A better algorithm for centering library items in the tree.

It still doesn't center as wxWidgets' API is poorly suited for that.
But it does now at least keep it off the very top or bottom.

common/lib_tree_model_adapter.cpp

@@ -368,11 +368,17 @@ unsigned int LIB_TREE_MODEL_ADAPTER::GetChildren( const wxDataViewItem&   aItem,
 {
     const LIB_TREE_NODE* node = ( aItem.IsOk() ? ToNode( aItem ) : &m_tree );
 
-    if( node->m_Type != LIB_TREE_NODE::TYPE::LIBID
+    if( node->m_Type == LIB_TREE_NODE::TYPE::ROOT
+            || node->m_Type == LIB_TREE_NODE::LIB
             || ( m_show_units && node->m_Type == LIB_TREE_NODE::TYPE::LIBID ) )
+    {
         return IntoArray( *node, aChildren );
+    }
     else
+    {
         return 0;
+    }
+
 }
 
 

common/widgets/lib_tree.cpp

@@ -271,8 +271,49 @@ void LIB_TREE::selectIfValid( const wxDataViewItem& aTreeId )
 
 void LIB_TREE::centerIfValid( const wxDataViewItem& aTreeId )
 {
+    /*
+     * This doesn't actually center because the wxWidgets API is poorly suited to that (and
+     * it might be too noisy as well).
+     *
+     * It does try to keep the given item a bit off the top or bottom of the window.
+     */
+
     if( aTreeId.IsOk() )
+    {
+        LIB_TREE_NODE* node = m_adapter->GetTreeNodeFor( aTreeId );
+        LIB_TREE_NODE* parent = node->m_Parent;
+        LIB_TREE_NODE* grandParent = parent ? parent->m_Parent : nullptr;
+
+        if( parent )
+        {
+            wxDataViewItemArray siblings;
+            m_adapter->GetChildren( wxDataViewItem( parent ), siblings );
+
+            int idx = siblings.Index( aTreeId );
+
+            if( idx + 5 < (int) siblings.GetCount() )
+            {
+                m_tree_ctrl->EnsureVisible( siblings.at( idx + 5 ) );
+            }
+            else if( grandParent )
+            {
+                wxDataViewItemArray parentsSiblings;
+                m_adapter->GetChildren( wxDataViewItem( grandParent ), parentsSiblings );
+
+                int p_idx = parentsSiblings.Index( wxDataViewItem( parent ) );
+
+                if( p_idx + 1 < (int) parentsSiblings.GetCount() )
+                    m_tree_ctrl->EnsureVisible( parentsSiblings.at( p_idx + 1 ) );
+            }
+
+            if( idx - 5 >= 0 )
+                m_tree_ctrl->EnsureVisible( siblings.at( idx - 5 ) );
+            else
+                m_tree_ctrl->EnsureVisible( wxDataViewItem( parent ) );
+        }
+
         m_tree_ctrl->EnsureVisible( aTreeId );
+    }
 }
 
 
@@ -303,7 +344,7 @@ LIB_TREE::STATE LIB_TREE::getState() const
     wxDataViewItemArray items;
     m_adapter->GetChildren( wxDataViewItem( nullptr ), items );
 
-    for( const auto& item : items )
+    for( const wxDataViewItem& item : items )
     {
         if( m_tree_ctrl->IsExpanded( item ) )
             state.expanded.push_back( item );
@@ -319,7 +360,7 @@ void LIB_TREE::setState( const STATE& aState )
 {
     m_tree_ctrl->Freeze();
 
-    for( const auto& item : aState.expanded )
+    for( const wxDataViewItem& item : aState.expanded )
         m_tree_ctrl->Expand( item );
 
     // wxDataViewCtrl cannot be frozen when a selection