Calibre Expanding Vs Flattening a cell in Calibre DESIGNrev

Expanding a cell with the " $L expand cell" command flattens the references of the specified cell by bringing all geometries in the cell reference to the level of the parent cells, keeping any underlying hierarchy within the cell intact. Hence, the cell definition itself is left intact.

# Before: 
#                topcell -> a -> b -> c -> d 
#                topcell -> c -> d 

set inlayout [layout create "input.oas" -dt_expand -preservePaths -preserveTextAttributes] 
$inlayout expand cell b 
$inlayout oasisout out.oas 

# After: 
#                topcell -> a -> c -> d 
#                topcell -> c -> d 
#                b -> c -> d

 

On the other hand, flattening a cell with the " $L flatten cell" flattens all levels of hierarchy of the specified cell across all of its instances to the level of the parent cells, such that the cell and its underlying hierarchy are replaced by a flattened view of the shapes. Hence this impacts the cell definition, and all references to the cell.

# Before: 
#                topcell -> a -> b -> c -> d 
#                topcell -> b -> c -> d 
#                topcell -> c -> d 

set lay [layout create "abcd.gds" -dt_expand  -preservePaths -preserveTextAttributes] 
$lay flatten cell b 
$lay gdsout out.gds 

# After: 
#                topcell -> a -> b 
#                topcell -> b 
#                topcell -> c -> d 

So, in order to flatten the cell to the top level while keeping the hierarchy of the cell and its definition intact, go for "$L expand cell" whereas using "$L flatten cell" flattens all levels of hierarchy of the specified cell across all of its instances.