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How Bridgeplay works

By Bridgeplay · Last updated 29 October 2026

What happens when you press Play

1. Steam loads Bridgeplay’s library. Setup copies a library (notproton.dylib) into /Applications/Steam.app and makes Steam load it at startup. The library switches on Steam Play, which is present but inactive in Mac Steam, and registers Bridgeplay’s compatibility tools, so Windows games show Install and Play like Mac games. The approach comes from NotProton. ^{[1] [3]}
2. Steam starts the game through Bridgeplay’s run script. The script picks the engine and graphics backend set for that game, applies its per-game fixes and loads the small helper libraries that run inside the game. ^[3]
3. The game runs in Wine under Rosetta 2. The default engine is WineCX 11.17: CodeWeavers’ open-source Wine changes from CrossOver 26.3, rebased by dappermint onto upstream Wine, with CrossOver’s msync. It is an x86-64 build, so Rosetta 2 translates it for Apple Silicon. A WineHQ 11.15 build from Gcenx is the other free engine, and if you own CrossOver, Bridgeplay can run games on your copy instead. ^{[2] [4]}
4. Steam calls go back to Mac Steam. Inside the game, Steam calls reach the Steam client you’re signed in to through lsteamclient and steam.exe, macOS ports of pieces from Valve’s Proton. ^{[2] [5]}
5. DirectX becomes Metal. D3DMetal, from Apple’s Game Porting Toolkit 4.0 beta 3, runs DirectX 11 and 12. Per game you can pick DXMT instead (DirectX 10–11 straight to Metal), or DXVK-macOS (DirectX 10 and 11 to Vulkan) on top of MoltenVK (Vulkan to Metal). ^[2]
6. Metal draws the frame on your Mac’s Apple Silicon GPU, and it appears on screen.

Other pieces along the way

• DLSS requests go to MetalFX. Games on D3DMetal see an NVIDIA GeForce RTX 4090 by default, so they offer DLSS, and Apple’s Game Porting Toolkit does the upscaling with MetalFX. Setting NVAPI=0 turns this off. See the DLSS and frame generation guide. ^[2]
• Frame generation (experimental). Bridgeplay generates frames in the game’s own process, on its CAMetalLayer, for up to 3× the displayed frames with a little added latency. It’s off by default and turned on per game.
• Controllers. A controller layer for HID pads and SDL inside Wine let DualSense, Xbox, GameSir and other controllers work without a mapping screen. sn0wst0rm’s DualSense Bluetooth bridge and Steam rumble forwarding, shipped in Bridgeplay 0.7.51 and earlier, are paused until NotProton merges the same work.
• Function hooks. Bridgeplay uses the Dobby hooking library.
• Updates. Sparkle updates the Bridgeplay app. Bridgeplay also updates its patch in Steam and the engine, and re-applies the patch when Steam updates itself. ^[3]

Each game’s settings for these (graphics backend, Metal HUD, DLSS, frame generation, High Resolution, controllers) live in Steam: right-click the game, then Properties… › Bridgeplay.

The components

The credits on the home page list each license. Apple’s Game Porting Toolkit is Apple software under Apple’s license, which allows non-commercial distribution only; everything else here is open source except Steam and macOS themselves.

Contributors

Everyone with commits in the Bridgeplay repository, from GitHub’s contributor list as of 29 October 2026. Commit counts include history from NotProton and the other projects Bridgeplay is forked from. Each name links to that person’s GitHub profile.

• raymondchins354 commitsMaintainer
• Raystorms31 commitsMaintainer
• NotProtonNot156 commits
• LaganYT11 commits
• kevicebryan6 commits
• leonseemann5 commits
• natbro5 commits
• temamumtaza5 commits
• Ni-zav4 commits
• Ghostkwebb4 commits
• sn0wst0rm3 commits
• xmb92 commits
• Dino00052 commits
• schroedernils2 commits
• Alex00071 commit
• KameraZhao1 commit
• louisboii7471 commit
• Nael-Nathanael1 commit
• epsimatic1 commit
• woahitsraj1 commit
• jacobbinnie1 commit
• matthewwynne1 commit

What Bridgeplay itself adds

• The Mac app and Setup Assistant, which installs Rosetta, downloads Apple’s graphics files and the engine, checks each download against Bridgeplay’s signature, and walks you through Steam sign-in and the macOS permission prompts.
• Updates for the app, its patch in Steam and the engine, including re-patching Steam after Steam updates itself.
• Per-game settings in Steam’s Properties window, plus per-game fixes for specific games.
• The free WineCX engine package, pinned by hash and patched so the Steam bridge loads, and the DLSS-to-MetalFX routing, frame generation, High Resolution switch and controller layer described above.
• One-tap game reports that feed the compatibility list.

What comes from upstream

• NotProton (NotProtonNot and contributors): the idea and the code for running Steam Play inside Mac Steam. The Steam hooks, the Steam Play interface patches, the run script and the steamclient bridge all started as their work. Runtime names inside Bridgeplay, such as notproton.dylib, still carry NotProton’s name.
• Leon Seemann: NotProton-WineHQ, the fork Bridgeplay came from, which added a free WineHQ engine.
• CodeWeavers and the Wine project: Wine itself, and the CrossOver changes in WineCX (msync and the hooks D3DMetal needs). CodeWeavers is the biggest contributor to Wine.
• dappermint: the WineCX rebase onto upstream Wine and the winecx-gptk build Bridgeplay’s engine uses.
• Apple: D3DMetal and MetalFX in the Game Porting Toolkit, plus Rosetta 2 and Metal.
• Valve: Steam, and the Proton pieces lsteamclient and steam-helper that the Steam bridge is ported from.
• 3Shain (DXMT), Gcenx (DXVK-macOS and the WineHQ builds), the Khronos Group (MoltenVK), the SDL project, Dobby and Sparkle.
• sn0wst0rm: the DualSense Bluetooth bridge, Steam rumble forwarding and game-mode host that earlier Bridgeplay versions shipped.

NotProton in turn thanks the people who worked on the same idea before it, among them Nat Brown’s Kaon, mont127’s Neutron and Gio’s work on Steam Play in Mac Steam. ^[5]