1 /*
2 * Copyright (c) 2006-2009 Erin Catto http://www.box2d.org
3 *
4 * This software is provided 'as-is', without any express or implied
5 * warranty. In no event will the authors be held liable for any damages
6 * arising from the use of this software.
7 * Permission is granted to anyone to use this software for any purpose,
8 * including commercial applications, and to alter it and redistribute it
9 * freely, subject to the following restrictions:
10 * 1. The origin of this software must not be misrepresented; you must not
11 * claim that you wrote the original software. If you use this software
12 * in a product, an acknowledgment in the product documentation would be
13 * appreciated but is not required.
14 * 2. Altered source versions must be plainly marked as such, and must not be
15 * misrepresented as being the original software.
16 * 3. This notice may not be removed or altered from any source distribution.
17 */
18
19 #include <Box2D/Collision/Shapes/b2CircleShape.h>
20 #include <new>
21
Clone(b2BlockAllocator * allocator) const22 b2Shape* b2CircleShape::Clone(b2BlockAllocator* allocator) const
23 {
24 void* mem = allocator->Allocate(sizeof(b2CircleShape));
25 b2CircleShape* clone = new (mem) b2CircleShape;
26 *clone = *this;
27 return clone;
28 }
29
GetChildCount() const30 int32 b2CircleShape::GetChildCount() const
31 {
32 return 1;
33 }
34
TestPoint(const b2Transform & transform,const b2Vec2 & p) const35 bool b2CircleShape::TestPoint(const b2Transform& transform, const b2Vec2& p) const
36 {
37 b2Vec2 center = transform.p + b2Mul(transform.q, m_p);
38 b2Vec2 d = p - center;
39 return b2Dot(d, d) <= m_radius * m_radius;
40 }
41
42 // Collision Detection in Interactive 3D Environments by Gino van den Bergen
43 // From Section 3.1.2
44 // x = s + a * r
45 // norm(x) = radius
RayCast(b2RayCastOutput * output,const b2RayCastInput & input,const b2Transform & transform,int32 childIndex) const46 bool b2CircleShape::RayCast(b2RayCastOutput* output, const b2RayCastInput& input,
47 const b2Transform& transform, int32 childIndex) const
48 {
49 B2_NOT_USED(childIndex);
50
51 b2Vec2 position = transform.p + b2Mul(transform.q, m_p);
52 b2Vec2 s = input.p1 - position;
53 float32 b = b2Dot(s, s) - m_radius * m_radius;
54
55 // Solve quadratic equation.
56 b2Vec2 r = input.p2 - input.p1;
57 float32 c = b2Dot(s, r);
58 float32 rr = b2Dot(r, r);
59 float32 sigma = c * c - rr * b;
60
61 // Check for negative discriminant and short segment.
62 if (sigma < 0.0f || rr < b2_epsilon)
63 {
64 return false;
65 }
66
67 // Find the point of intersection of the line with the circle.
68 float32 a = -(c + b2Sqrt(sigma));
69
70 // Is the intersection point on the segment?
71 if (0.0f <= a && a <= input.maxFraction * rr)
72 {
73 a /= rr;
74 output->fraction = a;
75 output->normal = s + a * r;
76 output->normal.Normalize();
77 return true;
78 }
79
80 return false;
81 }
82
ComputeAABB(b2AABB * aabb,const b2Transform & transform,int32 childIndex) const83 void b2CircleShape::ComputeAABB(b2AABB* aabb, const b2Transform& transform, int32 childIndex) const
84 {
85 B2_NOT_USED(childIndex);
86
87 b2Vec2 p = transform.p + b2Mul(transform.q, m_p);
88 aabb->lowerBound.Set(p.x - m_radius, p.y - m_radius);
89 aabb->upperBound.Set(p.x + m_radius, p.y + m_radius);
90 }
91
ComputeMass(b2MassData * massData,float32 density) const92 void b2CircleShape::ComputeMass(b2MassData* massData, float32 density) const
93 {
94 massData->mass = density * b2_pi * m_radius * m_radius;
95 massData->center = m_p;
96
97 // inertia about the local origin
98 massData->I = massData->mass * (0.5f * m_radius * m_radius + b2Dot(m_p, m_p));
99 }
100