Positron — Steam Play for macOS

Positron is a free, open-source macOS Steam Play compatibility layer and native SwiftUI control center for Apple Silicon Macs. It lets the native macOS Steam client download, configure, and launch Windows-only Steam games—as well as standalone non-Steam .exe games—using your installed CrossOver (Stable or Preview) or Wine/FEX runtime, while keeping native macOS Steam games running natively.

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Highlights

• Positron.app as Your Single Source of Truth
  • Manage per-game CPU translators (Rosetta 2 x86_64 vs FEX ARM64EC), graphics backends (D3DMetal, DXMT, DXVK, WineD3D), synchronization (Msync / Esync), Launch in Fullscreen, Retina High-DPI, Metal HUD, and Wine prefixes in one unified interface.
  • Automatically hides Steam's redundant in-app Compatibility tab while enabling the green Install / Play button for every Windows game in your Steam library.
• 130+ Game Preset Library with Switchable Fixes
  • Ships with 51 hand-tuned game presets and 80+ engine-derived presets across DirectX 12, DirectX 11, DirectX 9, and Vulkan titles.
  • Every applied fix is individually toggleable ON or OFF in the UI—including game-specific runtime patches, individual WINEDLLOVERRIDES, environment flags, and global launch safeguards.
• Native macOS Game Protection
  • Automatically detects games that ship native macOS .app bundles (such as Cyberpunk 2077, Baldur's Gate 3, and Metro Exodus) and excludes them from Windows compatibility routing so they always run as native macOS binaries.
• External Drive & ExFAT Support
  • Discovers Steam libraries across internal APFS SSDs and external drives (APFS, ExFAT, HFS+).
  • Automatically redirects ExFAT Wine prefixes onto your internal APFS SSD (~/Library/Application Support/Positron/prefixes/<appid>), mounts the external Steam library as drive S:, and strips macOS ._* AppleDouble resource-fork files before launch so games never crash or kernel-panic on external drives.
• Live Download Detection & Non-Steam .exe Game Launcher
  • Watches your steamapps/ folders in real time—newly downloaded Steam games appear in Installed Games automatically within ~2 seconds of installation completing.
  • Add any non-Steam Windows game (.exe) via Add Non-Steam Game… to give it its own isolated prefix, auto-analyzed preset, and one-click Launch Game button.
• Integrated Wine Prefix Toolkit
  • Launch winecfg, regedit, control, uninstaller, or custom .exe / .msi / .bat installers inside any game's prefix, open Drive C: or Save Games in Finder, or rebuild a prefix while preserving all steamuser saves.

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Requirements

• Mac: Apple Silicon (M1 / M2 / M3 / M4 series, arm64)
• OS: macOS 15.0 (Sequoia) or newer
• Steam: Native macOS Steam client installed at /Applications/Steam.app
• Translation Runtime: CrossOver (26.x Stable or 27.x Preview) installed in /Applications

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Quick Start

1. Download & Install
   • Download the latest Positron-macOS-arm64.dmg (or .zip) from Releases, open it, and drag Positron.app to /Applications.
   • On first launch, if macOS Gatekeeper prompts that the app is ad-hoc signed, clear the quarantine attribute in Terminal:

     xattr -cr /Applications/Positron.app

2. Enable Positron in Steam (One Click)
   • Open Positron.app. If Positron is not yet active in Steam, click Enable Positron in Steam in the top banner (or on the Steam Setup tab).
   • Positron stages its runtime bridge, registers your CrossOver Rosetta & FEX engines in Steam, signs Steam.app, and restarts Steam automatically.
3. Configure & Play Your Games
   • In Steam, install any Windows game (use the Windows filter icon in your Steam Library if needed).
   • Once downloaded, the game appears automatically in Positron.app → Installed Games.
   • Select the game, review or customize its Suggested Best Profile and Game Fixes, and click Apply & Play in Steam.

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Built-In Game Fixes (Toggleable in UI)

Every runtime fix and DLL/environment override can be switched ON or OFF per game inside Installed Games → Game Fixes:

Game	AppID	Recommended Pipeline	Built-in Toggleable Fix
The Witcher 3: Wild Hunt — Remastered	292030	Rosetta 2 + D3DMetal (DX12)	Links bin/x64 -> x64_dx12, stages the MIT-licensed stream-output PSO #15 proxy (amd_fidelityfx_loader_dx12.dll) + SDR colour-space hook (dinput8.dll), bypasses REDprelauncher.exe, and disables winspool.drv.
Red Dead Redemption 2	1174180	Rosetta 2 + D3DMetal (DX12) + Esync	Disables D3DMetal's broken DLSS-to-MetalFX bridge (nvngx=d, D3DM_ENABLE_METALFX=0), clamps NaN/Inf shader samples, and configures system.xml for DX12 SDR + TAA High to eliminate 3D world blinking.
Fallout 76	1151340	Rosetta 2 + DXMT (DX11) + Msync	Pins CrossOver 26.3 Rosetta (avoiding FEX xtajit64.dll 1 MB stack overflow), keeps Fallout76.exe on DXMT despite its bundled libcef.dll, uses xaudio2_7=n,b, and syncs fullscreen preferences to Fallout76Prefs.ini.
Heroes of Might and Magic: Olden Era	3105440	Rosetta 2 + D3DMetal + Standard DPI	Uses D3DMetal on Rosetta 2 for Media Foundation .mp4 video playback, keeps Retina scaling off, and runs the prefix on internal APFS while cleaning ._* files on ExFAT drives.
STAR WARS: The Old Republic	1286830	Rosetta 2 (WoW64) + WineD3D	Detects the 32-bit CEF launcher.exe (libcef.dll), forces WineD3D + builtin vulkan-1=b;libglesv2=b, and disables the overlay shim so bundled SwiftShader DLLs cannot make the launcher window invisible.
Atomic Heart	668580	Rosetta 2 + D3DMetal (DX12) + AVX	Configures Rosetta 2 AVX + D3DMetal for Unreal Engine 4 DX12 rendering with xaudio2_9=n,b and native VC++ runtime overrides.
Fallout 2	38410	Rosetta 2 (32-bit) + WineD3D	Forces ddraw=n,b;dinput=n,b;dinput8=n,b so the bundled High-Resolution Patch (f2_res / sfall) loads cleanly.

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Frequently Asked Questions (FAQ)

For the complete troubleshooting and technical FAQ, see docs/FAQ.md.

Does Positron modify my native macOS Steam games?

No. Positron inspects both a curated native-Mac exclusion list (Cyberpunk 2077, Baldur's Gate 3, Metro Exodus, etc.) and each game's installation folder in steamapps/common/. Any game shipping a native macOS .app bundle is excluded from Positron's Windows compatibility catalog and runs natively on macOS.

When should I choose Rosetta 2 vs. FEX ARM64EC?

• Rosetta 2 (x86_64) is the most compatible choice and is required for:
  • All DirectX 12 games using Apple D3DMetal (GPTK)
  • Games requiring AVX / AVX2 / F16C instruction advertising (ROSETTA_ADVERTISE_AVX=1)
  • 32-bit (i386) games and 32-bit CEF launchers
  • Games with small 1 MB PE stack reserves or heavy anti-tamper unpackers (e.g., Fallout 76)
• FEX (ARM64EC) uses CrossOver Preview's native arm64 Wine loader with FEX JIT translation and pairs best with DXMT on clean 64-bit DirectX 11 games.

When should I choose D3DMetal vs. DXMT vs. WineD3D vs. DXVK?

• D3DMetal (Apple GPTK): Best for DirectX 12 games (The Witcher 3 DX12, Red Dead Redemption 2, Elden Ring, Atomic Heart, UE5 titles) and Unity games that need Media Foundation shared texture handles. Requires Rosetta 2.
• DXMT: Native Metal implementation of DirectX 11 (Fallout 76, Fallout 4, Skyrim SE, Frostpunk, Dark Souls III). Works on both Rosetta 2 and FEX and defaults to a safe 120 FPS cap on Apple Silicon.
• WineD3D: Best for 32-bit CEF launchers (STAR WARS: The Old Republic) and classic DirectX 9 / DirectDraw titles (Fallout 2, Source engine classics).
• DXVK: Translates DirectX 9/10/11 to Vulkan over MoltenVK; useful for Vulkan-native or idTech titles.

Can I store my Steam Library on an external ExFAT drive?

Yes. Wine prefixes themselves cannot run reliably on ExFAT (which lacks POSIX symlinks/hardlinks and creates macOS ._* AppleDouble files that crash games). Positron solves this automatically via two built-in safeguards:

1. Internal APFS Shadow Prefix: Your game's large asset files stay on the external drive (mapped as S:), while its small Wine prefix runs on your internal APFS SSD at ~/Library/Application Support/Positron/prefixes/<appid>.
2. AppleDouble (._*) Cleanup: Before launching a game on /Volumes/*, Positron runs dot_clean -m and removes stray ._* files so game engines scanning .zip / .ba2 / .pak archives never crash.

How do I launch non-Steam Windows games (.exe)?

Click Add Non-Steam Game… at the bottom-left of the Installed Games tab and select any Windows .exe. Positron assigns it a dedicated APFS prefix (~/Library/Application Support/Positron/prefixes/<virtual-id>), inspects its PE headers and engine DLLs to suggest a preset, and lets you start it directly with the green Launch Game button.

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Building from Source

# Clone the repository
git clone https://github.com/RayAnd/Positron.git
cd Positron

# Build C supervisor, Steam bridge dylib, Swift CLI, and signed out/Positron.app
make all

# Run all C and Swift test suites
make test

# Package distributable out/Positron-macOS-arm64.dmg and .zip
make package

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Project Documentation

• Architecture & Internals (ARCHITECTURE.md)
• Full FAQ & Troubleshooting (docs/FAQ.md)
• Contributing Guide (CONTRIBUTING.md)
• Code of Conduct (CODE_OF_CONDUCT.md)
• Security Policy (SECURITY.md)
• Changelog (CHANGELOG.md)
• Third-Party Open Source Notices (THIRD_PARTY_NOTICES.md)

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Support Positron ❤️

Positron is 100% free and open-source software (MIT License). If Positron helped you play your Windows library on macOS, voluntary contributions are always appreciated:

• ☕️ Ko-fi (Apple Pay, Card, PayPal — No Login Needed): https://ko-fi.com/rayand
• ❤️ GitHub Sponsors: https://github.com/sponsors/RayAnd