1 files changed, 259 insertions, 0 deletions
diff --git a/Source/external/Box2D/Rope/b2Rope.cpp b/Source/external/Box2D/Rope/b2Rope.cpp
new file mode 100644
index 0000000..847b11d
--- /dev/null
+++ b/Source/external/Box2D/Rope/b2Rope.cpp
@@ -0,0 +1,259 @@
+/*
+* Copyright (c) 2011 Erin Catto http://box2d.org
+*
+* 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/Rope/b2Rope.h"
+#include "Box2D/Common/b2Draw.h"
+
+b2Rope::b2Rope()
+{
+	m_count = 0;
+	m_ps = nullptr;
+	m_p0s = nullptr;
+	m_vs = nullptr;
+	m_ims = nullptr;
+	m_Ls = nullptr;
+	m_as = nullptr;
+	m_gravity.SetZero();
+	m_k2 = 1.0f;
+	m_k3 = 0.1f;
+}
+
+b2Rope::~b2Rope()
+{
+	b2Free(m_ps);
+	b2Free(m_p0s);
+	b2Free(m_vs);
+	b2Free(m_ims);
+	b2Free(m_Ls);
+	b2Free(m_as);
+}
+
+void b2Rope::Initialize(const b2RopeDef* def)
+{
+	b2Assert(def->count >= 3);
+	m_count = def->count;
+	m_ps = (b2Vec2*)b2Alloc(m_count * sizeof(b2Vec2));
+	m_p0s = (b2Vec2*)b2Alloc(m_count * sizeof(b2Vec2));
+	m_vs = (b2Vec2*)b2Alloc(m_count * sizeof(b2Vec2));
+	m_ims = (float32*)b2Alloc(m_count * sizeof(float32));
+
+	for (int32 i = 0; i < m_count; ++i)
+	{
+		m_ps[i] = def->vertices[i];
+		m_p0s[i] = def->vertices[i];
+		m_vs[i].SetZero();
+
+		float32 m = def->masses[i];
+		if (m > 0.0f)
+		{
+			m_ims[i] = 1.0f / m;
+		}
+		else
+		{
+			m_ims[i] = 0.0f;
+		}
+	}
+
+	int32 count2 = m_count - 1;
+	int32 count3 = m_count - 2;
+	m_Ls = (float32*)b2Alloc(count2 * sizeof(float32));
+	m_as = (float32*)b2Alloc(count3 * sizeof(float32));
+
+	for (int32 i = 0; i < count2; ++i)
+	{
+		b2Vec2 p1 = m_ps[i];
+		b2Vec2 p2 = m_ps[i+1];
+		m_Ls[i] = b2Distance(p1, p2);
+	}
+
+	for (int32 i = 0; i < count3; ++i)
+	{
+		b2Vec2 p1 = m_ps[i];
+		b2Vec2 p2 = m_ps[i + 1];
+		b2Vec2 p3 = m_ps[i + 2];
+
+		b2Vec2 d1 = p2 - p1;
+		b2Vec2 d2 = p3 - p2;
+
+		float32 a = b2Cross(d1, d2);
+		float32 b = b2Dot(d1, d2);
+
+		m_as[i] = b2Atan2(a, b);
+	}
+
+	m_gravity = def->gravity;
+	m_damping = def->damping;
+	m_k2 = def->k2;
+	m_k3 = def->k3;
+}
+
+void b2Rope::Step(float32 h, int32 iterations)
+{
+	if (h == 0.0)
+	{
+		return;
+	}
+
+	float32 d = expf(- h * m_damping);
+
+	for (int32 i = 0; i < m_count; ++i)
+	{
+		m_p0s[i] = m_ps[i];
+		if (m_ims[i] > 0.0f)
+		{
+			m_vs[i] += h * m_gravity;
+		}
+		m_vs[i] *= d;
+		m_ps[i] += h * m_vs[i];
+
+	}
+
+	for (int32 i = 0; i < iterations; ++i)
+	{
+		SolveC2();
+		SolveC3();
+		SolveC2();
+	}
+
+	float32 inv_h = 1.0f / h;
+	for (int32 i = 0; i < m_count; ++i)
+	{
+		m_vs[i] = inv_h * (m_ps[i] - m_p0s[i]);
+	}
+}
+
+void b2Rope::SolveC2()
+{
+	int32 count2 = m_count - 1;
+
+	for (int32 i = 0; i < count2; ++i)
+	{
+		b2Vec2 p1 = m_ps[i];
+		b2Vec2 p2 = m_ps[i + 1];
+
+		b2Vec2 d = p2 - p1;
+		float32 L = d.Normalize();
+
+		float32 im1 = m_ims[i];
+		float32 im2 = m_ims[i + 1];
+
+		if (im1 + im2 == 0.0f)
+		{
+			continue;
+		}
+
+		float32 s1 = im1 / (im1 + im2);
+		float32 s2 = im2 / (im1 + im2);
+
+		p1 -= m_k2 * s1 * (m_Ls[i] - L) * d;
+		p2 += m_k2 * s2 * (m_Ls[i] - L) * d;
+
+		m_ps[i] = p1;
+		m_ps[i + 1] = p2;
+	}
+}
+
+void b2Rope::SetAngle(float32 angle)
+{
+	int32 count3 = m_count - 2;
+	for (int32 i = 0; i < count3; ++i)
+	{
+		m_as[i] = angle;
+	}
+}
+
+void b2Rope::SolveC3()
+{
+	int32 count3 = m_count - 2;
+
+	for (int32 i = 0; i < count3; ++i)
+	{
+		b2Vec2 p1 = m_ps[i];
+		b2Vec2 p2 = m_ps[i + 1];
+		b2Vec2 p3 = m_ps[i + 2];
+
+		float32 m1 = m_ims[i];
+		float32 m2 = m_ims[i + 1];
+		float32 m3 = m_ims[i + 2];
+
+		b2Vec2 d1 = p2 - p1;
+		b2Vec2 d2 = p3 - p2;
+
+		float32 L1sqr = d1.LengthSquared();
+		float32 L2sqr = d2.LengthSquared();
+
+		if (L1sqr * L2sqr == 0.0f)
+		{
+			continue;
+		}
+
+		float32 a = b2Cross(d1, d2);
+		float32 b = b2Dot(d1, d2);
+
+		float32 angle = b2Atan2(a, b);
+
+		b2Vec2 Jd1 = (-1.0f / L1sqr) * d1.Skew();
+		b2Vec2 Jd2 = (1.0f / L2sqr) * d2.Skew();
+
+		b2Vec2 J1 = -Jd1;
+		b2Vec2 J2 = Jd1 - Jd2;
+		b2Vec2 J3 = Jd2;
+
+		float32 mass = m1 * b2Dot(J1, J1) + m2 * b2Dot(J2, J2) + m3 * b2Dot(J3, J3);
+		if (mass == 0.0f)
+		{
+			continue;
+		}
+
+		mass = 1.0f / mass;
+
+		float32 C = angle - m_as[i];
+
+		while (C > b2_pi)
+		{
+			angle -= 2 * b2_pi;
+			C = angle - m_as[i];
+		}
+
+		while (C < -b2_pi)
+		{
+			angle += 2.0f * b2_pi;
+			C = angle - m_as[i];
+		}
+
+		float32 impulse = - m_k3 * mass * C;
+
+		p1 += (m1 * impulse) * J1;
+		p2 += (m2 * impulse) * J2;
+		p3 += (m3 * impulse) * J3;
+
+		m_ps[i] = p1;
+		m_ps[i + 1] = p2;
+		m_ps[i + 2] = p3;
+	}
+}
+
+void b2Rope::Draw(b2Draw* draw) const
+{
+	b2Color c(0.4f, 0.5f, 0.7f);
+
+	for (int32 i = 0; i < m_count - 1; ++i)
+	{
+		draw->DrawSegment(m_ps[i], m_ps[i+1], c);
+	}
+}