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, 168 insertions, 0 deletions

diff --git a/test/flex_demo.cxx b/test/flex_demo.cxx
new file mode 100644
index 000000000..fb2b73cef
--- /dev/null
+++ b/test/flex_demo.cxx
@@ -0,0 +1,168 @@
+//
+// 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>
+
+#define DEBUG_GROUP (0)
+
+void debug_group(Fl_Group *g) {
+#if (DEBUG_GROUP)
+  printf("\nFl_Group (%p) has %d children:\n", g, g->children());
+  for (int i = 0; i < g->children(); i++) {
+    Fl_Widget *c = g->child(i);
+    printf("  child %2d: hidden = %-5s, (x,y,w,h) = (%3d, %3d, %3d, %3d), label = '%s'\n",
+           i, c->visible() ? "false" : "true", c->x(), c->y(), c->w(), c->h(),
+           c->label() ? c->label() : "(null)");
+  }
+#endif
+} // debug_group
+
+Fl_Button *createButton(const char *caption) {
+  Fl_Button *rtn = new Fl_Button(0, 0, 120, 30, caption);
+  rtn->color(fl_rgb_color(225, 225, 225));
+  return rtn;
+}
+
+void toggle_cb(Fl_Widget *w, void *v) {
+  static Fl_Box *b = 0;
+  Fl_Widget *o = (Fl_Widget *)v;
+  Fl_Flex *flex = (Fl_Flex *)o->parent();
+  if (o->visible()) {
+    o->hide();
+    w->label("show OK button");
+    flex->child(1)->hide();         // hide Box
+  } else {
+    o->show();
+    w->label("hide OK button");
+    flex->child(1)->show();         // show Box
+  }
+  flex->layout();
+
+  debug_group(flex);
+
+  // Yet another test: modify the first (top) Fl_Flex widget
+
+  flex = (Fl_Flex *)(flex->parent()->child(0));
+  Fl_Group::current(0);
+  if (!b) {
+    b = new Fl_Box(0, 0, 0, 0, "Box3");
+    flex->insert(*b, flex->children() - 1);
+  } else {
+    delete b;
+    b = 0;
+  }
+  flex->layout();
+  debug_group(flex);
+}
+
+Fl_Flex *createRow() {
+  Fl_Flex *row = new Fl_Flex(Fl_Flex::ROW);
+  {
+    Fl_Button *toggle = createButton("hide OK button");
+    toggle->tooltip("hide() or show() OK button");
+    Fl_Box *box2 = new Fl_Box(0, 0, 120, 10, "Box2");
+    Fl_Button * okay = createButton("OK");
+    new Fl_Input(0, 0, 120, 10, "");
+
+    toggle->callback(toggle_cb, okay);
+
+    Fl_Flex *col2 = new Fl_Flex(Fl_Flex::COLUMN);
+    {
+      createButton("Top2");
+      createButton("Bottom2");
+      col2->end();
+      col2->margin(0, 5);
+      col2->box(FL_FLAT_BOX);
+      col2->color(fl_rgb_color(255, 128, 128));
+    }
+
+    row->set_size(box2, 50);
+    row->set_size(col2, 100);
+    row->end();
+
+    // TEST
+    row->box(FL_DOWN_BOX);
+    row->color(FL_GREEN);
+  }
+
+  return row;
+}
+
+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);
+    {
+      Fl_Flex *row = new Fl_Flex(Fl_Flex::ROW);
+      row->color(FL_YELLOW);
+      row->box(FL_FLAT_BOX);
+      {
+        createButton("Cancel");
+        new Fl_Box(0, 0, 120, 10, "Box1");
+        createButton("OK");
+        new Fl_Input(0, 0, 120, 10, "");
+
+        Fl_Flex *col1 = new Fl_Flex(Fl_Flex::COLUMN);
+        {
+          createButton("Top1");
+          createButton("Bottom1");
+          col1->end();
+          col1->box(FL_FLAT_BOX);
+          col1->color(fl_rgb_color(255, 128, 128));
+          col1->margin(5, 5);
+        }
+
+        row->end();
+      }
+      col->set_size(createRow(), 90);
+      createButton("Something1");
+      row = new Fl_Flex(Fl_Flex::ROW);
+      {
+        Fl_Button *cancel = createButton("Cancel");
+        Fl_Button *ok = createButton("OK");
+        new Fl_Input(0, 0, 120, 10, "");
+
+        row->set_size(cancel, 100);
+        row->set_size(ok, 100);
+        row->end();
+      }
+      createButton("Something2");
+
+      col->set_size(row, 30);
+      col->margin(0, 6);
+      col->end();
+    }
+    window->resizable(col);
+    window->color(fl_rgb_color(160, 180, 240));
+    window->box(FL_FLAT_BOX);
+    window->end();
+  }
+
+  window->size_range(550, 330);
+  window->resize(0, 0, 640, 480);
+  window->show(argc, argv);
+
+  int ret = Fl::run();
+  delete window;
+  return ret;
+}