Qt: Try to fix un-maximize behavior on OS X.

On OS X, create dialogs with valid parents so that we don't trigger
QTBUG-46701. Document QDialog's "on top", maximize, and minimize
behaviors.

Bug: 12544
Change-Id: I32c0ef01dba3f7132e5fd0cd61f9feb654b92009
Reviewed-on: https://code.wireshark.org/review/16127
Reviewed-by: Gerald Combs <gerald@wireshark.org>
Petri-Dish: Gerald Combs <gerald@wireshark.org>
Tested-by: Petri Dish Buildbot <buildbot-no-reply@wireshark.org>
Reviewed-by: Anders Broman <a.broman58@gmail.com>

ui/qt/geometry_state_dialog.cpp

@@ -24,13 +24,6 @@
 #include "ui/recent.h"
 #include "ui/ui_util.h"
 
-
-GeometryStateDialog::GeometryStateDialog(QWidget *parent, Qt::WindowFlags f) :
-    QDialog(parent, f)
-{
-
-}
-
 GeometryStateDialog::~GeometryStateDialog()
 {
     saveGeometry();

ui/qt/geometry_state_dialog.h

@@ -29,7 +29,43 @@ class GeometryStateDialog : public QDialog
     Q_OBJECT
 
 public:
-    explicit GeometryStateDialog(QWidget *parent, Qt::WindowFlags f = 0);
+
+// As discussed in change 7072, QDialogs have different minimize and "on
+// top" behaviors depending on their parents, flags, and platforms.
+//
+// W = Windows, L = Linux, X = OS X
+//
+// QDialog(parent)
+//
+//   W,L: Always on top, no minimize button.
+//   X: Independent, no minimize button.
+//
+// QDialog(parent, Qt::Window)
+//
+//   W: Always on top, minimize button. Minimizes to a small title bar
+//      attached to the taskbar and not the taskbar itself. (The GTK+
+//      UI used to do this.)
+//   L: Always on top, minimize button.
+//   X: Independent, minimize button.
+//
+// QDialog(NULL)
+//
+//   W, L, X: Independent, no minimize button.
+//
+// QDialog(NULL, Qt::Window)
+//
+//   W, L, X: Independent, minimize button.
+//
+// Additionally, maximized, parent-less dialogs can close to a black screen
+// on OS X: https://bugs.wireshark.org/bugzilla/show_bug.cgi?id=12544
+//
+// Pass in the parent on OS X and NULL elsewhere so that we have an
+// independent window that un-maximizes correctly.
+#ifdef Q_OS_MAC
+    explicit GeometryStateDialog(QWidget *parent, Qt::WindowFlags f = 0) : QDialog(parent, f) {}
+#else
+    explicit GeometryStateDialog(QWidget *, Qt::WindowFlags f = 0) : QDialog(NULL, f) {}
+#endif
     ~GeometryStateDialog();
 
 protected:

ui/qt/wireshark_dialog.cpp

@@ -41,8 +41,8 @@
 // - Use a dynamic property + Q_PROPERTY for the subtitle.
 // - Make our nested event loop more robust. See tryDeleteLater for details.
 
-WiresharkDialog::WiresharkDialog(QWidget &, CaptureFile &capture_file) :
-    GeometryStateDialog(NULL, Qt::Window),
+WiresharkDialog::WiresharkDialog(QWidget &parent, CaptureFile &capture_file) :
+    GeometryStateDialog(&parent, Qt::Window),
     cap_file_(capture_file),
     file_closed_(false),
     retap_depth_(0),

ui/qt/wireshark_dialog.h

@@ -47,7 +47,7 @@ class WiresharkDialog : public GeometryStateDialog
 
 public:
     // XXX Unlike the entire QWidget API, parent is mandatory here.
-    explicit WiresharkDialog(QWidget &, CaptureFile &capture_file);
+    explicit WiresharkDialog(QWidget &parent, CaptureFile &capture_file);
 
 signals: