Add basic print functionality

Sadly, the line width depends on the widget's DPI, which seems to
even cause uneven lines on Windows, where virtual printers claim
high DPI.  It might also be an unrelated problem.

Similarly, selected objects are exported highlighted.

Other than that, it works quite well.

Add a manifest to make the print dialog look nice with the older
GTK+ bundle we depend upon.

The RC file could theoretically be scanned for /\s+"([^"]+)"\s*$/,
unescaped, and the results configure_file()-stamped.

src/ld-window-main.c

@@ -106,6 +106,9 @@ static void on_action_new (GtkAction *action, LdWindowMain *self);
 static void on_action_open (GtkAction *action, LdWindowMain *self);
 static void on_action_save (GtkAction *action, LdWindowMain *self);
 static void on_action_save_as (GtkAction *action, LdWindowMain *self);
+static void on_action_print (GtkAction *action, LdWindowMain *self);
+static void on_action_print_draw_page (GtkPrintOperation *operation,
+	GtkPrintContext *context, int page_nr, LdWindowMain *self);
 static void on_action_quit (GtkAction *action, LdWindowMain *self);
 static void on_action_user_guide (GtkAction *action, LdWindowMain *self);
 static void on_action_about (GtkAction *action, LdWindowMain *self);
@@ -146,11 +149,11 @@ static GtkActionEntry wm_action_entries[] =
 		{"SaveAs", GTK_STOCK_SAVE_AS, N_("Save _As..."), "<Shift><Ctrl>S",
 			N_("Save the current diagram with another name"),
 			G_CALLBACK (on_action_save_as)},
-/*
- *		{"Export", NULL, N_("_Export"), NULL,
- *			N_("Export the diagram"),
- *			NULL},
- */
+
+		{"Print", GTK_STOCK_PRINT, N_("_Print"), "<Ctrl>P",
+			N_("Print the diagram"),
+			G_CALLBACK (on_action_print)},
+
 		{"Quit", GTK_STOCK_QUIT, N_("_Quit"), "<Ctrl>Q",
 			N_("Quit the application"),
 			G_CALLBACK (on_action_quit)},
@@ -994,6 +997,87 @@ on_action_save_as (GtkAction *action, LdWindowMain *self)
 	diagram_show_save_as_dialog (self);
 }
 
+static void
+on_action_print (GtkAction *action, LdWindowMain *self)
+{
+	static GtkPrintSettings *settings = NULL;
+	GError *error = NULL;
+	GtkPrintOperation *print;
+	GtkPrintOperationResult res;
+	gchar *name;
+
+	print = gtk_print_operation_new ();
+	gtk_print_operation_set_n_pages (print, 1);
+	gtk_print_operation_set_embed_page_setup (print, TRUE);
+	gtk_print_operation_set_unit (print, GTK_UNIT_MM);
+
+	name = diagram_get_name (self);
+	gtk_print_operation_set_job_name (print, name);
+	g_free (name);
+
+	if (settings != NULL)
+		gtk_print_operation_set_print_settings (print, settings);
+	g_signal_connect (print, "draw-page",
+		G_CALLBACK (on_action_print_draw_page), self);
+
+	/* On Windows, it is not possible to get a print preview from the system
+	 * print dialog.  But in Windows XP previews do not work at all--unreadable
+	 * EMFs come out.  Windows 10 errors out with "A sharing violation occurred
+	 * while accessing" the temporary EMF file on our first run of
+	 * GtkPrintOperation, and following that it opens the previews up in
+	 * fucking Paint, so there is no point in trying.  It lacks a stage
+	 * or controls for setting up page parameters anyway.
+	 */
+	res = gtk_print_operation_run (print,
+		GTK_PRINT_OPERATION_ACTION_PRINT_DIALOG,
+		GTK_WINDOW (self), &error);
+	if (res == GTK_PRINT_OPERATION_RESULT_APPLY)
+	{
+		if (settings != NULL)
+			g_object_unref (settings);
+		settings
+			= g_object_ref (gtk_print_operation_get_print_settings (print));
+	}
+	if (error)
+		display_and_free_error (self, _("Error"), error);
+
+	g_object_unref (print);
+}
+
+static void
+on_action_print_draw_page (GtkPrintOperation *operation,
+	GtkPrintContext *context, int page_nr, LdWindowMain *self)
+{
+	cairo_t *cr;
+	LdDiagramView *view;
+	gdouble area_width_mm, area_height_mm;
+	gdouble diagram_width_mm, diagram_height_mm;
+	gdouble diagram_to_export_units, scale;
+	LdRectangle bounds;
+
+	cr = gtk_print_context_get_cairo_context (context);
+	view = self->priv->view;
+
+	area_width_mm = gtk_print_context_get_width (context);
+	area_height_mm = gtk_print_context_get_height (context);
+	diagram_to_export_units = ld_diagram_view_get_export_bounds (view, &bounds);
+
+	/* Scale for the view's constant, measured in milimetres. */
+	scale = 1 / diagram_to_export_units * LD_DIAGRAM_VIEW_BASE_UNIT_LENGTH;
+	diagram_width_mm = bounds.width * scale;
+	diagram_height_mm = bounds.height * scale;
+
+	/* Scale to fit the paper. */
+	if (area_width_mm < diagram_width_mm)
+		scale *= area_width_mm / diagram_width_mm;
+	if (area_height_mm < diagram_height_mm)
+		scale *= area_height_mm / diagram_height_mm;
+
+	cairo_scale (cr, scale, scale);
+	cairo_translate (cr, -bounds.x, -bounds.y);
+	ld_diagram_view_export (view, cr, &bounds);
+}
+
 static void
 on_action_quit (GtkAction *action, LdWindowMain *self)
 {