From f47aa91c49af61657c8d8bb5d8aa60556e251518 Mon Sep 17 00:00:00 2001
From: Huite Bootsma <huitebootsma@gmail.com>
Date: Sun, 13 Oct 2024 21:30:38 +0200
Subject: [PATCH] Fix line_box_clip test. Return NO_INTERSECTION consistently
 across methods.

---
 numba_celltree/algorithms/cohen_sutherland.py |  6 ++++++
 numba_celltree/algorithms/liang_barsky.py     |  5 +++++
 tests/test_algorithms/test_line_box_clip.py   | 11 +++++++++++
 3 files changed, 22 insertions(+)

diff --git a/numba_celltree/algorithms/cohen_sutherland.py b/numba_celltree/algorithms/cohen_sutherland.py
index 43c20b3..c58c512 100644
--- a/numba_celltree/algorithms/cohen_sutherland.py
+++ b/numba_celltree/algorithms/cohen_sutherland.py
@@ -92,4 +92,10 @@ def cohen_sutherland_line_box_clip(a: Point, b: Point, box: Box) -> Tuple[Point,
             b = Point(x, y)
             k2 = get_clip(b, box)
 
+        # Recompute (dx, dy) with new points.
+        dx = b.x - a.x
+        dy = b.y - a.y
+        if dx == 0.0 and dy == 0.0:
+            return NO_INTERSECTION
+
     return True, a, b
diff --git a/numba_celltree/algorithms/liang_barsky.py b/numba_celltree/algorithms/liang_barsky.py
index cde1190..5e5eb38 100644
--- a/numba_celltree/algorithms/liang_barsky.py
+++ b/numba_celltree/algorithms/liang_barsky.py
@@ -54,6 +54,11 @@ def liang_barsky_line_box_clip(
                 elif t < t1:
                     t1 = t
 
+    # TODO: Can this check be set as the first thing in the for loop for early
+    # exits?
+    if t0 == t1:
+        return NO_INTERSECTION
+
     c = Point(a.x + t0 * dx, a.y + t0 * dy)
     d = Point(a.x + t1 * dx, a.y + t1 * dy)
     return True, c, d
diff --git a/tests/test_algorithms/test_line_box_clip.py b/tests/test_algorithms/test_line_box_clip.py
index 3d3c50a..1b4702a 100644
--- a/tests/test_algorithms/test_line_box_clip.py
+++ b/tests/test_algorithms/test_line_box_clip.py
@@ -130,6 +130,8 @@ def assert_expected(
         b = Point(*b)
         # c, d are the clipped points
         actual, actual_c, actual_d = line_clip(a, b, box)
+        print(actual_c, c)
+        print(actual_d, d)
         assert intersects is actual
         assert np.allclose(actual_c, c, equal_nan=True)
         assert np.allclose(actual_d, d, equal_nan=True)
@@ -281,3 +283,12 @@ def assert_expected(
         (2.0, 0.0),
         (2.0, 2.0),
     )
+
+    # Diagonal line of length (1, 1), touching upper left corner.
+    assert_expected(
+        (-1.0, 1.0),
+        (0.0, 2.0),
+        False,
+        (np.nan, np.nan),
+        (np.nan, np.nan),
+    )