Add a dead zone when dragging tabs horizontally on Mac

chrome/browser/ui/cocoa/tabs/tab_strip_drag_controller.mm

 // Copyright (c) 2012 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 "chrome/browser/ui/cocoa/tabs/tab_strip_drag_controller.h"
 
 #include <Carbon/Carbon.h>
 
 #include "base/mac/scoped_cftyperef.h"
 #import "base/mac/sdk_forward_declarations.h"
 #import "chrome/browser/ui/cocoa/tabs/tab_controller.h"
 #import "chrome/browser/ui/cocoa/tabs/tab_controller_target.h"
 #import "chrome/browser/ui/cocoa/tabs/tab_strip_controller.h"
 #import "chrome/browser/ui/cocoa/tabs/tab_strip_view.h"
 #import "chrome/browser/ui/cocoa/tabs/tab_view.h"
 #import "chrome/browser/ui/cocoa/tabs/tab_window_controller.h"
 #include "ui/base/cocoa/cocoa_base_utils.h"
 #include "ui/gfx/mac/scoped_cocoa_disable_screen_updates.h"
 
+const CGFloat kHorizontalTearDistance = 10.0; // Using the same value as Views.
 const CGFloat kTearDistance = 36.0;
 const NSTimeInterval kTearDuration = 0.333;
 
 // Returns whether |screenPoint| is inside the bounds of |view|.
 static BOOL PointIsInsideView(NSPoint screenPoint, NSView* view) {
   if ([view window] == nil)
     return NO;
   NSPoint windowPoint =
       ui::ConvertPointFromScreenToWindow([view window], screenPoint);
   NSPoint viewPoint = [view convertPoint:windowPoint fromView:nil];
@@ skipping 134 matching lines @@
     return;
   }
 
   // First, go through the magnetic drag cycle. We break out of this if
   // "stretchiness" ever exceeds a set amount.
   tabWasDragged_ = YES;
 
   if (draggingWithinTabStrip_) {
     NSPoint thisPoint = [NSEvent mouseLocation];
     CGFloat offset = thisPoint.x - dragOrigin_.x;
-    [sourceController_ insertPlaceholderForTab:[draggedTab_ tabView]
-                                         frame:NSOffsetRect(sourceTabFrame_,
-                                                            offset, 0)];
+    // Only begin dragging the tab horizontally if it's torn out of its dead
+    // zone.
+    if (!outOfTabHorizontalDeadZone_ &&
+        fabs(offset) > kHorizontalTearDistance) {
+      outOfTabHorizontalDeadZone_ = YES;
+    }
+    if (outOfTabHorizontalDeadZone_) {

[erikchen, 2016/11/30 21:07:34]

I patched this in and tried tab dragging. It seemed to work fine, but I also saw
a large number of:

"""
tab_window_controller.mm(352)] Not implemented reached in -[TabWindowController
menubarOffset]
"""

It's not clear to me how you're actually preventing tab dragging by inserting a
placeholder on line 182. I imagine that you want an early return? Can you
explain how you're trying to prevent tab dragging? 

[njagsarran, 2016/12/02 16:43:12]

I'm seeing that error, too. I undid my changed and rebuilt, but I'm still seeing
that error. Do you also still see it without my patch, or am I missing
something?

I think the placeholder is the tab under the mouse when moving it within the
strip, so now it can't be created unless we drag beyond the dead zone. I don't
think we want an early return because we still want to check for vertical
dragging below.

[erikchen, 2016/12/07 17:53:20]

You're right. Tried again and I can reproduce the error withyour your CL. 

It looks like placeholderTab_ is used to determine "isDragSessionActive", which
is why setting it is required to start dragging.

+      [sourceController_ insertPlaceholderForTab:[draggedTab_ tabView]
+                                           frame:NSOffsetRect(sourceTabFrame_,
+                                                              offset, 0)];
+    }
     // Check that we haven't pulled the tab too far to start a drag. This
     // can include either pulling it too far down, or off the side of the tab
     // strip that would cause it to no longer be fully visible.
     BOOL stillVisible =
         [sourceController_ isTabFullyVisible:[draggedTab_ tabView]];
     CGFloat tearForce = fabs(thisPoint.y - dragOrigin_.y);
     if ([sourceController_ tabTearingAllowed] &&
         (tearForce > kTearDistance || !stillVisible)) {
       draggingWithinTabStrip_ = NO;
       // When you finally leave the strip, we treat that as the origin.
@@ skipping 209 matching lines @@
   // we want to hide the window background so the tab stands out for
   // positioning. If not, we want to show it so it looks like a new window will
   // be realized.
   BOOL chromeShouldBeVisible = targetController_ == nil;
   [self setWindowBackgroundVisibility:chromeShouldBeVisible];
 }
 
 - (void)endDrag:(NSEvent*)event {
   // Cancel any delayed -continueDrag: requests that may still be pending.
   [NSObject cancelPreviousPerformRequestsWithTarget:self];
+  outOfTabHorizontalDeadZone_ = NO;
 
   // Special-case this to keep the logic below simpler.
   if (moveWindowOnDrag_) {
     [self resetDragControllers];
     return;
   }
 
   // TODO(pinkerton): http://crbug.com/25682 demonstrates a way to get here by
   // some weird circumstance that doesn't first go through mouseDown:. We
   // really shouldn't go any farther.
@@ skipping 139 matching lines @@
     [[targetController_ window] makeMainWindow];
   } else {
     [dragWindow_ setAlphaValue:0.5];
     [[draggedController_ overlayWindow] setHasShadow:NO];
     [[draggedController_ window] makeMainWindow];
   }
   chromeIsVisible_ = shouldBeVisible;
 }
 
 @end