feat(wm): add alt-tab heuristics to wsr

This commit adds some rough heuristics to workspace_reconciliator which
should help with having the correct window focused after reconciliation
in the majority of, but probably not all, cases.

EnumWindows generally returns HWNDs according to z order, and a window
selected by alt-tab will almost always be put on the top of the z order.
Before sending a workspace_reconciliator::Notification, we store this
HWND along with an Instant and an AtomicBool telling us that we have a
candidate to focus after the workspace switch.

justfile

@@ -28,7 +28,6 @@ install:
     just install-target komorebi
 
 run:
-    just install-target komorebic
     cargo +stable run --bin komorebi --locked
 
 warn $RUST_LOG="warn":
@@ -44,7 +43,6 @@ trace $RUST_LOG="trace":
     just run
 
 deadlock $RUST_LOG="trace":
-    just install-komorebic
     cargo +stable run --bin komorebi --locked --features deadlock_detection
 
 docgen:

komorebi/src/border_manager/mod.rs

@@ -18,8 +18,11 @@ use std::sync::atomic::AtomicI32;
 use std::sync::atomic::AtomicU32;
 use std::sync::Arc;
 use std::sync::OnceLock;
+use std::time::Duration;
+use std::time::Instant;
 use windows::Win32::Foundation::HWND;
 
+use crate::workspace_reconciliator::ALT_TAB_HWND;
 use crate::Colour;
 use crate::Rect;
 use crate::Rgb;
@@ -121,23 +124,37 @@ pub fn handle_notifications(wm: Arc<Mutex<WindowManager>>) -> color_eyre::Result
     tracing::info!("listening");
 
     let receiver = event_rx();
+    let mut instant: Option<Instant> = None;
+    event_tx().send(Notification)?;
 
     'receiver: for _ in receiver {
+        if let Some(instant) = instant {
+            if instant.elapsed().lt(&Duration::from_millis(50)) {
+                continue 'receiver;
+            }
+        }
+
+        instant = Some(Instant::now());
+
         let mut borders = BORDER_STATE.lock();
         let mut borders_monitors = BORDERS_MONITORS.lock();
 
         // Check the wm state every time we receive a notification
         let state = wm.lock();
 
-        if !BORDER_ENABLED.load_consume() || state.is_paused {
-            if !borders.is_empty() {
-                for (_, border) in borders.iter() {
-                    border.destroy()?;
-                }
-
-                borders.clear();
+        // If borders are disabled
+        if !BORDER_ENABLED.load_consume()
+           // Or if the wm is paused
+            || state.is_paused
+            // Or if we are handling an alt-tab across workspaces
+            || ALT_TAB_HWND.load().is_some()
+        {
+            // Destroy the borders we know about
+            for (_, border) in borders.iter() {
+                border.destroy()?;
             }
 
+            borders.clear();
             continue 'receiver;
         }
 

komorebi/src/process_event.rs

@@ -1,6 +1,8 @@
 use std::fs::OpenOptions;
 use std::sync::atomic::Ordering;
 use std::sync::Arc;
+use std::time::Duration;
+use std::time::Instant;
 
 use color_eyre::eyre::anyhow;
 use color_eyre::Result;
@@ -23,6 +25,8 @@ use crate::window_manager_event::WindowManagerEvent;
 use crate::windows_api::WindowsApi;
 use crate::winevent::WinEvent;
 use crate::workspace_reconciliator;
+use crate::workspace_reconciliator::ALT_TAB_HWND;
+use crate::workspace_reconciliator::ALT_TAB_HWND_INSTANT;
 use crate::Notification;
 use crate::NotificationEvent;
 use crate::DATA_DIR;
@@ -271,6 +275,24 @@ impl WindowManager {
                 for (i, monitors) in self.monitors().iter().enumerate() {
                     for (j, workspace) in monitors.workspaces().iter().enumerate() {
                         if workspace.contains_window(window.hwnd) && focused_pair != (i, j) {
+                            // At this point we know we are going to send a notification to the workspace reconciliator
+                            // So we get the topmost window returned by EnumWindows, which is almost always the window
+                            // that has been selected by alt-tab
+                            if let Ok(alt_tab_windows) = WindowsApi::alt_tab_windows() {
+                                if let Some(first) =
+                                    alt_tab_windows.iter().find(|w| w.title().is_ok())
+                                {
+                                    // If our record of this HWND hasn't been updated in over a minute
+                                    let mut instant = ALT_TAB_HWND_INSTANT.lock();
+                                    if instant.elapsed().gt(&Duration::from_secs(1)) {
+                                        // Update our record with the HWND we just found
+                                        ALT_TAB_HWND.store(Some(first.hwnd));
+                                        // Update the timestamp of our record
+                                        *instant = Instant::now();
+                                    }
+                                }
+                            }
+
                             workspace_reconciliator::event_tx().send(
                                 workspace_reconciliator::Notification {
                                     monitor_idx: i,

komorebi/src/windows_api.rs

@@ -139,6 +139,7 @@ use crate::monitor::Monitor;
 use crate::ring::Ring;
 use crate::set_window_position::SetWindowPosition;
 use crate::windows_callbacks;
+use crate::Window;
 
 pub enum WindowsResult<T, E> {
     Err(E),
@@ -493,6 +494,16 @@ impl WindowsApi {
         unsafe { GetWindow(hwnd, GW_HWNDNEXT) }.process()
     }
 
+    pub fn alt_tab_windows() -> Result<Vec<Window>> {
+        let mut hwnds = vec![];
+        Self::enum_windows(
+            Some(windows_callbacks::alt_tab_windows),
+            &mut hwnds as *mut Vec<Window> as isize,
+        )?;
+
+        Ok(hwnds)
+    }
+
     #[allow(dead_code)]
     pub fn top_visible_window() -> Result<isize> {
         let hwnd = Self::top_window()?;

komorebi/src/windows_callbacks.rs

@@ -152,6 +152,26 @@ pub extern "system" fn enum_window(hwnd: HWND, lparam: LPARAM) -> BOOL {
     true.into()
 }
 
+pub extern "system" fn alt_tab_windows(hwnd: HWND, lparam: LPARAM) -> BOOL {
+    let windows = unsafe { &mut *(lparam.0 as *mut Vec<Window>) };
+
+    let is_visible = WindowsApi::is_window_visible(hwnd);
+    let is_window = WindowsApi::is_window(hwnd);
+    let is_minimized = WindowsApi::is_iconic(hwnd);
+
+    if is_visible && is_window && !is_minimized {
+        let window = Window { hwnd: hwnd.0 };
+
+        if let Ok(should_manage) = window.should_manage(None, &mut RuleDebug::default()) {
+            if should_manage {
+                windows.push(window);
+            }
+        }
+    }
+
+    true.into()
+}
+
 pub extern "system" fn win_event_hook(
     _h_win_event_hook: HWINEVENTHOOK,
     event: u32,

komorebi/src/workspace_reconciliator.rs

@@ -1,11 +1,16 @@
 #![deny(clippy::unwrap_used, clippy::expect_used)]
 
+use crate::border_manager;
 use crate::WindowManager;
 use crossbeam_channel::Receiver;
 use crossbeam_channel::Sender;
+use crossbeam_utils::atomic::AtomicCell;
+use lazy_static::lazy_static;
 use parking_lot::Mutex;
 use std::sync::Arc;
 use std::sync::OnceLock;
+use std::time::Duration;
+use std::time::Instant;
 
 #[derive(Copy, Clone)]
 pub struct Notification {
@@ -13,6 +18,12 @@ pub struct Notification {
     pub workspace_idx: usize,
 }
 
+pub static ALT_TAB_HWND: AtomicCell<Option<isize>> = AtomicCell::new(None);
+
+lazy_static! {
+    pub static ref ALT_TAB_HWND_INSTANT: Arc<Mutex<Instant>> = Arc::new(Mutex::new(Instant::now()));
+}
+
 static CHANNEL: OnceLock<(Sender<Notification>, Receiver<Notification>)> = OnceLock::new();
 
 pub fn channel() -> &'static (Sender<Notification>, Receiver<Notification>) {
@@ -34,7 +45,11 @@ pub fn listen_for_notifications(wm: Arc<Mutex<WindowManager>>) {
                 tracing::warn!("restarting finished thread");
             }
             Err(error) => {
-                tracing::warn!("restarting failed thread: {}", error);
+                if cfg!(debug_assertions) {
+                    tracing::error!("restarting failed thread: {:?}", error)
+                } else {
+                    tracing::error!("restarting failed thread: {}", error)
+                }
             }
         }
     });
@@ -43,9 +58,11 @@ pub fn handle_notifications(wm: Arc<Mutex<WindowManager>>) -> color_eyre::Result
     tracing::info!("listening");
 
     let receiver = event_rx();
+    let arc = wm.clone();
 
     for notification in receiver {
         tracing::info!("running reconciliation");
+
         let mut wm = wm.lock();
         let focused_monitor_idx = wm.focused_monitor_idx();
         let focused_workspace_idx =
@@ -62,6 +79,36 @@ pub fn handle_notifications(wm: Arc<Mutex<WindowManager>>) -> color_eyre::Result
                 monitor.focus_workspace(notification.workspace_idx)?;
                 monitor.load_focused_workspace(mouse_follows_focus)?;
             }
+
+            // Drop our lock on the window manager state here to not slow down updates
+            drop(wm);
+
+            // Check if there was an alt-tab across workspaces in the last second
+            if let Some(hwnd) = ALT_TAB_HWND.load() {
+                if ALT_TAB_HWND_INSTANT
+                    .lock()
+                    .elapsed()
+                    .lt(&Duration::from_secs(1))
+                {
+                    // Sleep for 100 millis to let other events pass
+                    std::thread::sleep(Duration::from_millis(100));
+                    tracing::info!("focusing alt-tabbed window");
+
+                    // Take a new lock on the wm and try to focus the container with
+                    // the recorded HWND from the alt-tab
+                    let mut wm = arc.lock();
+                    if let Ok(workspace) = wm.focused_workspace_mut() {
+                        // Regardless of if this fails, we need to get past this part
+                        // to unblock the border manager below
+                        let _ = workspace.focus_container_by_window(hwnd);
+                    }
+
+                    // Unblock the border manager
+                    ALT_TAB_HWND.store(None);
+                    // Send a notification to the border manager to update the borders
+                    border_manager::event_tx().send(border_manager::Notification)?;
+                }
+            }
         }
     }