Keepout exits and rule areas

A route may not leave a cell inside a wire keepout as a wire, nor reach
a pin there by one: it changes layer instead, and the via goes in the
pad. A pin whose every stub enters a keepout is reached by a via only.

A structure keepout named rule_area... (mckicad names KiCad rule areas
so) is checked for overlap only, as KiCad's DRC does, with the free ends
of each wire tested for their round caps.

bench/diagnose.py

@@ -26,6 +26,7 @@ import sys
 from freeroute.board import build_board
 from freeroute.board.search_tree import ShapeSearchTree
 from freeroute.dsn import parse_dsn
+from freeroute.geometry.octagon import overlaps_2d
 from freeroute.route import grid_router
 from freeroute.route.exact_router import route_board_exact
 from freeroute.route.grid_router import GridRouter, _ends_of
@@ -80,13 +81,24 @@ def _capture_conflicts() -> list:
     def conflict(self, box, net_no, layer, clearance, kind="wire"):
         hit = original(self, box, net_no, layer, clearance, kind)
         if hit:
+            # the shape that tripped the check, found the way the check does
+            other = None
             expanded = box.offset(clearance)
-            other = next(
-                (s for s in self.overlapping(expanded)
-                 if s.net_no != net_no and s.on_layer(layer)
-                 and (s.blocks == "all" or s.blocks == kind + "s")),
-                None,
-            )
+            for s in self.overlapping(expanded):
+                if s.net_no == net_no or not s.on_layer(layer):
+                    continue
+                if s.blocks != "all" and s.blocks != kind + "s":
+                    continue
+                if not s.clearance:
+                    if s.tile.overlaps(box):
+                        other = s
+                        break
+                    continue
+                if (s.exact is not None and overlaps_2d(s.exact, expanded)) or (
+                    s.exact is None and s.tile.overlaps(expanded)
+                ):
+                    other = s
+                    break
             log.append((net_no, kind, layer, box, clearance, other))
         return hit
 
@@ -177,10 +189,11 @@ def diagnose(
         if other is None:
             what = "?"
         elif other.net_no == -1:
-            what = "keepout"
+            what = "keepout" if other.clearance else "rule area"
         else:
             what = ("trace/via of " if other.routed else "pad of ") + names.get(other.net_no, "?")
-        short = (clearance - _gap(box, other.tile)) / scale / 1000 if other is not None else 0
+        need = clearance if other is None or other.clearance else 0
+        short = (need - _gap(box, other.tile)) / scale / 1000 if other is not None else 0
         per_net.setdefault(net_no, []).append(
             {"copper": kind, "layer": layer, "against": what, "short_mm": round(short, 4)}
         )

src/freeroute/board/build.py

@@ -333,10 +333,20 @@ def _insert_keepouts(dsn: DsnBoard, board: BasicBoard, transform: CoordinateTran
                     tiles=tiles,
                     blocks_wires=keepout.kind != "via_keepout",
                     blocks_vias=keepout.kind != "wire_keepout",
+                    clearance=not is_rule_area(keepout.area.name),
                 )
             )
 
 
+#: a structure keepout named with this prefix is a KiCad rule area (mckicad
+#: names them on export); it is checked for overlap only
+RULE_AREA_PREFIX = "rule_area"
+
+
+def is_rule_area(name: str | None) -> bool:
+    return bool(name) and name.startswith(RULE_AREA_PREFIX)
+
+
 def _area_border_tiles(shape: Shape, transform: CoordinateTransform) -> list:
     """Convex board tiles covering a keepout border shape.
 

src/freeroute/board/items.py

@@ -76,6 +76,11 @@ class ObstacleArea(Item):
     #: tracks" rule area, where vias are allowed), via_keepout only vias
     blocks_wires: bool = True
     blocks_vias: bool = True
+    #: False for a KiCad rule area: copper may not overlap it but may touch
+    #: it, since KiCad's DRC applies no clearance to a rule area. Every other
+    #: keepout may stand for copper (a net tie, a track kept as it is), so it
+    #: keeps the clearance unless named as a rule area.
+    clearance: bool = True
 
     def is_obstacle(self) -> bool:
         return True

src/freeroute/board/search_tree.py

@@ -50,6 +50,8 @@ class TreeShape:
     #: which copper a keepout tile stops: "all", "wires" (a wire_keepout,
     #: vias allowed) or "vias" (a via_keepout)
     blocks: str = "all"
+    #: False for a rule area: copper may touch it, only overlap counts
+    clearance: bool = True
 
     def on_layer(self, layer: int) -> bool:
         return layer in self.layers
@@ -129,6 +131,8 @@ class ShapeSearchTree:
 
         Uses a strict 2-D overlap of the ``clearance``-expanded box, so tiles
         exactly ``clearance`` apart (touching after expansion) are allowed.
+        A rule area (``clearance=False``) only has to be clear of the copper
+        itself.
         """
         expanded = box.offset(clearance)
         for shape in self.overlapping(expanded):
@@ -136,6 +140,10 @@ class ShapeSearchTree:
                 continue
             if shape.blocks != "all" and shape.blocks != kind + "s":
                 continue  # a wire-only keepout does not stop a via, and so on
+            if not shape.clearance:
+                if shape.tile.overlaps(box):
+                    return True
+                continue
             if shape.exact is not None:
                 if overlaps_2d(shape.exact, expanded):
                     return True
@@ -143,6 +151,17 @@ class ShapeSearchTree:
                 return True
         return False
 
+    def rule_area_overlap(self, box: IntBox, layer: int, kind: str = "wire") -> bool:
+        """True if ``box`` overlaps a rule area on ``layer`` that stops ``kind``."""
+        for shape in self.overlapping(box):
+            if shape.clearance or not shape.on_layer(layer):
+                continue
+            if shape.blocks != "all" and shape.blocks != kind + "s":
+                continue
+            if shape.tile.overlaps(box):
+                return True
+        return False
+
     def clearance_conflict_shape(
         self, region, net_no: int, layer: int
     ) -> bool:
@@ -178,6 +197,13 @@ class ShapeSearchTree:
                     continue  # static input pair (e.g. pad vs pad) — not a routing DRC
                 if not (shape.layers & other.layers):
                     continue
+                if not (shape.clearance and other.clearance):
+                    # a rule area: only an overlap is a violation
+                    mine = shape.exact if shape.exact is not None else shape.tile
+                    theirs = other.exact if other.exact is not None else other.tile
+                    if overlaps_2d(mine, theirs):
+                        return shape
+                    continue
                 if shape.exact is None and other.exact is None:
                     if other.tile.overlaps(expanded):  # byte-identical box path
                         return shape

src/freeroute/route/exact_router.py

@@ -42,6 +42,7 @@ from freeroute.geometry import (
     segment_octagon,
     shove_segment,
 )
+from freeroute.geometry.polyline import corner_box
 
 from .grid_router import RouteResult, route_board
 
@@ -157,7 +158,10 @@ def route_board_exact(
             box = tile.bounding_box()
             if not box.is_empty():
                 tree.insert(
-                    TreeShape(next(owner), -1, frozenset({obstacle.layer}), box, blocks=blocks)
+                    TreeShape(
+                        next(owner), -1, frozenset({obstacle.layer}), box,
+                        blocks=blocks, clearance=obstacle.clearance,
+                    )
                 )
 
     via_layers = frozenset(signal_layers)
@@ -178,7 +182,9 @@ def route_board_exact(
             )
             for i, (box, box_layers) in enumerate(boxes)
             for layer in box_layers
-        ) or (outline is not None and not all(outline.box_clear(b, edge) for b, _ in boxes)):
+        ) or _end_in_rule_area(tree, wires, half_width) or (
+            outline is not None and not all(outline.box_clear(b, edge) for b, _ in boxes)
+        ):
             rejected.append((net_no, *ends))
             continue  # exact-clearance conflict -> drop (may be recovered by shove)
         acc = accepted.get(net_no)
@@ -592,6 +598,17 @@ def _net_boxes(result, net_no, half_width, via_layers, via_half=None):
     )
 
 
+def _end_in_rule_area(tree, wires, half_width) -> bool:
+    """A wire's tiles stop at its end points, but a track ends in a round cap
+    half its width beyond them. Against other copper the pad or via there
+    covers it; a rule area has no clearance to absorb it, so check it."""
+    for layer, points in wires:
+        for end in (points[0], points[-1]):
+            if tree.rule_area_overlap(corner_box(end, half_width), layer):
+                return True
+    return False
+
+
 def _copper_boxes(wires, vias, half_width, via_layers, via_half=None):
     via_half = via_half or half_width
     boxes: list[tuple[IntBox, frozenset[int]]] = []

src/freeroute/route/grid_router.py

@@ -33,6 +33,7 @@ import random
 from freeroute.board.board import BasicBoard
 from freeroute.board.items import ConductionArea, ObstacleArea, Pin
 from freeroute.geometry import IntBox, IntPoint
+from freeroute.geometry.polyline import corner_box
 
 __all__ = ["GridRouter", "RouteResult", "route_board"]
 
@@ -298,7 +299,9 @@ class GridRouter:
         outline = self.board.outline
         self._via_edge_block: set[Cell] = set()
         # wire keepouts as boxes, to check a pin stub the way the exact engine will
-        self._keepout_boxes: dict[int, list[IntBox]] = {}
+        self._keepout_boxes: dict[int, list[tuple[IntBox, bool]]] = {}
+        # pin end nodes no wire can reach without entering a keepout
+        self._via_only: set[Node] = set()
         if outline is not None:
             # cells too close to the real outline (rounded corners included):
             # for a trace on every layer, and separately for a via's wider copper
@@ -336,8 +339,12 @@ class GridRouter:
                         continue
                     # the same distance the exact engine verifies against
                     if item.blocks_wires:
-                        self._keepout_boxes.setdefault(item.layer, []).append(box)
-                    for cell in self._cells_in_box(box, margin):
+                        self._keepout_boxes.setdefault(item.layer, []).append(
+                            (box, item.clearance)
+                        )
+                    # a rule area takes no clearance: a trace may touch it
+                    reach = margin if item.clearance else self.half_width
+                    for cell in self._cells_in_box(box, reach):
                         if item.blocks_wires:
                             self._keepout.add((*cell, item.layer))
                         if item.blocks_vias:
@@ -475,12 +482,19 @@ class GridRouter:
                     return path
             cx, cy, cl = current
             base = g_score[current]
-            for dx, dy in self._neighbours:
+            # A cell inside a wire keepout (a pin there, or where a via
+            # landed) may only be left by another via: a wire from it would
+            # start inside the keepout.
+            blocked = current in self._keepout or current in self._via_only
+            neighbours = () if blocked else self._neighbours
+            for dx, dy in neighbours:
                 cell = (cx + dx, cy + dy)
                 if not (0 <= cell[0] < self.cols and 0 <= cell[1] < self.rows):
                     continue
                 nxt = (*cell, cl)
                 if nxt in goal_stub:  # a pin end; a zone end is entered normally
+                    if nxt in self._keepout or nxt in self._via_only:
+                        continue  # a pin inside a keepout is reached by a via only
                     enter = goal_stub[nxt]
                 else:
                     enter = self._enter_cost(cell, cl, net_no, allow_ripup, conns)
@@ -528,7 +542,9 @@ class GridRouter:
             if _point_segment(self._cell_center(c), pin_location, end) < reach
         ]
 
-    def _stub_clear(self, pin: Pin, cell: Cell, layer: int, net_no: int, conns) -> bool:
+    def _stub_clear(
+        self, pin: Pin, cell: Cell, layer: int, net_no: int, conns, keepouts_only: bool = False
+    ) -> bool:
         keepouts = self._keepout_boxes.get(layer)
         if keepouts:
             # the stub is off the grid, so check it exactly, as the exact
@@ -539,8 +555,14 @@ class GridRouter:
             if end != pin.location:
                 for tile in PolylineShape(Polyline([pin.location, end]), self.half_width).tiles():
                     grown = tile.offset(self.clearance)
-                    if any(k.overlaps(grown) for k in keepouts):
+                    if any(k.overlaps(grown if needs else tile) for k, needs in keepouts):
                         return False
+                # the track's round end at the pin, for a rule area
+                cap = corner_box(pin.location, self.half_width)
+                if any(not needs and k.overlaps(cap) for k, needs in keepouts):
+                    return False
+        if keepouts_only:
+            return True
         for c in self._stub_cells(pin.location, cell):
             owner = self._cell_owner.get((*c, layer))
             if owner is not None and conns[owner].net_no != net_no:
@@ -646,6 +668,13 @@ class GridRouter:
             nodes |= self._escape_nodes(pin, net_no, conns, layers, (cx, cy))
         if not nodes:  # nothing clear: fall back to the nearest cell, as before
             nodes = {(cx, cy, layer) for layer in layers}
+            if self._keepout_boxes and not any(
+                self._stub_clear(pin, (cx, cy), layer, net_no, conns, keepouts_only=True)
+                for layer in layers
+            ):
+                # no wire can reach the pin without entering a keepout: the
+                # route has to arrive by a via, which goes in the pad
+                self._via_only.update(nodes)
         return nodes
 
     def _crowded(self, pin: Pin, net_no: int) -> bool:
@@ -800,7 +829,9 @@ class GridRouter:
         if len(wire_segs) > 1:
             for idx, pin in ((0, conn.a_end), (len(wire_segs) - 1, conn.b_end)):
                 layer, cells = wire_segs[idx]
-                if isinstance(pin, Pin) and len(cells) == 1 and (*cells[0], layer) in self._keepout:
+                node = (*cells[0], layer)
+                walled = node in self._keepout or node in self._via_only
+                if isinstance(pin, Pin) and len(cells) == 1 and walled:
                     in_pad[idx] = pin.location
         conn.wires = []
         for idx, (layer, cells) in enumerate(wire_segs):

tests/board/test_build.py

@@ -254,3 +254,37 @@ def test_via_size_comes_from_the_via_padstack():
     from freeroute.route.pipeline import _via_half_board
 
     assert _via_half_board(parse_dsn(_PAD_DSN), 10) == 3000   # 0.6 mm via, board units
+
+
+# --- rule areas: overlap only ------------------------------------------------
+
+_CHANNEL_DSN = """(pcb channel.dsn
+  (parser (string_quote ")) (resolution um 10) (unit um)
+  (structure
+    (layer F.Cu (type signal)) (layer B.Cu (type signal))
+    (boundary (path pcb 0  0 0  40000 0  40000 -30000  0 -30000  0 0))
+    (keepout "{name}top" (polygon signal 0  18000 0  22000 0  22000 -14750  18000 -14750))
+    (keepout "{name}bottom" (polygon signal 0  18000 -15250  22000 -15250  22000 -30000  18000 -30000))
+    (rule (width 250) (clearance 150)))
+  (placement (component P (place P1 5000 -15000 front 0) (place P2 35000 -15000 front 0)))
+  (library (image P (pin pad 1 0 0)) (padstack pad (shape (circle F.Cu 600)) (attach off)))
+  (network (net N (pins P1-1 P2-1))))"""
+
+
+def test_a_keepout_named_rule_area_takes_no_clearance():
+    named = _areas(_CHANNEL_DSN.format(name="rule_area_"))
+    plain = _areas(_CHANNEL_DSN.format(name=""))
+    assert named and not any(a.clearance for a in named)
+    assert plain and all(a.clearance for a in plain)
+
+
+def _route_channel(name):
+    from freeroute.route.pipeline import build_exact_routing_result
+
+    return build_exact_routing_result(parse_dsn(_CHANNEL_DSN.format(name=name)), resolution=2)
+
+
+def test_a_trace_may_run_beside_a_rule_area_closer_than_clearance():
+    # the 0.5 mm channel fits a 0.25 mm trace, but not with 0.15 mm each side
+    assert _route_channel("rule_area_").unrouted == []
+    assert _route_channel("").unrouted != []

tests/board/test_search_tree.py

@@ -62,3 +62,37 @@ def test_has_violation_ignores_static_pad_pairs():
     # a routed trace of net 3 within clearance of pad net 1 -> violation
     tree.insert(shape(2, 3, 0, IntBox(11, 0, 20, 10), routed=True))
     assert tree.has_violation(clearance=20) is not None
+
+
+def test_a_rule_area_conflicts_only_on_overlap():
+    tree = ShapeSearchTree()
+    tree.insert(TreeShape(1, -1, frozenset({0}), IntBox(100, 0, 200, 100), clearance=False))
+    near = IntBox(0, 0, 95, 100)  # 5 short of the area, well inside clearance 50
+    over = IntBox(0, 0, 105, 100)
+    assert not tree.clearance_conflict(near, 7, 0, 50)
+    assert tree.clearance_conflict(over, 7, 0, 50)
+
+
+def test_an_ordinary_keepout_still_needs_clearance():
+    tree = ShapeSearchTree()
+    tree.insert(TreeShape(1, -1, frozenset({0}), IntBox(100, 0, 200, 100)))
+    assert tree.clearance_conflict(IntBox(0, 0, 95, 100), 7, 0, 50)
+
+
+def test_the_routed_board_check_treats_a_rule_area_the_same_way():
+    tree = ShapeSearchTree()
+    tree.insert(TreeShape(1, -1, frozenset({0}), IntBox(100, 0, 200, 100), clearance=False))
+    tree.insert(TreeShape(2, 7, frozenset({0}), IntBox(0, 0, 95, 100), routed=True))
+    assert tree.has_violation(50) is None
+    tree.insert(TreeShape(3, 7, frozenset({0}), IntBox(150, 0, 160, 100), routed=True))
+    assert tree.has_violation(50) is not None
+
+
+
+def test_rule_area_overlap_sees_only_rule_areas():
+    tree = ShapeSearchTree()
+    tree.insert(TreeShape(1, -1, frozenset({0}), IntBox(100, 0, 200, 100), clearance=False))
+    tree.insert(TreeShape(2, -1, frozenset({0}), IntBox(300, 0, 400, 100)))
+    assert tree.rule_area_overlap(IntBox(90, 40, 110, 60), 0)
+    assert not tree.rule_area_overlap(IntBox(290, 40, 310, 60), 0)
+    assert not tree.rule_area_overlap(IntBox(90, 40, 110, 60), 1)