MacViews: Implement Tab Dragging

ui/views/cocoa/cocoa_window_move_loop.mm

+// Copyright 2016 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.
+
+#include "ui/views/cocoa/cocoa_window_move_loop.h"
+
+#import <Cocoa/Cocoa.h>
+
+#include "base/run_loop.h"
+#import "ui/gfx/mac/coordinate_conversion.mm"
+#import "ui/views/cocoa/bridged_content_view.h"
+#import "ui/views/cocoa/bridged_native_widget.h"
+
+// CocoaWindowMoveLoop can be deleted just before its local event monitor is
+// processed and in that case it's too late to call removeMonitor: and we have a
+// dangling this pointer. Use a proxy Obj-C class to store the weakptr.
+@interface WeakCocoaWindowMoveLoop : NSObject {
+ @private
+  base::WeakPtr<views::CocoaWindowMoveLoop> weak_;
+}
+@end
+
+@implementation WeakCocoaWindowMoveLoop
+- (id)initWithWeakPtr:(const base::WeakPtr<views::CocoaWindowMoveLoop>&)weak {
+  if ((self = [super init])) {
+    weak_ = weak;
+  }
+  return self;
+}
+
+- (base::WeakPtr<views::CocoaWindowMoveLoop>&)weak {
+  return weak_;
+}
+@end
+
+namespace {
+
+// Returns current mouse position in screen coordinates.
+gfx::Point GetMousePosition() {
+  CGPoint cg_point = CGEventGetLocation(
+      base::ScopedCFTypeRef<CGEventRef>(CGEventCreate(nullptr)));
+  return gfx::Point(cg_point.x, cg_point.y);
+}
+
+// Send the mouse event of |type| to the |expected_window|, located at
+// |mouse_position|. |expected_window| could be nil if we don't know which
+// window is supposed to receive it.
+void SendCustomLeftMouseEvent(NSWindow* expected_window,
+                              gfx::Point mouse_position,
+                              CGEventType type) {
+  DCHECK(type == kCGEventLeftMouseDown || type == kCGEventLeftMouseUp);
+
+  // Check that we're sending the event to the window we expect.
+  if (expected_window) {
+    NSPoint ns_mouse_position = gfx::ScreenPointToNSPoint(mouse_position);
+    NSInteger window_number = [NSWindow windowNumberAtPoint:ns_mouse_position
+                                belowWindowWithWindowNumber:0];
+    NSWindow* current_window = [[NSApplication sharedApplication]
+        windowWithWindowNumber:window_number];
+    DCHECK_EQ(expected_window, current_window);
+  }
+
+  base::ScopedCFTypeRef<CGEventRef> event(CGEventCreateMouseEvent(
+      nullptr, type, CGPointMake(mouse_position.x(), mouse_position.y()),
+      kCGMouseButtonLeft));
+
+  CGEventSetIntegerValueField(
+      event, kCGEventSourceUserData,
+      views::kCocoaWindowMoveLoopSimulatedEventUserData);
+  CGEventPost(kCGSessionEventTap, event);
+}
+
+}  // namespace
+
+namespace views {
+
+const int kCocoaWindowMoveLoopSimulatedEventUserData = 1;
+
+CocoaWindowMoveLoop::CocoaWindowMoveLoop(BridgedNativeWidget* owner,
+                                         gfx::Point initial_mouse_in_screen)
+    : owner_(owner),
+      run_loop_(new base::RunLoop),
+      initial_mouse_in_screen_(initial_mouse_in_screen),
+      quit_closure_(run_loop_->QuitClosure()),
+      weak_factory_(this) {
+  // AppKit continues to send mouse events to the window, but toolkit-views
+  // doesn't expect them during RunMoveLoop().
+  [BridgedContentView setIgnoreMouseEvents:YES];
+  owner_->SetDraggable(true);
+}
+
+CocoaWindowMoveLoop::~CocoaWindowMoveLoop() {
+  owner_->SetDraggable(false);
+  // Note the crafted events in Run() should not make their way through to
+  // toolkit-views, but regular events after that should be. So stop ignoring.
+  [BridgedContentView setIgnoreMouseEvents:NO];
+
+  // Handle the pathological case, where |this| is destroyed while running.
+  if (exit_reason_ref_) {
+    *exit_reason_ref_ = WINDOW_DESTROYED;
+    quit_closure_.Run();
+  }
+
+  owner_ = nullptr;
+}
+
+Widget::MoveLoopResult CocoaWindowMoveLoop::Run() {
+  LoopExitReason exit_reason = ENDED_EXTERNALLY;
+  exit_reason_ref_ = &exit_reason;
+  NSWindow* window = owner_->ns_window();
+
+  // Move the RunLoop to the stack so our destructor can be called while it is
+  // running.
+  scoped_ptr<base::RunLoop> run_loop(std::move(run_loop_));
+
+  // A new window may have just been created, so post an event at the session
+  // tap level to initiate a window drag.
+  SendCustomLeftMouseEvent(window, initial_mouse_in_screen_,
+                           kCGEventLeftMouseDown);
+
+  // Will be retained by the monitor handler block.
+  WeakCocoaWindowMoveLoop* weak_cocoa_window_move_loop =
+      [[[WeakCocoaWindowMoveLoop alloc]
+          initWithWeakPtr:weak_factory_.GetWeakPtr()] autorelease];
+
+  NSEventMask mask = NSLeftMouseUpMask | NSKeyDownMask | NSLeftMouseDraggedMask;
+  auto handler = ^NSEvent*(NSEvent* event) {
+    CocoaWindowMoveLoop* strong = [weak_cocoa_window_move_loop weak].get();
+    if (!strong) {
+      // By this point CocoaWindowMoveLoop was deleted while processing this
+      // same event, and this event monitor was not unregistered in time. It is
+      // reproducible by the PressEscapeWhileDetached test.
+      // Continue processing the event.
+      return event;
+    }
+
+    if ([event type] == NSLeftMouseDragged) {
+      // AppKit doesn't supply position updates during a drag, so post a task to
+      // notify observers once AppKit has moved the window.
+      base::MessageLoop::current()->PostTask(
+          FROM_HERE, base::Bind(&BridgedNativeWidget::OnPositionChanged,
+                                base::Unretained(strong->owner_)));
+      return event;
+    }
+
+    strong->quit_closure_.Run();
+    if ([event type] == NSLeftMouseUp) {
+      *strong->exit_reason_ref_ = MOUSE_UP;
+      return event;  // Process the MouseUp.
+    }
+    *strong->exit_reason_ref_ = ESCAPE_PRESSED;
+    return nil;  // Swallow the keypress.
+  };
+  id monitor =
+      [NSEvent addLocalMonitorForEventsMatchingMask:mask handler:handler];
+
+  // NSKeyDownMask doesn't work inside addLocalMonitorForEventsMatchingMask:
+  // the event is swallowed by the window move loop before it gets to -[NSApp
+  // sendEvent:]. To see an escape keypress, hook in an event tap lower.
+
+  run_loop->Run();
+  [NSEvent removeMonitor:monitor];
+
+  if (exit_reason != WINDOW_DESTROYED && exit_reason != ENDED_EXTERNALLY) {
+    exit_reason_ref_ = nullptr;  // Ensure End() doesn't replace the reason.
+    owner_->EndMoveLoop();       // Deletes |this|.
+  }
+
+  if (exit_reason != MOUSE_UP) {
+    // Tell AppKit to stop moving the window. Otherwise, AppKit will refuse to
+    // start a new window drag. Note the window being dragged is going away in
+    // this case, so it doesn't really matter where the event is located.
+
+    if (exit_reason == ENDED_EXTERNALLY) {
+      // When not canceled, the non-moving drag in the original window must
+      // resume. To do this, AppKit needs to see a mouseDown so that it sends
+      // the correct events. Ideally, it also needs to be at the original
+      // offset, so that it hits a non-draggable region of the original
+      // window: The tab being dragged may move some distance from the cursor
+      // when it "snaps in", so the cursor may not be over a tab. Sadly, this
+      // method doesn't know which window that is. But all that really needs
+      // to be done is to prevent a custom-dragging area from starting a
+      // window-drag. So hook into the logic in RepostEventIfHandledByWindow()
+      // by setting a flag here. Note this assumes the custom mouseDown event
+      // is guaranteed to hit another BridgedNativeWidget when it gets to the
+      // front of the event queue.
+      // TODO(tapted): A better fix would be to keep the temporary window
+      // around and never call EndMoveLoop() on Mac, making this block of code
+      // obsolete.
+      BridgedNativeWidget::IgnoreNextMouseDownForDraggableRegions();
+      SendCustomLeftMouseEvent(nil, GetMousePosition(),
+                               kCGEventLeftMouseDown);
+    } else {
+      SendCustomLeftMouseEvent(window, GetMousePosition(),
+                               kCGEventLeftMouseUp);
+    }
+  }
+
+  return exit_reason == ESCAPE_PRESSED ? Widget::MOVE_LOOP_CANCELED
+                                       : Widget::MOVE_LOOP_SUCCESSFUL;
+}
+
+void CocoaWindowMoveLoop::End() {
+  if (exit_reason_ref_) {
+    DCHECK_EQ(*exit_reason_ref_, ENDED_EXTERNALLY);
+    // Ensure the destructor doesn't replace the reason.
+    exit_reason_ref_ = nullptr;
+    quit_closure_.Run();
+  }
+}
+
+}  // namespace views