[gtk+] treeview: Make sure the editing widget's top left is always visible

[Matthias Clasen <matthiasc src gnome org>]

commit a47d9a7b65166eedd5b1ab5acb34a38f46725c31
Author: Colomban Wendling <ban herbesfolles org>
Date:   Wed Feb 10 19:43:34 2016 +0100

    treeview: Make sure the editing widget's top left is always visible
    
    https://bugzilla.gnome.org/show_bug.cgi?id=761838

 gtk/gtktreeview.c |    9 +++++++++
 1 files changed, 9 insertions(+), 0 deletions(-)
---
diff --git a/gtk/gtktreeview.c b/gtk/gtktreeview.c
index 7fca5f8..c17cca6 100644
--- a/gtk/gtktreeview.c
+++ b/gtk/gtktreeview.c
@@ -2978,6 +2978,7 @@ gtk_tree_view_size_allocate (GtkWidget     *widget,
       GtkTreeViewChild *child = tmp_list->data;
       GtkTreePath *path;
       GdkRectangle child_rect;
+      int min_x, max_x, min_y, max_y;
       int size;
 
       path = _gtk_tree_path_new_from_rbtree (child->tree, child->node);
@@ -3003,6 +3004,14 @@ gtk_tree_view_size_allocate (GtkWidget     *widget,
           child_rect.height += size;
         }
 
+      /* push the rect back in the visible area if needed, preferring the top left corner */
+      min_x = gtk_adjustment_get_value (tree_view->priv->hadjustment);
+      max_x = min_x + allocation->width - child_rect.width;
+      min_y = 0;
+      max_y = min_y + allocation->height - gtk_tree_view_get_effective_header_height (tree_view) - 
child_rect.height;
+      child_rect.x = MAX (min_x, MIN (child_rect.x, max_x));
+      child_rect.y = MAX (min_y, MIN (child_rect.y, max_y));
+
       gtk_tree_path_free (path);
       gtk_widget_size_allocate (child->widget, &child_rect);
     }