1 files changed, 43 insertions, 0 deletions
diff --git a/glfw/src/window.rs b/glfw/src/window.rs
index 40eb300..8ccb1d1 100644
--- a/glfw/src/window.rs
+++ b/glfw/src/window.rs
@@ -202,6 +202,20 @@ impl Window
         }
     }
 
+    /// Sets the callback called when the window gains or loses input focus.
+    pub fn set_focus_callback(&self, callback: impl Fn(bool) + 'static)
+    {
+        FOCUS_CALLBACK.with_borrow_mut(|focus_cb| {
+            *focus_cb = Some(Box::new(callback));
+        });
+
+        // SAFETY: The initialize function (called when the window is created) makes sure
+        // the current thread is the main thread
+        unsafe {
+            crate::ffi::glfwSetWindowFocusCallback(self.handle, Some(focus_callback));
+        }
+    }
+
     /// Returns the last reported state of a keyboard key.
     ///
     /// # Errors
@@ -680,6 +694,7 @@ type FramebufferSizeCb = Box<dyn Fn(Size)>;
 type KeyCallback = Box<dyn Fn(Key, i32, KeyState, KeyModifiers)>;
 type CursorPositionCallback = Box<dyn Fn(CursorPosition)>;
 type MouseButtonCallback = Box<dyn Fn(MouseButton, MouseButtonState, KeyModifiers)>;
+type FocusCallback = Box<dyn Fn(bool)>;
 
 thread_local! {
 static CLOSE_CALLBACK: RefCell<Option<CloseCallback>> = RefCell::new(None);
@@ -687,6 +702,7 @@ static FRAMEBUFFER_SIZE_CB: RefCell<Option<FramebufferSizeCb>> = RefCell::new(No
 static KEY_CALLBACK: RefCell<Option<KeyCallback>> = RefCell::new(None);
 static CURSOR_POS_CALLBACK: RefCell<Option<CursorPositionCallback>> = RefCell::new(None);
 static MOUSE_BUTTON_CALLBACK: RefCell<Option<MouseButtonCallback>> = RefCell::new(None);
+static FOCUS_CALLBACK: RefCell<Option<FocusCallback>> = RefCell::new(None);
 }
 
 extern "C" fn close_callback(_window: *mut crate::ffi::GLFWwindow)
@@ -845,3 +861,30 @@ extern "C" fn mouse_button_callback(
         write!(stdout(), "ERROR: Mouse button callback panicked: {res:?}").ok();
     }
 }
+
+extern "C" fn focus_callback(_window: *mut crate::ffi::GLFWwindow, focused: c_int)
+{
+    let is_focused = if focused == crate::ffi::GLFW_TRUE {
+        true
+    } else if focused == crate::ffi::GLFW_FALSE {
+        false
+    } else {
+        write!(stdout(), "Invalid focus state {focused}").ok();
+        return;
+    };
+
+    // Unwinds are catched because unwinding from Rust code into foreign code is UB.
+    let res = catch_unwind(|| {
+        FOCUS_CALLBACK
+            .try_with(|focus_callback| {
+                if let Some(cb) = focus_callback.borrow().as_deref() {
+                    cb(is_focused);
+                }
+            })
+            .ok();
+    });
+
+    if res.is_err() {
+        write!(stdout(), "ERROR: Focus callback panicked: {res:?}").ok();
+    }
+}