ui/cocoa: capture all keys and combos when mouse is grabbed

Applications such as Gnome may use Alt-Tab and Super-Tab for different
purposes, some use Ctrl-arrows so we want to allow qemu to handle
everything when it captures the mouse/keyboard.

However, Mac OS handles some combos like Command-Tab and Ctrl-arrows
at an earlier part of the event handling chain, not letting qemu see it.

We add a global Event Tap that allows qemu to see all events when the
mouse is grabbed. Note that this requires additional permissions.

See:

https://developer.apple.com/documentation/coregraphics/1454426-cgeventtapcreate?language=objc#discussion
https://support.apple.com/en-in/guide/mac-help/mh32356/mac

Acked-by: Markus Armbruster <armbru@redhat.com>
Signed-off-by: Gustavo Noronha Silva <gustavo@noronha.dev.br>
Message-Id: <20210713213200.2547-2-gustavo@noronha.dev.br>
Signed-off-by: Akihiko Odaki <akihiko.odaki@gmail.com>
Message-Id: <20220306121119.45631-2-akihiko.odaki@gmail.com>
Reviewed-by: Will Cohen <wwcohen@gmail.com>
Signed-off-by: Philippe Mathieu-Daudé <f4bug@amsat.org>

qapi/ui.json

@@ -1270,11 +1270,17 @@
 #                    host without sending this key to the guest when
 #                    "off". Defaults to "on"
 #
+# @full-grab: Capture all key presses, including system combos. This
+#             requires accessibility permissions, since it performs
+#             a global grab on key events. (default: off)
+#             See https://support.apple.com/en-in/guide/mac-help/mh32356/mac
+#
 # Since: 7.0
 ##
 { 'struct': 'DisplayCocoa',
   'data': {
-      '*left-command-key': 'bool'
+      '*left-command-key': 'bool',
+      '*full-grab': 'bool'
   } }
 
 ##

qemu-options.hx

@@ -1916,6 +1916,9 @@ DEF("display", HAS_ARG, QEMU_OPTION_display,
 #if defined(CONFIG_CURSES)
     "-display curses[,charset=<encoding>]\n"
 #endif
+#if defined(CONFIG_COCOA)
+    "-display cocoa[,full_grab=on|off]\n"
+#endif
 #if defined(CONFIG_OPENGL)
     "-display egl-headless[,rendernode=<file>]\n"
 #endif

ui/cocoa.m

@@ -309,11 +309,13 @@ static void handleAnyDeviceErrors(Error * err)
     BOOL isMouseGrabbed;
     BOOL isFullscreen;
     BOOL isAbsoluteEnabled;
+    CFMachPortRef eventsTap;
 }
 - (void) switchSurface:(pixman_image_t *)image;
 - (void) grabMouse;
 - (void) ungrabMouse;
 - (void) toggleFullScreen:(id)sender;
+- (void) setFullGrab:(id)sender;
 - (void) handleMonitorInput:(NSEvent *)event;
 - (bool) handleEvent:(NSEvent *)event;
 - (bool) handleEventLocked:(NSEvent *)event;
@@ -336,6 +338,19 @@ static void handleAnyDeviceErrors(Error * err)
 
 QemuCocoaView *cocoaView;
 
+static CGEventRef handleTapEvent(CGEventTapProxy proxy, CGEventType type, CGEventRef cgEvent, void *userInfo)
+{
+    QemuCocoaView *cocoaView = userInfo;
+    NSEvent *event = [NSEvent eventWithCGEvent:cgEvent];
+    if ([cocoaView isMouseGrabbed] && [cocoaView handleEvent:event]) {
+        COCOA_DEBUG("Global events tap: qemu handled the event, capturing!\n");
+        return NULL;
+    }
+    COCOA_DEBUG("Global events tap: qemu did not handle the event, letting it through...\n");
+
+    return cgEvent;
+}
+
 @implementation QemuCocoaView
 - (id)initWithFrame:(NSRect)frameRect
 {
@@ -361,6 +376,11 @@ QemuCocoaView *cocoaView;
     }
 
     qkbd_state_free(kbd);
+
+    if (eventsTap) {
+        CFRelease(eventsTap);
+    }
+
     [super dealloc];
 }
 
@@ -655,6 +675,36 @@ QemuCocoaView *cocoaView;
     }
 }
 
+- (void) setFullGrab:(id)sender
+{
+    COCOA_DEBUG("QemuCocoaView: setFullGrab\n");
+
+    CGEventMask mask = CGEventMaskBit(kCGEventKeyDown) | CGEventMaskBit(kCGEventKeyUp) | CGEventMaskBit(kCGEventFlagsChanged);
+    eventsTap = CGEventTapCreate(kCGHIDEventTap, kCGHeadInsertEventTap, kCGEventTapOptionDefault,
+                                 mask, handleTapEvent, self);
+    if (!eventsTap) {
+        warn_report("Could not create event tap, system key combos will not be captured.\n");
+        return;
+    } else {
+        COCOA_DEBUG("Global events tap created! Will capture system key combos.\n");
+    }
+
+    CFRunLoopRef runLoop = CFRunLoopGetCurrent();
+    if (!runLoop) {
+        warn_report("Could not obtain current CF RunLoop, system key combos will not be captured.\n");
+        return;
+    }
+
+    CFRunLoopSourceRef tapEventsSrc = CFMachPortCreateRunLoopSource(kCFAllocatorDefault, eventsTap, 0);
+    if (!tapEventsSrc ) {
+        warn_report("Could not obtain current CF RunLoop, system key combos will not be captured.\n");
+        return;
+    }
+
+    CFRunLoopAddSource(runLoop, tapEventsSrc, kCFRunLoopDefaultMode);
+    CFRelease(tapEventsSrc);
+}
+
 - (void) toggleKey: (int)keycode {
     qkbd_state_key_event(kbd, keycode, !qkbd_state_key_get(kbd, keycode));
 }
@@ -1281,6 +1331,13 @@ QemuCocoaView *cocoaView;
     [cocoaView toggleFullScreen:sender];
 }
 
+- (void) setFullGrab:(id)sender
+{
+    COCOA_DEBUG("QemuCocoaAppController: setFullGrab\n");
+
+    [cocoaView setFullGrab:sender];
+}
+
 /* Tries to find then open the specified filename */
 - (void) openDocumentation: (NSString *) filename
 {
@@ -1994,11 +2051,17 @@ static void cocoa_display_init(DisplayState *ds, DisplayOptions *opts)
     qemu_sem_wait(&app_started_sem);
     COCOA_DEBUG("cocoa_display_init: app start completed\n");
 
+    QemuCocoaAppController *controller = (QemuCocoaAppController *)[[NSApplication sharedApplication] delegate];
     /* if fullscreen mode is to be used */
     if (opts->has_full_screen && opts->full_screen) {
         dispatch_async(dispatch_get_main_queue(), ^{
             [NSApp activateIgnoringOtherApps: YES];
-            [(QemuCocoaAppController *)[[NSApplication sharedApplication] delegate] toggleFullScreen: nil];
+            [controller toggleFullScreen: nil];
+        });
+    }
+    if (opts->u.cocoa.has_full_grab && opts->u.cocoa.full_grab) {
+        dispatch_async(dispatch_get_main_queue(), ^{
+            [controller setFullGrab: nil];
         });
     }