For issue #358 - adds examples/cairo-draw-x.cxx

    Since this is the first cairo example in the examples directory,
    it necessarily involved changes to the Makefile and to fltk-config
    to properly handle the absence/existance of the cairo libs.

    TBD: Add docs to the cario widget describing coordinate system
    and how it differs from the default cairo normalized coordinate system.

1 files changed, 58 insertions, 0 deletions

diff --git a/examples/cairo-draw-x.cxx b/examples/cairo-draw-x.cxx
new file mode 100644
index 000000000..8129e607d
--- /dev/null
+++ b/examples/cairo-draw-x.cxx
@@ -0,0 +1,58 @@
+//
+// Simple demo of drawing an "X" in Cairo (antialiased lines)
+//
+// Copyright 1998-2022 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>               // includes <FL/fl_config.h>
+
+#ifdef FLTK_HAVE_CAIRO           // Builds example code only if cairo enabled
+#include <FL/Fl_Cairo_Window.H>
+
+// Cairo rendering cb called during Fl_Cairo_Window::draw()
+static void my_cairo_draw_cb(Fl_Cairo_Window *window, cairo_t *cr) {
+    const double xmax = (window->w() - 1);
+    const double ymax = (window->h() - 1);
+
+    // Draw green "X"
+    //     Draws an X to four corners of resizable window.
+    //     See Fl_Cairo_Window docs for more info.
+    //
+    cairo_set_antialias(cr, CAIRO_ANTIALIAS_BEST);                // use best antialiasing
+    cairo_set_line_width(cr, 1.00);                               // line width for drawing
+    cairo_set_source_rgb(cr, 1.0, 0.5, 0.0);                      // orange
+    cairo_move_to(cr, 0.0, 0.0);  cairo_line_to(cr, xmax, ymax);  // draw diagonal "\"
+    cairo_move_to(cr, 0.0, ymax); cairo_line_to(cr, xmax, 0.0);   // draw diagonal "/"
+    cairo_stroke(cr);                                             // stroke the lines
+}
+
+int main(int argc, char **argv) {
+    Fl_Cairo_Window window(300, 300, "Cairo Draw 'X'");
+    window.color(FL_BLACK);                                       // cairo window's default bg color
+    window.size_range(50,50,-1,-1);                               // allow resize 50,50 and up
+    window.resizable(&window);                                    // allow window to be resized
+    window.set_draw_cb(my_cairo_draw_cb);                         // draw callback for cairo drawing
+    window.show(argc, argv);
+    return Fl::run();
+}
+
+// The code that follows just allows the example to build even if cairo wasn't enabled.
+#else // (!FLTK_HAVE_CAIRO)
+#include <FL/fl_ask.H>
+int main(int argc, char **argv) {
+    fl_message_title("This program needs a Cairo enabled FLTK library");
+    fl_message("Please configure FLTK with Cairo enabled (--enable-cairo or --enable-cairoext)\n"
+               "or one of the CMake options OPTION_CAIRO or OPTION_CAIROEXT, respectively.");
+    return 0;
+}
+#endif // (FLTK_HAVE_CAIRO)