Add Fl_Flex widget from Karsten Pedersen (issue #255)

This work is based on the repository and latest commit:
  https://github.com/osen/FL_Flex.git

  commit 36e4ed75a00daac825b87e81295818b4650991f5
  Author: Karsten Pedersen <...>
  Date:   Fri Apr 23 12:06:16 2021 +0000

    Added Fltk (LGPL) license.

This widget is similar to Fl_Pack and supports either one row or one
column of widgets but has some more features. Test and demo programs
are included:

  test/flex_login.cxx: simple "login window" demo program
  test/flex_demo.cxx:  slightly more complex demo program

The original demo programs can still be compiled and built with
the new widget provided you '#include <FL/Fl_Flex.H>'.
Backwards compatible methods are included (except debug()).

The original widget has been modified to match FLTK standards and
enhanced in several ways, including:

- support box frames
- add HORIZONTAL and VERTICAL enum values (as in Fl_Pack)
- add horizontal() method (as in Fl_Pack)
- use type() rather than internal 'direction' variable
- add standard widget constructor (x, y, w, h, label)
- add margin and gap accessors rather than hard coding constants
- improve test and demo programs
- add documentation
- replace <vector> with array as required by FLTK CMP
- rename camelCase method names, keeping old names for compatibility:
  - change 'setSize(Fl_Widget*, int)'   to 'set_size(Fl_Widget*, int)'
  - change 'bool isSetSize(Fl_Widget*)' to 'int set_size(Fl_Widget*)'
- remove debug() method
- add a way to "unset" fixed size: set_size(Fl_Widget *, 0)
- add layout() method to force recalculation of children
- unify resizeRow() and resizeCol() methods to avoid code duplication
- improve widget size calculation.

1 files changed, 131 insertions, 0 deletions

diff --git a/test/flex_login.cxx b/test/flex_login.cxx
new file mode 100644
index 000000000..3923bcde3
--- /dev/null
+++ b/test/flex_login.cxx
@@ -0,0 +1,131 @@
+//
+// Fl_Flex demo program for the Fast Light Tool Kit (FLTK).
+//
+// Copyright 2020 by Karsten Pedersen
+// 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_Input.H>
+
+Fl_Button *createButton(const char *caption) {
+  Fl_Button *rtn = new Fl_Button(0, 0, 100, 25, caption);
+  rtn->color(fl_rgb_color(225, 225, 225));
+  return rtn;
+}
+
+void buttonsPanel(Fl_Flex *parent) {
+  new Fl_Box(0, 0, 0, 0, "");
+  Fl_Box *w = new Fl_Box(0, 0, 0, 0, "Welcome to Flex Login");
+
+  Fl_Flex *urow = new Fl_Flex(Fl_Flex::ROW);
+  {
+    Fl_Box *b = new Fl_Box(0, 0, 0, 0, "Username:");
+    b->align(FL_ALIGN_INSIDE | FL_ALIGN_RIGHT);
+    Fl_Input *username = new Fl_Input(0, 0, 0, 0, "");
+
+    urow->set_size(username, 180);
+    urow->end();
+  }
+
+  Fl_Flex *prow = new Fl_Flex(Fl_Flex::ROW);
+  {
+    Fl_Box *b = new Fl_Box(0, 0, 0, 0, "Password:");
+    b->align(FL_ALIGN_INSIDE | FL_ALIGN_RIGHT);
+    Fl_Input *password = new Fl_Input(0, 0, 0, 0, "");
+
+    prow->set_size(password, 180);
+    prow->end();
+  }
+
+  Fl_Box *pad = new Fl_Box(0, 0, 0, 0, "");
+
+  Fl_Flex *brow = new Fl_Flex(Fl_Flex::ROW);
+  {
+    new Fl_Box(0, 0, 0, 0, "");
+    Fl_Button *reg = createButton("Register");
+    Fl_Button *login = createButton("Login");
+
+    brow->set_size(reg, 80);
+    brow->set_size(login, 80);
+    brow->gap(20);
+
+    brow->end();
+  }
+
+  Fl_Box *b = new Fl_Box(0, 0, 0, 0, "");
+
+  parent->set_size(w, 60);
+  parent->set_size(urow, 30);
+  parent->set_size(prow, 30);
+  parent->set_size(pad, 1);
+  parent->set_size(brow, 30);
+  parent->set_size(b, 30);
+}
+
+void middlePanel(Fl_Flex *parent) {
+  new Fl_Box(0, 0, 0, 0, "");
+
+  Fl_Box *box = new Fl_Box(0, 0, 0, 0, "Image");
+  box->box(FL_BORDER_BOX);
+  box->color(fl_rgb_color(0, 200, 0));
+  Fl_Box *spacer = new Fl_Box(0, 0, 0, 0, "");
+
+  Fl_Flex *bp = new Fl_Flex(Fl_Flex::COLUMN);
+  buttonsPanel(bp);
+  bp->end();
+
+  new Fl_Box(0, 0, 0, 0, "");
+
+  parent->set_size(box, 200);
+  parent->set_size(spacer, 10);
+  parent->set_size(bp, 300);
+}
+
+void mainPanel(Fl_Flex *parent) {
+  new Fl_Box(0, 0, 0, 0, "");
+
+  Fl_Flex *mp = new Fl_Flex(Fl_Flex::ROW);
+  middlePanel(mp);
+  mp->end();
+
+  new Fl_Box(0, 0, 0, 0, "");
+
+  parent->set_size(mp, 200);
+}
+
+int main(int argc, char **argv) {
+
+  Fl_Window *window = new Fl_Double_Window(100, 100, "Simple GUI Example");
+  {
+    Fl_Flex *col = new Fl_Flex(5, 5, 90, 90, Fl_Flex::COLUMN);
+    mainPanel(col);
+    col->end();
+
+    window->resizable(col);
+    window->color(fl_rgb_color(250, 250, 250));
+    window->end();
+  }
+
+  window->resize(0, 0, 640, 480);
+  window->size_range(550, 250);
+  window->show(argc, argv);
+
+  int ret = Fl::run();
+  delete window;
+  return ret;
+}