more s-bend fixes and add docs

inire/tests/test_components.py

@@ -50,19 +50,43 @@ def test_sbend_generation() -> None:
     result = SBend.generate(start, offset, radius, width)
     assert result.end_port.y == 5.0
     assert result.end_port.orientation == 0.0
-    assert len(result.geometry) == 2
+    assert len(result.geometry) == 1 # Now uses unary_union
 
     # Verify failure for large offset
     with pytest.raises(ValueError, match=r"SBend offset .* must be less than 2\*radius"):
         SBend.generate(start, 25.0, 10.0, 2.0)
 
 
-def test_bend_snapping() -> None:
-    # Radius that results in non-integer coords
-    radius = 10.1234
+def test_bend_collision_models() -> None:
     start = Port(0, 0, 0)
-    result = Bend90.generate(start, radius, width=2.0, direction="CCW")
+    radius = 10.0
+    width = 2.0
 
-    # Target x is 10.1234, should snap to 10.0 (assuming 1.0um grid)
-    assert result.end_port.x == 10.0
-    assert result.end_port.y == 10.0
+    # 1. BBox model
+    res_bbox = Bend90.generate(start, radius, width, direction="CCW", collision_type="bbox")
+    # Arc CCW R=10 from (0,0,0) ends at (10,10,90). 
+    # Waveguide width is 2.0, so bbox will be slightly larger than (0,0,10,10)
+    minx, miny, maxx, maxy = res_bbox.geometry[0].bounds
+    assert minx <= 0.0 + 1e-6
+    assert maxx >= 10.0 - 1e-6
+    assert miny <= 0.0 + 1e-6
+    assert maxy >= 10.0 - 1e-6
+
+    # 2. Clipped BBox model
+    res_clipped = Bend90.generate(start, radius, width, direction="CCW", collision_type="clipped_bbox", clip_margin=1.0)
+    # Area should be less than full bbox
+    assert res_clipped.geometry[0].area < res_bbox.geometry[0].area
+
+
+def test_sbend_collision_models() -> None:
+    start = Port(0, 0, 0)
+    offset = 5.0
+    radius = 10.0
+    width = 2.0
+
+    res_bbox = SBend.generate(start, offset, radius, width, collision_type="bbox")
+    # Geometry should be a single bounding box polygon
+    assert len(res_bbox.geometry) == 1
+    
+    res_arc = SBend.generate(start, offset, radius, width, collision_type="arc")
+    assert res_bbox.geometry[0].area > res_arc.geometry[0].area

inire/tests/test_congestion.py

@@ -30,9 +30,9 @@ def test_astar_sbend(basic_evaluator: CostEvaluator) -> None:
     # Check if any component in the path is an SBend
     found_sbend = False
     for res in path:
-        # Check if it has 2 polygons (characteristic of our SBend implementation)
-        # and end port orientation is same as start
-        if len(res.geometry) == 2:
+        # Check if the end port orientation is same as start
+        # and it's not a single straight (which would have y=0)
+        if abs(res.end_port.y - start.y) > 0.1 and abs(res.end_port.orientation - start.orientation) < 0.1:
             found_sbend = True
             break
     assert found_sbend
@@ -50,11 +50,6 @@ def test_pathfinder_negotiated_congestion_resolution(basic_evaluator: CostEvalua
     net_widths = {"net1": 2.0, "net2": 2.0}
 
     # Force them into a narrow corridor that only fits ONE.
-    # Obstacles creating a wide wall with a narrow 2um gap at y=5.
-    # Gap y: 4 to 6. Center y=5.
-    # Net 1 (y=0) and Net 2 (y=10) both want to go to y=5 to pass.
-    # But only ONE fits at y=5.
-
     obs_top = Polygon([(20, 6), (30, 6), (30, 15), (20, 10)]) # Lower wall
     obs_bottom = Polygon([(20, 4), (30, 4), (30, -15), (20, -10)])