Add collision detection algorithms

physics/collision_detection.py

@@ -0,0 +1,299 @@
+"""
+Collision detection algorithms for 2D geometric shapes.
+
+Collision detection is a fundamental concept in computational geometry, physics
+simulations, and game development. It determines whether two or more geometric
+objects intersect or overlap in space.
+
+This module implements several common 2D collision detection algorithms:
+- Axis-Aligned Bounding Box (AABB) collision detection
+- Circle-circle collision detection
+- Circle-AABB collision detection
+- Point-in-rectangle detection
+- Point-in-circle detection
+
+Reference: https://en.wikipedia.org/wiki/Collision_detection
+Reference: https://developer.mozilla.org/en-US/docs/Games/Techniques/2D_collision_detection
+"""
+
+from __future__ import annotations
+
+from math import sqrt
+
+
+def is_aabb_collision(
+    x1: float, y1: float, w1: float, h1: float,
+    x2: float, y2: float, w2: float, h2: float,
+) -> bool:
+    """
+    Check if two Axis-Aligned Bounding Boxes (AABBs) are colliding.
+
+    Each rectangle is defined by its top-left corner (x, y), width (w),
+    and height (h).
+
+    >>> is_aabb_collision(0, 0, 10, 10, 5, 5, 10, 10)
+    True
+    >>> is_aabb_collision(0, 0, 10, 10, 20, 20, 10, 10)
+    False
+    >>> is_aabb_collision(0, 0, 10, 10, 10, 0, 10, 10)
+    False
+    >>> is_aabb_collision(0, 0, 5, 5, 3, 3, 5, 5)
+    True
+    >>> is_aabb_collision(-5, -5, 10, 10, 0, 0, 10, 10)
+    True
+    >>> is_aabb_collision(0, 0, -1, 10, 5, 5, 10, 10)
+    Traceback (most recent call last):
+        ...
+    ValueError: Width and height must be non-negative
+    >>> is_aabb_collision(0, 0, 10, 10, 5, 5, -1, 10)
+    Traceback (most recent call last):
+        ...
+    ValueError: Width and height must be non-negative
+    """
+    if w1 < 0 or h1 < 0 or w2 < 0 or h2 < 0:
+        raise ValueError("Width and height must be non-negative")
+
+    return x1 < x2 + w2 and x1 + w1 > x2 and y1 < y2 + h2 and y1 + h1 > y2
+
+
+def is_circle_collision(
+    cx1: float, cy1: float, r1: float,
+    cx2: float, cy2: float, r2: float,
+) -> bool:
+    """
+    Check if two circles are colliding.
+
+    Each circle is defined by its center (cx, cy) and radius (r).
+
+    >>> is_circle_collision(0, 0, 5, 8, 0, 5)
+    True
+    >>> is_circle_collision(0, 0, 5, 20, 20, 5)
+    False
+    >>> is_circle_collision(0, 0, 10, 5, 5, 10)
+    True
+    >>> is_circle_collision(0, 0, 1, 3, 0, 1)
+    False
+    >>> is_circle_collision(0, 0, 0, 0, 0, 0)
+    False
+    >>> is_circle_collision(0, 0, -1, 5, 5, 3)
+    Traceback (most recent call last):
+        ...
+    ValueError: Radius must be non-negative
+    """
+    if r1 < 0 or r2 < 0:
+        raise ValueError("Radius must be non-negative")
+
+    distance_squared = (cx2 - cx1) ** 2 + (cy2 - cy1) ** 2
+    radius_sum = r1 + r2
+    return distance_squared < radius_sum ** 2
+
+
+def is_circle_aabb_collision(
+    cx: float, cy: float, r: float,
+    rx: float, ry: float, rw: float, rh: float,
+) -> bool:
+    """
+    Check if a circle and an Axis-Aligned Bounding Box (AABB) are colliding.
+
+    The circle is defined by its center (cx, cy) and radius (r).
+    The rectangle is defined by its top-left corner (rx, ry), width (rw),
+    and height (rh).
+
+    >>> is_circle_aabb_collision(5, 5, 3, 0, 0, 10, 10)
+    True
+    >>> is_circle_aabb_collision(20, 20, 3, 0, 0, 10, 10)
+    False
+    >>> is_circle_aabb_collision(12, 5, 3, 0, 0, 10, 10)
+    True
+    >>> is_circle_aabb_collision(0, 0, 1, 5, 5, 10, 10)
+    False
+    >>> is_circle_aabb_collision(5, 5, -1, 0, 0, 10, 10)
+    Traceback (most recent call last):
+        ...
+    ValueError: Radius must be non-negative
+    >>> is_circle_aabb_collision(5, 5, 3, 0, 0, -1, 10)
+    Traceback (most recent call last):
+        ...
+    ValueError: Width and height must be non-negative
+    """
+    if r < 0:
+        raise ValueError("Radius must be non-negative")
+    if rw < 0 or rh < 0:
+        raise ValueError("Width and height must be non-negative")
+
+    closest_x = max(rx, min(cx, rx + rw))
+    closest_y = max(ry, min(cy, ry + rh))
+
+    distance_squared = (cx - closest_x) ** 2 + (cy - closest_y) ** 2
+    return distance_squared < r**2
+
+
+def is_point_in_rectangle(
+    px: float, py: float,
+    rx: float, ry: float, rw: float, rh: float,
+) -> bool:
+    """
+    Check if a point is inside an Axis-Aligned Bounding Box (rectangle).
+
+    The point is defined by (px, py).
+    The rectangle is defined by its top-left corner (rx, ry), width (rw),
+    and height (rh).
+
+    >>> is_point_in_rectangle(5, 5, 0, 0, 10, 10)
+    True
+    >>> is_point_in_rectangle(15, 15, 0, 0, 10, 10)
+    False
+    >>> is_point_in_rectangle(0, 0, 0, 0, 10, 10)
+    True
+    >>> is_point_in_rectangle(10, 10, 0, 0, 10, 10)
+    False
+    >>> is_point_in_rectangle(-1, 5, 0, 0, 10, 10)
+    False
+    >>> is_point_in_rectangle(5, 5, 0, 0, -1, 10)
+    Traceback (most recent call last):
+        ...
+    ValueError: Width and height must be non-negative
+    """
+    if rw < 0 or rh < 0:
+        raise ValueError("Width and height must be non-negative")
+
+    return rx <= px < rx + rw and ry <= py < ry + rh
+
+
+def is_point_in_circle(
+    px: float, py: float,
+    cx: float, cy: float, r: float,
+) -> bool:
+    """
+    Check if a point is inside a circle.
+
+    The point is defined by (px, py).
+    The circle is defined by its center (cx, cy) and radius (r).
+
+    >>> is_point_in_circle(3, 4, 0, 0, 10)
+    True
+    >>> is_point_in_circle(10, 10, 0, 0, 5)
+    False
+    >>> is_point_in_circle(0, 0, 0, 0, 1)
+    True
+    >>> is_point_in_circle(5, 0, 0, 0, 5)
+    False
+    >>> is_point_in_circle(3, 4, 0, 0, -1)
+    Traceback (most recent call last):
+        ...
+    ValueError: Radius must be non-negative
+    """
+    if r < 0:
+        raise ValueError("Radius must be non-negative")
+
+    distance_squared = (px - cx) ** 2 + (py - cy) ** 2
+    return distance_squared < r**2
+
+
+def detect_all_collisions(
+    objects: list[dict],
+) -> list[tuple[int, int]]:
+    """
+    Detect all pairwise collisions among a list of geometric objects.
+
+    Each object is a dictionary with a 'type' key ('circle' or 'rect') and
+    the corresponding geometric parameters.
+
+    Circle: {'type': 'circle', 'cx': float, 'cy': float, 'r': float}
+    Rectangle: {'type': 'rect', 'x': float, 'y': float, 'w': float, 'h': float}
+
+    Returns a list of tuples (i, j) where objects[i] and objects[j] collide.
+
+    >>> objects = [
+    ...     {'type': 'circle', 'cx': 0, 'cy': 0, 'r': 5},
+    ...     {'type': 'circle', 'cx': 3, 'cy': 0, 'r': 5},
+    ...     {'type': 'circle', 'cx': 100, 'cy': 100, 'r': 1},
+    ... ]
+    >>> detect_all_collisions(objects)
+    [(0, 1)]
+    >>> objects = [
+    ...     {'type': 'rect', 'x': 0, 'y': 0, 'w': 10, 'h': 10},
+    ...     {'type': 'rect', 'x': 5, 'y': 5, 'w': 10, 'h': 10},
+    ...     {'type': 'circle', 'cx': 20, 'cy': 20, 'r': 3},
+    ... ]
+    >>> detect_all_collisions(objects)
+    [(0, 1)]
+    >>> detect_all_collisions([])
+    []
+    """
+    collisions: list[tuple[int, int]] = []
+    for i in range(len(objects)):
+        for j in range(i + 1, len(objects)):
+            if _check_collision(objects[i], objects[j]):
+                collisions.append((i, j))
+    return collisions
+
+
+def _check_collision(obj1: dict, obj2: dict) -> bool:
+    """
+    Check collision between two geometric objects.
+
+    >>> _check_collision(
+    ...     {'type': 'circle', 'cx': 0, 'cy': 0, 'r': 5},
+    ...     {'type': 'circle', 'cx': 3, 'cy': 0, 'r': 5},
+    ... )
+    True
+    >>> _check_collision(
+    ...     {'type': 'rect', 'x': 0, 'y': 0, 'w': 10, 'h': 10},
+    ...     {'type': 'rect', 'x': 20, 'y': 20, 'w': 5, 'h': 5},
+    ... )
+    False
+    """
+    type1, type2 = obj1["type"], obj2["type"]
+
+    if type1 == "circle" and type2 == "circle":
+        return is_circle_collision(
+            obj1["cx"], obj1["cy"], obj1["r"],
+            obj2["cx"], obj2["cy"], obj2["r"],
+        )
+
+    if type1 == "rect" and type2 == "rect":
+        return is_aabb_collision(
+            obj1["x"], obj1["y"], obj1["w"], obj1["h"],
+            obj2["x"], obj2["y"], obj2["w"], obj2["h"],
+        )
+
+    if type1 == "circle" and type2 == "rect":
+        return is_circle_aabb_collision(
+            obj1["cx"], obj1["cy"], obj1["r"],
+            obj2["x"], obj2["y"], obj2["w"], obj2["h"],
+        )
+
+    if type1 == "rect" and type2 == "circle":
+        return is_circle_aabb_collision(
+            obj2["cx"], obj2["cy"], obj2["r"],
+            obj1["x"], obj1["y"], obj1["w"], obj1["h"],
+        )
+
+    msg = f"Unknown object types: {type1}, {type2}"
+    raise ValueError(msg)
+
+
+if __name__ == "__main__":
+    import doctest
+
+    doctest.testmod()
+
+    print("AABB collision:", is_aabb_collision(0, 0, 10, 10, 5, 5, 10, 10))
+    print("Circle collision:", is_circle_collision(0, 0, 5, 8, 0, 5))
+    print("Point in rect:", is_point_in_rectangle(5, 5, 0, 0, 10, 10))
+    print("Point in circle:", is_point_in_circle(3, 4, 0, 0, 10))
+    print(
+        "Circle-AABB collision:",
+        is_circle_aabb_collision(5, 5, 3, 0, 0, 10, 10),
+    )
+    print(
+        "Detect all:",
+        detect_all_collisions(
+            [
+                {"type": "circle", "cx": 0, "cy": 0, "r": 5},
+                {"type": "circle", "cx": 3, "cy": 0, "r": 5},
+                {"type": "rect", "x": 100, "y": 100, "w": 10, "h": 10},
+            ]
+        ),
+    )