internal/ui: use the cursor position to choose the initial monitor for Windows

Updates #1918
Updates #1982

internal/ui/ui_glfw.go

@@ -170,8 +170,12 @@ func initialize() error {
 	glfw.WindowHint(glfw.ClientAPI, glfw.NoAPI)
 
 	var m *glfw.Monitor
-	if runtime.GOOS == "darwin" {
+	if runtime.GOOS == "darwin" || runtime.GOOS == "windows" {
-		m = initialMonitorByOS()
+		var err error
+		m, err = initialMonitorByOS()
+		if err != nil {
+			return err
+		}
 		if m == nil {
 			m = glfw.GetPrimaryMonitor()
 		}
@@ -189,7 +193,10 @@ func initialize() error {
 		defer w.Destroy()
 		initializeWindowAfterCreation(w)
 		theUI.waitForFramebufferSizeCallback(w, nil)
-		m = initialMonitorByOS()
+		m, err = initialMonitorByOS()
+		if err != nil {
+			return err
+		}
 		if m == nil {
 			m = currentMonitorImpl(w)
 		}

internal/ui/ui_glfw_darwin.go

@@ -158,7 +158,7 @@ func (u *UserInterface) adjustWindowPosition(x, y int) (int, int) {
 	return x, y
 }
 
-func initialMonitorByOS() *glfw.Monitor {
+func initialMonitorByOS() (*glfw.Monitor, error) {
 	var cx, cy C.int
 	C.currentMouseLocation(&cx, &cy)
 	x, y := int(cx), int(cy)
@@ -176,11 +176,11 @@ func initialMonitorByOS() *glfw.Monitor {
 	for _, m := range ensureMonitors() {
 		w, h := m.vm.Width, m.vm.Height
 		if x >= m.x && x < m.x+w && y >= m.y && y < m.y+h {
-			return m.m
+			return m.m, nil
 		}
 	}
 
-	return nil
+	return nil, nil
 }
 
 func currentMonitorByOS(w *glfw.Window) *glfw.Monitor {

internal/ui/ui_glfw_unix.go

@@ -133,8 +133,8 @@ func (u *UserInterface) adjustWindowPosition(x, y int) (int, int) {
 	return x, y
 }
 
-func initialMonitorByOS() *glfw.Monitor {
+func initialMonitorByOS() (*glfw.Monitor, error) {
-	return nil
+	return nil, nil
 }
 
 func currentMonitorByOS(_ *glfw.Window) *glfw.Monitor {

internal/ui/ui_glfw_windows.go

@@ -46,12 +46,17 @@ type monitorInfo struct {
 	dwFlags   uint32
 }
 
+type point struct {
+	x int32
+	y int32
+}
+
 var (
 	// user32 is defined at hideconsole_windows.go
 	procGetSystemMetrics  = user32.NewProc("GetSystemMetrics")
-	procGetForegroundWindow = user32.NewProc("GetForegroundWindow")
 	procMonitorFromWindow = user32.NewProc("MonitorFromWindow")
 	procGetMonitorInfoW   = user32.NewProc("GetMonitorInfoW")
+	procGetCursorPos      = user32.NewProc("GetCursorPos")
 )
 
 func getSystemMetrics(nIndex int) (int32, error) {
@@ -64,11 +69,6 @@ func getSystemMetrics(nIndex int) (int32, error) {
 	return int32(r), nil
 }
 
-func getForegroundWindow() windows.HWND {
-	r, _, _ := procGetForegroundWindow.Call()
-	return windows.HWND(r)
-}
-
 func monitorFromWindow(hwnd windows.HWND, dwFlags uint32) uintptr {
 	r, _, _ := procMonitorFromWindow.Call(uintptr(hwnd), uintptr(dwFlags))
 	return r
@@ -85,6 +85,18 @@ func getMonitorInfoW(hMonitor uintptr, lpmi *monitorInfo) error {
 	return nil
 }
 
+func getCursorPos() (int32, int32, error) {
+	var pt point
+	r, _, e := procGetCursorPos.Call(uintptr(unsafe.Pointer(&pt)))
+	if r == 0 {
+		if e != nil && e != windows.ERROR_SUCCESS {
+			return 0, 0, fmt.Errorf("ui: GetCursorPos failed: error code: %w", e)
+		}
+		return 0, 0, fmt.Errorf("ui: GetCursorPos failed: returned 0")
+	}
+	return pt.x, pt.y, nil
+}
+
 // clearVideoModeScaleCache must be called from the main thread.
 func clearVideoModeScaleCache() {}
 
@@ -120,14 +132,22 @@ func (u *UserInterface) adjustWindowPosition(x, y int) (int, int) {
 	return x, y
 }
 
-func initialMonitorByOS() *glfw.Monitor {
+func initialMonitorByOS() (*glfw.Monitor, error) {
-	// Get the foreground window, that is common among multiple processes.
+	px, py, err := getCursorPos()
-	w := getForegroundWindow()
+	if err != nil {
-	if w == 0 {
+		return nil, err
-		// GetForegroundWindow can return null according to the document.
-		return nil
 	}
-	return monitorFromWin32Window(w)
+	x, y := int(px), int(py)
+
+	// Find the monitor including the cursor.
+	for _, m := range ensureMonitors() {
+		w, h := m.vm.Width, m.vm.Height
+		if x >= m.x && x < m.x+w && y >= m.y && y < m.y+h {
+			return m.m, nil
+		}
+	}
+
+	return nil, nil
 }
 
 func currentMonitorByOS(w *glfw.Window) *glfw.Monitor {