Add some hysterisis to tab dragging on Mac.

http://code.google.com/p/chromium/issues/detail?id=9670

Review URL: http://codereview.chromium.org/60072

git-svn-id: svn://svn.chromium.org/chrome/trunk/src@13104 0039d316-1c4b-4281-b951-d872f2087c98

1 files changed, 19 insertions, 0 deletions

diff --git a/chrome/browser/cocoa/tab_view.mm b/chrome/browser/cocoa/tab_view.mm
index fa624a7..2aef856 100644
--- a/chrome/browser/cocoa/tab_view.mm
+++ b/chrome/browser/cocoa/tab_view.mm
@@ -73,6 +73,11 @@
   BOOL dragging = YES;
   BOOL moved = NO;
 
+  // Do not start dragging until the user has "torn" the tab off by
+  // moving more than 3 pixels.
+  BOOL torn = NO;
+  static const double kDragStartDistance = 3.0;
+
   NSDate* targetDwellDate = nil; // The date this target was first chosen
   NSMutableArray* targets = [NSMutableArray array];
 
@@ -86,6 +91,20 @@
                               inMode:NSDefaultRunLoopMode dequeue:YES];
     NSPoint thisPoint = [NSEvent mouseLocation];
 
+    // TODO(alcor): Pinkerton indicated that cole is adding a more
+    // formal concept of "magnetism" to tab detachment, which would
+    // be an alternative solution.
+    if (!torn) {
+      double dx = thisPoint.x - lastPoint.x;
+      double dy = thisPoint.y - lastPoint.y;
+
+      if (dx * dx + dy * dy < kDragStartDistance * kDragStartDistance
+	  && [theEvent type] == NSLeftMouseDragged) {
+	continue;
+      }
+      torn = YES;
+    }
+
     // Find all the windows that could be a target. It has to be of the
     // appropriate class, and visible (obviously).
     if (![targets count]) {