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Arwinss is an alternative implementation of the core Win32 subsystem components. Technical information about implementation details is available at this page: Arwinss technical.


Before continuing, I'd recommend a separate build folder for building Arwinss. Otherwise you'll have to revert the Arwinss changes and rebuild ReactOS.

Checkout the arwinss branch (cgit/github; git clone -b arwinss), into a folder that can really be anywhere. Copy the arwinss (and win32csr?) folder and trunk.diff into your dedicated build folder containing the "normal" ReactOS code. Apply trunk.diff and hope that it applies with no problem. Afterwards, you can compile using the normal build commands:

ninja bootcd
ninja livecd
ninja hybridcd

This will build a copy of trunk with the alternate subsystem enabled.

If you want to build the winex11 module, you must first copy the lib/3rdparty/libX11/libX11.a file from your working copy to the obj-i386/lib/3rdparty/libX11 directory (creating it if it does not exist). This will fix the winex11.drv linking issues, and you can just type

ninja winex11

to build this optional module.

If the patch fail to apply, watch this page for updates. You may also have some luck with applying it to its contemporary (~2015) ReactOS code and rebasing the newer changes in, in light of some changes to how the code is organized. (Most notably with win32csr being refactored and moved around.) Remember to post your updates here if you got it to work.


Arwinss uses parts of the Wine architecture and parts of Windows NT architecture in appropriate places and in a good way. The overall call flow / architecture of Arwinss looks like this:


It consists of the following modules, one of them being optional (winex11.drv):

  • arwinss/freetype – implements usermode font rendering (FreeType library, with small ReactOS glue), used by GDI32.DLL
  • arwinss/client/user32 – implements USER API, maps to wine dlls/user32
  • arwinss/client/gdi32 – implements GDI API,maps to wine dlls/gdi32
  • arwinss/client/winent.drv/winent.drv – implements native graphics and user drivers, ReactOS implemented
  • arwinss/client/winex11.drv/ – implements X11 X-windows graphics and user drivers, maps to wine dlls/winex11.drv
  • win32ss – implements kernel mode counter part of the native graphics driver, a Simple Window Manager (SWM) and a kernel mode USER server.
  • win32csr – implements needed parts of the CSR subsystem along with handling user input


Most of the hacking happens in WINENT.DRV and WIN32K.SYS, with very rare fixes to the user32/gdi32 (mainly, because it's a tested Wine's code with only minor changes).

Convention for marking changes. C++ code comments (//) mean that the place has some special mark up for debugging. A typical use is for a

// FIXME: Something

One of the things you may want to mess around with the old code may be swapping out the old wine for a new one, given how many new things they have implemented. For those who are interested, the current code is based on wine 1.3.13 and 1.1.36 depending on which parts you are looking at. The arrangement of dll directories mostly stays the same, but winex11.drv has gone over some rearrangements that might make your job harder. (Some of the REAL cool things, such as newer DX support for games, are outside of the scope of arwinss and should be tried directly on the master branch.)

Potential Benefits

These bugs would be fixed if Arwinss was ready (just a short list):

As one can see from these bug titles it mainly boils down to drastically improved user32 and gdi32 support.

TODO list

See full list of bugs at

  1. Fix redrawing issues (see bug #19) and (see bug #26)
  2. Fix crash that prevents booting in VirtualBox
  3. Fix installer/uninstaller crash (see bug #75)
  4. Fix garbage on desktop after closing some apps (see bug #63)
  5. Fix zoom and tabs in Firefox (see bug #76)
  6. Fix "Window titles are shown as inactive (gray) while being active" (see bug #7)
  7. Fix arwinss related program crashes (see bug #73))
  8. Fix interaction of windows in apps with few windows (see bug #32)
  9. Fix low level input hooks (used for example in DosBox)

Unimplemented/Fixme that appear during work

  1. fixme:(dll\win32\arwinss\winent.drv\userdrv.c:665) RosDrv_SetWindowStyle is UNIMPLEMENTED!
  2. fixme:(dll\win32\arwinss\winent.drv\userdrv.c:642) RosDrv_SetWindowIcon is UNIMPLEMENTED!
  3. (subsystems\win32\win32k_arwinss\wine\queue.c:814) TODO: Check if anyone is waiting on queue is missing!
  4. (subsystems\win32\win32k_arwinss\eng\device.c:927) FIXME: DeviceName is NULL, trying display nr. 1 (TuxRacer)
  5. fixme:(dll\win32\arwinss\winent.drv\userdrv.c:636) RosDrv_SetWindowRgn is UNIMPLEMENTED! (Reget)
  6. fixme:(dll\win32\arwinss\winent.drv\userdrv.c:626) RosDrv_SetLayeredWindowAttributes is UNIMPLEMENTED! (Qutim)
  7. err:(dll\win32\arwinss\winent.drv\gdidrv.c:353) ExtEscape for escape 8 is unimplemented! (SuperTux 0.3.3; ROS text screensaver)
  8. fixme:(dll\win32\arwinss\winent.drv\clipboard.c:2440) NTDRV_CLIPBOARD_IsSelectionOwner is UNIMPLEMENTED! (AbiWord. Notepad++)
  9. fixme:(dll\win32\arwinss\winent.drv\gdidrv.c:451) RosDrv_GetTextExtentExPoint is UNIMPLEMENTED!
  10. fixme:(dll\win32\arwinss\winent.drv\gdidrv.c:609) RosDrv_RealizePalette is UNIMPLEMENTED!
  11. fixme:(dll\win32\arwinss\winent.drv\gdidrv.c:959) RosDrv_UnrealizePalette is UNIMPLEMENTED!
  12. fixme:(dll\win32\arwinss\winent.drv\gdidrv.c:433) RosDrv_GetNearestColor is UNIMPLEMENTED!


You can get the latest ARWINSS ISO here.

See Also