The Geometry Digests Button: List Cell Geometry Digests

This panel, brought up with the Geometry Digests button in the File Menu, provides a list of Cell Geometry Digests currently in memory. A Cell Geometry Digest (CGD) is a per-layer/per-cell database of highly compacted representations of cell geometry. Logically, a cell name and layer name are passed to the database, which returns a data block which when expanded yields a representation of the geometry on the given layer in the given cell. The database contains no information about cell instances, and text labels and object properties are excluded.

This is basically a companion to the Cell Hierarchy Digest (CHD), which contains hierarchy information but no geometry information. The two data types together provide complete physical information about the file.

A CGD can be linked to a CHD. After linking, the CHD will retrieve needed geometrical information from the linked CGD, rather than from the original layout file. This can be faster, since the CGD geometry data may be in memory, and are sorted by layer and compacted. Even with all geometry data residing in memory, the combined size of the CHD/CGD structures is still much smaller than the memory required for loading the original layout file into the main database in the normal way. The main database, however, provides the spatial sorting for fast access of objects at a given location, which is absent in the CHD/CGD combination.

Each saved CGD is given a unique but otherwise arbitrary name, which is used to access the CGD. The CGDs presently in memory are listed by name, and can be selected by clicking.

The listing contains a middle column labeled Type, Linked, which will contain Mem, File, or Rem indicating the geometry storage type of the CGD. This will be followed by yes if the CGD is linked to a CHD. An asterisk `*' will follow yes if the CGD will be destroyed when unlinked from its CHD. The right column contains the source file name, if any. The Info button will provide more information about the CGD, including the full path to the source file.

The selected CGD is used as input for operations initiated by the row of buttons arrayed across the top of the panel. These buttons are:

Add
This button brings up the Open Cell Geometry Digest panel, from which a new CGD can be created and added to the list (see 8.11).

Save
The currently selected CGD can be saved to a file, for later recall. This button brings up a pop-up which solicits a name for this file. Pressing Apply will save the selected CGD to a disk representation in the given file path. A previously saved CHD can be recalled into memory from the panel brought up by the Add button.

Delete
This will destroy the selected CGD, after confirmation. Only CGDs that are not currently linked to a CHD can be destroyed.

Contents
This will pop up or update a listing of the cells found in the selected CGD. With a name selected, the Info button becomes active. Clicking Info will pop up or update another window, which lists the layers used in the selected cell. Only layers that have associated geometry are saved in the CGD. Each layer is listed with two numbers, representing the size of the compressed data stream for the layer ('c') and the uncompressed size ('u'). These aren't particularly useful to the user, but do give some indication of how much geometry is associated with each layer. Beware, however, that gigabytes of replicated features may be represented by only a few bytes.

Info
This button pops up a window listing information about the selected CGD. The information includes the type of CGD, and other parameters such as memory use, cell count, etc.