Mac: Handle "Displays have separate Spaces"

- Using JNI, detect whether "Displays have separate Spaces" is enabled
  in the system settings, and don't try to enable multi-screen spanning
  if so.  (Otherwise, if the viewer tries to create a multi-screen
  window, only the part of the window on the primary display will be
  visible.  If there is a vertical scrollbar, it will be inaccessible,
  and if there is a horizontal scrollbar, it will be incorrectly sized.)

- To be safe, also don't try to enable multi-screen spanning if the
  TurboVNC Helper is unavailable (which means that the state of
  "Displays have separate Spaces" cannot be determined.)

- Modify the description of the Span parameter on macOS to document the
  need to disable "Displays have separate Spaces" in order to use
  multi-screen spanning.

ChangeLog.md

@@ -21,6 +21,12 @@ and CVE-2024-31083) from the xorg-server 21.1.x code base.
 a TurboVNC session if the initial resolution of any of the screens in the
 session matched one of the default X RandR modes.
 
+5. Fixed an issue in the Mac TurboVNC Viewer whereby the viewer window did not
+display a vertical scrollbar, and the horizontal scrollbar was incorrectly
+sized, if multi-screen spanning was enabled, the scaled remote desktop was
+larger than the viewer window, and "Displays have separate Spaces" was enabled
+in the system settings.
+
 
 3.1.3
 =====

java/com/turbovnc/rfb/Helper.java

@@ -1,5 +1,5 @@
-/* Copyright (C) 2015, 2017-2018, 2020-2022 D. R. Commander.
- *                                          All Rights Reserved.
+/* Copyright (C) 2015, 2017-2018, 2020-2022, 2025 D. R. Commander.
+ *                                                All Rights Reserved.
  *
  * This is free software; you can redistribute it and/or modify
  * it under the terms of the GNU General Public License as published by
@@ -53,6 +53,9 @@ private static synchronized void printMissingFeatures() {
     if (Utils.osEID())
       vlog.info("  - Extended input device support");
     if (Utils.isX11()) {
+      vlog.info("  - Multi-screen spanning in full-screen mode");
+    }
+    if (Utils.isMac()) {
       vlog.info("  - Multi-screen spanning");
     }
     if (Utils.isWindows())

java/com/turbovnc/rfb/Params.java

@@ -1,4 +1,4 @@
-/* Copyright (C) 2012-2018, 2020-2024 D. R. Commander.  All Rights Reserved.
+/* Copyright (C) 2012-2018, 2020-2025 D. R. Commander.  All Rights Reserved.
  * Copyright (C) 2021 Steffen Kieß
  * Copyright (C) 2011-2012, 2016 Brian P. Hinz
  * Copyright (C) 2002-2005 RealVNC Ltd.  All Rights Reserved.
@@ -795,9 +795,13 @@ public void save(String node) {
 
   "When using automatic desktop resizing, \"Auto\" has the same effect as " +
   "\"Primary\" when in windowed mode and the same effect as \"All\" when in " +
-  "full-screen mode.  Due to general issues with spanning windows across " +
-  "multiple monitors in X11, this parameter does not work on Un*x/X11 " +
-  "platforms except in full-screen mode.", SpanParameter.AUTO);
+  "full-screen mode." +
+  (Utils.isX11() ? "  Due to general issues with spanning windows across " +
+  "multiple monitors in X11, this parameter has no effect on Un*x/X11 " +
+  "platforms except in full-screen mode." : "") +
+  (Utils.isMac() ? "  This parameter has no effect on macOS unless " +
+   "\"Displays have separate Spaces\" is disabled in the system settings." :
+   ""), SpanParameter.AUTO);
 
   public BoolParameter toolbar =
   new BoolParameter("Toolbar", this, true,

java/com/turbovnc/rfb/Utils.java

@@ -1,4 +1,4 @@
-/* Copyright (C) 2012, 2015, 2018, 2020, 2022-2024 D. R. Commander.
+/* Copyright (C) 2012, 2015, 2018, 2020, 2022-2025 D. R. Commander.
  *                                                 All Rights Reserved.
  * Copyright (C) 2012 Brian P. Hinz
  *
@@ -57,6 +57,12 @@ public static boolean osGrab() {
     return !isMac();
   }
 
+  private static native boolean displaysHaveSeparateSpaces();
+
+  public static boolean displaysHaveSeparateSpacesHelper() {
+    return isMac() && (!Helper.isAvailable() || displaysHaveSeparateSpaces());
+  }
+
   public static boolean getBooleanProperty(String key, boolean def) {
     String prop = System.getProperty(key, def ? "True" : "False");
     if (prop != null && prop.length() > 0) {

java/com/turbovnc/vncviewer/CConn.java

@@ -1,4 +1,4 @@
-/* Copyright (C) 2011-2024 D. R. Commander.  All Rights Reserved.
+/* Copyright (C) 2011-2025 D. R. Commander.  All Rights Reserved.
  * Copyright (C) 2021 Steffen Kieß
  * Copyright 2009-2011, 2016-2019 Pierre Ossman <[email protected]>
  *                                for Cendio AB
@@ -1367,7 +1367,11 @@ public Rectangle getSpannedSize() {
         // under X11 except for full-screen windows, and even then, the
         // appropriate WM hints must be set using C.)
         (Utils.isX11() &&
-         (!params.fullScreen.get() || !Helper.isAvailable()))) {
+         (!params.fullScreen.get() || !Helper.isAvailable())) ||
+        // We're using macOS, and "Displays have separate Spaces" is enabled in
+        // the system settings (or the state of "Displays have separate Spaces"
+        // cannot be determined because the helper library isn't available.)
+        (Utils.isMac() && Utils.displaysHaveSeparateSpacesHelper())) {
       span = primary;
       viewport.leftMon = viewport.rightMon = viewport.topMon =
         viewport.bottomMon = primaryID;

unix/vncviewer/com_turbovnc_rfb_Utils.h

@@ -0,0 +1,20 @@
+#include <jni.h>
+/* Header for class com_turbovnc_rfb_Utils */
+
+#ifndef _Included_com_turbovnc_rfb_Utils
+#define _Included_com_turbovnc_rfb_Utils
+#ifdef __cplusplus
+extern "C" {
+#endif
+/*
+ * Class:     com_turbovnc_rfb_Utils
+ * Method:    displaysHaveSeparateSpaces
+ * Signature: ()Z
+ */
+JNIEXPORT jboolean JNICALL Java_com_turbovnc_rfb_Utils_displaysHaveSeparateSpaces
+  (JNIEnv *, jobject);
+
+#ifdef __cplusplus
+}
+#endif
+#endif

unix/vncviewer/turbovnchelper.m

@@ -1,5 +1,5 @@
-/* Copyright (C) 2015-2017, 2019, 2021-2022 D. R. Commander.
- *                                          All Rights Reserved.
+/* Copyright (C) 2015-2017, 2019, 2021-2022, 2025 D. R. Commander.
+ *                                                All Rights Reserved.
  * Copyright 2014, 2017 Pierre Ossman for Cendio AB
  *
  * This is free software; you can redistribute it and/or modify
@@ -48,6 +48,7 @@
 #include <string.h>
 #include <dlfcn.h>
 #include <unistd.h>
+#include "com_turbovnc_rfb_Utils.h"
 #include "com_turbovnc_vncviewer_Viewport.h"
 #include <Cocoa/Cocoa.h>
 #import <Carbon/Carbon.h>
@@ -380,3 +381,10 @@ - (void)newSendEvent:(NSEvent *)event
   bailout:
   return;
 }
+
+
+JNIEXPORT jboolean JNICALL Java_com_turbovnc_rfb_Utils_displaysHaveSeparateSpaces
+  (JNIEnv *env, jobject obj)
+{
+  return (jboolean)[NSScreen screensHaveSeparateSpaces];
+}