From 6ae2001400c19a62c2a9e33a26dc6757818d61ff Mon Sep 17 00:00:00 2001
From: Patrick Shriwise <pshriwise@gmail.com>
Date: Fri, 21 Feb 2025 14:58:37 -0600
Subject: [PATCH] Enable overlap plotting from Python API (#3310)

Co-authored-by: Paul Romano <paul.k.romano@gmail.com>
---
 openmc/model/model.py          |  5 +++++
 openmc/plots.py                | 13 +++++++++----
 tests/unit_tests/test_model.py | 11 +++++++++++
 3 files changed, 25 insertions(+), 4 deletions(-)

diff --git a/openmc/model/model.py b/openmc/model/model.py
index c7f358ce8e..e8558f4ad0 100644
--- a/openmc/model/model.py
+++ b/openmc/model/model.py
@@ -863,6 +863,8 @@ class Model:
         legend: bool = False,
         axis_units: str = 'cm',
         outline: bool | str = False,
+        show_overlaps: bool = False,
+        overlap_color: Sequence[int] | str | None = None,
         n_samples: int | None = None,
         plane_tolerance: float = 1.,
         legend_kwargs: dict | None = None,
@@ -941,6 +943,9 @@ class Model:
             plot.pixels = pixels
             plot.basis = basis
             plot.color_by = color_by
+            plot.show_overlaps = show_overlaps
+            if overlap_color is not None:
+                plot.overlap_color = overlap_color
             if colors is not None:
                 plot.colors = colors
             self.plots.append(plot)
diff --git a/openmc/plots.py b/openmc/plots.py
index 2460765984..9c1e31575e 100644
--- a/openmc/plots.py
+++ b/openmc/plots.py
@@ -209,16 +209,21 @@ _PLOT_PARAMS = """
         legend : bool
             Whether a legend showing material or cell names should be drawn
 
+            .. versionadded:: 0.14.0
+        axis_units : {'km', 'm', 'cm', 'mm'}
+            Units used on the plot axis
+
             .. versionadded:: 0.14.0
         outline : bool or str
             Whether outlines between color boundaries should be drawn. If set to
             'only', only outlines will be drawn.
 
             .. versionadded:: 0.14.0
-        axis_units : {'km', 'm', 'cm', 'mm'}
-            Units used on the plot axis
-
-            .. versionadded:: 0.14.0
+        show_overlaps: bool
+            Indicate whether or not overlapping regions are shown.
+            Default is False.
+        overlap_color: Iterable of int or str
+            Color to apply to overlapping regions. Default is red.
         n_samples : int, optional
             The number of source particles to sample and add to plot. Defaults
             to None which doesn't plot any particles on the plot.
diff --git a/tests/unit_tests/test_model.py b/tests/unit_tests/test_model.py
index 4d7d5be2bc..ee5d8895ca 100644
--- a/tests/unit_tests/test_model.py
+++ b/tests/unit_tests/test_model.py
@@ -638,3 +638,14 @@ def test_model_plot():
     plot = model.plot(n_samples=1, plane_tolerance=0.1, basis="xy")
     coords = plot.axes.collections[0].get_offsets().data.flatten()
     assert (coords == np.array([])).all()
+
+    # modify model to include another cell that overlaps the original cell entirely
+    model.geometry.root_universe.add_cell(openmc.Cell(region=-surface))
+    axes = model.plot(show_overlaps=True)
+    white = np.array((1.0, 1.0, 1.0))
+    red = np.array((1.0, 0.0, 0.0))
+    axes_image = axes.get_images()[0]
+    image_data = axes_image.get_array()
+    # ensure that all of the data in the image data is either white or red
+    test_mask = (image_data == white) | (image_data == red)
+    assert np.all(test_mask), "Colors other than white or red found in overlap plot image"