stray-dlss

A ReShade add-on that injects NVIDIA DLSS Super Resolution into Stray, which shipped without it.

Stray runs on Unreal Engine 4.27.2 over D3D12. The add-on finds the engine's own temporal AA compute pass (FTAAStandaloneCS), takes the colour, depth, motion-vector and jitter inputs it was about to consume, hands them to DLSS instead, and writes the result into the same UAV the engine reads back as next frame's temporal history. The engine never knows the difference.

Status: early development. Nothing here is playable yet. The plumbing is being built and verified stage by stage. See Roadmap.

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Why this is not just "turn on DLSS"

Stray has no DLSS support to enable and no upscaler plugin to swap. Everything DLSS needs has to be recovered from a running D3D12 process:

• The right pass, out of 728 shaders. UE 4.27 compiles FTAAStandaloneCS in several permutations. We identify the exact one by hashing its DXBC.
• Jitter, from a constant buffer. DLSS needs the sub-pixel jitter the engine used. It lives in UE4's View uniform buffer, which we read at known row offsets.
• Dense motion vectors, which the game does not have. UE 4.27 writes velocity only for moving objects. Every static pixel — the whole world, whenever the camera moves — carries nothing. And the format it does write, R16G16B16A16_UNORM, is not one DLSS accepts. So we run our own compute pass that decodes the sparse velocity where it is valid, reconstructs camera motion from reversed-Z depth and the ClipToPrevClip matrix everywhere else, and writes the dense RG16_FLOAT field DLSS actually wants.
• Camera cuts. DLSS has to be told to reset its history on a cut, or it smears across the transition. UE4 leaks this three different ways, and we need all three.

The engine-side facts this is built on were measured against the running game, not assumed. They are written down in docs/STRAY-RENDERING-FACTS.md, and the external API and engine research that backs the design — each claim verified against primary sources and then adversarially rechecked — is in docs/RESEARCH.md.

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Target platform

This is developed for Linux / Proton, which is where it will actually be used:

GPU	NVIDIA RTX (developed against a 4090)
Driver	610.43.02, open kernel modules
OS	SteamOS / Linux, Proton GE-Proton-dxvk301-ds5-clean-nowl
D3D12	vkd3d-proton
Display	gamescope, DRM backend, HDR enabled
ReShade	6.8.0 or newer (hard requirement, see below), with add-on support

Windows is not currently a target. It may work; it is not tested.

Does DLSS even work here? Yes.

This was the project's main open risk and it is now settled. D3D12 DLSS under vkd3d-proton is an NVIDIA-authored path, present since vkd3d-proton 2.5: nvngx_dlss.dll runs as an ordinary Windows PE in the prefix, and its CUDA kernels reach the GPU through NvAPI_D3D12_* cubin entry points in DXVK-NVAPI, which forward into vkd3d-proton's ID3D12DeviceExt and on to VK_NVX_binary_import. nvngx_dlss.dll never touches native handles — it creates ordinary D3D12 descriptors — so an ID3D12Resource really being a VkImage turns out not to matter.

ReShade 6.8.0 is a hard minimum. ReShade-with-add-ons plus D3D12 DLSS under vkd3d used to crash: ReShade rewrites descriptor handles for add-on tracking, and vkd3d's own GetCudaTextureObject bypassed ReShade's hooks, so unconverted handles got through. crosire fixed it in two commits, both of which are in the v6.8.0 tag. 6.7.3 is still broken.

The full chain, the runtime prerequisites (nvngx.dll/_nvngx.dll in the prefix, the NGXCore registry key, nvidia_uvm loaded) and the diagnostic environment variables are documented in docs/RESEARCH.md §1.

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Installation

Not yet. Once there are releases:

1. Install ReShade 6.8+ with add-on support into <SteamLibrary>/steamapps/common/Stray/Hk_project/Binaries/Win64/.
2. Drop stray-dlss.addon64 and nvngx_dlss.dll in the same folder.
3. On Linux, install msvcrt40 and vcrun2022 into the prefix with protontricks.
4. Launch Stray, press Home for the ReShade overlay, and open the Stray DLSS tab.

Note that Stray reads its configuration from the Proton prefix, not the game directory:

<compatdata>/1332010/pfx/drive_c/users/steamuser/AppData/Local/Hk_project/Saved/Config/WindowsNoEditor/Engine.ini

Engine.ini settings take effect on this title; command-line arguments do not. Anything the add-on needs the engine to do (such as lowering internal render resolution for true super-resolution) goes through that file.

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Building

There is no local build. Everything is compiled by GitHub Actions with MSVC, and releases are produced as CI artifacts.

.github/workflows/     CI: build, unit tests, package, release
CMakeLists.txt         CMake + MSVC, x64, /MT, warnings as errors
src/                   add-on source
shaders/               our own HLSL (motion-vector resolve, debug views)
tests/                 unit tests for everything provable without a GPU
docs/                  measured engine facts and design notes

The parts that can be tested without a GPU are tested in CI: DXBC hashing, the UE4 velocity decode, jitter conversion, the ClipToPrevClip reconstruction math, and DLSS quality-mode selection. The part that cannot — the actual NGX evaluation — is kept as thin as possible.

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Roadmap

• v0.1 — DLAA. Render resolution equals output resolution, so there is no screen-percentage problem to solve. This exists to answer one question: are colour, depth, motion vectors and jitter correct? If DLAA looks right, everything downstream is built on solid ground.
• v0.2 — DLSS Super Resolution. Rather than fighting the engine, set r.ScreenPercentage=<N> and r.TemporalAA.Upsampling=1 in Engine.ini. UE4 then renders at N%, allocates a full-res output, and expects its TAA pass to upscale — which is exactly DLSS's contract. It also switches the jitter sequence to plain Halton (what DLSS was trained on), auto-scales the phase count, and sets the correct texture mip bias, all for free. The cost is that this changes the shader permutation and therefore the hash we hook.
• Later, maybe. DLSS preset selection, sharpening, a Vulkan-interop path, an FSR fallback for non-NVIDIA hardware.

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Credits and prior art

• ReShade by crosire — the add-on API this is built on.
• Luma-Framework by Filoppi — a ReShade-add-on modding framework that injects DLSS into DX11 games that never shipped it. Its NGX lifecycle and its SuperResolutionImpl abstraction are the architectural reference for this project.
• OptiScaler — upscaler replacement across APIs, and the deepest well of Proton-specific upscaler knowledge.
• NVIDIA DLSS SDK — the NGX headers and programming guide.

Licence

The add-on source is MIT. nvngx_dlss.dll is NVIDIA's, redistributed under the NVIDIA RTX SDKs licence and never committed to this repository — CI fetches it from the official DLSS release.

This is an unofficial fan project. It is not affiliated with or endorsed by BlueTwelve Studio, Annapurna Interactive, or NVIDIA.