Implement focus-follows-mouse

niri-config/src/lib.rs

@@ -71,6 +71,8 @@ pub struct Input {
     pub disable_power_key_handling: bool,
     #[knuffel(child)]
     pub warp_mouse_to_focus: bool,
+    #[knuffel(child)]
+    pub focus_follows_mouse: bool,
 }
 
 #[derive(knuffel::Decode, Debug, Default, PartialEq, Eq)]
@@ -1596,6 +1598,7 @@ mod tests {
                 disable-power-key-handling
 
                 warp-mouse-to-focus
+                focus-follows-mouse
             }
 
             output "eDP-1" {
@@ -1736,6 +1739,7 @@ mod tests {
                     },
                     disable_power_key_handling: true,
                     warp_mouse_to_focus: true,
+                    focus_follows_mouse: true,
                 },
                 outputs: vec![Output {
                     off: false,

resources/default-config.kdl

@@ -70,6 +70,9 @@ input {
 
     // Uncomment this to make the mouse warp to the center of newly focused windows.
     // warp-mouse-to-focus
+
+    // Focus windows and outputs automatically when moving the mouse into them.
+    // focus-follows-mouse
 }
 
 // You can configure outputs by their name, which you can find

src/input.rs

@@ -903,6 +903,8 @@ impl State {
             }
         }
 
+        self.niri.handle_focus_follows_mouse(&under);
+
         // Activate a new confinement if necessary.
         self.niri.maybe_activate_pointer_constraint(new_pos, &under);
 
@@ -967,6 +969,9 @@ impl State {
         }
 
         let under = self.niri.surface_under_and_global_space(pos);
+
+        self.niri.handle_focus_follows_mouse(&under);
+
         self.niri.maybe_activate_pointer_constraint(pos, &under);
         self.niri.pointer_focus.clone_from(&under);
 

src/niri.rs

@@ -3305,6 +3305,28 @@ impl Niri {
             warn!("error spawning a thread to send MonitorsChanged: {err:?}");
         }
     }
+
+    pub fn handle_focus_follows_mouse(&mut self, new_focus: &PointerFocus) {
+        if !self.config.borrow().input.focus_follows_mouse {
+            return;
+        }
+
+        if self.seat.get_pointer().unwrap().is_grabbed() {
+            return;
+        }
+
+        if let Some(output) = &new_focus.output {
+            if self.pointer_focus.output.as_ref() != Some(output) {
+                self.layout.focus_output(output);
+            }
+        }
+
+        if let Some(window) = &new_focus.window {
+            if self.pointer_focus.window.as_ref() != Some(window) {
+                self.layout.activate_window(window);
+            }
+        }
+    }
 }
 
 pub struct ClientState {