internal/uidriver/glfw: Use the correct initial monitor on Linux/UNIX

Closes #1827

internal/glfw/glfw_notwindows.go

@@ -141,6 +141,10 @@ func (w *Window) GetSize() (width, height int) {
 	return w.w.GetSize()
 }
 
+func (w *Window) Hide() {
+	w.w.Hide()
+}
+
 func (w *Window) Iconify() {
 	w.w.Iconify()
 }

internal/glfw/glfw_windows.go

@@ -182,6 +182,11 @@ func (w *Window) GetSize() (int, int) {
 	return int(width), int(height)
 }
 
+func (w *Window) Hide() {
+	glfwDLL.call("glfwHideWindow", w.w)
+	panicError()
+}
+
 func (w *Window) Iconify() {
 	glfwDLL.call("glfwIconifyWindow", w.w)
 	panicError()

internal/uidriver/glfw/ui.go

@@ -185,9 +185,8 @@ func initialize() error {
 		panic("glfw: glfw.CreateWindow must not return nil")
 	}
 	defer w.Destroy()
+	initializeWindowAfterCreation(w)
 
-	// TODO: The first current monitor should be determined without a window.
-	// On Linux, the first window position is always (0, 0) and not reliable to detect a monitor.
 	m := currentMonitor(w)
 	theUI.initMonitor = m
 	v := m.GetVideoMode()
@@ -753,6 +752,8 @@ func (u *UserInterface) createWindow() error {
 	if err != nil {
 		return err
 	}
+	initializeWindowAfterCreation(window)
+
 	u.window = window
 
 	if u.Graphics().IsGL() {
@@ -890,6 +891,7 @@ func (u *UserInterface) init() error {
 	if err := u.createWindow(); err != nil {
 		return err
 	}
+
 	u.setSizeCallbackEnabled = true
 
 	setSize := func() {

internal/uidriver/glfw/ui_darwin.go

@@ -193,3 +193,6 @@ func (u *UserInterface) adjustViewSize() {
 	}
 	C.adjustViewSize(C.uintptr_t(u.window.GetCocoaWindow()))
 }
+
+func initializeWindowAfterCreation(w *glfw.Window) {
+}

internal/uidriver/glfw/ui_unix.go

@@ -164,3 +164,10 @@ func (u *UserInterface) setNativeFullscreen(fullscreen bool) {
 
 func (u *UserInterface) adjustViewSize() {
 }
+
+func initializeWindowAfterCreation(w *glfw.Window) {
+	// Show the window once before getting the position of the window.
+	// On Linux/Unix, the window position is not reliable before showing.
+	w.Show()
+	w.Hide()
+}

internal/uidriver/glfw/ui_windows.go

@@ -140,6 +140,8 @@ func (u *UserInterface) adjustWindowPosition(x, y int) (int, int) {
 }
 
 func currentMonitorByOS(_ *glfw.Window) *glfw.Monitor {
+	// TODO: Why not using the given window?
+
 	// TODO: Should we return nil here?
 	w, err := getActiveWindow()
 	if err != nil {
@@ -206,3 +208,6 @@ func (u *UserInterface) setNativeFullscreen(fullscreen bool) {
 
 func (u *UserInterface) adjustViewSize() {
 }
+
+func initializeWindowAfterCreation(w *glfw.Window) {
+}