate or use windows extensively.
  • Zero GC allocations on during window messages, and event loop cycles.
  • Fundamental concepts similar to ATL/WTL, but in a C# idiomatic way.
  • NativeWindow class is a very thin Window class that processes no messages, and provides no extra functionality. Great for using with custom GUI toolkits, DirectX, OpenGL games.
  • NativeWindow can also be extended to work with any subclasses like Button, ComboBox, etc, with the same principles.
  • A GUI wrapper for Win32 that can work with CoreCLR.
  • Can be wrapped over any existing windows, just by using the handle.
  • Strict pay-only-for-what-you-use model.
  • Several different event loops depending on the need (For example, RealtimeEventLoop for games while the simple EventLoop is ideal for normal applications).


  • Every single method is hand-written from a combination of auto-generation from Windows SDK headers and MSDN, and tested for correctness.
  • Provide both safe (through helpers, and safety wrappers like SafeHandles, CriticalHandles), and unsafe wrappers (pure with minimal performance impact), in a clean way supplemented with inline documentation.
  • Provide a single DLL that can over time, be a direct equivalent of C/C++ windows.h header file for the CLR. Other Windows SDK wrappers may, or may not be in fragmented into separate packages.
  • Sufficient base to be able to write custom toolkits over Win32 based on Direct2D, Direct3D or even an external graphics library like Skia, without depending on WPF or WinForms - Examples of usage with Direct2D, 3D, Skia, OpenGL are all in the samples.
  • Always retain parity with the native API when it comes to constants (Eg: WS_OVERLAPPEDWINDOW, will never be changed to OverlappedWindow to look more like C#. The only exceptions: WM and VirtualKey - the message id, and virtual key constants for simpler usability).
  • WinApi.Windows - See below.
  • All structs, flags, should always have the names in the idiomatic C# style. (Eg: public enum WindowStyles { .. WS_OVERLAPPEDWINDOW = 0x00. }). Never WINDOWSTYLE, or MARGINS or RECT. Always Margin, Rectangle, etc. (It actually is surprisingly clean once drop the usual depencendies like WinForms, or WPF which always provide alternative forms).
  • Use variants such as int for Windows types like BOOL - to ensure minimum Marashalling impact when inside a structure. Using bool requires another copy, since bool in CLR is 1 byte, but the unmanaged variant could be 1, 2 or 4 bytes, depending on the context. However, when it comes to functions bool is used directly, since int conversion there is not only tedious but is bound to loose semantic value.

Secondary goals

  • Provide fully documented API (both from headers and MSDN, where-ever applicable) in the releases. Everything should be IntelliSense capable. No MSDN round-trips, while doing low level programming with CLR.


  • All methods in its minimal interop form (no SafeHandles, CriticalHandles, etc) unless absolutely required, for maximum micro-optimization of interop scenarios in the class with Methods suffix. (User32Methods, Kernel32Methods, DwmApiMethods, etc). Prefered to use int, uint etc inside the *Methods class to ensure parity with native APIs. Enums can be used for flags only if the value is a strictly well defined constant set. Otherwise prefer int, uint, etc. However, type safe wrappers can be supplemented in the Helpers.
  • All methods with handles, enums and other supplemented types go into Helpers (User32Helpers, Kernel32Helpers, etc).
  • Everything that uses undocumented APIs is maintained in a separate Experimental namespace similarly.

Why re-invent the wheel?

While there aren't many well defined reliable wrappers, there are a few - my favorite being Pinvoke (https://github.com/AArnott/pinvoke). While Goals above, should explain the reasons for re-inventing the wheel, it's also mostly a matter for coding style, and about having the ability to micro-optimize when you really need to.

Filesystem structure

--- LibraryName
    --  Types.cs (Structs, enums and other constants)
    --  Methods.cs (All direct native methods)
    --  Helpers.cs (All the helper methods with type safety wrappers)
    ##  Constants.cs (Optionally, if there are too many types, split constants (enums) from pure structs)


C/C++ Samples to serve as comparison standard:

C# Samples using WinApi:


  • Please follow the file structure detailed.
  • Please avoid batching up commits in your PRs. Keep pure Win32 methods, and constants in a separate one so they can easily be merged. (Anything that usually belongs in Methods.cs or Constants.cs)
  • Use your discretion to decide whether Helpers.cs, and/or any other library features require a separate PR as well. When in doubt, separate it out.
  • Beyond that feel free to follow your usual standards - feature/bugfix, etc based batching.

Community projects using WinApi

(This section is community editable. Please help yourself)

  • Chromely : Build .NET/.NET Core HTML5 desktop apps using cross-platform native GUI API.


Thanks to JetBrains for the OSS license of Resharper Ultimate.

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