Calculate distance to rectange border

Use negative numbers to denote distance to the border from inside the
rectangle.

gaphas/geometry.py

@@ -291,26 +291,38 @@ def distance_point_point_fast(point1: Point, point2: Point = (0.0, 0.0)) -> floa
     return abs(dx) + abs(dy)
 
 
-def distance_rectangle_point(rect: Rect | Rectangle, point: Point) -> float:
+def distance_rectangle_border_point(rect: Rect | Rectangle, point: Point) -> float:
     """Return the distance (fast) from a rectangle ``(x, y, width,height)`` to
     a ``point``."""
     dx = dy = 0.0
     px, py = point
     rx, ry, rw, rh = rect  # typing: ignore[misc]
+    rx1 = rx + rw
+    ry1 = ry + rh
+
+    if rx < px < rx1 and ry < py < ry1:
+        return -min(px - rx, rx1 - px, py - ry, ry1 - py)
 
     if px < rx:
         dx = rx - px
-    elif px > rx + rw:
-        dx = px - (rx + rw)
+    elif px > rx1:
+        dx = px - rx1
 
     if py < ry:
         dy = ry - py
-    elif py > ry + rh:
-        dy = py - (ry + rh)
+    elif py > ry1:
+        dy = py - ry1
 
     return abs(dx) + abs(dy)
 
 
+def distance_rectangle_point(rect: Rect | Rectangle, point: Point) -> float:
+    """Return the distance (fast) from a rectangle ``(x, y, width,height)`` to
+    a ``point``."""
+    d = distance_rectangle_border_point(rect, point)
+    return 0 if d < 0 else d
+
+
 def point_on_rectangle(
     rect: Rect | Rectangle, point: Point, border: bool = False
 ) -> Point:

tests/test_geometry.py

@@ -5,6 +5,7 @@ import pytest
 from gaphas.geometry import (
     Rectangle,
     distance_line_point,
+    distance_rectangle_border_point,
     distance_rectangle_point,
     intersect_line_line,
     point_on_rectangle,
@@ -72,6 +73,14 @@ def test_distance_with_negative_numbers_in_rectangle():
     assert distance_rectangle_point((-50, -100, 100, 100), (-17, -65)) == 0
 
 
+def test_distance_rectangle_border_point():
+    assert distance_rectangle_border_point((2, 0, 2, 2), (0, 0)) == 2
+    assert distance_rectangle_border_point(Rectangle(0, 0, 10, 10), (11, -1)) == 2
+    assert distance_rectangle_border_point((0, 0, 10, 10), (11, -1)) == 2
+    assert distance_rectangle_border_point((0, 0, 10, 10), (3, 4)) == -3
+    assert distance_rectangle_border_point((0, 0, 2, 2), (1, 1)) == -1
+
+
 def test_point_on_rectangle():
     assert point_on_rectangle((2, 2, 2, 2), (0, 0)) == (2, 2)
     assert point_on_rectangle((2, 2, 2, 2), (3, 0)) == (3, 2)