[MacViews] Enable dragging a window by its caption/draggable areas.

ui/views/cocoa/cocoa_non_client_drag.mm

+// Copyright 2015 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_non_client_drag.h"
+
+#import <Cocoa/Cocoa.h>
+
+#include "base/logging.h"
+#import "base/mac/foundation_util.h"
+#include "base/process/process_handle.h"
+
+@implementation CocoaNonClientDragMaskView
+
+- (BOOL)mouseDownCanMoveWindow {
+  return NO;
+}
+
+- (NSView*)hitTest:(NSPoint)aPoint {
+  return nil;
+}
+
+@end
+
+namespace views {
+
+namespace {
+
+int g_ref_count = 0;
+CGEventRef g_last_reposted_event = 0;
+
+CFRunLoopSourceRef g_run_loop_source = 0;
+CFMachPortRef g_mach_port = 0;
+
+id g_event_monitor = nil;
+
+bool RepostEventIfHandledByWindow(NSWindow* window,
+                                  NSPoint location,
+                                  CGEventRef event) {
+  if ([window respondsToSelector:@selector(willReceiveLeftMouseDown:)] &&
+      [base::mac::ObjCCast<NativeWidgetMacNSWindow>(window)
+          willReceiveLeftMouseDown:location]) {
+    if (g_last_reposted_event != event) {
+      g_last_reposted_event = event;
+      CGEventPost(kCGSessionEventTap, event);  // Repost event.
+    } else {
+      LOG(INFO) << "reposting already reposted event " << event;
+    }
+    return true;
+  }
+
+  return false;
+}
+
+CGEventRef EventTapCallBack(CGEventTapProxy proxy,
+                            CGEventType type,
+                            CGEventRef cg_event,
+                            void* refcon) {
+  LOG(INFO) << "EventTapCallBack " << cg_event;
+  // Disable CGEventTap mechanism.
+  return cg_event;
+
+  pid_t target_pid =
+      CGEventGetIntegerValueField(cg_event, kCGEventTargetUnixProcessID);
+  if (base::GetCurrentProcId() != target_pid)
+    return cg_event;
+
+  if (type != kCGEventLeftMouseDown)
+    return cg_event;
+
+  NSPoint location = NSPointFromCGPoint(CGEventGetUnflippedLocation(cg_event));
+
+  // Find the window this event lands on.
+  NSWindow* target = nil;
+  for (NSWindow* window in [NSApp windows]) {
+    if (NSPointInRect(location, [window frame])) {
+      target = window;
+      break;
+    }
+  }
+  if (!target)
+    return cg_event;
+
+  if (RepostEventIfHandledByWindow(
+          target, [target convertScreenToBase:location], cg_event)) {
+    return nil;
+  }
+
+  return cg_event;
+}
+
+}  // namespace
+
+CocoaNonClientDrag::CocoaNonClientDrag() {
+  if (g_ref_count)
+    return;
+
+////////////////////////////////////////////////////////////////////////////////
+// CGEventTap setup.
+  if (!g_mach_port) {
+    // We cant use kCGAnnotatedSessionEventTap or CGEventTapCreateForPSN because
+    // they both happen after window movement happens.
+    g_mach_port = CGEventTapCreate(
+        kCGSessionEventTap,  // After event has been annotated to flow to an
+                             // application.
+        kCGHeadInsertEventTap,
+        kCGEventTapOptionDefault,  // An active listener, can swallow events.
+        1 << kCGEventLeftMouseDown, &EventTapCallBack, NULL);
+  }
+  if (!g_run_loop_source)
+    g_run_loop_source = CFMachPortCreateRunLoopSource(NULL, g_mach_port, 0);
+
+  CFRunLoopAddSource(CFRunLoopGetMain(), g_run_loop_source,
+                     kCFRunLoopCommonModes);
+  CGEventTapEnable(g_mach_port, true);
+//
+////////////////////////////////////////////////////////////////////////////////
+// NSEvent local monitor setup.
+  NSEvent* (^monitor_callback)(NSEvent* ns_event);
+  monitor_callback = ^NSEvent*(NSEvent* ns_event) {
+    CGEventRef cg_event = [ns_event CGEvent];
+    LOG(INFO) << "MonitorCallback " << cg_event;
+    if (RepostEventIfHandledByWindow([ns_event window],
+                                     [ns_event locationInWindow],
+                                     cg_event)) {
+      return nil;
+    }
+    return ns_event;
+  };
+
+  g_event_monitor =
+      [NSEvent addLocalMonitorForEventsMatchingMask:NSLeftMouseDownMask
+                                            handler:monitor_callback];
+//
+////////////////////////////////////////////////////////////////////////////////
+
+  ++g_ref_count;
+}
+
+CocoaNonClientDrag::~CocoaNonClientDrag() {
+  --g_ref_count;
+  if (g_ref_count)
+    return;
+
+////////////////////////////////////////////////////////////////////////////////
+// CGEventTap cleanup.
+  CFRunLoopRemoveSource(CFRunLoopGetMain(), g_run_loop_source,
+                        kCFRunLoopCommonModes);
+//
+////////////////////////////////////////////////////////////////////////////////
+// NSEvent local monitor cleanup.
+  if (g_event_monitor) {
+    [NSEvent removeMonitor:g_event_monitor];
+    g_event_monitor = nil;
+  }
+//
+////////////////////////////////////////////////////////////////////////////////
+}
+
+}  // namespace views