--window-reroute N: route a finer grid around each connection still stuck

After the exact engine, every net routed wholly inside a window around a
stuck connection's pins is ripped, the rest of the board is laid down as
fixed copper, and the window alone is routed again at --window-resolution
(default 4) with the stuck net and the ripped nets only. The result is kept
only if fewer connections are left unrouted; each round doubles the margin.
The grid and exact routers gain only_nets and bounds for it. Off by default.

src/freeroute/cli.py

@@ -31,7 +31,10 @@ from freeroute.ses import write_ses
 #: an engine is rejected by :func:`_validate` rather than quietly ignored.
 ENGINE_OPTIONS: dict[str, frozenset[str]] = {
     "grid": frozenset({"rip_up", "max_passes", "seed", "orders", "promote", "access", "negotiate", "rollback", "tree"}),
-    "exact": frozenset({"shove", "diagonal", "rip_up", "max_passes", "seed", "orders", "promote", "access", "negotiate", "rollback", "tree"}),
+    "exact": frozenset({
+        "shove", "diagonal", "rip_up", "max_passes", "seed", "orders", "promote", "access",
+        "negotiate", "rollback", "tree", "window",
+    }),
     "room": frozenset({"shove", "pack"}),
 }
 
@@ -49,6 +52,7 @@ _FLAG_NAMES = {
     "negotiate": "--negotiate",
     "rollback": "--no-rollback",
     "tree": "--no-tree",
+    "window": "--window-reroute",
 }
 
 
@@ -194,6 +198,29 @@ def build_parser() -> argparse.ArgumentParser:
         "paired by a minimum spanning tree and a connection may end on copper its net "
         "has already routed",
     )
+    parser.add_argument(
+        "--window-reroute",
+        type=int,
+        metavar="N",
+        help="exact engine: after routing, N rounds of window re-routes: around each "
+        "connection still unrouted, the nets routed wholly inside a window are ripped and "
+        "the window routed again on a finer grid, kept only if fewer connections are left "
+        "unrouted; each round doubles the window's margin (default 0: off)",
+    )
+    parser.add_argument(
+        "--window-resolution",
+        type=int,
+        default=4,
+        metavar="K",
+        help="the window re-route's grid resolution (default 4)",
+    )
+    parser.add_argument(
+        "--window-margin",
+        type=float,
+        default=1.5,
+        metavar="MM",
+        help="the first round's window margin around the stuck connection's pins (default 1.5)",
+    )
     parser.add_argument(
         "--hole-to-hole",
         type=float,
@@ -234,6 +261,7 @@ def main(argv: list[str] | None = None) -> int:
             ("negotiate", args.negotiate is not None),
             ("rollback", not args.rollback),
             ("tree", not args.tree_nets),
+            ("window", args.window_reroute is not None),
         )
         if asked
     ]
@@ -272,6 +300,9 @@ def main(argv: list[str] | None = None) -> int:
             "hole_to_hole_mm": args.hole_to_hole,
             "rollback": args.rollback,
             "tree_nets": args.tree_nets,
+            "window_reroute": args.window_reroute or 0,
+            "window_resolution": args.window_resolution,
+            "window_margin_mm": args.window_margin,
         }
     elif args.engine == "grid":
         options = {

src/freeroute/route/exact_router.py

@@ -106,6 +106,8 @@ def route_board_exact(
     net_widths: dict[int, int] | None = None,
     via_drill: int | None = None,
     hole_to_hole: int = 0,
+    only_nets: frozenset | None = None,
+    bounds: IntBox | None = None,
 ) -> ExactRouteResult:
     """Route ``board`` orthogonally and verify the result with exact geometry.
 
@@ -143,6 +145,8 @@ def route_board_exact(
         net_widths=net_widths,
         via_drill=via_drill,
         hole_to_hole=hole_to_hole,
+        only_nets=only_nets,
+        bounds=bounds,
     )
     edge = 0 if edge_clearance is None else edge_clearance
     outline = board.outline
@@ -259,7 +263,10 @@ def route_board_exact(
     # a net is dropped if it has a real ratsnest (>= 2 pins on a signal layer)
     # but was not accepted — whether the grid failed to route it or its exact
     # copper conflicted.
-    dropped = sorted(_routable_nets(board, signal_layers) - set(accepted))
+    routable = _routable_nets(board, signal_layers)
+    if only_nets is not None:  # a window re-route: the other nets are not ours to route
+        routable &= set(only_nets)
+    dropped = sorted(routable - set(accepted))
 
     shoves = 0
     if shove and dropped:
@@ -284,7 +291,7 @@ def route_board_exact(
 
     if diagonal:
         outline = board.bounding_box
-        for net_no in sorted(_routable_nets(board, signal_layers)):
+        for net_no in sorted(routable):
             _diagonalize(
                 net_no, board, tree, accepted, owner, signal_layers, half_width, clearance, outline
             )

src/freeroute/route/grid_router.py

@@ -203,8 +203,14 @@ class GridRouter:
         via_drill: int | None = None,
         hole_to_hole: int = 0,
         tree_nets: bool = True,
+        only_nets: frozenset | None = None,
+        bounds: IntBox | None = None,
     ) -> None:
         self.board = board
+        # A window re-route routes some nets inside part of the board: only
+        # these nets get connections, and the grid covers only ``bounds``
+        # (cells outside it do not exist, so nothing is routed there).
+        self.only_nets = frozenset(only_nets) if only_nets is not None else None
         # Multi-pin nets: pair a net's pin groups by a minimum spanning tree,
         # and let a connection start or end on copper its net already routed
         # (a T into the tree), not only on one chosen pin.
@@ -324,6 +330,11 @@ class GridRouter:
         self.layers = list(layers)
 
         box = board.bounding_box
+        if bounds is not None:
+            box = IntBox(
+                max(box.ll.x, bounds.ll.x), max(box.ll.y, bounds.ll.y),
+                min(box.ur.x, bounds.ur.x), min(box.ur.y, bounds.ur.y),
+            )
         self.origin_x = box.ll.x
         self.origin_y = box.ll.y
         self.cols = max(1, math.ceil((box.ur.x - box.ll.x) / self.step) + 1)
@@ -1837,6 +1848,8 @@ class GridRouter:
         self._plane_nets: set[int] = set()
         nets = set(pins_by_net) | set(zones_by_net) | set(planes_by_net)
         # deterministic: fewer-pin nets first, then by net number
+        if self.only_nets is not None:
+            nets &= self.only_nets
         for net_no in sorted(nets, key=lambda n: (len(pins_by_net.get(n, [])), n)):
             zones = zones_by_net.get(net_no, []) + planes_by_net.get(net_no, [])
             groups = _connected_groups(
@@ -2196,6 +2209,8 @@ def route_board(
     net_widths: dict[int, int] | None = None,
     via_drill: int | None = None,
     hole_to_hole: int = 0,
+    only_nets: frozenset | None = None,
+    bounds: IntBox | None = None,
 ) -> RouteResult:
     """Convenience wrapper: build a :class:`GridRouter` and route the board."""
     router = GridRouter(
@@ -2220,5 +2235,7 @@ def route_board(
         net_widths=net_widths,
         via_drill=via_drill,
         hole_to_hole=hole_to_hole,
+        only_nets=only_nets,
+        bounds=bounds,
     )
     return router.route()

src/freeroute/route/pipeline.py

@@ -21,6 +21,7 @@ from freeroute.ses import RoutedVia, RoutedWire, RoutingResult, write_ses
 from .exact_router import ExactRouteResult, route_board_exact
 from .grid_router import RouteResult, route_board
 from .room_router import route_board_rooms
+from .window import window_reroute as window_reroute_stage
 
 __all__ = ["route", "route_dsn_board", "build_routing_result"]
 
@@ -237,6 +238,9 @@ def route_dsn_board_exact(
     hole_to_hole_mm: float = 0.25,
     rollback: bool = True,
     tree_nets: bool = True,
+    window_reroute: int = 0,
+    window_resolution: int = 4,
+    window_margin_mm: float = 1.5,
 ) -> tuple[ExactRouteResult, int, list[str]]:
     """Route a parsed :class:`DsnBoard` with the exact-geometry (orthogonal,
     DRC-verified) track; return the exact result, the scale, and layer names.
@@ -248,28 +252,43 @@ def route_dsn_board_exact(
     edge_clearance_board = _mm_to_board(dsn, scale, edge_clearance_mm)
     width_board = round(_rule_width_dsn(dsn) * scale)
     clearance_board = round(_rule_clearance_dsn(dsn) * scale)
+    # the settings a window re-route repeats, at its own resolution
+    common = {
+        "heuristic_weight": heuristic_weight,
+        "via_half": _via_half_board(dsn, scale),
+        "edge_clearance": edge_clearance_board,
+        "trace_width": width_board,
+        "clearance": clearance_board,
+        "layers": layers,
+        "max_passes": max_passes,
+        "rip_up": rip_up,
+        "shove": shove,
+        "diagonal": diagonal,
+        "rollback": rollback,
+        "tree_nets": tree_nets,
+        "net_widths": _net_widths_board(dsn, scale),
+        "via_drill": _via_drill_board(dsn, scale),
+        "hole_to_hole": _mm_to_board(dsn, scale, hole_to_hole_mm) or 0,
+    }
     exact = route_board_exact(
         board,
         resolution=resolution,
-        heuristic_weight=heuristic_weight,
-        via_half=_via_half_board(dsn, scale),
-        edge_clearance=edge_clearance_board,
-        trace_width=width_board,
-        clearance=clearance_board,
-        layers=layers,
-        max_passes=max_passes,
-        rip_up=rip_up,
-        shove=shove,
-        diagonal=diagonal,
         seed=seed,
         route_first=route_first,
         access_cost=access_cost,
         negotiate=negotiate,
-        rollback=rollback,
-        tree_nets=tree_nets,
-        net_widths=_net_widths_board(dsn, scale),
-        via_drill=_via_drill_board(dsn, scale),
-        hole_to_hole=_mm_to_board(dsn, scale, hole_to_hole_mm) or 0,
+        **common,
+    )
+    if window_reroute > 0:
+        via_half = common["via_half"] or max(width_board // 2, 1)
+        exact.result = window_reroute_stage(
+            dsn, exact.result, common,
+            rounds=window_reroute,
+            resolution=max(int(window_resolution), resolution),
+            margin=_mm_to_board(dsn, scale, window_margin_mm) or 0,
+            via_half=via_half,
+            via_drill=common["via_drill"] or 2 * via_half,
+            via_name=_via_padstack(dsn),
         )
     return exact, scale, [layer.name for layer in dsn.layers]
 
@@ -292,6 +311,9 @@ def build_exact_routing_result(
     hole_to_hole_mm: float = 0.25,
     rollback: bool = True,
     tree_nets: bool = True,
+    window_reroute: int = 0,
+    window_resolution: int = 4,
+    window_margin_mm: float = 1.5,
 ) -> RoutingResult:
     """Route ``dsn`` (exact track) and convert to a DSN-unit RoutingResult."""
     exact, scale, layer_names = route_dsn_board_exact(
@@ -311,6 +333,9 @@ def build_exact_routing_result(
         hole_to_hole_mm=hole_to_hole_mm,
         rollback=rollback,
         tree_nets=tree_nets,
+        window_reroute=window_reroute,
+        window_resolution=window_resolution,
+        window_margin_mm=window_margin_mm,
     )
     return _to_routing_result(exact.result, dsn, scale, layer_names)
 

src/freeroute/route/window.py

@@ -0,0 +1,176 @@
+"""Window re-route: a last stage for the connections still unrouted.
+
+Around each stuck connection a window is cut: the box of its two end pins
+plus a margin. Every net whose routed copper lies wholly inside it is
+ripped; everything else stays, as fixed copper. The window is then routed
+again on its own, on a finer grid than the whole board can afford, the
+stuck connection's net and the ripped nets only. The result is kept only
+if fewer connections are left unrouted than before; otherwise the board is
+as it was. Each round doubles the margin for the connections still stuck.
+
+What makes it differ from re-running the same search near the failure: the
+finer grid finds gaps the board's grid steps over, and the ripped nets go in
+again in a new order around the stuck one. A finer grid on the whole board
+costs routes elsewhere (its cells are slower and its order changes); inside
+a small window it only ever replaces what it can improve.
+"""
+
+from __future__ import annotations
+
+from typing import Any
+
+from freeroute.board import build_board
+from freeroute.board.items import Trace, Via
+from freeroute.dsn import DsnBoard
+from freeroute.geometry import IntBox, IntPoint
+
+from .exact_router import route_board_exact
+from .grid_router import RouteResult
+
+Copper = tuple[list[tuple[int, list[IntPoint]]], list[IntPoint]]
+
+
+def _pin_labels(board) -> dict[tuple[int, str], IntPoint]:
+    """Each pin's location by (net, label), the label a failure names it by."""
+    found: dict[tuple[int, str], IntPoint] = {}
+    for pin in board.get_pins():
+        for net in pin.net_nos:
+            found.setdefault((net, f"{pin.component_ref}-{pin.name}"), pin.location)
+    return found
+
+
+def _end_point(labels, net: int, label: str) -> IntPoint | None:
+    """Where a failure's end is: the first pin its label names."""
+    return labels.get((net, label.split("/")[0]))
+
+
+def _inside(copper: Copper, window: IntBox) -> bool:
+    wires, vias = copper
+    points = [p for _layer, path in wires for p in path] + list(vias)
+    return bool(points) and all(
+        window.ll.x <= p.x <= window.ur.x and window.ll.y <= p.y <= window.ur.y for p in points
+    )
+
+
+def _board_with(
+    dsn: DsnBoard, copper: dict[int, Copper], keep: set[int], half: dict[int, int],
+    default_half: int, via_half: int, via_drill: int, layers: list[int], via_name: str,
+):
+    """The board with the routed copper of ``keep`` laid down as fixed copper."""
+    board = build_board(dsn)
+    for net in keep:
+        wires, vias = copper.get(net, ([], []))
+        width = half.get(net, default_half)
+        for layer, path in wires:
+            if len(path) >= 2:
+                board.insert(Trace(net_nos=[net], fixed=True, layer=layer, half_width=width, corners=list(path)))
+        for location in dict.fromkeys(vias):
+            board.insert(Via(
+                net_nos=[net], fixed=True, padstack_name=via_name, drill=via_drill,
+                location=location, layers=list(layers),
+                shape=IntBox(location.x - via_half, location.y - via_half,
+                             location.x + via_half, location.y + via_half),
+            ))
+    return board
+
+
+def _open(failed) -> list:
+    """Failures that are real opens, not connections left to a zone fill."""
+    return [f for f in failed if not (len(f) > 3 and f[3])]
+
+
+def window_reroute(
+    dsn: DsnBoard,
+    result: RouteResult,
+    route_args: dict[str, Any],
+    *,
+    rounds: int,
+    resolution: int,
+    margin: int,
+    via_half: int,
+    via_drill: int,
+    via_name: str,
+) -> RouteResult:
+    """Re-route a window around each still-failing connection; keep only gains.
+
+    ``route_args`` are the exact engine's settings for the whole board (width,
+    clearance, layers, shove, ...); the window runs them at ``resolution``.
+    ``margin`` is the first round's window margin in board units."""
+    if rounds < 1 or not _open(result.failed):
+        return result
+    default_half = result.half_width
+    copper: dict[int, Copper] = {
+        net: (list(result.wires.get(net, [])), list(result.vias.get(net, [])))
+        for net in set(result.wires) | set(result.vias)
+    }
+    half = dict(result.net_half)
+    failed = list(result.failed)
+    layers = route_args.get("layers") or [
+        i for i, layer in enumerate(build_board(dsn).layer_structure.arr) if layer.is_signal
+    ]
+    labels = _pin_labels(build_board(dsn))
+
+    changed = False
+    for rnd in range(rounds):
+        reach = margin * (2 ** rnd)
+        progress = False
+        for entry in _open(list(failed)):
+            if entry not in failed:
+                continue  # an earlier window routed it
+            net = entry[0]
+            ends = [_end_point(labels, net, label) for label in entry[1:3]]
+            ends = [p for p in ends if p is not None]
+            if not ends:
+                continue
+            window = IntBox(
+                min(p.x for p in ends) - reach, min(p.y for p in ends) - reach,
+                max(p.x for p in ends) + reach, max(p.y for p in ends) + reach,
+            )
+            victims = {n for n, c in copper.items() if _inside(c, window)}
+            affected = victims | {net}
+            before = _open(f for f in failed if f[0] in affected)
+            keep = set(copper) - victims
+            board = _board_with(dsn, copper, keep, half, default_half, via_half, via_drill, layers, via_name)
+            sub = route_board_exact(
+                board, **route_args, resolution=resolution,
+                only_nets=frozenset(affected), bounds=window,
+                route_first=frozenset((f[0], f[1], f[2]) for f in before),
+            ).result
+            after = _open(f for f in sub.failed if f[0] in affected)
+            if len(after) >= len(before):
+                continue
+            # a net keeping some of its copper is written at one width: the
+            # window's new copper has to have gone in at that width too
+            if any(
+                n not in victims and copper.get(n) and (sub.wires.get(n) or sub.vias.get(n))
+                and sub.net_half.get(n, default_half) != half.get(n, default_half)
+                for n in affected
+            ):
+                continue
+            for n in affected:
+                kept_wires, kept_vias = copper.get(n, ([], [])) if n not in victims else ([], [])
+                copper[n] = (kept_wires + sub.wires.get(n, []), kept_vias + sub.vias.get(n, []))
+                if n in victims:
+                    half.pop(n, None)
+                    if n in sub.net_half:
+                        half[n] = sub.net_half[n]
+            failed = [f for f in failed if f[0] not in affected] + [
+                f for f in sub.failed if f[0] in affected
+            ]
+            progress = changed = True
+        if not progress and not _open(failed):
+            break
+
+    if not changed:
+        return result
+    out = RouteResult(default_half)
+    for net, (wires, vias) in copper.items():
+        for layer, path in wires:
+            out.add_wire(net, layer, path)
+        for location in dict.fromkeys(vias):
+            out.add_via(net, location)
+    out.failed = failed
+    out.unrouted = len(_open(failed))
+    out.net_half = half
+    out.narrowed = list(result.narrowed)
+    return out

tests/route/test_window_reroute.py

@@ -0,0 +1,95 @@
+"""Window re-route: a finer grid around a stuck connection, kept only when
+it leaves fewer connections unrouted."""
+
+from __future__ import annotations
+
+from freeroute.board import build_board
+from freeroute.dsn import parse_dsn
+from freeroute.geometry import IntBox
+from freeroute.route.grid_router import GridRouter
+from freeroute.route.pipeline import _rule_clearance_dsn, _rule_width_dsn, route_dsn_board_exact
+
+
+def _slot(gap: int = 640, far: bool = False) -> str:
+    """A wall across the board with a slot in it. A trace fits the slot
+    only along a narrow band of heights that the board's 1x grid has no row
+    in and a 4x grid does. ``far`` adds a second net nowhere near the wall."""
+    yc = -5000
+    lo, hi = yc - gap // 2, yc + gap // 2
+    extra_place = "(place Q1 2000 -1000 front 0) (place Q2 6000 -1000 front 0)" if far else ""
+    extra_net = "(net M (pins Q1-1 Q2-1))" if far else ""
+    return f"""(pcb "slot.dsn"
+  (parser (string_quote ") (space_in_quoted_tokens on) (host_cad "t") (host_version "1"))
+  (resolution um 10)
+  (unit um)
+  (structure
+    (layer F.Cu (type signal) (property (index 0)))
+    (boundary (path pcb 0  0 0  20000 0  20000 -10000  0 -10000  0 0))
+    (keepout "" (rect F.Cu 9000 -10000 11000 {lo}))
+    (keepout "" (rect F.Cu 9000 {hi} 11000 0))
+    (rule (width 200) (clearance 200))
+  )
+  (library
+    (padstack Rect_Pad (shape (rect F.Cu -100 -100 100 100)) (attach off))
+    (image PAD (pin Rect_Pad 1 0 0))
+  )
+  (placement
+    (component PAD
+      (place P1 3000 {yc} front 0)
+      (place P2 17000 {yc} front 0)
+      {extra_place}
+    )
+  )
+  (network
+    (net N (pins P1-1 P2-1))
+    {extra_net}
+    (class default (rule (width 200) (clearance 200)))
+  )
+  (wiring)
+)
+"""
+
+
+def _route(text: str, rounds: int):
+    exact, _scale, _layers = route_dsn_board_exact(
+        parse_dsn(text), resolution=1, window_reroute=rounds, window_resolution=4,
+    )
+    return exact.result
+
+
+def test_the_board_grid_misses_the_slot_and_a_finer_window_finds_it():
+    plain = _route(_slot(), 0)
+    assert len(plain.failed) == 1
+    windowed = _route(_slot(), 1)
+    assert windowed.failed == []
+    assert windowed.wires  # and the copper it found is in the result
+
+
+def test_a_window_that_cannot_help_leaves_the_board_as_it_was():
+    plain = _route(_slot(gap=500, far=True), 0)  # too narrow for any grid
+    windowed = _route(_slot(gap=500, far=True), 2)
+    assert len(windowed.failed) == len(plain.failed) == 1
+    assert windowed.wires == plain.wires
+    assert windowed.vias == plain.vias
+
+
+def test_copper_outside_the_window_is_kept_as_it_was():
+    plain = _route(_slot(far=True), 0)
+    windowed = _route(_slot(far=True), 1)
+    assert windowed.failed == []
+    far_net = 2  # M, the second net in the DSN
+    assert windowed.wires[far_net] == plain.wires[far_net]
+
+
+def test_a_router_limited_to_some_nets_and_a_box_builds_only_those():
+    dsn = parse_dsn(_slot(far=True))
+    s = dsn.resolution.value
+    board = build_board(dsn)
+    whole = GridRouter(board, trace_width=round(_rule_width_dsn(dsn) * s),
+                       clearance=round(_rule_clearance_dsn(dsn) * s), orthogonal=True)
+    part = GridRouter(board, trace_width=round(_rule_width_dsn(dsn) * s),
+                      clearance=round(_rule_clearance_dsn(dsn) * s), orthogonal=True,
+                      only_nets=frozenset({2}), bounds=IntBox(0, -20000, 80000, 0))
+    assert {c.net_no for c in whole._build_connections()} == {1, 2}
+    assert {c.net_no for c in part._build_connections()} == {2}
+    assert part.cols * part.rows < whole.cols * whole.rows

tests/test_cli.py

@@ -161,6 +161,7 @@ def test_cli_supported_combinations_are_accepted(tmp_path):
         "negotiate": ["--negotiate", "2"],
         "rollback": ["--no-rollback"],
         "tree": ["--no-tree"],
+        "window": ["--window-reroute", "1"],
     }
     for engine, options in ENGINE_OPTIONS.items():
         for option in options: