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

1 files changed, 32 insertions, 4 deletions

diff --git a/gtk/gtktreeview.c b/gtk/gtktreeview.c
index a1a76f9dd6..f6f0c1c8a8 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);