LatencyFleX (LFX)

Vendor agnostic latency reduction middleware. An alternative to NVIDIA Reflex.

Why LatencyFleX?

To get an idea why queuing happens in video games and why it causes increased latency, watch this video.

To learn more about LatencyFleX's internals, check out the blog post.

Limitations

• LatencyFleX current does not provide any benefits when VSync is enabled.
  This is blocked on presentation timing support.
• LatencyFleX introduces jitter in frame time as a part of its algorithm, which results in microstutters.
  Though, most games tend to have a larger frame time fluctuation already, so this is likely unperceivable.

Known issues

• Minor stutters might happen.

  Tip: If you are using AMD GPUs, try modifying the power profile to reduce power management induced stutters: https://gitlab.freedesktop.org/drm/amd/-/issues/1500#note_1228253

• GPU utilization will be lower (around 95% when GPU bound).

• It might take one second or two to adapt to large frame rate increases (e.g. if the game sets a background frame limit).

Building from source

See docs/BUILDING.md

Usage

For now, LatencyFleX can be used on Linux through one of the following injection method. Game engine integration is planned.

Running games with LatencyFleX

Warning: Be careful when using LatencyFleX with games having anti-cheat:

• Direct hooking (UE4 hook) can trip the game's integrity check and directly get you banned.
• Proton NVAPI integration is relatively safe, but I am not responsible for any bans issued due to LatencyFleX.

Please do it at your own risk.

Tested games:

Game	Support	Method
Apex Legends 1	✅	Proton NVAPI
Titanfall 2 w/ Northstar	✅	Proton (Native)
Overwatch 1	✅	Proton NVAPI
Splitgate 2	❌	N/A
Ghostrunner	✅	Proton NVAPI
God of War	✅	Proton NVAPI
Spider-Man Remastered	✅	Proton NVAPI

Game supported but not in list? File a PR to update the table.

Proton NVAPI (for games that already have NVIDIA Reflex integration)

1. Install the Vulkan layer, wine extension and DXVK-NVAPI with LFX support.

2. Put the following in dxvk.conf ³. If you haven't created one, create it next to the game executable. If there are multiple executables, try copying and putting dxvk.conf next to every executable.

   dxgi.nvapiHack = False
   dxgi.customVendorId = 10de # If running on non-NVIDIA GPU

3. Launch with the following environment variables:

   PROTON_ENABLE_NVAPI=1 DXVK_NVAPI_DRIVER_VERSION=49729 DXVK_NVAPI_ALLOW_OTHER_DRIVERS=1 LFX=1 %command%

4. Don't forget to enable Reflex Low-Latency in-game.

Not working? See troubleshooting guide

UE4 Hook

Supported platforms: Linux (see note)

Note: for now, the UE4 hook only supports Linux UE4 builds with PIE disabled.

1. Install the Vulkan layer.

2. Obtain an offset to FEngineLoop::Tick. If the game ships with debug symbols, the offset can be obtained with the command:

   readelf -Ws PortalWars/Binaries/Linux/PortalWars-Linux-Shipping.debug | c++filt | grep FEngineLoop::Tick

   Find the line corresponding to the actual function (other entries are for types used in the function and unrelated):

   268: 00000000026698e0  9876 FUNC    LOCAL  HIDDEN    15 FEngineLoop::Tick()
   

   Here 26698e0 is the offset we need. We will call it <OFFSET> below.

3. Modify the launch command-line as follows.

   LFX=1 LFX_UE4_HOOK=0x<OFFSET> %command%

Unity Mod/Hook

Supported platforms: Proton, Linux

1. Install the Vulkan layer. Also install the Wine extension if the game runs on Wine/Proton.
2. Install BepInEx Bleeding Edge to the game directory.
3. Run the game once to generate BepInEx directory structure, config files and startup log. Obtain the Unity version from the first line of BepInEx/LogOutput.log.
4. Drop unity/<RUNTIME>-<VERSION>/LatencyFleX.dll (from release artifacts) into BepInEx/plugins. <RUNTIME> is mono or il2cpp. <VERSION> is:
   • 2018.1 for any version higher or equal to 2018.1 (This is currently unsupported for IL2CPP)
   • 2019.3 for any version higher or equal to 2019.3
   • Older versions (5.x, 4.x) are unsupported.
5. Use the following launch command-line.

   LFX=1 %command% -force-vulkan # for native
   WINEDLLOVERRIDES="winhttp=n,b" LFX=1 %command% # for Proton

Installation

LatencyFleX Vulkan layer (essential)

For Debian-like distros, copy the following files from release artifacts to your root filesystem.

/usr/lib/x86_64-linux-gnu/liblatencyflex_layer.so
/usr/share/vulkan/implicit_layer.d/latencyflex.json

For Arch-like distros, you need to copy /usr/lib/x86_64-linux-gnu/liblatencyflex_layer.so -> /usr/lib/liblatencyflex_layer.so and additionally update the path specified in /usr/share/vulkan/implicit_layer.d/latencyflex.json.

LatencyFleX Wine extensions (required for Proton Reflex integration)

Note: The Wine extensions are migrated to a new Wine API in this version. Wine 7.0 or later is recommended, older versions might be unsupported.

1. Copy the following files from release artifacts to your Wine installation location.

   For Wine 7.x: change /usr/lib/wine to wherever Wine/Proton is installed. For Proton and certain distros, you also need to change lib to lib64. Copy the following files.

   /usr/lib/wine/x86_64-unix/latencyflex_layer.so
   /usr/lib/wine/x86_64-windows/latencyflex_layer.dll
   /usr/lib/wine/x86_64-windows/latencyflex_wine.dll
   

   For Wine <= 6.x: copy the files as follows.

   /usr/lib/wine/x86_64-unix/latencyflex_layer.dll.so -> lib/wine/latencyflex_layer.so
   /usr/lib/wine/x86_64-windows/latencyflex_layer.dll -> lib/wine/fakedlls/latencyflex_layer.dll
   /usr/lib/wine/x86_64-windows/latencyflex_wine.dll -> lib/wine/fakedlls/latencyflex_wine.dll
   

2. Create symbolic links to latencyflex_layer.dll and latencyflex_wine.dll, inside drive_c/windows/system32/ under your prefix.

   (Alternatively, copy these files. The drawback is that you need to copy these files on every LFX update.)

   Proton prefixes can be found under ~/.local/share/Steam/steamapps/compatdata/<appid>/pfx.

DXVK-NVAPI with LatencyFleX integration (required for Proton Reflex integration)

Obtain binaries from GitHub Releases. Minimum version with LatencyFlex integration is 0.5.3.

For Proton, copy nvapi64.dll into dist/lib64/wine/nvapi.

For other Wine installations, see DXVK-NVAPI documentation.

MangoHud with metric support (optional)

Obtain binaries from GitHub Actions and install it to your system.

Put the following line in MangoHud.conf to have real-time latency metrics:

graphs=custom_Latency

Footnotes

1. Uses anti-cheat. Use at your own risk. ↩ ↩²

2. Game was previously supported with manual UE4 Linux hook. This is no longer possible in an easy way as the game does not ship with symbols now. ↩

3. A previous version of this document claimed that this is DX11 only. This is not true and it's required for DX12 too as they use DXVK's DXGI implementation. ↩