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

Updates #1982

internal/ui/ui_glfw.go

@@ -169,21 +169,32 @@ func initialize() error {
 	glfw.WindowHint(glfw.Visible, glfw.False)
 	glfw.WindowHint(glfw.ClientAPI, glfw.NoAPI)
 
-	// Create a window to set the initial monitor.
+	var m *glfw.Monitor
-	// TODO: Instead of a dummy window, get a mouse cursor position and get a monitor from it (#1982).
+	if runtime.GOOS == "darwin" {
-	w, err := glfw.CreateWindow(16, 16, "", nil, nil)
+		m = initialMonitorByOS()
-	if err != nil {
+		if m == nil {
-		return err
+			m = glfw.GetPrimaryMonitor()
+		}
+	} else {
+		// Create a window to set the initial monitor.
+		// TODO: Instead of a dummy window, get a mouse cursor position and get a monitor from it (#1982).
+		w, err := glfw.CreateWindow(16, 16, "", nil, nil)
+		if err != nil {
+			return err
+		}
+		if w == nil {
+			// This can happen on Windows Remote Desktop (#903).
+			panic("ui: glfw.CreateWindow must not return nil")
+		}
+		defer w.Destroy()
+		initializeWindowAfterCreation(w)
+		theUI.waitForFramebufferSizeCallback(w, nil)
+		m = initialMonitorByOS()
+		if m == nil {
+			m = currentMonitorImpl(w)
+		}
 	}
-	if w == nil {
-		// This can happen on Windows Remote Desktop (#903).
-		panic("ui: glfw.CreateWindow must not return nil")
-	}
-	defer w.Destroy()
-	initializeWindowAfterCreation(w)
-	theUI.waitForFramebufferSizeCallback(w, nil)
 
-	m := initialMonitor(w)
 	theUI.initMonitor = m
 	// GetVideoMode must be called from the main thread, then call this here and record
 	// initFullscreen{Width,Height}InDIP.
@@ -914,8 +925,10 @@ func (u *UserInterface) init() error {
 	// Set the window size and the window position in this order on Linux or other UNIX using X (#1118),
 	// but this should be inverted on Windows. This is very tricky, but there is no obvious way to solve
 	// this. This doesn't matter on macOS.
+	// TODO: Set the position first even on X. setWindowSizeInDIP uses the monitor of the window, and
+	// if the window position is not reliable, the device scale factor is also not reliable (#1118, #1982).
 	wx, wy := u.getInitWindowPositionInDIP()
-	if runtime.GOOS == "windows" {
+	if runtime.GOOS == "windows" || runtime.GOOS == "darwin" {
 		u.setWindowPositionInDIP(wx, wy, u.initMonitor)
 		setSize()
 	} else {
@@ -1345,18 +1358,6 @@ func (u *UserInterface) updateVsync() {
 	Graphics().SetVsyncEnabled(u.fpsMode == FPSModeVsyncOn)
 }
 
-// initialMonitor returns the initial monitor to show the window.
-//
-// The given window is just a hint and might not be used to determine the initial monitor.
-//
-// initialMonitor must be called on the main thread.
-func initialMonitor(window *glfw.Window) *glfw.Monitor {
-	if m := initialMonitorByOS(); m != nil {
-		return m
-	}
-	return currentMonitorImpl(window)
-}
-
 // currentMonitor returns the current active monitor.
 //
 // currentMonitor must be called on the main thread.

internal/ui/ui_glfw_darwin.go

@@ -120,6 +120,12 @@ package ui
 //   }
 //   [cursor push];
 // }
+//
+// static void currentMouseLocation(int* x, int* y) {
+//   NSPoint location = [NSEvent mouseLocation];
+//   *x = (int)(location.x);
+//   *y = (int)(location.y);
+// }
 import "C"
 
 import (
@@ -153,12 +159,32 @@ func (u *UserInterface) adjustWindowPosition(x, y int) (int, int) {
 }
 
 func initialMonitorByOS() *glfw.Monitor {
+	var cx, cy C.int
+	C.currentMouseLocation(&cx, &cy)
+	x, y := int(cx), int(cy)
+
+	// Flip Y.
+	for _, m := range ensureMonitors() {
+		if m.x == 0 && m.y == 0 {
+			y = -y
+			y += m.vm.Height
+			break
+		}
+	}
+
+	// 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
+		}
+	}
+
 	return nil
 }
 
 func currentMonitorByOS(w *glfw.Window) *glfw.Monitor {
-	x := C.int(0)
+	var x, y C.int
-	y := C.int(0)
 	// Note: [NSApp mainWindow] is nil when it doesn't have its border. Use w here.
 	win := w.GetCocoaWindow()
 	C.currentMonitorPos(C.uintptr_t(win), &x, &y)