100 lines
3.0 KiB
C++
100 lines
3.0 KiB
C++
/*
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* Copyright (c) 2006-2009 Erin Catto http://www.box2d.org
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*
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* This software is provided 'as-is', without any express or implied
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* warranty. In no event will the authors be held liable for any damages
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* arising from the use of this software.
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* Permission is granted to anyone to use this software for any purpose,
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* including commercial applications, and to alter it and redistribute it
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* freely, subject to the following restrictions:
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* 1. The origin of this software must not be misrepresented; you must not
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* claim that you wrote the original software. If you use this software
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* in a product, an acknowledgment in the product documentation would be
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* appreciated but is not required.
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* 2. Altered source versions must be plainly marked as such, and must not be
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* misrepresented as being the original software.
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* 3. This notice may not be removed or altered from any source distribution.
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*/
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#include "Box2D/Collision/Shapes/b2CircleShape.h"
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#include <new>
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b2Shape* b2CircleShape::Clone(b2BlockAllocator* allocator) const
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{
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void* mem = allocator->Allocate(sizeof(b2CircleShape));
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b2CircleShape* clone = new (mem) b2CircleShape;
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*clone = *this;
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return clone;
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}
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int32 b2CircleShape::GetChildCount() const
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{
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return 1;
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}
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bool b2CircleShape::TestPoint(const b2Transform& transform, const b2Vec2& p) const
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{
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b2Vec2 center = transform.p + b2Mul(transform.q, m_p);
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b2Vec2 d = p - center;
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return b2Dot(d, d) <= m_radius * m_radius;
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}
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// Collision Detection in Interactive 3D Environments by Gino van den Bergen
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// From Section 3.1.2
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// x = s + a * r
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// norm(x) = radius
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bool b2CircleShape::RayCast(b2RayCastOutput* output, const b2RayCastInput& input,
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const b2Transform& transform, int32 childIndex) const
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{
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B2_NOT_USED(childIndex);
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b2Vec2 position = transform.p + b2Mul(transform.q, m_p);
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b2Vec2 s = input.p1 - position;
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float32 b = b2Dot(s, s) - m_radius * m_radius;
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// Solve quadratic equation.
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b2Vec2 r = input.p2 - input.p1;
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float32 c = b2Dot(s, r);
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float32 rr = b2Dot(r, r);
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float32 sigma = c * c - rr * b;
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// Check for negative discriminant and short segment.
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if (sigma < 0.0f || rr < b2_epsilon)
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{
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return false;
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}
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// Find the point of intersection of the line with the circle.
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float32 a = -(c + b2Sqrt(sigma));
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// Is the intersection point on the segment?
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if (0.0f <= a && a <= input.maxFraction * rr)
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{
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a /= rr;
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output->fraction = a;
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output->normal = s + a * r;
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output->normal.Normalize();
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return true;
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}
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return false;
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}
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void b2CircleShape::ComputeAABB(b2AABB* aabb, const b2Transform& transform, int32 childIndex) const
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{
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B2_NOT_USED(childIndex);
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b2Vec2 p = transform.p + b2Mul(transform.q, m_p);
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aabb->lowerBound.Set(p.x - m_radius, p.y - m_radius);
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aabb->upperBound.Set(p.x + m_radius, p.y + m_radius);
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}
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void b2CircleShape::ComputeMass(b2MassData* massData, float32 density) const
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{
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massData->mass = density * b2_pi * m_radius * m_radius;
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massData->center = m_p;
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// inertia about the local origin
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massData->I = massData->mass * (0.5f * m_radius * m_radius + b2Dot(m_p, m_p));
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}
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