box and circle collisions c 2b 2b

1bool AABBvsCircle( Manifold *m )
2{
3  // Setup a couple pointers to each object
4  Object *A = m->A
5  Object *B = m->B
6 
7  // Vector from A to B
8  Vec2 n = B->pos - A->pos
9 
10  // Closest point on A to center of B
11  Vec2 closest = n
12 
13  // Calculate half extents along each axis
14  float x_extent = (A->aabb.max.x - A->aabb.min.x) / 2
15  float y_extent = (A->aabb.max.y - A->aabb.min.y) / 2
16 
17  // Clamp point to edges of the AABB
18  closest.x = Clamp( -x_extent, x_extent, closest.x )
19  closest.y = Clamp( -y_extent, y_extent, closest.y )
20 
21  bool inside = false
22 
23  // Circle is inside the AABB, so we need to clamp the circle's center
24  // to the closest edge
25  if(n == closest)
26  {
27    inside = true
28 
29    // Find closest axis
30    if(abs( n.x ) > abs( n.y ))
31    {
32      // Clamp to closest extent
33      if(closest.x > 0)
34        closest.x = x_extent
35      else
36        closest.x = -x_extent
37    }
38 
39    // y axis is shorter
40    else
41    {
42      // Clamp to closest extent
43      if(closest.y > 0)
44        closest.y = y_extent
45      else
46        closest.y = -y_extent
47    }
48  }
49 
50  Vec2 normal = n - closest
51  real d = normal.LengthSquared( )
52  real r = B->radius
53 
54  // Early out of the radius is shorter than distance to closest point and
55  // Circle not inside the AABB
56  if(d > r * r && !inside)
57    return false
58 
59  // Avoided sqrt until we needed
60  d = sqrt( d )
61 
62  // Collision normal needs to be flipped to point outside if circle was
63  // inside the AABB
64  if(inside)
65  {
66    m->normal = -n
67    m->penetration = r - d
68  }
69  else
70  {
71    m->normal = n
72    m->penetration = r - d
73  }
74 
75  return true
76}
77