feat(windows/capture): GDI cursor-shape poller — masked/monochrome cursors for the cursor channel
The M2c redesign (design/remote-desktop-sweep.md §8): the IddCx hardware- cursor query is alpha-only by design — IDDCX_CURSOR_SHAPE_TYPE has no monochrome value, the OS pre-converts monochrome to masked-color, and masked-color delivery is dead code on modern builds (proven on-glass at every ColorXorCursorSupport level). The driver keeps its hardware cursor declared (XOR FULL) purely so DWM excludes every cursor type from the IDD frame; the SHAPE now comes from a GDI poller in the capture host — which runs as SYSTEM inside the interactive session, so no helper process is needed. CursorPoller (idd_push/cursor_poll.rs, the RustDesk/WebRTC/OBS pattern): ~60 Hz GetCursorInfo on a dedicated thread; rasterise via CopyIcon→GetIconInfo→GetDIBits only when the HCURSOR value changes; monochrome via the WebRTC truth table with invert pixels as opaque black plus a white outline; AND-mask alpha for alpha-less color cursors; CURSOR_SUPPRESSED = hidden; per-output visibility via the target's desktop rect; per-monitor-V2 DPI awareness thread-scoped; input-desktop reattach on failure + 2 s cadence (GetCursorInfo on a stale desktop succeeds with stale data). Spawned iff the cursor channel was delivered; a live poller is the sole overlay source (no serial-namespace mixing) — the driver shm read remains as fallback if the poller dies. Not chosen: DXGI Desktop Duplication GetFramePointerShape — PointerPosition.Visible goes stale under injected-only input on current Win11 (Sunshine #5293, exactly our topology), it burns one of the session's four duplication slots, and IDD-output metadata has conflicting field reports. Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>
This commit is contained in:
Claude Opus 4.8
@@ -0,0 +1,442 @@
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//! GDI cursor poller — the Windows cursor-SHAPE source for the cursor-forward channel
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//! (design/remote-desktop-sweep.md §8, the M2c redesign).
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//!
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//! Why not the IddCx hardware-cursor query (the v5 `CursorShm` path, now the fallback): it is
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//! alpha-only BY DESIGN — `IDDCX_CURSOR_SHAPE_TYPE` has no monochrome value, the OS pre-converts
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//! monochrome to masked-color (IDDCX_CURSOR_CAPS docs), and masked-color delivery is dead code on
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//! modern builds (proven on-glass at every `ColorXorCursorSupport` level; no public evidence of a
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//! MASKED_COLOR delivery anywhere). The driver keeps its hardware cursor declared at XOR FULL
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//! purely so DWM EXCLUDES every cursor type from the IDD frame.
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//!
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//! Why not DXGI Desktop Duplication `GetFramePointerShape`: its `PointerPosition.Visible` goes
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//! stale when the cursor moves only via injected input on current Win11 (Sunshine #5293 — exactly
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//! a Punktfunk session's topology), it burns one of the session's four duplication slots, and its
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//! per-output metadata on IDD monitors has conflicting field reports. The GDI path below is the
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//! metadata-forwarding-remote-desktop pattern (RustDesk, WebRTC/Chrome Remote Desktop, OBS): the
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//! cursor is per-session global state in win32k, readable cross-process, and `CURSOR_SHOWING` is
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//! the logical visibility — immune to all of the above.
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//!
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//! Works because the capture host runs as SYSTEM *inside the interactive session* on
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//! `winsta0\default` (the service supervisor retargets the token — `windows/service.rs`
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//! `spawn_host`), so the poller thread sees the session's cursor directly; no helper process.
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// Every `unsafe` block in this file carries a `// SAFETY:` proof; enforce it (unsafe-proof program).
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#![deny(clippy::undocumented_unsafe_blocks)]
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use super::*;
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use windows::Win32::Graphics::Gdi::{
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DeleteObject, GetDC, GetDIBits, GetObjectW, ReleaseDC, BITMAP, BITMAPINFO, BITMAPINFOHEADER,
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BI_RGB, DIB_RGB_COLORS, HBITMAP, HDC,
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};
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use windows::Win32::System::StationsAndDesktops::{
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CloseDesktop, OpenInputDesktop, SetThreadDesktop, DESKTOP_ACCESS_FLAGS, DESKTOP_CONTROL_FLAGS,
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HDESK,
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};
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use windows::Win32::UI::HiDpi::{
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SetThreadDpiAwarenessContext, DPI_AWARENESS_CONTEXT_PER_MONITOR_AWARE_V2,
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};
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use windows::Win32::UI::WindowsAndMessaging::{
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CopyIcon, DestroyIcon, GetCursorInfo, GetIconInfo, CURSORINFO, HICON, ICONINFO,
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};
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/// `CURSORINFO.flags` bits (WindowsAndMessaging): the pointer is logically shown /
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/// touch-or-pen-suppressed. Named locally so the visibility rule below reads as the docs do.
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const CURSOR_SHOWING: u32 = 0x1;
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const CURSOR_SUPPRESSED: u32 = 0x2;
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/// A converted shape: the cache the per-tick overlay is assembled from. `rgba` is `Arc` so the
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/// slot publish (and every downstream frame attach) is a refcount bump.
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struct Shape {
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rgba: std::sync::Arc<Vec<u8>>,
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w: u32,
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h: u32,
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hot_x: u32,
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hot_y: u32,
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serial: u64,
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}
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/// Off-thread GDI cursor poller. Samples `GetCursorInfo` at ~60 Hz, rasterises the `HCURSOR` only
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/// when its handle value changes, and publishes a ready [`pf_frame::CursorOverlay`] snapshot; the
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/// capture thread's per-tick cost is one uncontended mutex read + an `Arc` clone
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/// (same split as [`DescriptorPoller`], and for the same reason: user32/gdi32 calls have no place
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/// on the capture/encode thread).
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pub(super) struct CursorPoller {
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slot: Arc<Mutex<Option<pf_frame::CursorOverlay>>>,
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stop: Arc<AtomicBool>,
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thread: Option<std::thread::JoinHandle<()>>,
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}
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impl CursorPoller {
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/// ~60 Hz: a shape change lands within one client frame; the steady-state cost is a single
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/// `GetCursorInfo` syscall per tick.
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const INTERVAL: Duration = Duration::from_millis(16);
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/// Unconditional input-desktop reattach cadence — catches secure-desktop (UAC/lock) switches
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/// without a failure signal (`GetCursorInfo` on a stale desktop *succeeds* with stale data).
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const REATTACH: Duration = Duration::from_secs(2);
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/// Spawn the poller for the virtual display `target_id`. `rect` = the target's desktop rect
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/// (`source_desktop_rect` order: x, y, w, h) — cursor positions are desktop-global; the
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/// overlay wants frame-relative, and a pointer outside the rect reports `visible: false`
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/// (per-output semantics, matching the driver shm path and the Linux portal).
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pub(super) fn spawn(target_id: u32, rect: (i32, i32, i32, i32)) -> Self {
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let slot: Arc<Mutex<Option<pf_frame::CursorOverlay>>> = Arc::new(Mutex::new(None));
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let stop = Arc::new(AtomicBool::new(false));
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let (slot_t, stop_t) = (slot.clone(), stop.clone());
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let thread = std::thread::Builder::new()
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.name("pf-cursor-poll".into())
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.spawn(move || run(target_id, rect, &slot_t, &stop_t))
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.ok();
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if thread.is_none() {
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tracing::warn!("cursor poller thread spawn failed — cursor falls back to driver shm");
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}
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Self { slot, stop, thread }
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}
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/// The latest overlay snapshot (`None` until the first successful shape rasterisation).
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pub(super) fn read(&self) -> Option<pf_frame::CursorOverlay> {
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self.slot.lock().unwrap_or_else(|p| p.into_inner()).clone()
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}
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/// Whether the worker thread is (still) alive — `false` degrades the capturer to the shm read.
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pub(super) fn alive(&self) -> bool {
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self.thread.as_ref().is_some_and(|t| !t.is_finished())
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}
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}
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impl Drop for CursorPoller {
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fn drop(&mut self) {
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self.stop.store(true, Ordering::Relaxed);
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if let Some(t) = self.thread.take() {
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let _ = t.join(); // worker sleeps ≤ INTERVAL — a bounded join
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}
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}
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}
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/// The poll loop. Owns the thread's input-desktop binding and the shape cache.
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fn run(
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target_id: u32,
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rect: (i32, i32, i32, i32),
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slot: &Mutex<Option<pf_frame::CursorOverlay>>,
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stop: &AtomicBool,
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) {
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// Physical-pixel coordinates on this thread regardless of the process's DPI awareness:
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// `rect` comes from CCD (always physical), and a DPI-virtualized `GetCursorInfo` position
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// would land in the wrong frame pixel on any scaled display. Thread-scoped, so the rest of
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// the host is untouched.
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// SAFETY: takes and returns only a by-value context handle; affects this thread only.
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let _ = unsafe { SetThreadDpiAwarenessContext(DPI_AWARENESS_CONTEXT_PER_MONITOR_AWARE_V2) };
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let mut desktop = DesktopBinding::default();
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desktop.reattach(); // best-effort: already on winsta0\default if this fails
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let mut last_attach = Instant::now();
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let mut shape: Option<Shape> = None;
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let mut cached_handle: isize = 0;
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let mut failed_handle: isize = 0; // don't re-rasterise a failing handle every tick
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let mut serial: u64 = 0;
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let mut logged_live = false;
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while !stop.load(Ordering::Relaxed) {
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std::thread::sleep(CursorPoller::INTERVAL);
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if last_attach.elapsed() >= CursorPoller::REATTACH {
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last_attach = Instant::now();
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desktop.reattach();
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}
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let mut ci = CURSORINFO {
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cbSize: std::mem::size_of::<CURSORINFO>() as u32,
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..Default::default()
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};
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// SAFETY: `ci` is a live, correctly-sized out-param for this synchronous call; no pointer
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// escapes it.
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if unsafe { GetCursorInfo(&mut ci) }.is_err() {
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// Desktop went away under us (secure-desktop switch mid-call) — rebind and retry
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// next tick; the slot keeps its last snapshot meanwhile.
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desktop.reattach();
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last_attach = Instant::now();
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continue;
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}
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let flags = ci.flags.0;
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let showing = flags & CURSOR_SHOWING != 0 && flags & CURSOR_SUPPRESSED == 0;
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// Rasterise on handle change only (position-only ticks are a header update). Hidden
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// cursors keep the cached shape — the forwarder's hidden-but-known contract needs the
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// bitmap to have been seen. v1: animated cursors publish their first frame (the OBS
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// behavior); frame cycling via DrawIconEx istep is a known follow-up.
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let handle = ci.hCursor.0 as isize;
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if showing && handle != 0 && handle != cached_handle && handle != failed_handle {
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match rasterize(ci.hCursor) {
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Some((rgba, w, h, hot_x, hot_y)) => {
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serial += 1;
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shape = Some(Shape {
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rgba: std::sync::Arc::new(rgba),
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w,
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h,
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hot_x,
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hot_y,
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serial,
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});
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cached_handle = handle;
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failed_handle = 0;
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if !logged_live {
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logged_live = true;
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tracing::info!(
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target_id,
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"cursor poller live — GDI shape source publishing (serial 1: {w}x{h})"
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);
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}
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}
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None => {
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// The owning app may have destroyed the cursor mid-read; keep the previous
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// shape and don't hammer this handle again until it changes.
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failed_handle = handle;
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}
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}
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}
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let overlay = shape.as_ref().map(|s| {
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let (px, py) = (ci.ptScreenPos.x - rect.0, ci.ptScreenPos.y - rect.1);
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let in_rect = px >= 0 && py >= 0 && px < rect.2 && py < rect.3;
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pf_frame::CursorOverlay {
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// Overlay x/y = bitmap top-left (reported position − hotspot), frame pixels.
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x: px - s.hot_x as i32,
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y: py - s.hot_y as i32,
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w: s.w,
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h: s.h,
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rgba: s.rgba.clone(),
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serial: s.serial,
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hot_x: s.hot_x,
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hot_y: s.hot_y,
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visible: showing && in_rect,
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}
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});
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*slot.lock().unwrap_or_else(|p| p.into_inner()) = overlay;
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}
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}
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/// The thread's owned input-desktop handle — the [`SendInputInjector`] reattach model
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/// (`pf-inject` sendinput.rs): keep the current binding, swap on demand, close exactly once.
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#[derive(Default)]
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struct DesktopBinding(Option<HDESK>);
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impl DesktopBinding {
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fn reattach(&mut self) {
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const GENERIC_ALL: u32 = 0x1000_0000;
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// SAFETY: `OpenInputDesktop`/`SetThreadDesktop`/`CloseDesktop` take only by-value args.
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// `OpenInputDesktop` yields an owned `HDESK` only on `Ok`; it is either installed (and the
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// previously-owned handle closed exactly once) or closed on failure — no handle is leaked
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// or used after close. `SetThreadDesktop` rebinds only this calling thread (which owns
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// no windows/hooks, so the rebind cannot fail on that account).
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unsafe {
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match OpenInputDesktop(
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DESKTOP_CONTROL_FLAGS(0),
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false,
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DESKTOP_ACCESS_FLAGS(GENERIC_ALL),
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) {
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Ok(h) => {
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if SetThreadDesktop(h).is_ok() {
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if let Some(old) = self.0.replace(h) {
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let _ = CloseDesktop(old);
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}
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} else {
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let _ = CloseDesktop(h);
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}
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}
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Err(_) => { /* not privileged for this desktop; stay put */ }
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}
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}
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}
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}
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impl Drop for DesktopBinding {
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fn drop(&mut self) {
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if let Some(h) = self.0.take() {
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// SAFETY: `h` is our owned desktop handle, closed exactly once here.
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let _ = unsafe { CloseDesktop(h) };
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}
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}
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}
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/// Rasterise `hcursor` to straight-alpha RGBA: `(rgba, w, h, hot_x, hot_y)`. `None` on any
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/// failure (caller keeps the previous shape).
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fn rasterize(hcursor: windows::Win32::UI::WindowsAndMessaging::HCURSOR) -> RasterOut {
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// CopyIcon first: the owning process can destroy its HCURSOR between GetCursorInfo and the
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// reads below; the copy is ours (the OBS/WebRTC guard).
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// SAFETY: `HICON(hcursor.0)` reinterprets the cursor handle as an icon handle (cursors ARE
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// icons in user32); CopyIcon yields an owned HICON we destroy below.
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let Ok(icon) = (unsafe { CopyIcon(HICON(hcursor.0)) }) else {
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return None;
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};
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let mut ii = ICONINFO::default();
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// SAFETY: `ii` is a live out-param. On Ok it hands us COPIES of the mask/color bitmaps —
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// both deleted below (GDI-handle leak otherwise).
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let got = unsafe { GetIconInfo(icon, &mut ii) };
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let out = if got.is_ok() { convert(&ii) } else { None };
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// SAFETY: deleting the two bitmap copies GetIconInfo returned (null-safe: DeleteObject on a
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// null HGDIOBJ fails harmlessly) and the icon copy — each exactly once.
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unsafe {
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let _ = DeleteObject(ii.hbmColor.into());
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let _ = DeleteObject(ii.hbmMask.into());
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let _ = DestroyIcon(icon);
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}
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out.map(|(rgba, w, h)| {
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let hot_x = ii.xHotspot.min(w.saturating_sub(1));
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let hot_y = ii.yHotspot.min(h.saturating_sub(1));
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(rgba, w, h, hot_x, hot_y)
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})
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}
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type RasterOut = Option<(Vec<u8>, u32, u32, u32, u32)>;
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/// Convert the ICONINFO bitmaps to straight RGBA. Two families:
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/// - color (`hbmColor` set): 32bpp BGRA; if the alpha channel is entirely empty (old-style
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/// cursors) the AND mask supplies it (mask bit 1 = transparent).
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/// - monochrome (`hbmColor` null): `hbmMask` is DOUBLE height — AND plane over XOR plane, the
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/// WebRTC truth table: (0,0) black, (0,1) white, (1,0) transparent, (1,1) invert. Invert
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/// pixels — unrepresentable in straight alpha — become opaque black with a white outline
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/// grown into adjacent transparency (the WebRTC approximation; keeps the I-beam legible on
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/// any background, which the old translucent-gray stand-in did not).
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fn convert(ii: &ICONINFO) -> Option<(Vec<u8>, u32, u32)> {
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// SAFETY: GetDC(None) yields the screen DC, released below on every path; it is only used
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// as the GetDIBits reference DC.
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let dc = unsafe { GetDC(None) };
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let result = (|| {
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if !ii.hbmColor.is_invalid() {
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let color = read_bitmap_32(dc, ii.hbmColor)?;
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let (w, h) = (color.w as u32, color.h as u32);
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let mut rgba = bgra_to_rgba(&color.bgra);
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if rgba.chunks_exact(4).all(|p| p[3] == 0) {
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// Alpha-less color cursor: transparency lives in the AND mask.
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let mask = read_bitmap_32(dc, ii.hbmMask)?;
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if mask.w != color.w || mask.h < color.h {
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return None;
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}
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for (px, m) in rgba.chunks_exact_mut(4).zip(mask.bgra.chunks_exact(4)) {
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px[3] = if m[0] != 0 { 0 } else { 0xFF }; // mask white (AND=1) = transparent
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}
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}
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Some((rgba, w, h))
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} else {
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let mask = read_bitmap_32(dc, ii.hbmMask)?;
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if mask.h < 2 || mask.h % 2 != 0 {
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return None;
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}
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let (w, h) = (mask.w as usize, (mask.h / 2) as usize);
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let row = w * 4;
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let (and_plane, xor_plane) = mask.bgra.split_at(h * row);
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let mut rgba = vec![0u8; w * h * 4];
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let mut invert = vec![false; w * h];
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for i in 0..w * h {
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let (a, x) = (and_plane[i * 4] != 0, xor_plane[i * 4] != 0);
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let px = &mut rgba[i * 4..i * 4 + 4];
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match (a, x) {
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(false, false) => px.copy_from_slice(&[0, 0, 0, 0xFF]),
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(false, true) => px.copy_from_slice(&[0xFF, 0xFF, 0xFF, 0xFF]),
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(true, false) => {} // transparent (already zeroed)
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(true, true) => {
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px.copy_from_slice(&[0, 0, 0, 0xFF]);
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invert[i] = true;
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}
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}
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}
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// White outline around invert regions so the (now black) shape survives dark
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// backgrounds: any transparent 8-neighbor of an invert pixel turns opaque white.
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for y in 0..h as i32 {
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for x in 0..w as i32 {
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if !invert[(y * w as i32 + x) as usize] {
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continue;
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}
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for (dx, dy) in NEIGHBORS {
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let (nx, ny) = (x + dx, y + dy);
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if nx < 0 || ny < 0 || nx >= w as i32 || ny >= h as i32 {
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continue;
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}
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let o = (ny * w as i32 + nx) as usize * 4;
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if rgba[o + 3] == 0 {
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rgba[o..o + 4].copy_from_slice(&[0xFF, 0xFF, 0xFF, 0xFF]);
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}
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}
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}
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}
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Some((rgba, w as u32, h as u32))
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}
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})();
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// SAFETY: releasing the screen DC obtained above, exactly once.
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||||
unsafe {
|
||||
ReleaseDC(None, dc);
|
||||
}
|
||||
result
|
||||
}
|
||||
|
||||
const NEIGHBORS: [(i32, i32); 8] = [
|
||||
(-1, -1),
|
||||
(0, -1),
|
||||
(1, -1),
|
||||
(-1, 0),
|
||||
(1, 0),
|
||||
(-1, 1),
|
||||
(0, 1),
|
||||
(1, 1),
|
||||
];
|
||||
|
||||
struct RawBitmap {
|
||||
w: i32,
|
||||
h: i32,
|
||||
/// 32bpp top-down BGRA rows, `w*h*4` (monochrome sources arrive expanded: 0x00/0xFF channels).
|
||||
bgra: Vec<u8>,
|
||||
}
|
||||
|
||||
/// Read any GDI bitmap as 32bpp top-down via `GetDIBits` (which performs the 1bpp→32bpp
|
||||
/// expansion for the mask planes).
|
||||
fn read_bitmap_32(dc: HDC, hbm: HBITMAP) -> Option<RawBitmap> {
|
||||
let mut bm = BITMAP::default();
|
||||
// SAFETY: `bm` is a live out-param sized exactly as passed; GetObjectW only writes into it.
|
||||
let n = unsafe {
|
||||
GetObjectW(
|
||||
hbm.into(),
|
||||
std::mem::size_of::<BITMAP>() as i32,
|
||||
Some((&mut bm as *mut BITMAP).cast()),
|
||||
)
|
||||
};
|
||||
if n == 0 || bm.bmWidth <= 0 || bm.bmHeight <= 0 || bm.bmWidth > 512 || bm.bmHeight > 1024 {
|
||||
return None; // 512/1024: sanity caps (256² is the wire max; XL accessibility ≤ that)
|
||||
}
|
||||
let (w, h) = (bm.bmWidth, bm.bmHeight);
|
||||
let mut info = BITMAPINFO {
|
||||
bmiHeader: BITMAPINFOHEADER {
|
||||
biSize: std::mem::size_of::<BITMAPINFOHEADER>() as u32,
|
||||
biWidth: w,
|
||||
biHeight: -h, // top-down
|
||||
biPlanes: 1,
|
||||
biBitCount: 32,
|
||||
biCompression: BI_RGB.0,
|
||||
..Default::default()
|
||||
},
|
||||
..Default::default()
|
||||
};
|
||||
let mut buf = vec![0u8; (w as usize) * (h as usize) * 4];
|
||||
// SAFETY: `buf` spans exactly `h` rows of `w` 32bpp pixels as described by `info`; both are
|
||||
// live locals for this synchronous call, `hbm` is a live bitmap not selected into any DC
|
||||
// (fresh GetIconInfo copies).
|
||||
let rows = unsafe {
|
||||
GetDIBits(
|
||||
dc,
|
||||
hbm,
|
||||
0,
|
||||
h as u32,
|
||||
Some(buf.as_mut_ptr().cast()),
|
||||
&mut info,
|
||||
DIB_RGB_COLORS,
|
||||
)
|
||||
};
|
||||
(rows != 0).then_some(RawBitmap { w, h, bgra: buf })
|
||||
}
|
||||
|
||||
fn bgra_to_rgba(bgra: &[u8]) -> Vec<u8> {
|
||||
let mut out = bgra.to_vec();
|
||||
for px in out.chunks_exact_mut(4) {
|
||||
px.swap(0, 2);
|
||||
}
|
||||
out
|
||||
}
|
||||
Reference in New Issue
Block a user