[gtk/wip/otte/listview: 3/4] listview: Implement an anchor

[Benjamin Otte <otte src gnome org>]

commit 69acde53ced3207f914dbe2fc73063aab5714f01
Author: Benjamin Otte <otte redhat com>
Date:   Wed Sep 19 07:08:30 2018 +0200

    listview: Implement an anchor
    
    The anchor selection is very basic: just anchor the top row.
    
    That's vastly better than any other widget already though.

 gtk/gtklistview.c | 162 ++++++++++++++++++++++++++++++++++++++++++++++++++++--
 1 file changed, 157 insertions(+), 5 deletions(-)
---
diff --git a/gtk/gtklistview.c b/gtk/gtklistview.c
index 4768daffab..17a312a82a 100644
--- a/gtk/gtklistview.c
+++ b/gtk/gtklistview.c
@@ -52,6 +52,12 @@ struct _GtkListView
 
   GtkCssRbTree *rows;
   int list_width;
+
+  /* managing the visible region */
+  guint anchor_pos;
+  int anchor_dy;
+  guint first_visible_pos;
+  guint lasst_visible_pos;
 };
 
 struct _ListRow
@@ -158,6 +164,102 @@ gtk_list_view_get_row (GtkListView *self,
   return row;
 }
 
+static guint
+list_row_get_position (GtkListView *self,
+                       ListRow     *row)
+{
+  ListRow *parent;
+  int pos = 0;
+
+  pos = 0; 
+  for (parent = gtk_css_rb_tree_get_parent (self->rows, row);
+       parent != NULL;
+       parent = gtk_css_rb_tree_get_parent (self->rows, row))
+    {
+      ListRow *left = gtk_css_rb_tree_get_left (self->rows, parent);
+
+      if (left != row)
+        {
+          if (left)
+            {
+              ListRowAugment *aug = gtk_css_rb_tree_get_augment (self->rows, left);
+              pos += aug->n_rows;
+            }
+          pos += parent->n_rows;
+        }
+
+      row = parent;
+    }
+
+  return pos;
+}
+
+static ListRow *
+gtk_list_view_get_row_at_y (GtkListView *self,
+                            int          y,
+                            int         *offset)
+{
+  ListRow *row, *tmp;
+
+  row = gtk_css_rb_tree_get_root (self->rows);
+
+  while (row)
+    {
+      tmp = gtk_css_rb_tree_get_left (self->rows, row);
+      if (tmp)
+        {
+          ListRowAugment *aug = gtk_css_rb_tree_get_augment (self->rows, tmp);
+          if (y < aug->height)
+            {
+              row = tmp;
+              continue;
+            }
+          y -= aug->height;
+        }
+
+      if (y < row->height)
+        break;
+      y -= row->height;
+
+      row = gtk_css_rb_tree_get_right (self->rows, row);
+    }
+
+  if (offset)
+    *offset = row ? y : 0;
+
+  return row;
+}
+
+static int
+list_row_get_y (GtkListView *self,
+                ListRow     *row)
+{
+  ListRow *parent;
+  int y = 0;
+
+  y = 0; 
+  for (parent = gtk_css_rb_tree_get_parent (self->rows, row);
+       parent != NULL;
+       parent = gtk_css_rb_tree_get_parent (self->rows, row))
+    {
+      ListRow *left = gtk_css_rb_tree_get_left (self->rows, parent);
+
+      if (left != row)
+        {
+          if (left)
+            {
+              ListRowAugment *aug = gtk_css_rb_tree_get_augment (self->rows, left);
+              y += aug->height;
+            }
+          y += parent->height;
+        }
+
+      row = parent;
+    }
+
+  return y ;
+}
+
 static int
 gtk_list_view_get_list_height (GtkListView *self)
 {
@@ -185,15 +287,23 @@ gtk_list_view_update_adjustments (GtkListView    *self,
       value = 0;
       if (_gtk_widget_get_direction (GTK_WIDGET (self)) == GTK_TEXT_DIR_RTL)
         value = upper - page_size - value;
+      value = gtk_adjustment_get_value (self->adjustment[orientation]);
     }
   else
     {
+      ListRow *row;
+
       page_size = gtk_widget_get_height (GTK_WIDGET (self));
       upper = gtk_list_view_get_list_height (self);
-      value = 0;
+
+      row = gtk_list_view_get_row (self, self->anchor_pos, NULL);
+      if (row)
+        value = list_row_get_y (self, row);
+      else
+        value = 0;
+      value += self->anchor_dy;
     }
   upper = MAX (upper, page_size);
-  value = gtk_adjustment_get_value (self->adjustment[orientation]);
 
   gtk_adjustment_configure (self->adjustment[orientation],
                             value,
@@ -345,11 +455,24 @@ gtk_list_view_remove_rows (GtkListView *self,
                            guint        n_rows)
 {
   ListRow *row;
-  guint i;
+  guint i, n_remaining;
 
   if (n_rows == 0)
     return;
 
+  n_remaining = self->model ? g_list_model_get_n_items (self->model) : 0;
+  if (self->anchor_pos >= position + n_rows)
+    {
+      self->anchor_pos -= n_rows;
+    }
+  else if (self->anchor_pos >= position)
+    {
+      self->anchor_pos = position;
+      if (self->anchor_pos > 0 && self->anchor_pos >= n_remaining)
+        self->anchor_pos = n_remaining - 1;
+      self->anchor_dy = 0;
+    }
+
   row = gtk_list_view_get_row (self, position, NULL);
 
   for (i = 0; i < n_rows; i++)
@@ -368,11 +491,18 @@ gtk_list_view_add_rows (GtkListView *self,
                         guint        n_rows)
 {
   ListRow *row;
-  guint i;
+  guint i, n_total;
 
   if (n_rows == 0)
     return;
 
+  n_total = self->model ? g_list_model_get_n_items (self->model) : 0;
+  if (self->anchor_pos >= position)
+    {
+      if (n_total != n_rows) /* the model was not empty before */
+        self->anchor_pos += n_rows;
+    }
+
   row = gtk_list_view_get_row (self, position, NULL);
 
   for (i = 0; i < n_rows; i++)
@@ -420,7 +550,29 @@ static void
 gtk_list_view_adjustment_value_changed_cb (GtkAdjustment *adjustment,
                                            GtkListView   *self)
 {
-  gtk_widget_queue_allocate (GTK_WIDGET (self));
+  if (adjustment == self->adjustment[GTK_ORIENTATION_VERTICAL])
+    {
+      ListRow *row;
+      guint pos;
+      int dy;
+
+      row = gtk_list_view_get_row_at_y (self, gtk_adjustment_get_value (adjustment), &dy);
+      if (row)
+        pos = list_row_get_position (self, row);
+      else
+        pos = 0;
+
+      if (pos != self->anchor_pos || dy != self->anchor_dy)
+        {
+          self->anchor_pos = pos;
+          self->anchor_dy = dy;
+          gtk_widget_queue_allocate (GTK_WIDGET (self));
+        }
+    }
+  else
+    { 
+      gtk_widget_queue_allocate (GTK_WIDGET (self));
+    }
 }
 
 static void