b2CircleShape.cpp
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上传日期:2022-01-07
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- /*
- * Copyright (c) 2006-2009 Erin Catto http://www.gphysics.com
- *
- * This software is provided 'as-is', without any express or implied
- * warranty. In no event will the authors be held liable for any damages
- * arising from the use of this software.
- * Permission is granted to anyone to use this software for any purpose,
- * including commercial applications, and to alter it and redistribute it
- * freely, subject to the following restrictions:
- * 1. The origin of this software must not be misrepresented; you must not
- * claim that you wrote the original software. If you use this software
- * in a product, an acknowledgment in the product documentation would be
- * appreciated but is not required.
- * 2. Altered source versions must be plainly marked as such, and must not be
- * misrepresented as being the original software.
- * 3. This notice may not be removed or altered from any source distribution.
- */
- #include <Box2D/Collision/Shapes/b2CircleShape.h>
- #include <new>
- b2Shape* b2CircleShape::Clone(b2BlockAllocator* allocator) const
- {
- void* mem = allocator->Allocate(sizeof(b2CircleShape));
- b2CircleShape* clone = new (mem) b2CircleShape;
- *clone = *this;
- return clone;
- }
- bool b2CircleShape::TestPoint(const b2Transform& transform, const b2Vec2& p) const
- {
- b2Vec2 center = transform.position + b2Mul(transform.R, m_p);
- b2Vec2 d = p - center;
- return b2Dot(d, d) <= m_radius * m_radius;
- }
- // Collision Detection in Interactive 3D Environments by Gino van den Bergen
- // From Section 3.1.2
- // x = s + a * r
- // norm(x) = radius
- bool b2CircleShape::RayCast(b2RayCastOutput* output, const b2RayCastInput& input, const b2Transform& transform) const
- {
- b2Vec2 position = transform.position + b2Mul(transform.R, m_p);
- b2Vec2 s = input.p1 - position;
- float32 b = b2Dot(s, s) - m_radius * m_radius;
- // Solve quadratic equation.
- b2Vec2 r = input.p2 - input.p1;
- float32 c = b2Dot(s, r);
- float32 rr = b2Dot(r, r);
- float32 sigma = c * c - rr * b;
- // Check for negative discriminant and short segment.
- if (sigma < 0.0f || rr < b2_epsilon)
- {
- return false;
- }
- // Find the point of intersection of the line with the circle.
- float32 a = -(c + b2Sqrt(sigma));
- // Is the intersection point on the segment?
- if (0.0f <= a && a <= input.maxFraction * rr)
- {
- a /= rr;
- output->fraction = a;
- output->normal = s + a * r;
- output->normal.Normalize();
- return true;
- }
- return false;
- }
- void b2CircleShape::ComputeAABB(b2AABB* aabb, const b2Transform& transform) const
- {
- b2Vec2 p = transform.position + b2Mul(transform.R, m_p);
- aabb->lowerBound.Set(p.x - m_radius, p.y - m_radius);
- aabb->upperBound.Set(p.x + m_radius, p.y + m_radius);
- }
- void b2CircleShape::ComputeMass(b2MassData* massData, float32 density) const
- {
- massData->mass = density * b2_pi * m_radius * m_radius;
- massData->center = m_p;
- // inertia about the local origin
- massData->I = massData->mass * (0.5f * m_radius * m_radius + b2Dot(m_p, m_p));
- }