Revert "fix(host/windows): rebuild the output fresh on every WGC↔DDA source switch"

This reverts commit 3f191ba2ea.

crates/punktfunk-host/src/capture/composed_flip.rs

@@ -17,21 +17,19 @@
 
 use std::sync::atomic::{AtomicBool, Ordering};
 use std::sync::Arc;
-use windows::core::w;
+use windows::core::{w, PCWSTR};
 use windows::Win32::Foundation::{HWND, LPARAM, LRESULT, WPARAM};
-use windows::Win32::Graphics::Gdi::{GetStockObject, BLACK_BRUSH, HBRUSH};
 use windows::Win32::System::LibraryLoader::GetModuleHandleW;
 use windows::Win32::System::StationsAndDesktops::{
     CloseDesktop, GetUserObjectInformationW, OpenInputDesktop, SetThreadDesktop,
     DESKTOP_ACCESS_FLAGS, DESKTOP_CONTROL_FLAGS, UOI_NAME,
 };
 use windows::Win32::UI::WindowsAndMessaging::{
-    CreateWindowExW, DefWindowProcW, DestroyWindow, DispatchMessageW, GetSystemMetrics,
+    CreateWindowExW, DefWindowProcW, DestroyWindow, DispatchMessageW, PeekMessageW, RegisterClassW,
-    PeekMessageW, RegisterClassW, SetLayeredWindowAttributes, SetWindowPos, ShowWindow,
+    SetLayeredWindowAttributes, SetWindowPos, ShowWindow, TranslateMessage, HWND_TOPMOST,
-    TranslateMessage, HWND_TOPMOST, LWA_COLORKEY, MSG, PM_REMOVE, SM_CXVIRTUALSCREEN,
+    LWA_ALPHA, MSG, PM_REMOVE, SWP_NOACTIVATE, SWP_NOMOVE, SWP_NOSIZE, SW_SHOWNOACTIVATE,
-    SM_CYVIRTUALSCREEN, SM_XVIRTUALSCREEN, SM_YVIRTUALSCREEN, SWP_NOACTIVATE, SWP_NOMOVE,
+    WNDCLASSW, WS_EX_LAYERED, WS_EX_NOACTIVATE, WS_EX_TOOLWINDOW, WS_EX_TOPMOST, WS_EX_TRANSPARENT,
-    SWP_NOSIZE, SW_SHOWNOACTIVATE, WNDCLASSW, WS_EX_LAYERED, WS_EX_NOACTIVATE, WS_EX_TOOLWINDOW,
+    WS_POPUP,
-    WS_EX_TOPMOST, WS_EX_TRANSPARENT, WS_POPUP,
 };
 
 /// A running force-composed-flip overlay. Drop signals the thread to tear down its window + exit.
@@ -107,8 +105,6 @@ unsafe fn make_overlay() -> Option<HWND> {
         lpfnWndProc: Some(wndproc),
         hInstance: hinst.into(),
         lpszClassName: class,
-        // Paint the window black so LWA_COLORKEY(black) keys it out → visually invisible.
-        hbrBackground: HBRUSH(GetStockObject(BLACK_BRUSH).0),
         ..Default::default()
     };
     let atom = RegisterClassW(&wc);
@@ -119,24 +115,15 @@ unsafe fn make_overlay() -> Option<HWND> {
             tracing::warn!(err = e.0, "force-composed-flip: RegisterClassW failed");
         }
     }
-    // Cover the WHOLE virtual screen (all outputs incl. the SudoVDA): a 1x1 corner window may not even
-    // sit on the captured output's rect, and independent-flip is per-output. A window overlapping the
-    // output is what disqualifies its flip.
-    let (vx, vy, vw, vh) = (
-        GetSystemMetrics(SM_XVIRTUALSCREEN),
-        GetSystemMetrics(SM_YVIRTUALSCREEN),
-        GetSystemMetrics(SM_CXVIRTUALSCREEN).max(1),
-        GetSystemMetrics(SM_CYVIRTUALSCREEN).max(1),
-    );
     let hwnd = match CreateWindowExW(
         WS_EX_LAYERED | WS_EX_TRANSPARENT | WS_EX_TOPMOST | WS_EX_NOACTIVATE | WS_EX_TOOLWINDOW,
         class,
         w!(""),
         WS_POPUP,
-        vx,
+        0,
-        vy,
+        0,
-        vw,
+        1,
-        vh,
+        1,
         None,
         None,
         Some(hinst.into()),
@@ -150,16 +137,8 @@ unsafe fn make_overlay() -> Option<HWND> {
             return None;
         }
     };
-    // Color-key on black: the window is painted black (its WNDCLASS background brush) and black is keyed
+    // alpha=1: technically visible (so it disqualifies independent-flip) but imperceptible.
-    // out, so it's visually invisible — but DWM counts it as a real opaque window covering the output,
+    let _ = SetLayeredWindowAttributes(hwnd, windows::Win32::Foundation::COLORREF(0), 1, LWA_ALPHA);
-    // which is what disqualifies the fullscreen independent-flip (a near-zero ALPHA layered window is
-    // often ignored by the flip-eligibility check; a color-keyed one is not).
-    let _ = SetLayeredWindowAttributes(
-        hwnd,
-        windows::Win32::Foundation::COLORREF(0x0000_0000),
-        0,
-        LWA_COLORKEY,
-    );
     let _ = ShowWindow(hwnd, SW_SHOWNOACTIVATE);
     let _ = SetWindowPos(
         hwnd,

crates/punktfunk-host/src/m3.rs

@@ -2453,40 +2453,26 @@ fn virtual_stream_relay(
                 },
                 "two-process: source switch"
             );
-            // Rebuild the SudoVDA output FRESH on every source switch — the key insight: a fresh
-            // reconnect captures the secure desktop but the live transition (which reused the
-            // session-start output, created while on the NORMAL desktop) does not. `build` does the
-            // exact reconnect setup: REMOVE + fresh ADD of the virtual monitor + re-isolate + a fresh
-            // capturer, so the new output is in the clean state that DDA can duplicate on the secure
-            // desktop. Drop the old DDA (it's bound to the old target); reopen on the new one.
-            match build(&mut vd, cur_mode) {
-                Ok((ka, rl, tg, hz)) => {
-                    relay = rl; // fresh helper (drops the old) ...
-                    _keepalive = ka; // ... then releases the old output
-                    target = tg;
-                    effective_hz = hz;
-                    interval = std::time::Duration::from_secs_f64(1.0 / hz.max(1) as f64);
-                }
-                Err(e) => {
-                    tracing::error!(error = %format!("{e:#}"),
-                        "two-process: source-switch rebuild failed — staying on the current source");
-                }
-            }
-            dda = None; // old DDA was on the old target
             if secure {
-                match open_dda(&target, cur_mode.width, cur_mode.height, effective_hz) {
+                if dda.is_none() {
-                    Ok(mut p) => {
+                    match open_dda(&target, cur_mode.width, cur_mode.height, effective_hz) {
-                        p.enc.request_keyframe();
+                        Ok(p) => dda = Some(p),
-                        dda = Some(p);
+                        Err(e) => {
-                    }
+                            tracing::error!(error = %format!("{e:#}"),
-                    Err(e) => {
+                                "two-process: DDA open failed — secure desktop will freeze on last frame");
-                        tracing::error!(error = %format!("{e:#}"),
+                        }
-                            "two-process: DDA open failed — secure desktop will freeze on last frame");
                     }
                 }
+                if let Some(d) = dda.as_mut() {
+                    d.enc.request_keyframe();
+                }
                 next = std::time::Instant::now();
+            } else {
+                // Returning to the helper: drain stale buffered AUs (encoded while we ignored it) and
+                // force a fresh IDR; await_idr then skips the stale deltas until that IDR arrives.
+                while relay.try_recv().is_ok() {}
+                relay.request_keyframe();
             }
-            // (normal: the fresh helper's first frame is its opening IDR — await_idr clears on it.)
         }
         if want_kf {
             if secure {