How to dim a tree item?

[OHE]

Do you know a trick to do the same using CVI 2010 ?

I know that my checkbox won't be dimmed, but I want to keep the active state. Example :

+ root

 |   + item 1

 |   + item 2 (dimmed)

 |   + item 3

All my checkboxes are unchecked except the item 2. If I try to uncheck the item 2 in this configuration : no worries. If I check the item 3, then I can uncheck as I want the item 2....

Here is my code sample :

int  CVICALLBACK tree_interact(int panel, int control, int event, void *callbackData,
    int eventData1, int eventData2)
{
    int testIndex = 0;
    int testStatusDimmed = 0;
    
    switch (event)
    {
        case EVENT_MARK_STATE_CHANGE:
        {
            GetCtrlIndex (panel, control, &testIndex);
            GetTreeItemAttribute(PANEL, PANEL_TREE, testIndex, ATTR_CELL_DIMMED, &testStatusDimmed);
            
            if(checks[testIndex].dimmed != 0)
            {
                SetTreeItemAttribute(PANEL, PANEL_TREE, testIndex, ATTR_MARK_STATE, checks[testIndex].checked);    
            }
            break;
        }
    }
    return 0;
}