perf: fix RDP window drag blockiness — full window drag + remove throttle

Root cause: PerformanceFlags::default() included DISABLE_FULLWINDOWDRAG
which told the RDP server to skip window contents during drag operations.
Additionally, the frame_gen % 2 backend throttle dropped 50% of frame
notifications during rapid updates.

Fix:
- PerformanceFlags: removed DISABLE_FULLWINDOWDRAG, added DISABLE_WALLPAPER,
  DISABLE_CURSOR_SHADOW, ENABLE_DESKTOP_COMPOSITION for optimal rendering
- Removed backend frame throttle — frontend rAF coalescing handles rate limiting
- Simplified buffer architecture: eliminated back_buffer and TokioMutex,
  RDP thread writes directly to front_buffer via RwLock write lock
- Removed unused tokio::sync::Mutex import

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

src-tauri/src/rdp/mod.rs

@@ -13,7 +13,7 @@ use serde::{Deserialize, Serialize};
 use tokio::io::{AsyncRead, AsyncWrite};
 use tokio::net::TcpStream;
 use tokio::sync::mpsc;
-use tokio::sync::Mutex as TokioMutex;
+
 
 use ironrdp::connector::{self, ClientConnector, ConnectionResult, Credentials, DesktopSize};
 use ironrdp::graphics::image_processing::PixelFormat;
@@ -71,15 +71,10 @@ struct RdpSessionHandle {
     hostname: String,
     width: u16,
     height: u16,
-    /// Double-buffered: back_buffer is written by the RDP thread,
+    /// Frame buffer: RDP thread writes via RwLock write, IPC reads via RwLock read.
-    /// front_buffer is read by the IPC command. Swap on GraphicsUpdate
+    /// Brief write-lock per GraphicsUpdate, concurrent reads for get_frame.
-    /// so reads never block writes. Arcs kept alive via struct ownership.
     front_buffer: Arc<std::sync::RwLock<Vec<u8>>>,
-    #[allow(dead_code)]
-    back_buffer: Arc<TokioMutex<Vec<u8>>>,
     frame_dirty: Arc<AtomicBool>,
-    #[allow(dead_code)]
-    frame_generation: Arc<std::sync::atomic::AtomicU64>,
     input_tx: mpsc::UnboundedSender<InputEvent>,
 }
 
@@ -106,10 +101,8 @@ impl RdpService {
         for pixel in initial_buf.chunks_exact_mut(4) {
             pixel[3] = 255;
         }
-        let front_buffer = Arc::new(std::sync::RwLock::new(initial_buf.clone()));
+        let front_buffer = Arc::new(std::sync::RwLock::new(initial_buf));
-        let back_buffer = Arc::new(TokioMutex::new(initial_buf));
         let frame_dirty = Arc::new(AtomicBool::new(false));
-        let frame_generation = Arc::new(std::sync::atomic::AtomicU64::new(0));
 
         let (input_tx, input_rx) = mpsc::unbounded_channel();
 
@@ -119,9 +112,7 @@ impl RdpService {
             width,
             height,
             front_buffer: front_buffer.clone(),
-            back_buffer: back_buffer.clone(),
             frame_dirty: frame_dirty.clone(),
-            frame_generation: frame_generation.clone(),
             input_tx,
         });
 
@@ -167,10 +158,8 @@ impl RdpService {
                 if let Err(e) = run_active_session(
                     connection_result,
                     framed,
-                    back_buffer,
                     front_buffer,
                     frame_dirty,
-                    frame_generation,
                     input_rx,
                     width as u16,
                     height as u16,
@@ -319,7 +308,11 @@ fn build_connector_config(config: &RdpConfig) -> Result<connector::Config, Strin
         request_data: None,
         autologon: false,
         enable_audio_playback: false,
-        performance_flags: PerformanceFlags::default(),
+        performance_flags: PerformanceFlags::DISABLE_WALLPAPER
+            | PerformanceFlags::DISABLE_MENUANIMATIONS
+            | PerformanceFlags::DISABLE_CURSOR_SHADOW
+            | PerformanceFlags::ENABLE_FONT_SMOOTHING
+            | PerformanceFlags::ENABLE_DESKTOP_COMPOSITION,
         desktop_scale_factor: 0,
         hardware_id: None,
         license_cache: None,
@@ -349,7 +342,7 @@ async fn establish_connection(config: connector::Config, hostname: &str, port: u
     Ok((connection_result, upgraded_framed))
 }
 
-async fn run_active_session(connection_result: ConnectionResult, framed: UpgradedFramed, back_buffer: Arc<TokioMutex<Vec<u8>>>, front_buffer: Arc<std::sync::RwLock<Vec<u8>>>, frame_dirty: Arc<AtomicBool>, frame_generation: Arc<std::sync::atomic::AtomicU64>, mut input_rx: mpsc::UnboundedReceiver<InputEvent>, width: u16, height: u16, app_handle: tauri::AppHandle, session_id: String) -> Result<(), String> {
+async fn run_active_session(connection_result: ConnectionResult, framed: UpgradedFramed, front_buffer: Arc<std::sync::RwLock<Vec<u8>>>, frame_dirty: Arc<AtomicBool>, mut input_rx: mpsc::UnboundedReceiver<InputEvent>, width: u16, height: u16, app_handle: tauri::AppHandle, session_id: String) -> Result<(), String> {
     let (mut reader, mut writer) = split_tokio_framed(framed);
     let mut image = DecodedImage::new(PixelFormat::RgbA32, width, height);
     let mut active_stage = ActiveStage::new(connection_result);
@@ -408,24 +401,16 @@ async fn run_active_session(connection_result: ConnectionResult, framed: Upgrade
             match out {
                 ActiveStageOutput::ResponseFrame(frame) => { writer.write_all(&frame).await.map_err(|e| format!("Failed to write RDP response frame: {}", e))?; }
                 ActiveStageOutput::GraphicsUpdate(_region) => {
-                    // Write to back buffer (async mutex, no contention with reads)
+                    // Write decoded image directly to front buffer.
+                    // Single RwLock write — readers use read lock, no contention.
                     {
-                        let mut buf = back_buffer.lock().await;
                         let src = image.data();
-                        if src.len() == buf.len() { buf.copy_from_slice(src); } else { *buf = src.to_vec(); }
-                    }
-                    // Swap into front buffer (RwLock write — brief, readers use read lock)
-                    {
-                        let back = back_buffer.lock().await;
                         let mut front = front_buffer.write().unwrap_or_else(|e| e.into_inner());
-                        front.copy_from_slice(&back);
+                        if src.len() == front.len() { front.copy_from_slice(src); } else { *front = src.to_vec(); }
                     }
-                    let frame_gen = frame_generation.fetch_add(1, Ordering::Release);
                     frame_dirty.store(true, Ordering::Release);
-                    // Throttle: only emit event every other frame to avoid flooding IPC
+                    // Signal frontend — rAF coalescing prevents flood
-                    if frame_gen % 2 == 0 {
+                    let _ = app_handle.emit(&format!("rdp:frame:{}", session_id), ());
-                        let _ = app_handle.emit(&format!("rdp:frame:{}", session_id), ());
-                    }
                 }
                 ActiveStageOutput::Terminate(reason) => { info!("RDP session terminated: {:?}", reason); return Ok(()); }
                 ActiveStageOutput::DeactivateAll(_) => { warn!("RDP server sent DeactivateAll — reconnection not yet implemented"); return Ok(()); }