Add Window::show_window_menu

Add a method to request a system menu. The implementation
is provided only on Windows for now.

Co-authored-by: daxpedda <daxpedda@gmail.com>
Co-authored-by: Kirill Chibisov <contact@kchibisov.com>

src/platform_impl/windows/window.rs

@@ -40,15 +40,19 @@ use windows_sys::Win32::{
             Touch::{RegisterTouchWindow, TWF_WANTPALM},
         },
         WindowsAndMessaging::{
-            CreateWindowExW, FlashWindowEx, GetClientRect, GetCursorPos, GetForegroundWindow,
-            GetSystemMetrics, GetWindowPlacement, GetWindowTextLengthW, GetWindowTextW,
-            IsWindowVisible, LoadCursorW, PeekMessageW, PostMessageW, RegisterClassExW, SetCursor,
-            SetCursorPos, SetForegroundWindow, SetWindowDisplayAffinity, SetWindowPlacement,
-            SetWindowPos, SetWindowTextW, CS_HREDRAW, CS_VREDRAW, CW_USEDEFAULT, FLASHWINFO,
+            CreateWindowExW, EnableMenuItem, FlashWindowEx, GetClientRect, GetCursorPos,
+            GetForegroundWindow, GetSystemMenu, GetSystemMetrics, GetWindowPlacement,
+            GetWindowTextLengthW, GetWindowTextW, IsWindowVisible, LoadCursorW, PeekMessageW,
+            PostMessageW, RegisterClassExW, SetCursor, SetCursorPos, SetForegroundWindow,
+            SetMenuDefaultItem, SetWindowDisplayAffinity, SetWindowPlacement, SetWindowPos,
+            SetWindowTextW, TrackPopupMenu, CS_HREDRAW, CS_VREDRAW, CW_USEDEFAULT, FLASHWINFO,
             FLASHW_ALL, FLASHW_STOP, FLASHW_TIMERNOFG, FLASHW_TRAY, GWLP_HINSTANCE, HTBOTTOM,
             HTBOTTOMLEFT, HTBOTTOMRIGHT, HTCAPTION, HTLEFT, HTRIGHT, HTTOP, HTTOPLEFT, HTTOPRIGHT,
-            NID_READY, PM_NOREMOVE, SM_DIGITIZER, SWP_ASYNCWINDOWPOS, SWP_NOACTIVATE, SWP_NOSIZE,
-            SWP_NOZORDER, WDA_EXCLUDEFROMCAPTURE, WDA_NONE, WM_NCLBUTTONDOWN, WNDCLASSEXW,
+            MENU_ITEM_STATE, MFS_DISABLED, MFS_ENABLED, MF_BYCOMMAND, NID_READY, PM_NOREMOVE,
+            SC_CLOSE, SC_MAXIMIZE, SC_MINIMIZE, SC_MOVE, SC_RESTORE, SC_SIZE, SM_DIGITIZER,
+            SWP_ASYNCWINDOWPOS, SWP_NOACTIVATE, SWP_NOSIZE, SWP_NOZORDER, TPM_LEFTALIGN,
+            TPM_RETURNCMD, WDA_EXCLUDEFROMCAPTURE, WDA_NONE, WM_NCLBUTTONDOWN, WM_SYSCOMMAND,
+            WNDCLASSEXW,
         },
     },
 };
@@ -475,6 +479,83 @@ impl Window {
         Ok(())
     }
 
+    unsafe fn handle_showing_window_menu(&self, position: Position) {
+        unsafe {
+            let point = {
+                let mut point = POINT { x: 0, y: 0 };
+                let scale_factor = self.scale_factor();
+                let (x, y) = position.to_physical::<i32>(scale_factor).into();
+                point.x = x;
+                point.y = y;
+                if ClientToScreen(self.hwnd(), &mut point) == false.into() {
+                    warn!("Can't convert client-area coordinates to screen coordinates when showing window menu.");
+                    return;
+                }
+                point
+            };
+
+            // get the current system menu
+            let h_menu = GetSystemMenu(self.hwnd(), 0);
+            if h_menu == 0 {
+                warn!("The corresponding window doesn't have a system menu");
+                // This situation should not be treated as an error so just return without showing menu.
+                return;
+            }
+
+            fn enable(b: bool) -> MENU_ITEM_STATE {
+                if b {
+                    MFS_ENABLED
+                } else {
+                    MFS_DISABLED
+                }
+            }
+
+            // Change the menu items according to the current window status.
+
+            let restore_btn = enable(self.is_maximized() && self.is_resizable());
+            let size_btn = enable(!self.is_maximized() && self.is_resizable());
+            let maximize_btn = enable(!self.is_maximized() && self.is_resizable());
+
+            EnableMenuItem(h_menu, SC_RESTORE, MF_BYCOMMAND | restore_btn);
+            EnableMenuItem(h_menu, SC_MOVE, MF_BYCOMMAND | enable(!self.is_maximized()));
+            EnableMenuItem(h_menu, SC_SIZE, MF_BYCOMMAND | size_btn);
+            EnableMenuItem(h_menu, SC_MINIMIZE, MF_BYCOMMAND | MFS_ENABLED);
+            EnableMenuItem(h_menu, SC_MAXIMIZE, MF_BYCOMMAND | maximize_btn);
+            EnableMenuItem(h_menu, SC_CLOSE, MF_BYCOMMAND | MFS_ENABLED);
+
+            // Set the default menu item.
+            SetMenuDefaultItem(h_menu, SC_CLOSE, 0);
+
+            // Popup the system menu at the position.
+            let result = TrackPopupMenu(
+                h_menu,
+                TPM_RETURNCMD | TPM_LEFTALIGN, // for now im using LTR, but we have to use user layout direction
+                point.x,
+                point.y,
+                0,
+                self.hwnd(),
+                std::ptr::null_mut(),
+            );
+
+            if result == 0 {
+                // User canceled the menu, no need to continue.
+                return;
+            }
+
+            // Send the command that the user select to the corresponding window.
+            if PostMessageW(self.hwnd(), WM_SYSCOMMAND, result as _, 0) == 0 {
+                warn!("Can't post the system menu message to the window.");
+            }
+        }
+    }
+
+    #[inline]
+    pub fn show_window_menu(&self, position: Position) {
+        unsafe {
+            self.handle_showing_window_menu(position);
+        }
+    }
+
     #[inline]
     pub fn set_cursor_hittest(&self, hittest: bool) -> Result<(), ExternalError> {
         let window = self.window.clone();