Add Fl_Flex demo "howto-flex-simple" to examples

This demo program uses an Fl_Flex widget with one row of buttons.

examples/CMakeLists.txt

@@ -1,7 +1,7 @@
 #
 # CMakeLists.txt used to build example apps by the CMake build system
 #
-# Copyright 2020-2021 by Bill Spitzak and others.
+# Copyright 2020-2022 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
@@ -37,6 +37,7 @@ set (SIMPLE_SOURCES
   howto-browser-with-icons
   howto-drag-and-drop
   howto-draw-an-x
+  howto-flex-simple
   howto-menu-with-images
   howto-parse-args
   howto-remap-numpad-keyboard-keys

examples/Makefile

@@ -1,3 +1,20 @@
+#
+# Makefile used to build example apps by 'make'
+#
+# Copyright 2020-2022 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
+# file is missing or damaged, see the license at:
+#
+#     https://www.fltk.org/COPYING.php
+#
+# Please see the following page on how to report bugs and issues:
+#
+#     https://www.fltk.org/bugs.php
+#
+################################################################################
+
 include Makefile.FLTK
 
 RM    = rm -f
@@ -13,6 +30,7 @@ ALL = browser-simple$(EXEEXT) \
       howto-browser-with-icons$(EXEEXT) \
       howto-drag-and-drop$(EXEEXT) \
       howto-draw-an-x$(EXEEXT) \
+      howto-flex-simple$(EXEEXT) \
       howto-menu-with-images$(EXEEXT) \
       howto-parse-args$(EXEEXT) \
       howto-remap-numpad-keyboard-keys$(EXEEXT) \

examples/Makefile.FLTK

@@ -1,3 +1,20 @@
+#
+# Included Makefile used to build example apps by 'make'
+#
+# Copyright 2020-2022 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
+# file is missing or damaged, see the license at:
+#
+#     https://www.fltk.org/COPYING.php
+#
+# Please see the following page on how to report bugs and issues:
+#
+#     https://www.fltk.org/bugs.php
+#
+################################################################################
+
 #
 # Stuff every FLTK application might need
 #

examples/howto-flex-simple.cxx

@@ -0,0 +1,63 @@
+//
+// Very simple Fl_Flex demo program for the Fast Light Tool Kit (FLTK).
+//
+// Copyright 2022 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
+// file is missing or damaged, see the license at:
+//
+//     https://www.fltk.org/COPYING.php
+//
+// Please see the following page on how to report bugs and issues:
+//
+//     https://www.fltk.org/bugs.php
+//
+
+#include <FL/Fl.H>
+#include <FL/Fl_Double_Window.H>
+#include <FL/Fl_Flex.H>
+#include <FL/Fl_Box.H>
+#include <FL/Fl_Button.H>
+#include <FL/fl_ask.H>
+
+// the 'Exit' button callback closes the window and terminates the program
+void exit_cb(Fl_Widget *w, void *) {
+  fl_message("The '%s' button closes the window\nand terminates the program.", w->label());
+  w->window()->hide();
+}
+
+// common callback for all other buttons
+void button_cb(Fl_Widget *w, void *) {
+  fl_message("The '%s' button does nothing.", w->label());
+}
+
+int main(int argc, char **argv) {
+  Fl_Double_Window window(410, 40, "Simple Fl_Flex Demo");
+  Fl_Flex flex(5, 5, window.w() - 10, window.h() - 10, Fl_Flex::HORIZONTAL);
+  Fl_Button b1(0, 0, 0, 0, "File");
+  Fl_Button b2(0, 0, 0, 0, "New");
+  Fl_Button b3(0, 0, 0, 0, "Save");
+  Fl_Box    bx(0, 0, 0, 0); // empty space
+  Fl_Button eb(0, 0, 0, 0, "Exit");
+
+  // assign callbacks to buttons
+  b1.callback(button_cb);
+  b2.callback(button_cb);
+  b3.callback(button_cb);
+  eb.callback(exit_cb);
+
+  // set gap between adjacent buttons and extra spacing (invisible box size)
+  flex.gap(10);
+  flex.set_size(bx, 30); // total 50: 2 * gap + 30
+
+  // end() groups
+  flex.end();
+  window.end();
+
+  // set resizable, minimal window size, show() window, and execute event loop
+  window.resizable(flex);
+  window.size_range(300, 30);
+  window.show(argc, argv);
+  return Fl::run();
+}