Add Fl_Grid widget and test and demo programs

- FL/Fl_Grid.H: header file
- src/Fl_Grid.cxx: implementation

- examples/grid-simple.cxx: simple example program
- test/cube.cxx:            use Fl_Grid for layout
- test/grid_alignment.cxx:  test cell alignment and other functions
- test/grid_buttons.cxx:    demo program as discussed in fltk.general
- test/grid_login.cxx:      like test/flex_login.cxx but with Fl_Grid
- test/flex_login.cxx:      modified to match test/grid_login.cxx

1 files changed, 75 insertions, 0 deletions

diff --git a/test/grid_buttons.cxx b/test/grid_buttons.cxx
new file mode 100644
index 000000000..a00a69a64
--- /dev/null
+++ b/test/grid_buttons.cxx
@@ -0,0 +1,75 @@
+//
+// Fl_Grid demo program for the Fast Light Tool Kit (FLTK).
+//
+// Copyright 2021 by Albrecht Schlosser
+// Copyright 2022-2023 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
+//
+
+// Q: How to achieve a spaced out layout?
+// https://groups.google.com/g/fltkgeneral/c/haet7hOQR0g
+
+// A: We use an Fl_Grid with 1 x 7 cells (5 buttons) as requested:
+// [New] [Options] <gap> [About] [Help] <gap> [Quit]
+
+#include <FL/Fl.H>
+#include <FL/Fl_Double_Window.H>
+#include <FL/Fl_Grid.H>
+#include <FL/Fl_Button.H>
+
+int main(int argc, char **argv) {
+
+  Fl_Double_Window *win = new Fl_Double_Window(460, 200, "Fl_Grid Row with 5 Buttons");
+
+  Fl_Grid *grid = new Fl_Grid(0, 0, win->w(), 50);
+  grid->layout(1, 7, 10, 10);
+
+  // create the buttons
+
+  Fl_Button *b0 = new Fl_Button(0, 0, 80, 30, "New");
+  Fl_Button *b1 = new Fl_Button(0, 0, 80, 30, "Options");
+  Fl_Button *b3 = new Fl_Button(0, 0, 80, 30, "About");
+  Fl_Button *b4 = new Fl_Button(0, 0, 80, 30, "Help");
+  Fl_Button *b6 = new Fl_Button(0, 0, 80, 30, "Quit");
+
+  grid->end();
+
+  // assign buttons to grid positions
+
+  grid->widget(b0, 0, 0);
+  grid->widget(b1, 0, 1); grid->col_gap(1, 0);
+  grid->widget(b3, 0, 3);
+  grid->widget(b4, 0, 4); grid->col_gap(4, 0);
+  grid->widget(b6, 0, 6);
+
+  // set column weights for resizing (only empty columns resize)
+
+  int weight[] = { 0, 0, 50, 0, 0, 50, 0 };
+  grid->col_weight(weight, 7);
+
+  grid->end();
+  // grid->show_grid(1);     // enable to display grid helper lines
+
+  // add content ...
+
+  Fl_Group *g1 = new Fl_Group(0, 50, win->w(), win->h() - 50);
+  // add more widgets ...
+
+  win->end();
+  win->resizable(g1);
+  win->size_range(win->w(), 100);
+  win->show(argc, argv);
+
+  int ret = Fl::run();
+  delete win; // not necessary but useful to test for memory leaks
+  return ret;
+}