bugfixes and improvements

Bugfixes:

Simplify and correct one derivation of a second derivative of energy function.

Clear dynamic variables for static shapes

Invalidate contact for a particle when its type switches from dynamic to static

Improvements:

Allow user to apply force to a particle

Allow user to displace a particle

Compute kinetic energy

Store the mass of each particle, not only its inverse. It can improve performance because the solver needs the masses most of the time for computations

Add some code to find shared and non-shared edges. These algorithms don't work for non-manifold meshes

Remove some unecessary temporaries decreasing code readability

include/bounce/dynamics/cloth/spring_cloth.h

@@ -69,8 +69,17 @@ struct b3SpringClothDef
 	b3Vec3 gravity;
 };
 
+enum b3SpringType
+{
+	e_strechSpring,
+	e_bendSpring
+};
+
 struct b3Spring
 {
+	// Spring type
+	b3SpringType type;
+
 	// Mass 1
 	u32 i1;
 
@@ -124,6 +133,9 @@ public:
 	//
 	void Initialize(const b3SpringClothDef& def);
 
+	//
+	b3Mesh* GetMesh() const;
+
 	//
 	void SetGravity(const b3Vec3& gravity);
 
@@ -136,6 +148,18 @@ public:
 	//
 	b3MassType GetType(u32 i) const;
 
+	// Note, the position will be changed only after performing a time step.
+	void SetPosition(u32 i, const b3Vec3& translation);
+
+	//
+	const b3Vec3& GetPosition(u32 i) const;
+
+	//
+	void ApplyForce(u32 i, const b3Vec3& force);
+
+	//
+	float32 GetKineticEnergy() const;
+	
 	//
 	void AddShape(b3Shape* shape);
 
@@ -173,6 +197,7 @@ protected:
 	b3Vec3* m_x;
 	b3Vec3* m_v;
 	b3Vec3* m_f;
+	float32* m_m;
 	float32* m_inv_m;
 	b3Vec3* m_y;
 	b3MassType* m_types;
@@ -189,6 +214,11 @@ protected:
 	b3SpringClothStep m_step;
 };
 
+inline b3Mesh* b3SpringCloth::GetMesh() const
+{
+	return m_mesh;
+}
+
 inline const b3Vec3& b3SpringCloth::GetGravity() const
 {
 	return m_gravity;
@@ -208,7 +238,57 @@ inline b3MassType b3SpringCloth::GetType(u32 i) const
 inline void b3SpringCloth::SetType(u32 i, b3MassType type)
 {
 	B3_ASSERT(i < m_massCount);
+	if (m_types[i] == type)
+	{
+		return;
+	}
+
 	m_types[i] = type;
+	
+	m_f[i].SetZero();
+	
+	if (type == e_staticMass)
+	{
+		m_v[i].SetZero();
+		m_y[i].SetZero();
+		
+		m_contacts[i].lockOnSurface = false;
+	}
+}
+
+inline void b3SpringCloth::SetPosition(u32 i, const b3Vec3& position)
+{
+	B3_ASSERT(i < m_massCount);
+	m_y[i] += position - m_x[i];
+}
+
+inline const b3Vec3& b3SpringCloth::GetPosition(u32 i) const
+{
+	B3_ASSERT(i < m_massCount);
+	return m_x[i];
+}
+
+inline void b3SpringCloth::ApplyForce(u32 i, const b3Vec3& force)
+{
+	B3_ASSERT(i < m_massCount);
+	
+	if (m_types[i] != e_dynamicMass)
+	{
+		return;
+	}
+
+	m_f[i] += force;
+}
+
+inline float32 b3SpringCloth::GetKineticEnergy() const
+{
+	float32 E = 0.0f;
+	for (u32 i = 0; i < m_massCount; ++i)
+	{
+		b3Vec3 P = m_m[i] * m_v[i];
+		E += b3Dot(P, m_v[i]);
+	}
+	return E;
 }
 
 inline u32 b3SpringCloth::GetShapeCount() const

include/bounce/dynamics/cloth/spring_solver.h

@@ -74,6 +74,7 @@ private:
 	b3Vec3* m_x;
 	b3Vec3* m_v;
 	b3Vec3* m_f;
+	float32* m_m;
 	float32* m_inv_m;
 	b3Vec3* m_y;
 	b3MassType* m_types;