yabridge/README.md

yabridge

Yet Another way to use Windows VST2 plugins in Linux VST hosts.

TODOs

There are a few things that should be done before releasing this, including:

• Implement missing features:
  • GUIs. Wine's XEmbed implementation is causing X11 draw calls to fail so there's probably something right. Right now GUIs do work if you disable the XEmbed messages or skip reparenting altogether, but that's of course not ideal.
• Fix implementation bugs:
  • KiloHearts plugins fail during initialization.
  • Serum crashes when closing bitwig (but otherwise exits just fine).
  • Melda plugins crash when opening their GUI.
• Add missing details if any to the architecture section.
• Document what this has been tested on and what does or does not work.
• Document wine32 support.

There are also some features that would be nice to implement but that I haven't had the need to implement yet. Let me know if any of these features are required for a plugin to run:

• Double precision audio (processDoubleReplacing).
• Vendor specific extensions (for instance, for Reaper).

Usage

There are two ways to use yabridge.

Symlinking (recommended)

The recommended way to use yabridge is through symbolic links. This allows you to update yabridge for all of your plugins in one go, and it also avoids having to install it globally.

You can either use the precompiled binaries from the GitHub releases section, or you could build yabridge directly from source. If you use the precompiled binaries, then simply extract them to ~/.local/share/yabridge or any other place in your home directory. If you choose to build from source, then you can directly use the binaries from the build/ directory. For the section below I'm going to assume you've placed the files in ~/.local/share/yabridge.

To set up yabridge for a VST plugin called ~/.wine/drive_c/Program Files/Steinberg/VstPlugins/plugin.dll, simply create a symlink from ~/.local/share/yabridge/libyabridge.so to ~/.wine/drive_c/Program Files/Steinberg/VstPlugins/plugin.so like so:

ln -s ~/.local/share/yabridge/libyabridge.so "$HOME/.wine/drive_c/Program Files/Steinberg/VstPlugins/plugin.so"

For instance, if you wanted to set up yabridge for any of the VST plugins under ~/.wine/drive_c/Program Files/Steinberg/VstPlugins, you could do something like this:

find "$HOME/.wine/drive_c/Program Files/Steinberg/VstPlugins" -type f -iname '*.dll' -print0 \
  | sed -z 's/\.dll$/.so/' \
  | xargs -0 -n1 ln -sf ~/.local/share/yabridge/libyabridge.so

Copying

It's also possible to use yabridge by making copies of libyabridge.so instead of creating symlinks. This is not recommended as it makes updating a hassle. If you choose to do this, then you'll have to make sure yabridge-host.exe and yabridge-host.exe.so are somewhere in your search path as otherwise yabridge won't know where to find them. Either copy them to /usr/local/bin (not recommended) or to ~/.local/bin and make sure that the directory is in your PATH environment variable.

Building

To compile yabridge, you'll need Meson and the following dependencies:

• gcc (tested using GCC 9.2)
• A Wine installation with wiengcc and the development headers.
• Boost
• xcb

The following dependencies are included as a Meson wrap:

• bitsery

The project can then be compiled as follows:

meson setup --buildtype=release --cross-file cross-wine64.conf build
ninja -C build

When developing or debugging yabridge you can change the build type to either debug enable debug symbols and disable optimizations.

Debugging

Wine's error messages and warning are typically very helpful whenever a plugin doesn't work right away. Sadly this information is not always available. For instance Bitwig hides a plugin's STDOUT and STDERR streams from you. To make it easier to debug malfunctioning plugins, yabridge offers two environment variables:

• YABRIDGE_DEBUG_FILE=<path> allows you to write the Wine VST host's STDOUT and STDERR messages to a file. For example, you could launch your DAW with env YABRIDGE_DEBUG_FILE=/tmp/yabridge.log <daw>, and then use tail -F /tmp/yabridge.log to keep track of that file. If this option is not absent then yabridge will write its debug messages to STDERR instead.

• YABRIDGE_DEBUG_LEVEL={0,1} allows you to set the verbosity of the debug information. Every level increases the verbosity of the debug information:

  • A value of 0 (the default) means that yabridge will only output messages from the Wine process and some basic information such as the plugin being loaded and the wineprefix being used.
  • A value of 1 will log information about all events and function calls being sent between the VST host and the plugin. This can be very verbose but it makes it easier to see if yabridge is handling things incorrectly.

  More detailed information about these levels can be found in src/common/logging.h.

Attaching a debugger

When needed, I found the easiest way to debug the plugin to be to load it in an instance of Carla with gdb attached:

env YABRIDGE_DEBUG_FILE=/tmp/yabridge.log YABRIDGE_DEBUG_LEVEL=1 carla --gdb

Doing the same thing for the Wine VST host can be a bit trick., You'll need to launch winedbg in a seperate detached terminal emulator so it doesn't with the plugin, and winedbg can be a bit picky in the arguments it accepts. I've already set this up behind a feature flag for KDE Plasma. Other desktop environments and window managers will require some slight modifications in src/plugin/host-bridge.cpp. To enable this, simply run:

meson configure build --buildtype=debug -Duse-winedbg=true

Rationale

I started this project because the alternatives were either unmaintained, not self-contained or very difficult to work with. With this implementation I'd like to prioritize maintainability and correctness, with performance being a secondary goal. Please let me know if you have any suggestions on how to improve this!

Architecture

The project consists of two components, a Linux native VST plugin (libyabridge.so) and a VST host that runs under Wine (yabridge-host.exe/yabridge-host.exe.so). I'll refer to a copy of or a symlink to libyabridge.so as the plugin, the native Linux VST host that's hosting the plugin as the native VST host, the Wine VST host that's hosting a Windows .dll file as the Wine VST host, and the Windows VST plugin that's loaded in the Wine VST host is simply the Windows VST plugin. The whole process works as follows:

1. Some copy of or a symlink to libyabridge.so gets loaded as a VST plugin in a Linux VST host. This file should have been renamed to match a Windows VST plugin .dll file in the same directory. For instance, if there's a Serum_x64.dll file you'd like to bridge, then there should be a symlink to libyabridge.so named Serum_x64.so.

2. The plugin first attempts to locate:

   • The location of yabridge-host.exe. For this it will first search for the file either alongside libyabridge.so. This is useful for development, as it allows you to use a symlink from the build directory to cause yabridge to use the yabridge-host.exe from that same build directory. If this file can't be found, then it will fall back to searching through the search path.
   • The wine prefix plugin is located in.
   • The corresponding Windows VST plugin .dll file.

3. The plugin then sets up a Unix domain socket endpoint to communicate with the Wine VST host somewhere in a temporary directory and starts listening on it. I chose to use Unix domain sockets rather than shared memory because this way you get low latency communication with without any busy waits or manual synchronisation for free. The added benefit is that it also makes it possible to send arbitrarily large data without having to split it up into chunks first, which is useful for transmitting audio and preset data which may have any arbitrary size.

4. The plugin launches the Wine VST host in the detected wine prefix, passing the name of the .dll file it should be loading and the path to the Unix domain socket that was just created.

5. Communication gets set up using multiple sockets over the same end point. This allows us to use blocking read operations from multiple threads to handle multiple different events without the risk of receiving packets in the wrong order. The following types of events get assigned a socket:

   • Calls from the native VST host to the plugin's dispatch() function. These get forwarded to the Windows VST plugin through the Wine VST host.

   • Calls from the native VST host to the plugin's dispatch() function with opcode=effProcessEvents. These get forwarded to the Windows VST plugin through the Wine VST host. This has to be handled separately from all other events because of limitations of the Win32 API. Otherwise the plugin would not receive any midi events while the GUI is being resized or a dropdown menu or message box is open.

   • Host callback calls from the Windows VST plugin loaded into the Wine VST host through the audioMasterCallback function. These get forwarded to the native VST host through the plugin.

     Both the dispatch() and audioMasterCallback() functions are handled in the same way, with some minor variations on how payload data gets serialized depending on the opcode of the event being sent.

   • Calls from the native VST host to the plugin's getParameter() and setParameter() functions. Both functions get forwarded to the Windows VST plugin through the Wine VST host using a single socket because they're very similar and don't need any complicated behaviour.

   • Calls from the native VST host to the plugin's process() and processReplacing() functions. Both functions get forwarded to the Windows VST plugin through the Wine VST host using a single socket. The process() function has been deprecated, so a VST host will never call it if processReplacing() is supported by the plugin.

   • Updates of the Windows VST plugin's AEffect object. This object tells the host about the plugin's capabilities. A copy of this is sent over a socket from the Wine VST hsot to the plugin after it loads the Windows VST plugin so it can return a pointer to it to the native VST host. Whenever this struct updates, the Windows VST plugin will call the audioMasterIOChanged host callback and we'll repeat this process.

   The operations described above are all handled by first serializing the function parameters and any payload into an object before they can be sent over a socket. The objects used for encoding both the requests and and the responses for theses events can be found in src/common/communication.h along with functions that read and write these objects over streams and sockets. The actual binary serialization is handled using bitsery.

   Sending and receiving events happen in the send_event() and passthrough_event() functions. The passthrough_event() function calls the callback functions and handles the marshalling between our data types and the VST API's different pointer types. Reading data and writing the results back for host-to-plugin dispatcher() calls and for plugin-to-host audioMaster() callbacks happen in the DispatchDataConverter and HostCallbackDataConverter classes respectively, with a bit of extra glue for GUI related operations in PluginBridge::dispatch_wrapper. Rewriting all of this tightly coupled logic to be all in one place sadly only makes things even more complicated.

6. The Wine VST host loads the Windows VST plugin and starts forwarding messages over the sockets described above.

7. After the Windows VST plugin has started loading we will forward all values from the plugin's AEffect struct to the Linux native VST plugin using the socket described above. After this point the plugin will stop blocking and has finished loading.