[gtk+] print operation: let subclasses use a custom paginate

[Paolo Borelli <pborelli src gnome org>]

commit 9f9c5ca49ada3e9345a48fd8d642883c0f7339fb
Author: Paolo Borelli <pborelli gnome org>
Date:   Mon Aug 17 18:31:15 2015 +0200

    print operation: let subclasses use a custom paginate
    
    GtkPrintOperation was emitting paginate only if a signal was
    connected, this meant that subclassing and overriding the
    paginate vfunc lead to the unexpected result that paginate did
    not run.
    Instead we always emit the signal and use a custom accumulator:
    if there is a signal we just run that and avoid the default
    handler, otherwise we run the default handler which can be the
    one by the subclass or the default handler that just skips
    pagination.
    
    Patch by Yevgen Muntyan, fixes #345345

 gtk/gtkprintoperation.c |   36 +++++++++++++++++++++++++++---------
 1 files changed, 27 insertions(+), 9 deletions(-)
---
diff --git a/gtk/gtkprintoperation.c b/gtk/gtkprintoperation.c
index 929cdaf..6dc7fb2 100644
--- a/gtk/gtkprintoperation.c
+++ b/gtk/gtkprintoperation.c
@@ -696,6 +696,14 @@ gtk_print_operation_create_custom_widget (GtkPrintOperation *operation)
   return NULL;
 }
 
+static gboolean
+gtk_print_operation_paginate (GtkPrintOperation *operation,
+                              GtkPrintContext   *context)
+{
+  /* assume the number of pages is already set and pagination is not needed */
+  return TRUE;
+}
+
 static void
 gtk_print_operation_done (GtkPrintOperation       *operation,
                           GtkPrintOperationResult  result)
@@ -726,6 +734,19 @@ custom_widget_accumulator (GSignalInvocationHint *ihint,
   return continue_emission;
 }
 
+static gboolean
+paginate_accumulator (GSignalInvocationHint *ihint,
+                      GValue                *return_accu,
+                      const GValue          *handler_return,
+                      gpointer               dummy)
+{
+  *return_accu = *handler_return;
+
+  /* Stop signal emission on first invocation, so if it's a callback then
+   * the default handler won't run. */
+  return FALSE;
+}
+
 static void
 gtk_print_operation_class_init (GtkPrintOperationClass *class)
 {
@@ -737,6 +758,7 @@ gtk_print_operation_class_init (GtkPrintOperationClass *class)
  
   class->preview = gtk_print_operation_preview_handler; 
   class->create_custom_widget = gtk_print_operation_create_custom_widget;
+  class->paginate = gtk_print_operation_paginate;
   class->done = gtk_print_operation_done;
 
   /**
@@ -817,7 +839,7 @@ gtk_print_operation_class_init (GtkPrintOperationClass *class)
                  G_TYPE_FROM_CLASS (gobject_class),
                  G_SIGNAL_RUN_LAST,
                  G_STRUCT_OFFSET (GtkPrintOperationClass, paginate),
-                 _gtk_boolean_handled_accumulator, NULL,
+                 paginate_accumulator, NULL,
                  _gtk_marshal_BOOLEAN__OBJECT,
                  G_TYPE_BOOLEAN, 1, GTK_TYPE_PRINT_CONTEXT);
 
@@ -2697,6 +2719,7 @@ prepare_data (PrintPagesData *data)
 {
   GtkPrintOperationPrivate *priv;
   GtkPageSetup             *page_setup;
+  gboolean                  paginated = FALSE;
   gint                      i, j, counter;
 
   priv = data->op->priv;
@@ -2725,14 +2748,9 @@ prepare_data (PrintPagesData *data)
       return;
     }
 
-  if (g_signal_has_handler_pending (data->op, signals[PAGINATE], 0, FALSE))
-    {
-      gboolean paginated = FALSE;
-
-      g_signal_emit (data->op, signals[PAGINATE], 0, priv->print_context, &paginated);
-      if (!paginated)
-        return;
-    }
+  g_signal_emit (data->op, signals[PAGINATE], 0, priv->print_context, &paginated);
+  if (!paginated)
+    return;
 
   /* Initialize parts of PrintPagesData that depend on nr_of_pages
    */