Add a mirror transformation to functions

src/classy_blocks/util/functions.py

@@ -212,3 +212,41 @@ def arc_mid(axis: VectorType, center: PointType, radius: float, point_1: PointTy
     sec_ort = np.cross(sec, axis)
 
     return center + unit_vector(sec_ort) * radius
+
+
+def mirror(point: PointType, normal: VectorType, origin: PointType):
+    """Mirror a point around a plane, given by a normal and origin"""
+    # brainlessly copied from https://gamemath.com/book/matrixtransforms.html
+    point = np.asarray(point)
+    normal = unit_vector(normal)
+    origin = np.asarray(origin)
+
+    n_x = normal[0]
+    n_y = normal[1]
+    n_z = normal[2]
+
+    matrix = np.array(
+        [
+            [
+                1 - 2 * n_x**2,
+                -2 * n_x * n_y,
+                -2 * n_x * n_z,
+            ],
+            [
+                -2 * n_x * n_y,
+                1 - 2 * n_y**2,
+                -2 * n_y * n_z,
+            ],
+            [
+                -2 * n_x * n_z,
+                -2 * n_y * n_z,
+                1 - 2 * n_z**2,
+            ],
+        ]
+    )
+
+    point -= origin
+    rotated = point.dot(matrix)
+    rotated += origin
+
+    return rotated

tests/test_util/test_functions.py

@@ -158,3 +158,51 @@ def test_arc_length_3point_zero(self):
 
         with self.assertRaises(ValueError):
             self.assertAlmostEqual(f.arc_length_3point(a, b, c), 0)
+
+    def test_mirror_yz(self):
+        point = [2, 0, 0]
+        mirrored = f.mirror(point, [1, 0, 0], [0, 0, 0])
+
+        np.testing.assert_almost_equal(mirrored, [-2, 0, 0])
+
+    def test_mirror_yz_origin(self):
+        point = [2, 0, 0]
+        mirrored = f.mirror(point, [1, 0, 0], [1, 1, 1])
+
+        np.testing.assert_almost_equal(mirrored, [0, 0, 0])
+
+    def test_mirror_xz(self):
+        point = [0, 2, 0]
+        mirrored = f.mirror(point, [0, 1, 0], [0, 0, 0])
+
+        np.testing.assert_almost_equal(mirrored, [0, -2, 0])
+
+    def test_mirror_xz_origin(self):
+        point = [0, 2, 0]
+        mirrored = f.mirror(point, [0, 1, 0], [0, 1, 0])
+
+        np.testing.assert_almost_equal(mirrored, [0, 0, 0])
+
+    def test_mirror_xy(self):
+        point = [0, 0, 2]
+        mirrored = f.mirror(point, [0, 0, 1], [0, 0, 0])
+
+        np.testing.assert_almost_equal(mirrored, [0, 0, -2])
+
+    def test_mirror_xy_origin(self):
+        point = [0, 0, 2]
+        mirrored = f.mirror(point, [0, 0, 1], [0, 0, 1])
+
+        np.testing.assert_almost_equal(mirrored, [0, 0, 0])
+
+    def test_mirror_arbitrary(self):
+        point = [2, 2, 2]
+        mirrored = f.mirror(point, [1, 1, 1], [0, 0, 0])
+
+        np.testing.assert_almost_equal(mirrored, [-2, -2, -2])
+
+    def test_mirror_arbitrary_origin(self):
+        point = [2, 2, 2]
+        mirrored = f.mirror(point, [1, 1, 1], [1, 1, 1])
+
+        np.testing.assert_almost_equal(mirrored, [0, 0, 0])