[gtk+] GtkTreeView: change child repositioning to preserve locality

[Руслан Ижбулатов <ruslanizhb src gnome org>]

commit 96c18db0daf922e7f02f54c26043d1d2ac98f5cc
Author: Руслан Ижбулатов <lrn1986 gmail com>
Date:   Tue Apr 26 21:45:15 2016 +0000

    GtkTreeView: change child repositioning to preserve locality
    
    If there was a piece of text in the cell, then when the edit
    entry is shown for that cell, it should have a piece of text
    in it roughly at the same location.
    
    Therefore, when child widget is enlarged (child preferred
    size exceeds cell size), extra width should be added by
    extending either left or right edge depending on text direction.
    
    If after that the child sticks outside of the treeivew visible region,
    try to push it back inside (breaking its alignment with the
    cell), again, giving preference (i.e. adjusting it last)
    to either left or right edge depending on text direction.
    
    https://bugzilla.gnome.org/show_bug.cgi?id=765471

 gtk/gtktreeview.c |   36 ++++++++++++++++++++++++++++++++----
 1 files changed, 32 insertions(+), 4 deletions(-)
---
diff --git a/gtk/gtktreeview.c b/gtk/gtktreeview.c
index a1a76f9..f6f0c1c 100644
--- a/gtk/gtktreeview.c
+++ b/gtk/gtktreeview.c
@@ -2980,7 +2980,9 @@ gtk_tree_view_size_allocate (GtkWidget     *widget,
       GdkRectangle child_rect;
       int min_x, max_x, min_y, max_y;
       int size;
+      GtkTextDirection direction;
 
+      direction = gtk_widget_get_direction (child->widget);
       path = _gtk_tree_path_new_from_rbtree (child->tree, child->node);
       gtk_tree_view_get_cell_area (tree_view, path, child->column, &child_rect);
       child_rect.x += child->border.left;
@@ -2989,9 +2991,16 @@ gtk_tree_view_size_allocate (GtkWidget     *widget,
       child_rect.height -= child->border.top + child->border.bottom;
 
       gtk_widget_get_preferred_width (GTK_WIDGET (child->widget), &size, NULL);
+
       if (size > child_rect.width)
         {
-          child_rect.x -= (size - child_rect.width) / 2;
+          /* Enlarge the child, extending it to the left (RTL) */
+          if (direction == GTK_TEXT_DIR_RTL)
+            child_rect.x -= (size - child_rect.width);
+          /* or to the right (LTR) */
+          else
+            child_rect.x += 0;
+
           child_rect.width = size;
         }
 
@@ -3000,17 +3009,36 @@ gtk_tree_view_size_allocate (GtkWidget     *widget,
                                                  &size, NULL);
       if (size > child_rect.height)
         {
+          /* Enlarge the child, extending in both directions equally */
           child_rect.y -= (size - child_rect.height) / 2;
           child_rect.height = size;
         }
 
-      /* push the rect back in the visible area if needed, preferring the top left corner */
+      /* push the rect back in the visible area if needed,
+       * preferring the top left corner (for RTL)
+       * or top right corner (for LTR)
+       */
       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));
+
+      if (direction == GTK_TEXT_DIR_LTR)
+        /* Ensure that child's right edge is not sticking to the right
+         * (if (child_rect.x > max_x) child_rect.x = max_x),
+         * then ensure that child's left edge is visible and is not sticking to the left
+         * (if (child_rect.x < min_x) child_rect.x = min_x).
+         */
+        child_rect.x = MAX (min_x, MIN (max_x, child_rect.x));
+      else
+        /* Ensure that child's left edge is not sticking to the left
+         * (if (child_rect.x < min_x) child_rect.x = min_x),
+         * then ensure that child's right edge is visible and is not sticking to the right
+         * (if (child_rect.x > max_x) child_rect.x = max_x).
+         */
+        child_rect.x = MIN (max_x, MAX (min_x, child_rect.x));
+
+      child_rect.y = MAX (min_y, MIN (max_y, child_rect.y));
 
       gtk_tree_path_free (path);
       gtk_widget_size_allocate (child->widget, &child_rect);