parametrized s-bend

DOCS.md

@@ -11,7 +11,7 @@ The `AStarRouter` is the core pathfinding engine. It can be configured directly
 | `node_limit`          | `int`         | 1,000,000          | Maximum number of states to explore per net. Increase for very complex paths.         |
 | `straight_lengths`    | `list[float]` | `[1.0, 5.0, 25.0]` | Discrete step sizes for straight waveguides (µm). Larger steps speed up search.       |
 | `bend_radii`          | `list[float]` | `[10.0]`           | Available radii for 90-degree turns (µm). Multiple values allow best-fit selection.   |
-| `sbend_offsets`       | `list[float]` | `[-5, -2, 2, 5]`   | Lateral offsets for parametric S-bends (µm).                                          |
+| `sbend_offsets`       | `list[float] \| None` | `None` (Auto)      | Lateral offsets for parametric S-bends. `None` uses automatic grid-aligned steps. |
 | `sbend_radii`         | `list[float]` | `[10.0]`           | Available radii for S-bends (µm).                                                     |
 | `snap_to_target_dist` | `float`       | 20.0               | Distance (µm) at which the router attempts an exact bridge to the target port.        |
 | `bend_penalty`        | `float`       | 50.0               | Flat cost added for every 90-degree bend. Higher values favor straight lines.         |
@@ -87,4 +87,7 @@ In multi-net designs, if nets are overlapping:
 3.  If a solution is still not found, check if the `clearance` is physically possible given the design's narrowest bottlenecks.
 
 ### S-Bend Usage
-Parametric S-bends are triggered by the `sbend_offsets` list. If you need a specific lateral shift (e.g., 5.86µm for a 45° switchover), add it to `sbend_offsets`. The router will only use an S-bend if it can reach a state that is exactly on the lattice or the target.
+Parametric S-bends bridge lateral gaps without changing the waveguide's orientation. 
+- **Automatic Selection**: If `sbend_offsets` is set to `None` (the default), the router automatically chooses from a set of "natural" offsets (Fibonacci-aligned grid steps) and the offset needed to hit the target.
+- **Specific Offsets**: To use specific offsets (e.g., 5.86µm for a 45° switchover), provide them in the `sbend_offsets` list. The router will prioritize these but will still try to align with the target if possible.
+- **Constraints**: S-bends are only used for offsets $O < 2R$. For larger shifts, the router naturally combines two 90° bends and a straight segment.

examples/07_large_scale_routing.py

@@ -29,7 +29,7 @@ def main() -> None:
 
     evaluator = CostEvaluator(engine, danger_map, greedy_h_weight=1.5, unit_length_cost=0.1, bend_penalty=100.0, sbend_penalty=400.0, congestion_penalty=100.0)
 
-    router = AStarRouter(evaluator, node_limit=2000000, snap_size=5.0, bend_radii=[50.0], sbend_radii=[50.0], use_analytical_sbends=False)
+    router = AStarRouter(evaluator, node_limit=2000000, snap_size=5.0, bend_radii=[50.0], sbend_radii=[50.0])
     pf = PathFinder(router, evaluator, max_iterations=15, base_congestion_penalty=100.0, congestion_multiplier=1.4)
 
     # 2. Define Netlist

inire/router/astar.py

@@ -204,24 +204,6 @@ class AStarRouter:
              if max_reach >= proj_t - 0.01:
                   self._process_move(current, target, net_width, net_id, open_set, closed_set, snap, f'S{proj_t}', 'S', (proj_t,), skip_congestion, skip_static=True, snap_to_grid=False)
 
-        # B. SBend Jump (Direct to Target)
-        if self.config.use_analytical_sbends and proj_t > 0 and abs(cp.orientation - target.orientation) < 0.1 and abs(perp_t) > 1e-3:
-             # Calculate required radius to hit target exactly: R = (dx^2 + dy^2) / (4*|dy|)
-             req_radius = (proj_t**2 + perp_t**2) / (4.0 * abs(perp_t))
-             
-             min_radius = min(self.config.sbend_radii) if self.config.sbend_radii else 50.0
-             
-             if req_radius >= min_radius:
-                  # We can hit it exactly!
-                  self._process_move(current, target, net_width, net_id, open_set, closed_set, snap, f'SB_Direct_R{req_radius:.1f}', 'SB', (perp_t, req_radius), skip_congestion, snap_to_grid=False)
-             else:
-                  # Required radius is too small. We must use a larger radius and some straight segments.
-                  # A* will handle this through Priority 3 SBends + Priority 2 Straights.
-                  pass
-
-                  # In super sparse mode, we can return here, but A* needs other options for optimality.
-                  # return 
-
         # 2. VISIBILITY JUMPS & MAX REACH (Priority 2)
         max_reach = self.cost_evaluator.collision_engine.ray_cast(cp, base_ori, self.config.max_straight_length)
         
@@ -309,14 +291,35 @@ class AStarRouter:
                         continue
                 self._process_move(current, target, net_width, net_id, open_set, closed_set, snap, f'B{radius}{direction}', 'B', (radius, direction), skip_congestion)
 
-        if dist_sq < 400*400:
+        # 4. SBENDS
-            offsets = set(self.config.sbend_offsets)
+        max_sbend_r = max(self.config.sbend_radii) if self.config.sbend_radii else 0
+        if max_sbend_r > 0:
+            user_offsets = self.config.sbend_offsets
+            offsets: set[float] = set(user_offsets) if user_offsets is not None else set()
+            
             dx_local = (target.x - cp.x) * cos_v + (target.y - cp.y) * sin_v
             dy_local = -(target.x - cp.x) * sin_v + (target.y - cp.y) * cos_v
-            if 0 < dx_local < self.config.snap_to_target_dist:
+            
+            # Always try aligning with target if it's forward and within reach
+            if dx_local > 0 and abs(dy_local) < 2 * max_sbend_r:
+                 # Check if we have enough distance for the SBend
+                 # Min distance D = sqrt(4RO - O^2). Smallest R is O/2.
+                 min_d = numpy.sqrt(max(0, 4 * (abs(dy_local)/2.0) * abs(dy_local) - dy_local**2))
+                 if dx_local >= min_d:
                       offsets.add(dy_local)
             
-            for offset in offsets:
+            # If no offsets provided by user (None), the router "chooses" offsets 
+            # by trying grid-aligned steps up to the reach of the largest radius.
+            if user_offsets is None:
+                 # Try a selection of grid-aligned offsets. 
+                 # Fibonacci-ish steps are useful to cover different scales efficiently.
+                 for sign in [-1, 1]:
+                      for i in [1, 2, 3, 5, 8, 13, 21, 34, 55, 89]:
+                           o = sign * i * snap
+                           if abs(o) < 2 * max_sbend_r:
+                                offsets.add(o)
+
+            for offset in sorted(offsets):
                 for radius in self.config.sbend_radii:
                     if abs(offset) >= 2 * radius: continue
                     self._process_move(current, target, net_width, net_id, open_set, closed_set, snap, f'SB{offset}R{radius}', 'SB', (offset, radius), skip_congestion)

inire/router/config.py

@@ -16,8 +16,8 @@ class RouterConfig:
     num_straight_samples: int = 5
     min_straight_length: float = 5.0
     
-    # Offsets for SBends (still list-based for now, or could range)
+    # Offsets for SBends (None = automatic grid-based selection)
-    sbend_offsets: list[float] = field(default_factory=lambda: [-100.0, -50.0, -10.0, 10.0, 50.0, 100.0])
+    sbend_offsets: list[float] | None = None
     
     # Deprecated but kept for compatibility during refactor
     straight_lengths: list[float] = field(default_factory=list) 
@@ -25,7 +25,6 @@ class RouterConfig:
     bend_radii: list[float] = field(default_factory=lambda: [50.0, 100.0])
     sbend_radii: list[float] = field(default_factory=lambda: [50.0, 100.0, 500.0])
     snap_to_target_dist: float = 1000.0
-    use_analytical_sbends: bool = True
     bend_penalty: float = 250.0
     sbend_penalty: float = 500.0
     bend_collision_type: Literal["arc", "bbox", "clipped_bbox"] | Any = "arc"

inire/tests/test_cost.py

@@ -9,17 +9,31 @@ def test_cost_calculation() -> None:
     # 50x50 um area, 1um resolution
     danger_map = DangerMap(bounds=(0, 0, 50, 50))
     danger_map.precompute([])
-    evaluator = CostEvaluator(engine, danger_map)
+    # Use small penalties for testing
+    evaluator = CostEvaluator(engine, danger_map, bend_penalty=10.0)
 
     p1 = Port(0, 0, 0)
     p2 = Port(10, 10, 0)
 
     h = evaluator.h_manhattan(p1, p2)
-    # Manhattan distance = 20. Orientation penalty = 0.
+    # Manhattan distance = 20. 
-    # Weighted by 1.1 -> 22.0
+    # Jog alignment penalty = 2*bp = 20.
-    assert abs(h - 22.0) < 1e-6
+    # Side check penalty = 2*bp = 20.
+    # Total = 1.1 * (20 + 40) = 66.0
+    assert abs(h - 66.0) < 1e-6
 
-    # Orientation penalty
+    # Orientation difference
     p3 = Port(10, 10, 90)
-    h_wrong = evaluator.h_manhattan(p1, p3)
+    h_90 = evaluator.h_manhattan(p1, p3)
-    assert h_wrong > h
+    # diff = 90. penalty += 1*bp = 10.
+    # Side check: 2*bp = 20. (Total penalty = 30)
+    # Total = 1.1 * (20 + 30) = 55.0
+    assert abs(h_90 - 55.0) < 1e-6
+
+    # Traveling away
+    p4 = Port(10, 10, 180)
+    h_away = evaluator.h_manhattan(p1, p4)
+    # diff = 180. penalty += 2*bp = 20.
+    # Side check: 2*bp = 20.
+    # Total = 1.1 * (20 + 40) = 66.0
+    assert h_away >= h_90