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, 94 insertions, 0 deletions

diff --git a/test/grid_login.cxx b/test/grid_login.cxx
new file mode 100644
index 000000000..fb10bb649
--- /dev/null
+++ b/test/grid_login.cxx
@@ -0,0 +1,94 @@
+//
+// 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
+//
+
+#include <FL/Fl.H>
+#include <FL/Fl_Double_Window.H>
+#include <FL/Fl_Grid.H>
+#include <FL/Fl_Button.H>
+#include <FL/Fl_Input.H>
+#include <FL/Fl_Box.H>
+
+int main(int argc, char **argv) {
+
+  Fl_Double_Window *win = new Fl_Double_Window(480, 200, "Fl_Grid \"Login\" Layout");
+
+  // Fl_Grid of 6 x 6 cells, margin 2 and gap 2
+
+  Fl_Grid *grid = new Fl_Grid(5, 5, 470, 190);
+  grid->layout(6, 6, 2, 2);  // 6 rows, 6 columns, margin 2, gap 2
+
+  // image (150x200) in left column
+
+  Fl_Box *ibox = new Fl_Box(0, 0, 150, 200, "Image");
+  ibox->box(FL_BORDER_BOX);
+  ibox->color(fl_rgb_color(0, 200, 0));
+  grid->widget(ibox, 1, 1, 4, 1, FL_GRID_CENTER);
+
+  // the title spans 2 columns (3 - 4)
+
+  Fl_Box *title = new Fl_Box(0, 0, 200, 60);
+  title->label("Welcome to Fl_Grid");
+  title->align(FL_ALIGN_CENTER);
+  title->labelfont(FL_BOLD + FL_ITALIC);
+  title->labelsize(16);
+  grid->widget(title, 1, 3, 1, 2, FL_GRID_HORIZONTAL | FL_GRID_CENTER);
+
+  grid->col_width(2, 90);  // placeholder for labels
+
+  // input widgets with fixed height and horizontal stretching
+
+  Fl_Input *i1 = new Fl_Input(0, 0, 150, 30, "Username:");
+  grid->widget(i1, 2, 3, 1, 2, FL_GRID_HORIZONTAL);
+  grid->row_gap(2, 10); // gap below username
+
+  Fl_Input *i2 = new Fl_Input(0, 0, 150, 30, "Password:");
+  grid->widget(i2, 3, 3, 1, 2, FL_GRID_HORIZONTAL);
+  grid->row_gap(3, 10); // gap below password
+
+  // register and login buttons
+
+  Fl_Button *btr = new Fl_Button(0, 0, 80, 30, "Register");
+  grid->widget(btr, 4, 3, 1, 1, FL_GRID_HORIZONTAL);
+  grid->col_gap(3, 20); // gap right of the register button
+
+  Fl_Button *btl = new Fl_Button(0, 0, 80, 30, "Login");
+  grid->widget(btl, 4, 4, 1, 1, FL_GRID_HORIZONTAL);
+
+  // set column and row weights for resizing behavior (optional)
+
+  int cw[] = { 20,  0,  0, 10, 10, 20};  // column weights
+  int rw[] = { 10,  0,  0,  0,  0, 10};  // row weights
+  grid->col_weight(cw, 6);
+  grid->row_weight(rw, 6);
+
+  grid->end();
+  grid->layout();
+  // grid->debug(1);
+  // grid->show_grid(1);     // enable to display grid helper lines
+  win->end();
+  grid->color(fl_rgb_color(250, 250, 250));
+  win->color(fl_rgb_color(250, 250, 250));
+
+  win->resizable(grid);
+  win->resize(0, 0, 600, 300);   // same size as flex_login
+  win->size_range(550, 250);
+  win->show(argc, argv);
+
+  int ret = Fl::run();
+  delete win; // not necessary but useful to test for memory leaks
+  return ret;
+}