internal/ui: bug fix: initialMonitorByOS could return nil on macOS

initialMonitorByOS could return nil when a cursor was at an extreme
position like the bottom of the display. Apparently, a cursor position
could take an inclusive range of the monitor size.

This change fixes this issue by fixing the comparison.

Even if initialMonitorByOS returns nil, a fallback primary monitor
should be used, so this is not a critical issue.

Updates #2794

internal/ui/monitor_glfw.go

@@ -99,13 +99,15 @@ func (m *monitors) monitorFromID(id int) *Monitor {
 
 // monitorFromPosition returns a monitor for the given position (x, y),
 // or returns nil if monitor is not found.
+// The position is in GLFW pixels.
 func (m *monitors) monitorFromPosition(x, y int) *Monitor {
 	m.m.Lock()
 	defer m.m.Unlock()
 
 	for _, m := range m.monitors {
+		// Use an inclusive range. On macOS, the cursor position can take this range (#2794).
 		// TODO: Fix incorrectness in the cases of https://github.com/glfw/glfw/issues/1961.
-		if m.x <= x && x < m.x+m.videoMode.Width && m.y <= y && y < m.y+m.videoMode.Height {
+		if m.x <= x && x <= m.x+m.videoMode.Width && m.y <= y && y <= m.y+m.videoMode.Height {
 			return m
 		}
 	}

internal/ui/ui_glfw_darwin.go

@@ -239,7 +239,7 @@ var (
 	sel_windowWillExitFullScreen      = objc.RegisterName("windowWillExitFullScreen:")
 )
 
-func currentMouseLocationInDIP() (x, y int) {
+func currentMouseLocation() (x, y int) {
 	sig := cocoa.NSMethodSignature_signatureWithObjCTypes("{NSPoint=dd}@:")
 	inv := cocoa.NSInvocation_invocationWithMethodSignature(sig)
 	inv.SetTarget(objc.ID(class_NSEvent))
@@ -248,8 +248,6 @@ func currentMouseLocationInDIP() (x, y int) {
 	var point cocoa.NSPoint
 	inv.GetReturnValue(unsafe.Pointer(&point))
 
-	// On macOS, the unit of GLFW (OS-native) pixels' scale and device-independent pixels's scale are the same.
-	// The monitor sizes' scales are also the same.
 	x, y = int(point.X), int(point.Y)
 
 	// On macOS, the Y axis is upward. Adjust the Y position (#807, #2794).
@@ -260,17 +258,10 @@ func currentMouseLocationInDIP() (x, y int) {
 }
 
 func initialMonitorByOS() (*Monitor, error) {
-	x, y := currentMouseLocationInDIP()
+	x, y := currentMouseLocation()
 
 	// Find the monitor including the cursor.
-	for _, m := range theMonitors.append(nil) {
+	return theMonitors.monitorFromPosition(x, y), nil
-		w, h := m.videoMode.Width, m.videoMode.Height
-		if x >= m.x && x < m.x+w && y >= m.y && y < m.y+h {
-			return m, nil
-		}
-	}
-
-	return nil, nil
 }
 
 func monitorFromWindowByOS(w *glfw.Window) *Monitor {

internal/ui/ui_glfw_linbsd.go

@@ -145,14 +145,7 @@ func initialMonitorByOS() (*Monitor, error) {
 	x, y := int(rep.RootX), int(rep.RootY)
 
 	// Find the monitor including the cursor.
-	for _, m := range theMonitors.append(nil) {
+	return theMonitors.monitorFromPosition(x, y), nil
-		w, h := m.videoMode.Width, m.videoMode.Height
-		if x >= m.x && x < m.x+w && y >= m.y && y < m.y+h {
-			return m, nil
-		}
-	}
-
-	return nil, nil
 }
 
 func monitorFromWindowByOS(_ *glfw.Window) *Monitor {

internal/ui/ui_glfw_windows.go

@@ -136,14 +136,7 @@ func initialMonitorByOS() (*Monitor, error) {
 	x, y := int(px), int(py)
 
 	// Find the monitor including the cursor.
-	for _, m := range theMonitors.append(nil) {
+	return theMonitors.monitorFromPosition(x, y), nil
-		w, h := m.videoMode.Width, m.videoMode.Height
-		if x >= m.x && x < m.x+w && y >= m.y && y < m.y+h {
-			return m, nil
-		}
-	}
-
-	return nil, nil
 }
 
 func monitorFromWindowByOS(w *glfw.Window) *Monitor {