# low_latency_layer

A C++23 implicit Vulkan layer that reduces click-to-photon latency by implementing both AMD and NVIDIA's latency reduction technologies.

The layer allows AMD or Intel hardware to provide implementations for and switch between `VK_NV_low_latency2` and `VK_AMD_anti_lag` device extensions. This capability, coupled with work that forwards relevant calls in [dvxk-nvapi](https://github.com/jp7677/dxvk-nvapi/), allows the use of these technologies despite the lack of a driver-level implementation.

The layer also eliminates a hardware support disparity as considerably more applications support NVIDIA's Reflex than AMD's Anti-Lag.

[Benchmarks are available here.](#benchmarks)

# Planned

- Respect the provided framerate limit.
- Cross-platform builds.
- Improvements to logging and statistics.
- HUD with latency information.

# Dependencies

- [CMake](https://cmake.org): A cross-platform, open-source build system generator.
- [Vulkan Headers](https://github.com/KhronosGroup/Vulkan-Headers): Vulkan header files and API registry.
- [Vulkan Utility Libraries](https://github.com/KhronosGroup/Vulkan-Utility-Libraries): Library to share code across various Vulkan repositories.

# Building from Source and Installation

Clone this repo.

```
    $ git clone https://git.nj3.xyz/low_latency_layer
    $ cd low_latency_layer
```

Create an out-of-tree build directory (creatively we'll use 'build') and install.

> ⚠️ **WARNING:** You are likely going to have to install your distro's `vulkan-headers`, `vulkan-utility-libraries`, and possibly even `cmake` packages before proceeding. If you see an error here their absense is almost certainly the reason.

```
    $ cmake -B build ./
    $ cd ./build
    $ sudo make install
```

To verify that the installation succeeded you can run this command. If it prints '1' the loader can see the layer and installation was successful.

```
    $ vulkaninfo 2>/dev/null | grep -q VK_LAYER_NJ3AHXAC_LowLatency && echo 1 || echo 0
```

# Usage and Configuration

By default, the layer exposes the `VK_AMD_anti_lag` device extension. For Linux native applications like *Counter-Strike 2* this works out-of-the-box, allowing you to toggle AMD's Anti-Lag in its menus. You can further customize the layer's behavior using the environment variables listed below.

| Variable | Description |
| :--- | :--- |
| `LOW_LATENCY_LAYER_EXPOSE_REFLEX` | Set to `1` to expose `VK_NV_low_latency2` instead of `VK_AMD_anti_lag`. |
| `LOW_LATENCY_LAYER_SPOOF_NVIDIA` | Set to `1` to report the device as an NVIDIA GPU to the application, regardless of actual hardware. This is necessary for many applications to expose Reflex as an option. It _might_ be beneficial to keep this off when the application allows it. |
| `DISABLE_LOW_LATENCY_LAYER` | Set to `1` to disable the layer. |


For Proton-based applications, you must enable NVAPI support alongside the layer's configuration. Use the `PROTON_FORCE_NVAPI=1` environment variable to force this support regardless of your hardware.

**Steam launch options example:**
```
PROTON_FORCE_NVAPI=1 LOW_LATENCY_LAYER_EXPOSE_REFLEX=1 LOW_LATENCY_LAYER_SPOOF_NVIDIA=1 %command%
```

The 'Boost' mode of Reflex is supported but is functionally identical to 'On' - the layer treats both modes identically.

# Benchmarks 

WIP - not updated for reflex merge

## Counter-Strike 2
![cs2](http://git.nj3.xyz/files/plain/low_latency_layer/cs2.png?h=main)

## The Finals
![tf](http://git.nj3.xyz/files/plain/low_latency_layer/tf.png?h=main)