Visibility of cells

["Padraig O'Briain" <Padraig Obriain Sun COM>]

In the implementation for atk_component_get_extents() for cells in a GtkTreeView 
I attempt to set the cell's position to (-1, -1) if the cell is not visible.

Currently a cell is visible if any part of the cell is in the visible area.

I do not think that this definition is adequate as a cell would be regarded as 
visible even if its origin is not.

Does anyone have strong views on what visibility of a cell should mean?

For example, should all of the cell be visible, or the origin?

Padraig