Warning, file /education/gcompris/external/qml-box2d/Box2D/Rope/b2Rope.cpp was not indexed or was modified since last indexation (in which case cross-reference links may be missing, inaccurate or erroneous).

 /*
 * 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 = NULL;
     m_p0s = NULL;
     m_vs = NULL;
     m_ims = NULL;
     m_Ls = NULL;
     m_as = NULL;
     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);
     }
 }