Added regular_polygon draw method

Tests/test_imagedraw.py

@@ -1092,3 +1092,95 @@ def test_same_color_outline():
                     operation, mode
                 )
                 assert_image_similar_tofile(im, expected, 1)
+
+
+@pytest.mark.parametrize(
+    "n_sides, rotation, polygon_name",
+    [(4, 0, "square"), (8, 0, "regular_octagon"), (4, 45, "square")],
+)
+def test_draw_regular_polygon(n_sides, rotation, polygon_name):
+    im = Image.new("RGBA", size=(W, H), color=(255, 0, 0, 0))
+    filename_base = f"Tests/images/imagedraw_{polygon_name}"
+    filename = (
+        f"{filename_base}.png"
+        if rotation == 0
+        else f"{filename_base}_rotate_{rotation}.png"
+    )
+    draw = ImageDraw.Draw(im)
+    bounding_circle = ((W // 2, H // 2), 25)
+    draw.regular_polygon(bounding_circle, n_sides, rotation=rotation, fill="red")
+    assert_image_equal(im, Image.open(filename))
+
+
+@pytest.mark.parametrize(
+    "n_sides, expected_vertices",
+    [
+        (3, [(28.35, 62.5), (71.65, 62.5), (50.0, 25.0)]),
+        (4, [(32.32, 67.68), (67.68, 67.68), (67.68, 32.32), (32.32, 32.32)]),
+        (
+            5,
+            [
+                (35.31, 70.23),
+                (64.69, 70.23),
+                (73.78, 42.27),
+                (50.0, 25.0),
+                (26.22, 42.27),
+            ],
+        ),
+        (
+            6,
+            [
+                (37.5, 71.65),
+                (62.5, 71.65),
+                (75.0, 50.0),
+                (62.5, 28.35),
+                (37.5, 28.35),
+                (25.0, 50.0),
+            ],
+        ),
+    ],
+)
+def test_compute_regular_polygon_vertices(n_sides, expected_vertices):
+    bounding_circle = (W // 2, H // 2, 25)
+    vertices = ImageDraw._compute_regular_polygon_vertices(bounding_circle, n_sides, 0)
+    assert vertices == expected_vertices
+
+
+@pytest.mark.parametrize(
+    "n_sides, bounding_circle, rotation, expected_error, error_message",
+    [
+        (None, (50, 50, 25), 0, TypeError, "n_sides should be an int"),
+        (1, (50, 50, 25), 0, ValueError, "n_sides should be an int > 2"),
+        (3, 50, 0, TypeError, "bounding_circle should be a tuple"),
+        (
+            3,
+            (50, 50, 100, 100),
+            0,
+            ValueError,
+            "bounding_circle should contain 2D coordinates "
+            "and a radius (e.g. (x, y, r) or ((x, y), r) )",
+        ),
+        (
+            3,
+            (50, 50, "25"),
+            0,
+            ValueError,
+            "bounding_circle should only contain numeric data",
+        ),
+        (
+            3,
+            ((50, 50, 50), 25),
+            0,
+            ValueError,
+            "bounding_circle centre should contain 2D coordinates (e.g. (x, y))",
+        ),
+        (3, (50, 50, 0), 0, ValueError, "bounding_circle radius should be > 0",),
+        (3, (50, 50, 25), "0", ValueError, "rotation should be an int or float",),
+    ],
+)
+def test_compute_regular_polygon_vertices_input_error_handling(
+    n_sides, bounding_circle, rotation, expected_error, error_message
+):
+    with pytest.raises(expected_error) as e:
+        ImageDraw._compute_regular_polygon_vertices(bounding_circle, n_sides, rotation)
+    assert str(e.value) == error_message

docs/reference/ImageDraw.rst

@@ -254,6 +254,24 @@ Methods
     :param outline: Color to use for the outline.
     :param fill: Color to use for the fill.
 
+
+.. py:method:: ImageDraw.regular_polygon(bounding_circle, n_sides, rotation=0, fill=None, outline=None)
+
+    Draws a regular polygon inscribed in ``bounding_circle``,
+    with ``n_sides``, and rotation of ``rotation`` degrees.
+
+    :param bounding_circle: The bounding circle is a tuple defined
+        by a point and radius.
+        (e.g. ``bounding_circle=(x, y, r)`` or ``((x, y), r)``).
+        The polygon is inscribed in this circle.
+    :param n_sides: Number of sides
+        (e.g. ``n_sides=3`` for a triangle, ``6`` for a hexagon).
+    :param rotation: Apply an arbitrary rotation to the polygon
+        (e.g. ``rotation=90``, applies a 90 degree rotation).
+    :param fill: Color to use for the fill.
+    :param outline: Color to use for the outline.
+
+
 .. py:method:: ImageDraw.rectangle(xy, fill=None, outline=None, width=1)
 
     Draws a rectangle.

src/PIL/ImageDraw.py

@@ -242,6 +242,13 @@ def polygon(self, xy, fill=None, outline=None):
         if ink is not None and ink != fill:
             self.draw.draw_polygon(xy, ink, 0)
 
+    def regular_polygon(
+        self, bounding_circle, n_sides, rotation=0, fill=None, outline=None
+    ):
+        """Draw a regular polygon."""
+        xy = _compute_regular_polygon_vertices(bounding_circle, n_sides, rotation)
+        self.polygon(xy, fill, outline)
+
     def rectangle(self, xy, fill=None, outline=None, width=1):
         """Draw a rectangle."""
         ink, fill = self._getink(outline, fill)
@@ -555,6 +562,123 @@ def floodfill(image, xy, value, border=None, thresh=0):
         edge = new_edge
 
 
+def _compute_regular_polygon_vertices(bounding_circle, n_sides, rotation):
+    """
+    Generate a list of vertices for a 2D regular polygon.
+
+    :param bounding_circle: The bounding circle is a tuple defined
+        by a point and radius. The polygon is inscribed in this circle.
+        (e.g. ``bounding_circle=(x, y, r)`` or ``((x, y), r)``)
+    :param n_sides: Number of sides
+        (e.g. ``n_sides=3`` for a triangle, ``6`` for a hexagon)
+    :param rotation: Apply an arbitrary rotation to the polygon
+        (e.g. ``rotation=90``, applies a 90 degree rotation)
+    :return: List of regular polygon vertices
+        (e.g. ``[(25, 50), (50, 50), (50, 25), (25, 25)]``)
+
+    How are the vertices computed?
+    1. Compute the following variables
+        - theta: Angle between the apothem & the nearest polygon vertex
+        - side_length: Length of each polygon edge
+        - centroid: Center of bounding circle (1st, 2nd elements of bounding_circle)
+        - polygon_radius: Polygon radius (last element of bounding_circle)
+        - angles: Location of each polygon vertex in polar grid
+            (e.g. A square with 0 degree rotation => [225.0, 315.0, 45.0, 135.0])
+
+    2. For each angle in angles, get the polygon vertex at that angle
+        The vertex is computed using the equation below.
+            X= xcos(φ) + ysin(φ)
+            Y= −xsin(φ) + ycos(φ)
+
+        Note:
+            φ = angle in degrees
+            x = 0
+            y = polygon_radius
+
+        The formula above assumes rotation around the origin.
+        In our case, we are rotating around the centroid.
+        To account for this, we use the formula below
+            X = xcos(φ) + ysin(φ) + centroid_x
+            Y = −xsin(φ) + ycos(φ) + centroid_y
+    """
+    # 1. Error Handling
+    # 1.1 Check `n_sides` has an appropriate value
+    if not isinstance(n_sides, int):
+        raise TypeError("n_sides should be an int")
+    if n_sides < 3:
+        raise ValueError("n_sides should be an int > 2")
+
+    # 1.2 Check `bounding_circle` has an appropriate value
+    if not isinstance(bounding_circle, (list, tuple)):
+        raise TypeError("bounding_circle should be a tuple")
+
+    if len(bounding_circle) == 3:
+        *centroid, polygon_radius = bounding_circle
+    elif len(bounding_circle) == 2:
+        centroid, polygon_radius = bounding_circle
+    else:
+        raise ValueError(
+            "bounding_circle should contain 2D coordinates "
+            "and a radius (e.g. (x, y, r) or ((x, y), r) )"
+        )
+
+    if not all(isinstance(i, (int, float)) for i in (*centroid, polygon_radius)):
+        raise ValueError("bounding_circle should only contain numeric data")
+
+    if not len(centroid) == 2:
+        raise ValueError(
+            "bounding_circle centre should contain 2D coordinates (e.g. (x, y))"
+        )
+
+    if polygon_radius <= 0:
+        raise ValueError("bounding_circle radius should be > 0")
+
+    # 1.3 Check `rotation` has an appropriate value
+    if not isinstance(rotation, (int, float)):
+        raise ValueError("rotation should be an int or float")
+
+    # 2. Define Helper Functions
+    def _apply_rotation(point, degrees, centroid):
+        return (
+            round(
+                point[0] * math.cos(math.radians(360 - degrees))
+                - point[1] * math.sin(math.radians(360 - degrees))
+                + centroid[0],
+                2,
+            ),
+            round(
+                point[1] * math.cos(math.radians(360 - degrees))
+                + point[0] * math.sin(math.radians(360 - degrees))
+                + centroid[1],
+                2,
+            ),
+        )
+
+    def _compute_polygon_vertex(centroid, polygon_radius, angle):
+        start_point = [polygon_radius, 0]
+        return _apply_rotation(start_point, angle, centroid)
+
+    def _get_angles(n_sides, rotation):
+        angles = []
+        degrees = 360 / n_sides
+        # Start with the bottom left polygon vertex
+        current_angle = (270 - 0.5 * degrees) + rotation
+        for _ in range(0, n_sides):
+            angles.append(current_angle)
+            current_angle += degrees
+            if current_angle > 360:
+                current_angle -= 360
+        return angles
+
+    # 3. Variable Declarations
+    angles = _get_angles(n_sides, rotation)
+
+    # 4. Compute Vertices
+    return [
+        _compute_polygon_vertex(centroid, polygon_radius, angle) for angle in angles
+    ]
+
+
 def _color_diff(color1, color2):
     """
     Uses 1-norm distance to calculate difference between two values.