macOS: Simplify mouse tracking

We don't need to react to updateTrackingAreas, as we only have a
single tracking area that we can add once and forget. By asking
AppKit to track all events in the visible rect, we can also pass
a zero-rect for the tracking area.

Change-Id: I2545712adc49b51904d5adc11f1faca36901b49d
Reviewed-by: Tor Arne Vestbø <tor.arne.vestbo@qt.io>

src/plugins/platforms/cocoa/qnsview.mm

@@ -85,6 +85,7 @@
 @end
 
 @interface QT_MANGLE_NAMESPACE(QNSView) (Mouse)
+- (void)initMouse;
 - (NSPoint)screenMousePoint:(NSEvent *)theEvent;
 - (void)mouseMovedImpl:(NSEvent *)theEvent;
 - (void)mouseEnteredImpl:(NSEvent *)theEvent;
@@ -114,7 +115,6 @@
 
 @implementation QT_MANGLE_NAMESPACE(QNSView) {
     QPointer<QCocoaWindow> m_platformWindow;
-    NSTrackingArea *m_trackingArea;
     Qt::MouseButtons m_buttons;
     Qt::MouseButtons m_acceptedMouseDowns;
     Qt::MouseButtons m_frameStrutButtons;
@@ -150,7 +150,6 @@
         m_currentlyInterpretedKeyEvent = nil;
         m_dontOverrideCtrlLMB = qt_mac_resolveOption(false, platformWindow->window(),
             "_q_platform_MacDontOverrideCtrlLMB", "QT_MAC_DONT_OVERRIDE_CTRL_LMB");
-        m_trackingArea = nil;
 
         self.focusRingType = NSFocusRingTypeNone;
         self.cursor = nil;
@@ -159,6 +158,7 @@
         self.previousWindow = nil;
 
         [self initDrawing];
+        [self initMouse];
         [self registerDragTypes];
 
         [[NSNotificationCenter defaultCenter] addObserver:self
@@ -173,10 +173,6 @@
 {
     qCDebug(lcQpaWindow) << "Deallocating" << self;
 
-    if (m_trackingArea) {
-        [self removeTrackingArea:m_trackingArea];
-        [m_trackingArea release];
-    }
     [m_inputSource release];
     [[NSNotificationCenter defaultCenter] removeObserver:self];
     [m_mouseMoveHelper release];

src/plugins/platforms/cocoa/qnsview_mouse.mm

@@ -151,6 +151,28 @@
 
 @implementation QT_MANGLE_NAMESPACE(QNSView) (Mouse)
 
+- (void)initMouse
+{
+    NSUInteger trackingOptions = NSTrackingActiveInActiveApp
+        | NSTrackingMouseEnteredAndExited | NSTrackingCursorUpdate;
+
+    // Ideally, NSTrackingMouseMoved should be turned on only if QWidget::mouseTracking
+    // is enabled, hover is on, or a tool tip is set. Unfortunately, Qt will send "tooltip"
+    // events on mouse moves, so we need to turn it on in ALL case. That means EVERY QWindow
+    // gets to pay the cost of mouse moves delivered to it (Apple recommends keeping it OFF
+    // because there is a performance hit).
+    trackingOptions |= NSTrackingMouseMoved;
+
+    // Using NSTrackingInVisibleRect means AppKit will automatically synchronize the
+    // tracking rect with changes in the view's visible area, so leave it undefined.
+    trackingOptions |= NSTrackingInVisibleRect;
+    static const NSRect trackingRect = NSZeroRect;
+
+    QMacAutoReleasePool pool;
+    [self addTrackingArea:[[[NSTrackingArea alloc] initWithRect:trackingRect
+        options:trackingOptions owner:m_mouseMoveHelper userInfo:nil] autorelease]];
+}
+
 - (BOOL)acceptsFirstMouse:(NSEvent *)theEvent
 {
     Q_UNUSED(theEvent)
@@ -422,35 +444,9 @@
         [super otherMouseUp:theEvent];
 }
 
-- (void)updateTrackingAreas
-{
-    [super updateTrackingAreas];
-
-    QMacAutoReleasePool pool;
-
-    // NSTrackingInVisibleRect keeps care of updating once the tracking is set up, so bail out early
-    if (m_trackingArea && [[self trackingAreas] containsObject:m_trackingArea])
-        return;
-
-    // Ideally, we shouldn't have NSTrackingMouseMoved events included below, it should
-    // only be turned on if mouseTracking, hover is on or a tool tip is set.
-    // Unfortunately, Qt will send "tooltip" events on mouse moves, so we need to
-    // turn it on in ALL case. That means EVERY QWindow gets to pay the cost of
-    // mouse moves delivered to it (Apple recommends keeping it OFF because there
-    // is a performance hit). So it goes.
-    NSUInteger trackingOptions = NSTrackingMouseEnteredAndExited | NSTrackingActiveInActiveApp
-                                 | NSTrackingInVisibleRect | NSTrackingMouseMoved | NSTrackingCursorUpdate;
-    [m_trackingArea release];
-    m_trackingArea = [[NSTrackingArea alloc] initWithRect:[self frame]
-                                                  options:trackingOptions
-                                                    owner:m_mouseMoveHelper
-                                                 userInfo:nil];
-    [self addTrackingArea:m_trackingArea];
-}
-
 - (void)cursorUpdate:(NSEvent *)theEvent
 {
-    qCDebug(lcQpaMouse) << "[QNSView cursorUpdate:]" << self.cursor;
+    qCDebug(lcQpaMouse) << "Updating cursor for" << self << "to" << self.cursor;
 
     // Note: We do not get this callback when moving from a subview that
     // uses the legacy cursorRect API, so the cursor is reset to the arrow