Windows Host
Feasibility and scoping for a Windows host backend.
Status: scoped, deferred — but de-risked. A Windows host is architecturally an "add a backend"
job, not a parallel port. The one thing that used to make it large — the per-client virtual
output, which has no user-mode Windows API and seemingly needed a self-signed kernel Indirect
Display Driver (IDD) — is solved by reusing SudoVDA, the
Sunshine Virtual Display Adapter: a pre-built, signed IDD that creates virtual displays at
arbitrary WxH@Hz on demand. We install it and drive its control interface; no driver to write or
WHQL-sign. That turns the headline feature from XL into a medium backend. This doc records what's
left so the work can be picked up deliberately.
(Grounded in a 4-agent read of the host crate, 2026-06-10; SudoVDA path added 2026-06-11.)
What's already done for us
punktfunk is cleanly layered. ~95% of the codebase is platform-agnostic and reuses verbatim:
| Reusable as-is | Why |
|---|---|
punktfunk-core (protocol, FEC, crypto, session, transport, C ABI) | Zero platform deps — no cfg(linux) anywhere; the C ABI is already cross-platform |
QUIC control plane (quic.rs, pairing, mode negotiation) | quinn + tokio are portable |
GameStream P1.1 (mDNS, serverinfo, pairing, RTSP, ENet) — except stream.rs/audio.rs | pure wire logic |
Management REST API (mgmt.rs) + OpenAPI | axum/tokio, portable |
Pipeline + m3.rs orchestration | trait-generic — calls capturer.next_frame(), encoder.submit/poll(); needs zero changes |
The trait boundaries themselves: Capturer, Encoder, VirtualDisplay, InputInjector, AudioCapturer, VirtualMic | platform-neutral signatures; Linux deps are already isolated under [target.'cfg(target_os="linux")'.dependencies] |
So a Windows host is new #[cfg(target_os = "windows")] backend modules behind the existing
traits — the per-frame path, protocol, and control plane don't move. No architectural refactor is
required; the boundaries are already in the right places.
What a Windows host needs (new code)
Each row is a Linux backend that needs a Windows sibling. Effort is the implementation effort; all reuse the existing trait.
| Subsystem | Linux today | Windows equivalent | Effort | Notes |
|---|---|---|---|---|
| Capture | xdg ScreenCast portal → PipeWire (dmabuf) | DXGI Desktop Duplication (or Windows.Graphics.Capture) → D3D11 texture | M | DXGI gives a GPU B8G8R8A8 texture directly |
| Virtual display | KWin/Mutter/Sway/gamescope protocols | SudoVDA (pre-built signed IDD) — install + drive its control API to add/remove a WxH@Hz virtual monitor per session | M | ✅ no longer the blocker: SudoVDA is the same IDD Sunshine ships, so no driver to author or sign. The VirtualDisplay backend = enable the adapter, create a monitor at the client's mode, capture it (DXGI), tear it down on session end. Fallback if SudoVDA is absent: capture an existing monitor (loses native-resolution) |
| Encode | ffmpeg-next NVENC, CUDA hwframes | Media Foundation H.264/HEVC/AV1, or NVENC SDK direct with a D3D11 device context (AVD3D11VADeviceContext) | M–L | encode.rs AU/codec logic + NVENC option strings are portable; only the hwdevice + frame-pool glue swaps |
| Zero-copy bridge | dmabuf → EGL/Vulkan → CUDA | D3D11 texture → NVENC (shared texture / cudaImportExternalMemory + D3D12 fence) | M | optional — a portable CPU-copy path already exists, so v1 can skip this |
| Input (ptr/kbd) | libei (RemoteDesktop portal) / wlr protocols | SendInput (keybd_event/mouse_event) | S | the VK→evdev table just becomes VK→VIRTUAL_KEY (already Win32-native) |
| Input (gamepads) | uinput X-Box-360 pad + FF rumble | ViGEm (Virtual Gamepad Emulation) + HID reports | M | rumble back-channel maps to ViGEm notifications |
| Audio capture | PipeWire sink-monitor | WASAPI loopback (IAudioCaptureClient) | S–M | also produces interleaved f32 — same AudioCapturer contract |
| Virtual mic | PipeWire Audio/Source | virtual audio device (VB-Cable-style WDM driver) or WASAPI render-to-fake-device | M | needs a driver or a bundled 3rd-party cable |
sendmmsg batching | gamestream/stream.rs | already has a cfg(not(linux)) per-packet fallback | — | nothing to do |
Rough total: ~2,000–4,000 LOC of new Rust (no C++ driver — SudoVDA is reused as-is), spread over capture/encode/vdisplay/input/audio. With the driver problem solved, the overall effort is now medium; the input+audio layer alone is small–medium.
Recommended phasing (when picked up)
- Phase 0 — "basic Windows host" (no virtual display). Capture an existing monitor (DXGI Desktop Duplication) → Media Foundation/NVENC encode → SendInput + WASAPI loopback. This proves the whole stack on Windows with the smallest surface, reusing all of core/QUIC/GameStream/mgmt. It loses the per-client native-resolution output but is a working Windows host quickly.
- Phase 1 — the virtual display via SudoVDA. A
VirtualDisplaybackend that enables SudoVDA, creates a monitor at the client's exactWxH@Hz, captures it (DXGI), and tears it down on session end — restoring punktfunk's headline feature with no driver authoring or signing. (Ship/guide the SudoVDA install as a host prerequisite, like the udev rule on Linux.) - Phase 2 — input + audio parity. ViGEm gamepads + rumble; WASAPI virtual mic; D3D11→NVENC zero-copy.
Why it's deferred (not started now)
- The remaining work is medium and mechanical, but none of it is buildable or testable on the Linux dev box — it would be unvalidated code until there's a Windows box in the loop.
- SudoVDA removed the hard blocker (the signed kernel driver); what's left is a backend port, picked up whenever a Windows target is in scope.
The architecture is ready whenever the work is scheduled; this doc + the clean trait boundaries are the down payment. Start at Phase 0 for the fastest path to a working Windows host.
Implementation Plan
The full design: protocol core, milestones, and architecture.
Apple Stage-2 Presenter (handoff)
Implementation plan for the explicit VTDecompressionSession → CAMetalLayer presenter — hand-paced present + true decode→present (glass-to-glass) measurement. Written so a Mac agent can pick it up.