DevilutionX — Vulkan GPU & libretro Shader Mod

A standalone mod of DevilutionX that adds Vulkan GPU rendering and libretro shader support to Diablo & Hellfire on modern operating systems.

---

_{(The health-bar and XP-bar are off by default but can be enabled in the game settings. Widescreen can also be disabled if preferred.)}

Important

This is a standalone mod, not the official DevilutionX. The GPU shader work in this repository originally targeted upstream (PR #8737). As of October 11, 2026, development continues here as an independent mod, branched from upstream 1.6.0-dev.

• Report bugs and request features in this repository — please do not send mod-specific reports to upstream.
• The official project lives at https://github.com/diasurgical/DevilutionX.

Project Status — October 2026

The audit phase is complete, and the shader pipeline has moved into its own library. Where things stand and where development happens now:

• master (this branch) is the audit home. The fork's full audit history lives here: the finding ledger and field-sweep write-ups in docs/audit.md and docs/audit/, the delta ledger in docs/deltas.md, and the release-by-release record in the fork changelog. Every High and Medium audit finding has been closed — the gates that gated first upstream contact are done, with only Low-severity notes remaining.
• Shader work beyond this fork master continued at VTSTech/libslang-vk, now at milestone M4.05. With the High/Medium bar cleared, the shader pipeline was ported out of the game tree into libslang-vk — an embeddable C++23 library (MIT, clean-room) that parses, translates and compiles libretro slang presets (.slangp / .slang) with a full Vulkan execution path. It vendors glslang, Vulkan-Headers, volk and VMA with SHA-256 pinning (no Vulkan SDK needed at link time), runs a full-corpus compile sweep against libretro's slang-shaders in CI, and is usable by any SDL3/Vulkan project — the long-term goal originally sketched in docs/diablo-handoff.md, §14.
• DevilutionX work continues on the libslang-vk branch of this repository. The game integration consumes the library via CMake FetchContent (pinned M4.05) and carries the current integration work: SDL3 display/DPI fixes, scaler mouse-coordinate mapping (MapWindowToGame), MSVC static and nonstatic (DLL) build fixes, a fork-only CI build gate, and the r4 upstream-prep tooling. See the branch's gpu-scaler-build CI for the current green state.
• Upstream merge track, updated: the phased plan shared with upstream maintainers on October 16, 2026 (docs/merge-plan-draft-r2.md) got its reply — individual changes. Per docs/merge-plan-r4.md on the libslang-vk branch, the payload is split into one topical branch (and PR) per change — pr/1-sdl3-build-fixes through pr/6-sdl3-main-glue — each reviewable and buildable on its own, EOL-normalized against upstream and stamped with attribution. Nothing has been merged upstream yet.

Where	What
master (this branch)	Audited standalone mod — release line, full audit history and ledger
libslang-vk branch	Active DevilutionX integration — consumes the libslang-vk library (M4.05)
VTSTech/libslang-vk	The standalone, reusable C++23 shader library — shader development beyond fork master (now M4.05)
wav-mixer-fix branch	Standalone fix for Diablo's 1996-era WAV decoding under SDL3_mixer

What is DevilutionX

DevilutionX is a port of Diablo and Hellfire that strives to make it simple to run the game while providing engine improvements, bug fixes, and some optional quality of life features.

Check out the wiki for available features and how to take advantage of them.

For a full list of base-game changes, see the upstream changelog.

What this mod adds

This mod keeps the stock SDL render path fully intact and layers a GPU shader pipeline on top of it:

• Vulkan GPU render path — the game still renders internally at its native 640x480/960x540 8-bit paletted surface, but when a shader filter is active, the frame is uploaded to a GPU texture each frame and pushed through an SDL3 GPU (SDL_GPU) pipeline backed by Vulkan on Windows and Linux (Metal on macOS). If no compatible GPU device can be created — driver update, remote desktop, VM without GPU — the shader simply reports as (Unavailable) and the game keeps running on the stock render path.
• libretro shader preset support — load .slangp/.slang presets from a shaders/ folder next to the executable. Multi-pass chains are translated in-process with glslang to SPIR-V at runtime, with a content-addressed disk cache and sidecar .spv fast path for near-instant reloads. There are no baked-in shaders: the filters you get are exactly the presets you install (see Setting Up Shaders).
• The full RetroArch shader ecosystem — CRT simulation, xBR, ScaleFX, HQx, and hundreds more, straight from libretro's slang-shaders collection. Unlike the stock renderer's plain stretch, these GPU filters reconstruct pixel-art detail: sharper edges, smoother diagonals, and cleaner corner transitions. Some presets (e.g. the HQx family) load PNG lookup textures at runtime.
• Live shader feedback — the on-screen overlay always shows the active filter and backend (e.g. Shader: ScaleFX 3x (Vulkan) or Shader: Off). If a shader fails to compile or load, the overlay reports it as (Unavailable) — and you can select a new shader right from that state without restarting. Every change is also logged to gpu-scaler.log, and the choice persists in diablo.ini under the Shader Filter key.
• Audio fix available — a standalone fix for decoding Diablo's 1996-era WAV files (zero-length RIFF chunks fail on current SDL3_mixer) is maintained on the wav-mixer-fix branch.
• Documented and audited — feature docs in docs/GPU_SHADERS.md, architecture notes in docs/diablo-handoff.md, and the complete audit trail (per-preset compatibility audits, field-sweep test lists, finding ledger) under docs/audit.md and docs/audit/. This audit is what gated the port into the standalone library — see Project Status.

See it in action: shader demo video.

Requirements

• A GPU with Vulkan support (or Metal on macOS) and a driver new enough for that API. Vulkan is the only actively-supported backend on Windows and Linux.
• A build with SDL3 (USE_SDL3=ON). USE_GPU_SCALER is a dependent option that defaults to ON whenever USE_SDL3 is ON and USE_SDL1 is OFF.
• The in-game Upscale option enabled (it is on by default).
• git-lfs installed when cloning the shader pack (some presets load PNG lookup textures at runtime — see Setting Up Shaders).

How to Install

Note: You'll need access to the data from the original game. If you don't have an original CD, you can buy Diablo from GoG.com or Battle.net. Alternatively, you can use spawn.mpq from the shareware [2] version, in place of DIABDAT.MPQ, to play the shareware portion of the game.

Download the latest release and extract the contents to a location of your choosing, or build from source. Releases are built by CI for Windows x64 and Linux x64; other platforms require building from source.

• Copy DIABDAT.MPQ from the CD or Diablo installation (or extract it from the GoG installer) to the DevilutionX folder.
• To run the Diablo: Hellfire expansion, you will also need to copy hellfire.mpq, hfmonk.mpq, hfmusic.mpq, and hfvoice.mpq.
• Optional: install the libretro shader pack — see Setting Up Shaders (on Windows, run the included install_shaders.cmd; on Linux, install_shaders.sh).

For more detailed instructions: Installation Instructions.

Setting Up Shaders

Shader presets are loaded at runtime from a shaders/ folder next to the executable — nothing is baked into the binary. The easiest way to populate it is to clone libretro's shader collection directly into your Diablo folder:

git clone https://github.com/libretro/slang-shaders shaders
cd shaders
git lfs pull

The git lfs pull step matters: some presets (like HQ2x) reference PNG lookup textures, and without pulling the LFS assets those PNGs are left as pointer stubs, so the presets that need them will fail to load or render incorrectly. Make sure git-lfs is installed and initialized (git lfs install) before cloning.

The release zips ship helper scripts beside the executable that automate the above:

• install_shaders.cmd (Windows) / install_shaders.sh (Linux) — wipes and re-downloads shaders/ beside the executable (fresh clone plus git lfs pull; needs git and git-lfs — the Linux script prints the per-distro install command if either is missing).
• clear_shader_cache.cmd (Windows) / clear_shader_cache.sh (Linux) — deletes shaders/cache/, the translated-shader compile cache. It is rebuilt automatically on the next preset load; run it after a corpus update or a game update if presets misbehave.
• install_git.cmd (Windows) — one-time helper for machines without git: installs Git for Windows (bundling Git LFS) via winget so install_shaders.cmd can run.

Presets are selected from the in-game folder browser, so you can keep the whole collection or just the handful of .slangp files you actually use.

Using Shaders

1. Install the shader pack as described in Setting Up Shaders.
2. Start the game and open Main Menu → Options → Graphics Options.
3. Scroll to Shader Filter and pick a preset from the folder browser (Off uses the stock renderer).
4. Confirm — the renderer is recreated and the filter applies immediately from the menu. The option is disabled during an ongoing game because it forces a renderer recreation.
5. Shaders are loaded immediately upon selecting them — no restart required. If a shader fails to compile or load, the overlay reports it as (Unavailable); you can select a new shader straight from that state and it will load.

The GPU backend can be forced explicitly with the DEVILUTIONX_GPU_BACKEND=vulkan environment variable.

Building from Source

Want to compile the program by yourself? Great! Follow the general build instructions, and see docs/GPU_SHADERS.md for the full mod-specific build matrix (including the MinGW-w64 Windows cross-build). Quick start on Linux:

cmake -S . -B build -G Ninja -DCMAKE_BUILD_TYPE=Release -DUSE_SDL3=ON \
  -DDEVILUTIONX_SYSTEM_SDL3=OFF -DDEVILUTIONX_SYSTEM_LIBSODIUM=OFF \
  -DBUILD_TESTING=OFF
cmake --build build -j$(nproc)

Build notes:

• USE_GPU_SCALER defaults to ON when USE_SDL3=ON and USE_SDL1=OFF.
• On this branch (master), shader presets are compiled at runtime by the bundled glslang (3rdParty/glslang) — no external shader toolchain is needed at build time.
• On the libslang-vk branch, the in-tree preset/translator stack is replaced by the standalone libslang-vk library (C++23, fetched and pinned at M4.05 by CMake), which builds its own glslang — still no Vulkan SDK or shader toolchain required. That branch also ships tools/build-local-win11.ps1, a local Windows 11 build script mirroring its CI (static, nonstatic DLL, or both).
• The SDL_GPU device, swapchain, and pipelines are created lazily and torn down on shutdown and renderer reinitialization, so switching a shader filter to Off (or losing the GPU) restores the exact stock render path.
• CI: gpu-shaders.yml builds Windows x64 and Linux x64 on this branch; the gpu-scaler-build.yml gate does the same (plus nonstatic DLL variants) on the libslang-vk branch.

Contributing

Development is split by branch: this master branch is the audit archive and release line — issues, regression reports and documentation fixes are all welcome here; active game-side development happens on the libslang-vk branch, and standalone shader-library development happens at VTSTech/libslang-vk. The upstream merge track follows the individual-change plan in docs/merge-plan-r4.md (one topical branch/PR per change, per the upstream maintainers' directive); until anything is merged there, this repository remains the single place where mod development happens. For engine behavior that this mod does not touch, the upstream wiki and contributing guide remain the best references.

Credits

• The original Devilution project: Devilution
• Everyone who worked on Devilution/DevilutionX
• Nikolay Popov for UI and graphics
• WiAParker for the Polish voice pack
• Shader authors whose work this mod builds on: ScaleFX by Sp00kyFox (MIT), the HQx family by Maxim Steppin, Adam Zemek and Blok (LGPL-2.1), and the wider libretro slang shaders ecosystem
• glslang by The Khronos Group for runtime shader translation (bundled on master, vendored by libslang-vk on the library track)
• The libslang-vk standalone library — the C++23 home of the shader pipeline (current milestone M4.05)
• Mod integration, audit and maintenance by VTSTech (vts-tech.org)

Legal

DevilutionX is made publicly available and released under the Sustainable Use License (see LICENSE). This mod is a derivative work of DevilutionX and is distributed under the same terms.

The source code in this repository is for non-commercial use only. If you use the source code, you may not charge others for access to it or any derivative work thereof.

Diablo® - Copyright © 1996 Blizzard Entertainment, Inc. All rights reserved. Diablo and Blizzard Entertainment are trademarks or registered trademarks of Blizzard Entertainment, Inc. in the U.S. and/or other countries.

DevilutionX and any of its maintainers are in no way associated with or endorsed by Blizzard Entertainment®.