public void RemoveElementAt( int _idx )
{
Element el = elements[_idx];
// get sprite animation clip by textureGUID, add them to rebuildAnimClipGUIDs
AddSpriteAnimClipForRebuilding(el);
needRebuild = true;
// register undo
Undo.RegisterUndo ( new Object[] {
exAtlasDB.DB(),
this
}, "RemoveElementAt" );
// remove element in atlas DB
exAtlasDB.RemoveElementInfo(exEditorHelper.AssetToGUID(el.texture));
//
elements.RemoveAt(_idx);
//
EditorUtility.SetDirty(this);
}