text: // MIT License
  
  // Copyright (c) 2019 Erin Catto
  
  // Permission is hereby granted, free of charge, to any person obtaining a copy
  // of this software and associated documentation files (the "Software"), to deal
  // in the Software without restriction, including without limitation the rights
  // to use, copy, modify, merge, publish, distribute, sublicense, and/or sell
  // copies of the Software, and to permit persons to whom the Software is
  // furnished to do so, subject to the following conditions:
  
  // The above copyright notice and this permission notice shall be included in all
  // copies or substantial portions of the Software.
  
  // THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
  // IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
  // FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE
  // AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
  // LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM,
  // OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE
  // SOFTWARE.
  
  #include "box2d/b2_chain_shape.h"
  #include "box2d/b2_edge_shape.h"
  
  #include "box2d/b2_block_allocator.h"
  
  #include <new>
  #include <string.h>
  
  b2ChainShape::~b2ChainShape()
  {
  	Clear();
  }
  
  void b2ChainShape::Clear()
  {
  	b2Free(m_vertices);
  	m_vertices = nullptr;
  	m_count = 0;
  }
  
  void b2ChainShape::CreateLoop(const b2Vec2* vertices, int32 count)
  {
  	b2Assert(m_vertices == nullptr && m_count == 0);
  	b2Assert(count >= 3);
  	if (count < 3)
  	{
  		return;
  	}
  
  	for (int32 i = 1; i < count; ++i)
  	{
  		b2Vec2 v1 = vertices[i-1];
  		b2Vec2 v2 = vertices[i];
  		// If the code crashes here, it means your vertices are too close together.
  		b2Assert(b2DistanceSquared(v1, v2) > b2_linearSlop * b2_linearSlop);
  	}
  
  	m_count = count + 1;
  	m_vertices = (b2Vec2*)b2Alloc(m_count * sizeof(b2Vec2));
  	memcpy(m_vertices, vertices, count * sizeof(b2Vec2));
  	m_vertices[count] = m_vertices[0];
  	m_prevVertex = m_vertices[m_count - 2];
  	m_nextVertex = m_vertices[1];
  }
  
  void b2ChainShape::CreateChain(const b2Vec2* vertices, int32 count,	const b2Vec2& prevVertex, const b2Vec2& nextVertex)
  {
  	b2Assert(m_vertices == nullptr && m_count == 0);
  	b2Assert(count >= 2);
  	for (int32 i = 1; i < count; ++i)
  	{
  		// If the code crashes here, it means your vertices are too close together.
  		b2Assert(b2DistanceSquared(vertices[i-1], vertices[i]) > b2_linearSlop * b2_linearSlop);
  	}
  
  	m_count = count;
  	m_vertices = (b2Vec2*)b2Alloc(count * sizeof(b2Vec2));
  	memcpy(m_vertices, vertices, m_count * sizeof(b2Vec2));
  
  	m_prevVertex = prevVertex;
  	m_nextVertex = nextVertex;
  }
  
  b2Shape* b2ChainShape::Clone(b2BlockAllocator* allocator) const
  {
  	void* mem = allocator->Allocate(sizeof(b2ChainShape));
  	b2ChainShape* clone = new (mem) b2ChainShape;
  	clone->CreateChain(m_vertices, m_count, m_prevVertex, m_nextVertex);
  	return clone;
  }
  
  int32 b2ChainShape::GetChildCount() const
  {
  	// edge count = vertex count - 1
  	return m_count - 1;
  }
  
  void b2ChainShape::GetChildEdge(b2EdgeShape* edge, int32 index) const
  {
  	b2Assert(0 <= index && index < m_count - 1);
  	edge->m_type = b2Shape::e_edge;
  	edge->m_radius = m_radius;
  
  	edge->m_vertex1 = m_vertices[index + 0];
  	edge->m_vertex2 = m_vertices[index + 1];
  	edge->m_oneSided = true;
  
  	if (index > 0)
  	{
  		edge->m_vertex0 = m_vertices[index - 1];
  	}
  	else
  	{
  		edge->m_vertex0 = m_prevVertex;
  	}
  
  	if (index < m_count - 2)
  	{
  		edge->m_vertex3 = m_vertices[index + 2];
  	}
  	else
  	{
  		edge->m_vertex3 = m_nextVertex;
  	}
  }
  
  bool b2ChainShape::TestPoint(const b2Transform& xf, const b2Vec2& p) const
  {
  	B2_NOT_USED(xf);
  	B2_NOT_USED(p);
  	return false;
  }
  
  void b2ChainShape::ComputeDistance(
  	const b2Transform& xf,
  	const b2Vec2& p,
  	float* distance,
  	b2Vec2* normal,
  	int32 childIndex) const
  {
  	b2EdgeShape edge;
  	GetChildEdge(&edge, childIndex);
  	edge.ComputeDistance(xf, p, distance, normal, 0);
  }
  
  bool b2ChainShape::RayCast(b2RayCastOutput* output, const b2RayCastInput& input,
                             const b2Transform& xf, int32 childIndex) const
  {
  	b2Assert(childIndex < m_count);
  
  	b2EdgeShape edgeShape;
  
  	int32 i1 = childIndex;
  	int32 i2 = childIndex + 1;
  	if (i2 == m_count)
  	{
  		i2 = 0;
  	}
  
  	edgeShape.m_vertex1 = m_vertices[i1];
  	edgeShape.m_vertex2 = m_vertices[i2];
  
  	return edgeShape.RayCast(output, input, xf, 0);
  }
  
  void b2ChainShape::ComputeAABB(b2AABB* aabb, const b2Transform& xf, int32 childIndex) const
  {
  	b2Assert(childIndex < m_count);
  
  	int32 i1 = childIndex;
  	int32 i2 = childIndex + 1;
  	if (i2 == m_count)
  	{
  		i2 = 0;
  	}
  
  	b2Vec2 v1 = b2Mul(xf, m_vertices[i1]);
  	b2Vec2 v2 = b2Mul(xf, m_vertices[i2]);
  
  	aabb->lowerBound = b2Min(v1, v2);
  	aabb->upperBound = b2Max(v1, v2);
  }
  
  void b2ChainShape::ComputeMass(b2MassData* massData, float density) const
  {
  	B2_NOT_USED(density);
  
  	massData->mass = 0.0f;
  	massData->center.SetZero();
  	massData->I = 0.0f;
  }
  