preparation

examples/testbed/tests/table_cloth.h

@@ -41,6 +41,7 @@ public:
 		b3ClothDef def;
 		def.mesh = &m_rectangleClothMesh;
 		def.density = 0.2f;
+		def.bending = 10000.0f;
 		def.structural = 10000.0f;
 		def.damping = 0.0f;
 

include/bounce/dynamics/cloth/bend_force.h

@@ -0,0 +1,158 @@
+/*
+* Copyright (c) 2016-2016 Irlan Robson http://www.irlan.net
+*
+* 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.
+*/
+
+#ifndef B3_BEND_FORCE_H
+#define B3_BEND_FORCE_H
+
+#include <bounce/dynamics/cloth/force.h>
+
+struct b3BendForceDef : public b3ForceDef
+{
+	b3BendForceDef()
+	{
+		type = e_bendForce;
+		p1 = nullptr;
+		p2 = nullptr;
+		p3 = nullptr;
+		p4 = nullptr;
+		restDistance = 0.0f;
+		restAngle = 0.0f;
+		structural = 0.0f;
+		damping = 0.0f;
+	}
+
+	// 
+	void Initialize(b3Particle* particle1, b3Particle* particle2, b3Particle* particle3, b3Particle* particle4, 
+		float32 structuralStiffness, float32 dampingStiffness);
+
+	// Particle 1
+	b3Particle* p1;
+
+	// Particle 2
+	b3Particle* p2;
+
+	// Particle 3
+	b3Particle* p3;
+	
+	// Particle 4
+	b3Particle* p4;
+	
+	// Rest distance
+	float32 restDistance;
+	
+	// Rest angle
+	float32 restAngle;
+
+	// Structural stiffness
+	float32 structural;
+
+	// Damping stiffness
+	float32 damping;
+};
+
+// 
+class b3BendForce : public b3Force
+{
+public:
+	b3Particle* GetParticle1();
+
+	b3Particle* GetParticle2();
+
+	b3Particle* GetParticle3();
+
+	b3Particle* GetParticle4();
+	
+	float32 GetRestDistance() const;
+	
+	float32 GetRestAngle() const;
+
+	float32 GetStructuralStiffness() const;
+
+	float32 GetDampingStiffness() const;
+private:
+	friend class b3Force;
+	friend class b3Cloth;
+
+	b3BendForce(const b3BendForceDef* def);
+	~b3BendForce();
+
+	void Apply(const b3ClothSolverData* data);
+
+	// Solver shared
+
+	// Particle 1
+	b3Particle* m_p1;
+
+	// Particle 2
+	b3Particle* m_p2;
+
+	// Particle 3
+	b3Particle* m_p3;
+	
+	// Particle 4
+	b3Particle* m_p4;
+
+	// Rest distance
+	float32 m_L0;
+
+	// Rest angle
+	float32 m_angle0;
+	
+	// Structural stiffness
+	float32 m_ks;
+
+	// Structural stiffness
+	float32 m_kd;
+};
+
+inline b3Particle* b3BendForce::GetParticle1()
+{
+	return m_p1;
+}
+
+inline b3Particle* b3BendForce::GetParticle2()
+{
+	return m_p2;
+}
+
+inline b3Particle* b3BendForce::GetParticle3()
+{
+	return m_p3;
+}
+
+inline b3Particle* b3BendForce::GetParticle4()
+{
+	return m_p4;
+}
+
+inline float32 b3BendForce::GetRestAngle() const
+{
+	return m_angle0;
+}
+
+inline float32 b3BendForce::GetStructuralStiffness() const
+{
+	return m_ks;
+}
+
+inline float32 b3BendForce::GetDampingStiffness() const
+{
+	return m_kd;
+}
+
+#endif

include/bounce/dynamics/cloth/force.h

@@ -31,6 +31,7 @@ enum b3ForceType
 {
 	e_frictionForce,
 	e_springForce,
+	e_bendForce,
 };
 
 struct b3ForceDef

include/bounce/dynamics/cloth/particle.h

@@ -143,6 +143,7 @@ private:
 	friend class b3ClothSolver;
 	friend class b3Force;
 	friend class b3SpringForce;
+	friend class b3BendForce;
 	friend class b3FrictionForce;
 
 	b3Particle(const b3ParticleDef& def, b3Cloth* cloth);

src/bounce/dynamics/cloth/bend_force.cpp

@@ -0,0 +1,128 @@
+/*
+* Copyright (c) 2016-2016 Irlan Robson http://www.irlan.net
+*
+* 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 <bounce/dynamics/cloth/bend_force.h>
+#include <bounce/dynamics/cloth/particle.h>
+#include <bounce/dynamics/cloth/cloth_solver.h>
+#include <bounce/dynamics/cloth/dense_vec3.h>
+#include <bounce/dynamics/cloth/sparse_sym_mat33.h>
+
+void b3BendForceDef::Initialize(b3Particle* particle1, b3Particle* particle2, b3Particle* particle3, b3Particle* particle4, float32 structuralStiffness, float32 dampingStiffness)
+{
+	type = e_bendForce;
+	p1 = particle1;
+	p2 = particle2;
+	p3 = particle3;
+	p4 = particle4;
+	
+	b3Vec3 x1 = p1->GetPosition();
+	b3Vec3 x2 = p2->GetPosition();
+	b3Vec3 x3 = p3->GetPosition();
+	b3Vec3 x4 = p4->GetPosition();
+
+	restDistance = b3Distance(x2, x3);
+	structural = structuralStiffness;
+	damping = dampingStiffness;
+}
+
+b3BendForce::b3BendForce(const b3BendForceDef* def)
+{
+	m_type = e_bendForce;
+	m_p1 = def->p1;
+	m_p2 = def->p2;
+	m_p3 = def->p3;
+	m_p4 = def->p4;
+	m_L0 = def->restDistance;
+	m_angle0 = def->restAngle;
+	m_ks = def->structural;
+	m_kd = def->damping;
+}
+
+b3BendForce::~b3BendForce()
+{
+
+}
+
+void b3BendForce::Apply(const b3ClothSolverData* data)
+{
+	b3DenseVec3& x = *data->x;
+	b3DenseVec3& v = *data->v;
+	b3DenseVec3& f = *data->f;
+	b3SparseSymMat33& dfdx = *data->dfdx;
+	b3SparseSymMat33& dfdv = *data->dfdv;
+
+	u32 i1 = m_p2->m_solverId;
+	u32 i2 = m_p3->m_solverId;
+
+	b3Vec3 x1 = x[i1];
+	b3Vec3 v1 = v[i1];
+
+	b3Vec3 x2 = x[i2];
+	b3Vec3 v2 = v[i2];
+
+	b3Mat33 I; I.SetIdentity();
+
+	b3Vec3 ef; ef.SetZero();
+
+	if (m_ks > 0.0f)
+	{
+		b3Vec3 dx = x1 - x2;
+
+		float32 L = b3Length(dx);
+
+		if (L >= m_L0)
+		{
+			// Apply tension
+			b3Vec3 n = dx / L;
+
+			ef += -m_ks * (L - m_L0) * n;
+
+			// Jacobian
+			b3Mat33 Jx11 = -m_ks * (b3Outer(dx, dx) + (1.0f - m_L0 / L) * (I - b3Outer(dx, dx)));
+			b3Mat33 Jx12 = -Jx11;
+			//b3Mat33 Jx21 = Jx12;
+			b3Mat33 Jx22 = Jx11;
+
+			dfdx(i1, i1) += Jx11;
+			dfdx(i1, i2) += Jx12;
+			//dfdx(i2, i1) += Jx21;
+			dfdx(i2, i2) += Jx22;
+		}
+	}
+
+	if (m_kd > 0.0f)
+	{
+		// Apply damping
+		b3Vec3 dv = v1 - v2;
+
+		ef += -m_kd * dv;
+
+		b3Mat33 Jv11 = -m_kd * I;
+		b3Mat33 Jv12 = -Jv11;
+		//b3Mat33 Jv21 = Jv12;
+		b3Mat33 Jv22 = Jv11;
+
+		dfdv(i1, i1) += Jv11;
+		dfdv(i1, i2) += Jv12;
+		//dfdv(i2, i1) += Jv21;
+		dfdv(i2, i2) += Jv22;
+	}
+
+	f[i1] += ef;
+	f[i2] -= ef;
+}

src/bounce/dynamics/cloth/cloth.cpp

@@ -21,6 +21,7 @@
 #include <bounce/dynamics/cloth/particle.h>
 #include <bounce/dynamics/cloth/force.h>
 #include <bounce/dynamics/cloth/spring_force.h>
+#include <bounce/dynamics/cloth/bend_force.h>
 #include <bounce/dynamics/cloth/cloth_solver.h>
 #include <bounce/dynamics/world.h>
 #include <bounce/dynamics/world_listeners.h>
@@ -30,10 +31,6 @@
 #include <bounce/common/memory/stack_allocator.h>
 #include <bounce/common/draw.h>
 
-#define B3_FORCE_THRESHOLD 0.005f
-
-#define B3_CLOTH_BENDING 0
-
 static B3_FORCE_INLINE u32 b3NextIndex(u32 i)
 {
 	return i + 1 < 3 ? i + 1 : 0;
@@ -204,24 +201,22 @@ b3Cloth::b3Cloth(const b3ClothDef& def, b3World* world) : m_particleBlocks(sizeo
 		CreateForce(fd);
 	}
 
-#if B3_CLOTH_BENDING
-
 	// Bending
 	for (u32 i = 0; i < sharedCount; ++i)
 	{
 		b3SharedEdge* e = sharedEdges + i;
 
-		b3Particle* p1 = m->particles[e->nsv1];
-		b3Particle* p2 = m->particles[e->nsv2];
+		b3Particle* p1 = m->particles[e->v1];
+		b3Particle* p2 = m->particles[e->v2];
+		b3Particle* p3 = m->particles[e->nsv1];
+		b3Particle* p4 = m->particles[e->nsv2];
 		
-		b3SpringForceDef fd;
-		fd.Initialize(p1, p2, def.bending, def.damping);
+		b3BendForceDef fd;
+		fd.Initialize(p1, p2, p3, p4, def.bending, def.damping);
 
 		CreateForce(fd);
 	}
 
-#endif
-
 	allocator->Free(sharedEdges);
 	allocator->Free(uniqueEdges);
 
@@ -579,7 +574,7 @@ void b3Cloth::UpdateContacts()
 			// The contact persists
 
 			// Has the contact constraint been satisfied?
-			if (c0.Fn <= -B3_FORCE_THRESHOLD)
+			if (c0.Fn <= 0.0f)
 			{
 				// Contact force is attractive.
 

src/bounce/dynamics/cloth/force.cpp

@@ -18,6 +18,7 @@
 
 #include <bounce/dynamics/cloth/force.h>
 #include <bounce/dynamics/cloth/spring_force.h>
+#include <bounce/dynamics/cloth/bend_force.h>
 
 b3Force* b3Force::Create(const b3ForceDef* def)
 {
@@ -30,6 +31,12 @@ b3Force* b3Force::Create(const b3ForceDef* def)
 		force = new (block) b3SpringForce((b3SpringForceDef*)def);
 		break;
 	}
+	case e_bendForce:
+	{
+		void* block = b3Alloc(sizeof(b3BendForce));
+		force = new (block) b3BendForce((b3BendForceDef*)def);
+		break;
+	}
 	default:
 	{
 		B3_ASSERT(false);
@@ -53,6 +60,13 @@ void b3Force::Destroy(b3Force* force)
 		b3Free(force);
 		break;
 	}
+	case e_bendForce:
+	{
+		b3BendForce* o = (b3BendForce*)force;
+		o->~b3BendForce();
+		b3Free(force);
+		break;
+	}
 	default:
 	{
 		B3_ASSERT(false);