MacViews: Implement capture using NSEvent local+global monitors

ui/views/cocoa/cocoa_mouse_capture.mm

+// Copyright 2014 The Chromium Authors. All rights reserved.
+// Use of this source code is governed by a BSD-style license that can be
+// found in the LICENSE file.
+
+#import "ui/views/cocoa/cocoa_mouse_capture.h"
+
+#import <Cocoa/Cocoa.h>
+
+#include "base/logging.h"
+#import "ui/views/cocoa/cocoa_mouse_capture_delegate.h"
+
+namespace views {
+
+// The ActiveEventTap is a RAII handle on the resources being used to capture
+// events. There is either 0 or 1 active instance of this class. If a second
+// instance is created, it will destroy the other instance before returning from
+// its constructor.
+class CocoaMouseCapture::ActiveEventTap {
+ public:
+  explicit ActiveEventTap(CocoaMouseCapture* owner);
+  ~ActiveEventTap();
+  void Init();
+
+ private:
+  // The currently active event tap, or null if there is none.
+  static ActiveEventTap* g_active_event_tap;
+
+  CocoaMouseCapture* owner_;  // Weak. Owns this.
+  id local_monitor_;
+  id global_monitor_;
+
+  DISALLOW_COPY_AND_ASSIGN(ActiveEventTap);
+};
+
+CocoaMouseCapture::ActiveEventTap*
+    CocoaMouseCapture::ActiveEventTap::g_active_event_tap = nullptr;
+
+CocoaMouseCapture::ActiveEventTap::ActiveEventTap(CocoaMouseCapture* owner)
+    : owner_(owner), local_monitor_(nil), global_monitor_(nil) {
+  if (g_active_event_tap)
+    g_active_event_tap->owner_->OnOtherClientGotCapture();
+  DCHECK(!g_active_event_tap);
+  g_active_event_tap = this;
+}
+
+CocoaMouseCapture::ActiveEventTap::~ActiveEventTap() {
+  DCHECK_EQ(g_active_event_tap, this);
+  [NSEvent removeMonitor:global_monitor_];
+  [NSEvent removeMonitor:local_monitor_];
+  g_active_event_tap = nullptr;
+  owner_->delegate_->OnMouseCaptureLost();
+}
+
+void CocoaMouseCapture::ActiveEventTap::Init() {
+  NSEventMask event_mask =
+      NSLeftMouseDownMask | NSLeftMouseUpMask | NSRightMouseDownMask |
+      NSRightMouseUpMask | NSMouseMovedMask | NSLeftMouseDraggedMask |
+      NSRightMouseDraggedMask | NSMouseEnteredMask | NSMouseExitedMask |
+      NSScrollWheelMask | NSOtherMouseDownMask | NSOtherMouseUpMask |
+      NSOtherMouseDraggedMask;
+
+  local_monitor_ = [NSEvent addLocalMonitorForEventsMatchingMask:event_mask
+      handler:^NSEvent*(NSEvent* event) {
+        owner_->delegate_->PostCapturedEvent(event);
+        return nil;  // Swallow all local events.
+      }];
+  global_monitor_ = [NSEvent addGlobalMonitorForEventsMatchingMask:event_mask
+      handler:^void(NSEvent* event) {
+        owner_->delegate_->PostCapturedEvent(event);
+      }];
+}
+
+CocoaMouseCapture::CocoaMouseCapture(CocoaMouseCaptureDelegate* delegate)
+    : delegate_(delegate), active_handle_(new ActiveEventTap(this)) {
+  active_handle_->Init();
+}
+
+CocoaMouseCapture::~CocoaMouseCapture() {
+}
+
+void CocoaMouseCapture::OnOtherClientGotCapture() {
+  DCHECK(active_handle_);
+  active_handle_.reset();
+}
+
+}  // namespace views