# Metal fill

This module inserts floating metal fill shapes to meet metal density
design rules while obeying DRC constraints. It is driven by a `json`
configuration file.

## Commands

```
% density_fill -rules <json_file> [-area <list of lx ly ux uy>]
```

If `-area` is not specified, the core area will be used.

## Example scripts

The rules `json` file controls fill and you can see an example
[here](https://github.com/The-OpenROAD-Project/OpenROAD-flow-scripts/blob/master/flow/platforms/sky130hd/fill.json).

The schema for the `json` is:

``` json
{
  "layers": {
    "<group_name>": {
      "layers": "<list of integer gds layers>",
      "names": "<list of name strings>",
      "opc": {
        "datatype":  "<list of integer gds datatypes>",
        "width":   "<list of widths in microns>",
        "height":   "<list of heightsin microns>",
        "space_to_fill": "<real: spacing between fills in microns>",
        "space_to_non_fill": "<real: spacing to non-fill shapes in microns>",
        "space_line_end": "<real: spacing to end of line in microns>"
      },
      "non-opc": {
        "datatype":  "<list of integer gds datatypes>",
        "width":   "<list of widths in microns>",
        "height":   "<list of heightsin microns>",
        "space_to_fill": "<real: spacing between fills in microns>",
        "space_to_non_fill": "<real: spacing to non-fill shapes in microns>"
      }
    }, ...
  }
}
```

The `opc` section is optional depending on your process.

The width/height lists are effectively parallel arrays of shapes to try
in left to right order (generally larger to smaller).

The layer grouping is for convenience. For example in some technologies many
layers have similar rules so it is convenient to have a `Mx`, `Cx` group.

This all started out in `klayout` so there are some obsolete fields that the
parser accepts but ignores (e.g., `space_to_outline`).

## Regression tests

## Limitations

## FAQs

Check out [GitHub discussion](https://github.com/The-OpenROAD-Project/OpenROAD/discussions/categories/q-a?discussions_q=category%3AQ%26A+metal%20fill+in%3Atitle)
about this tool.

## License

BSD 3-Clause License. See [LICENSE](LICENSE) file.