vyges-fin

Density fill over the OpenDB design database: metal shapes placed in the gaps between real routing, so each layer meets the foundry's minimum metal density.

vyges loom fin density-fill design.odb --rules fill.json

Correctness

Validated against OpenROAD's density fill at a pinned commit, across five designs chosen for the geometry they exercise — a power grid, a macro, a non-rectangular core, a near-empty floorplan, and a restricted --area. Every fill shape matches in layer, mask, OPC flag and coordinates.

Each design is additionally checked against invariants that need no reference at all: every fill is a whole shape of a declared size, and no two fills on a layer overlap. Those hold of any correct fill.

What it does

For each layer the rules mention, in order of the shape sizes given:

1. take the fill area (the core, or --area) minus the design's own metal, bloated by the fill-to-design spacing;
2. shrink then bloat by half the shape — which deletes anything too small to hold it and breaks big regions into pieces small enough to tile;
3. tile a fixed grid over each piece, keep only whole shapes, and place them;
4. subtract what was placed and try the next size down.

OPC fill, where a layer declares it, is a second pass that must also clear the fill just placed.

Fill is regenerated wholesale, never patched: existing fill is cleared first, so re-running is idempotent rather than cumulative.

Details that decide the output

• The long side follows the routing direction. A fill shape lying across the preferred direction is a manufacturing problem, not a smaller fill.
• Spacing is anisotropic: the line-end spacing applies along the routing direction only.
• Only whole shapes are placed. A tile clipped by the area it was tiled into is the wrong size, and a wrong-sized fill is a DRC violation rather than a smaller fill.
• Masks cycle; a single-mask layer writes no mask at all.
• A layer the rules do not mention is skipped and reported — the difference between "no rule" and "nothing to fill".

What it does not do

• The tiling is a fixed grid anchored at each piece's bounding box. Upstream notes that KLayout sweeps the tile origin looking for maximum fill and does not do so; neither does this. Fill density is not maximal by construction.
• prune is conservative: it forbids fill where two regions are closer than the fill spacing, which may exclude a position that would in fact have been legal.

Exit status

0	filled — fill was placed and the database written
1	refused — the design cannot be filled as asked (an empty fill area)
2	error — usage, unreadable database or rules, no DBU scale, or a failed write

Building

cargo build --release
cargo test

License

Apache-2.0. See LICENSE and NOTICE.