#include <gtk/gtk.h>
#include <cairo.h>
#include <stdlib.h>

/* compile with
 * gcc -Wall -g -o cairotest `pkg-config --libs --cflags cairo gtk+-2.0` cairotest.c
 */
void
draw (GtkWidget *darea)
{
  GtkAllocation *alloc;
  gdouble        scaling;
  cairo_t       *cr;
  gdouble dx = 1.0, dy = 1.0;


  cr = gdk_cairo_create (darea->window);

  alloc = &darea->allocation;
  scaling = MIN (alloc->width, alloc->height) / 2.2;
#if 0
  cairo_new_path (cr);
  cairo_rectangle (cr, 0, 0, alloc->width, alloc->height);
  cairo_clip (cr);
  cairo_stroke (cr);

#endif
  cairo_translate (cr, alloc->width / 2, alloc->height / 2);
  cairo_scale (cr, scaling, -scaling);

  cairo_device_to_user_distance (cr, &dx, &dy);
  cairo_set_line_width (cr, MAX (dx, dy));
  cairo_set_source_rgba (cr, 1.0, 0.0, 0.0, 1.0);

  /* this goes across the origin in the center of the window */
  cairo_new_path (cr);
  cairo_move_to (cr, -1000.0, -1000.0);
  cairo_line_to (cr, 1000.0, 1000.0);
  cairo_stroke (cr);

  /* this is a unit-box around the center of the window */
  cairo_set_source_rgba (cr, 0.0, 0.0, 1.0, 1.0);
  cairo_new_path (cr);
  cairo_rectangle (cr, -1, -1, 2, 2);
  cairo_stroke (cr);

  cairo_destroy (cr);
}


gboolean
expose_event (GtkWidget      *widget,
              GdkEventExpose *event,
              gpointer       *data)
{
  GtkWidget *darea = GTK_WIDGET (data);

  draw (darea);

  return FALSE;
}


void
create_window (void)
{
  GtkWidget *window, *darea;

  window = g_object_new (GTK_TYPE_WINDOW,
                         "title", "Test",
                         "default-width", 800,
                         "default-height", 600,
                         "visible", TRUE,
                         NULL);

  g_signal_connect (window,
                    "destroy", G_CALLBACK (gtk_main_quit), NULL);

  darea = g_object_new (GTK_TYPE_DRAWING_AREA,
                        "width-request", 100,
                        "height-request", 100,
                        "visible", TRUE,
                        "parent", window,
                        NULL);
  g_object_connect (G_OBJECT (darea),
                    "signal::expose-event",
                        G_CALLBACK (expose_event), darea,
                    NULL);
}


gint
main (gint argc, char *argv[])
{
  gtk_init (&argc, &argv);

  create_window ();

  gtk_main ();

  return 0;
}