Add support for detection and processing of clean program termination request.

The default handling of cmd-Q/Quit program under MacOS was to terminate the
program if all its windows are closed without returning from FLTK's event loop.
This was running against a strong design feature of FLTK that programs
should always complete their event loop and return from main() when cleanly
terminating.

In the new code for the MacOS platform, cmd-Q/Quit program no longer terminates
the program. Instead, the event loop is interrupted and a call to Fl::program_should_quit()
allows to detect that program termination has been requested, if necessary.

git-svn-id: file:///fltk/svn/fltk/branches/branch-1.4@12647 ea41ed52-d2ee-0310-a9c1-e6b18d33e121

2 files changed, 19 insertions, 2 deletions

diff --git a/FL/Fl.H b/FL/Fl.H
index 966e20ee1..8cfed7f05 100644
--- a/FL/Fl.H
+++ b/FL/Fl.H
@@ -259,7 +259,8 @@ public:
 private:  
   static unsigned char options_[OPTION_LAST];
   static unsigned char options_read_;
-  
+  static int program_should_quit_; // non-zero means the program was asked to cleanly terminate
+
 public:  
   /*
    Return a global setting for all FLTK applications, possibly overridden
@@ -412,6 +413,19 @@ public:
   static int check();
   static int ready();
   static int run();
+  static int run_also_windowless();
+  static int wait_also_windowless(double delay = 1e20);
+  /** Returns non-zero when a request for program termination was received and accepted.
+   On the MacOS platform, the "Quit xxx" item of the application menu is such a request,
+   that is considered accepted when all windows are closed. On other platforms, this function
+   returns 0 until \p Fl::program_should_quit(1) is called.
+   */
+  static int program_should_quit() {return program_should_quit_;}
+  /** Indicate to the FLTK library whether a program termination request was received and accepted.
+  A program may set this to 1, for example, while performing a platform-independent command asking the program to cleanly
+  terminate, similarly to the "Quit xxx" item of the application menu under MacOS. */
+  static void program_should_quit(int should_i) { program_should_quit_ = should_i; }
+
   static Fl_Widget* readqueue();
   /**
   Adds a one-shot timeout callback.  The function will be called by
diff --git a/FL/Fl_System_Driver.H b/FL/Fl_System_Driver.H
index 5bcd8e994..a543906fd 100644
--- a/FL/Fl_System_Driver.H
+++ b/FL/Fl_System_Driver.H
@@ -4,7 +4,7 @@
 // A base class for platform specific system calls
 // for the Fast Light Tool Kit (FLTK).
 //
-// Copyright 2010-2017 by Bill Spitzak and others.
+// Copyright 2010-2018 by Bill Spitzak and others.
 //
 // This library is free software. Distribution and use rights are outlined in
 // the file "COPYING" which should have been included with this file.  If this
@@ -225,6 +225,9 @@ public:
   virtual const char *meta_name() { return "Meta"; }
   virtual const char *alt_name() { return "Alt"; }
   virtual const char *control_name() { return "Ctrl"; }
+  // The default implementation of the next 2 functions may be enough.
+  virtual int run_also_windowless();
+  virtual int wait_also_windowless(double delay);
 };
 
 #endif // FL_SYSTEM_DRIVER_H