fxgl / steamac

# steamac — Valve's official ARM64 SteamOS (the Steam Frame image) in a VM on Apple Silicon
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On macOS 15 (Sequoia), Valve's actual SteamOS for Steam Frame runs in a lightweight VM on
Hypervisor.framework (libkrun) with GPU acceleration via Venus.
 [code] 
Vulkan on Metal — MoltenVK from the UTM fork (geometry shaders, robustness2) +
`VK_EXT_depth_clip_enable` (PR #2712) + our fixes, by default. KosmicKrisp (Mesa's Vulkan driver on
Metal 4) is an experimental alternative on macOS 26+ (see “Vulkan driver”).
## Requirements
- Apple Silicon Mac, macOS 15+, ~150 GB of free space (the disk image is sparse).
- Xcode 26+ (full installation: its `actool` builds the app icon from an Icon Composer document), Homebrew, rustup.
- KosmicKrisp (optional, alternative Vulkan driver): built only on macOS 26+; `host/kosmickrisp/build.sh`
 installs its Homebrew dependencies (`llvm spirv-llvm-translator spirv-tools vulkan-loader glslang`).
- OrbStack (or Docker with arm64 and `--privileged`): the kernel, Mesa, and disk image are built in Linux containers.
- Homebrew packages: `meson ninja pkg-config dtc xz lld sshpass go` (`go`: license inventory of the bundled gvproxy/desync).
- libepoxy 1.5.10 is built from pinned sources by `host/libepoxy/build.sh`, before virglrenderer and
 libkrun; all three use `MACOSX_DEPLOYMENT_TARGET=15.0`, including on macOS 26/27 build hosts.
 Bundling rejects Mach-O deployment targets above macOS 15.0 (KosmicKrisp alone may require 26.0).
## Building and running
 [code] 
Build parts separately: `./build.sh host`, `./build.sh guest`, or the scripts in the table below.
The SteamOS image is downloaded from Valve's servers (a signed RAUC bundle); its signature and
sha256 are verified.
Guest release artifacts have adjacent `.inputs.json` build receipts binding their selected Git
working-tree inputs to their output bytes. Relevant dirty edits invalidate them; unrelated commits
do not. `host/launcher/bundle.sh` refuses missing/stale receipts before modifying the app;
`dist.sh` also validates the receipts and resources inside an existing app before packaging it.
The error names the step to rerun. To refresh guest artifacts without touching an existing SteamOS
disk: `guest/kernel/build.sh` (only when its inputs changed or its receipt is missing),
`scripts/build-image.sh builder rootfs`, `guest/mesa/build.sh`, then
`scripts/build-image.sh initramfs layer`; finally `host/launcher/build.sh`. An unstamped artifact
needs its normal build once; kernel builds reuse the build volume without `clean`.
`ALLOW_NO_VENUS=1` layers are test-only and cannot be released.
VM options: `./run.sh --display 1920x1080 --cpus 10 --mem 24576` (full list:
`work/out/steamac-vm --help`).
Frame pacing: `./run.sh --perf-stats` (or `STEAMAC_PERF_STATS=1`) prints guest-frame and on-screen
frame intervals to the terminal every 5 s (p50/p95/p99/max, number of intervals > 25 and > 50 ms).
Stutters when a new effect first appears come from Metal shader co