Superposer

Getting started

How Superposer works

Pressing Play on a Windows game in Mac Steam sets this chain going:

  1. Steam starts the game as it does on any computer, but hands it to a compatibility tool: Superposer. Steam still does its own work (downloads, updates, the launch and DRM checks, cloud saves, playtime).
  2. Superposer's launcher picks how to run this game: a profile for games it knows, otherwise a setup drafted from the game's engine and graphics API. It prepares the game's own Windows environment (a "prefix", cloned from a ready template, which is why the first launch takes about a second).
  3. The Windows runtime (Superposer's build of the open-source Wine project) runs the game's Windows program, through Rosetta 2, which runs Intel code on Apple silicon.
  4. A graphics layer turns the game's DirectX calls into Metal, which your Mac's GPU understands. See Which graphics layer runs my game?.
  5. A small Steam bridge lets the game talk to your Mac's Steam client: achievements, cloud saves, playtime and the copy-protection handshake. See Steam integration, explained.
  6. Superposer's compositor sits between the game and the screen: it can upscale with MetalFX, cap the frame rate, pass HDR through, draw the HUD and the in-game overlay and take screenshots. Where code can't be loaded into a game (some games with protection), capture mode does the same by capturing the game's window instead; nothing is loaded into the game.

Each game has its own Windows environment, so one game's settings can't break another, and removing a game gives back its space. Everything Superposer changes on your Mac is recorded so it can be undone; see Changes to your Mac.