add baraff and witkin's mass-spring-based cloth

include/bounce/bounce.h

@@ -56,6 +56,7 @@
 
 #include <bounce/dynamics/rope/rope.h>
 #include <bounce/dynamics/cloth/cloth.h>
+#include <bounce/dynamics/cloth/spring_cloth.h>
 #include <bounce/dynamics/body.h>
 
 //#include <bounce/dynamics/tree/joints/tree_weld_joint.h>

include/bounce/dynamics/cloth/spring_cloth.h

@@ -0,0 +1,180 @@
+/*
+* 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_SPRING_CLOTH_H
+#define B3_SPRING_CLOTH_H
+
+#include <bounce/common/math/mat33.h>
+
+class b3StackAllocator;
+class b3Draw;
+
+struct b3Mesh;
+
+struct b3SpringClothDef
+{
+	b3SpringClothDef()
+	{
+		allocator = nullptr;
+		mesh = nullptr;
+		density = 0.0f;
+		ks = 0.0f;
+		kb = 0.0f;
+		kd = 0.0f;
+		gravity.SetZero();
+	}
+
+	// Stack allocator
+	b3StackAllocator* allocator;
+
+	// Cloth mesh	
+	b3Mesh* mesh;
+
+	// Cloth density in kg/m^2
+	float32 density;
+
+	// Streching stiffness
+	float32 ks;
+
+	// Bending stiffness
+	float32 kb;
+
+	// Damping stiffness
+	float32 kd;
+	
+	// Force due to gravity 
+	b3Vec3 gravity;
+};
+
+struct b3Spring
+{
+	// Mass 1
+	u32 i1;
+
+	// Mass 2
+	u32 i2;
+
+	// Rest length
+	float32 L0;
+
+	// Structural stiffness
+	float32 ks;
+	
+	// Damping stiffness
+	float32 kd;
+};
+
+// Static masses have zero mass and velocity, and therefore they can't move.
+// Dynamic masses have non-zero mass and can move due to internal and external forces.
+enum b3MassType
+{
+	e_staticMass,
+	e_dynamicMass
+};
+
+// Time step statistics
+struct b3SpringClothStep
+{
+	u32 iterations;
+};
+
+// This class implements a cloth. It treats cloth as a collection 
+// of masses connected by springs. 
+// Large time steps can be taken.
+// If accuracy and stability are required, not performance, 
+// you can use this class instead of using b3Cloth.
+class b3SpringCloth
+{
+public:
+	b3SpringCloth();
+	~b3SpringCloth();
+
+	//
+	void Initialize(const b3SpringClothDef& def);
+
+	//
+	void SetGravity(const b3Vec3& gravity);
+
+	//
+	const b3Vec3& GetGravity() const;
+
+	//
+	void SetType(u32 i, b3MassType type);
+
+	//
+	b3MassType GetType(u32 i) const;
+
+	// 
+	const b3SpringClothStep& GetStep() const;
+
+	//
+	void Step(float32 dt);
+
+	//
+	void Apply() const;
+
+	//
+	void Draw(b3Draw* draw) const;
+protected:
+	b3StackAllocator* m_allocator;
+
+	b3Mesh* m_mesh;
+
+	b3Vec3 m_gravity;
+
+	b3Vec3* m_x;
+	b3Vec3* m_v;
+	b3Vec3* m_f;
+	float32* m_inv_m;
+	b3MassType* m_massTypes;
+	u32 m_massCount;
+
+	b3Spring* m_springs;
+	u32 m_springCount;
+
+	b3SpringClothStep m_step;
+};
+
+inline const b3Vec3& b3SpringCloth::GetGravity() const
+{
+	return m_gravity;
+}
+
+inline void b3SpringCloth::SetGravity(const b3Vec3& gravity)
+{
+	m_gravity = gravity;
+}
+
+inline b3MassType b3SpringCloth::GetType(u32 i) const
+{
+	B3_ASSERT(i < m_massCount);
+	return m_massTypes[i];
+}
+
+inline void b3SpringCloth::SetType(u32 i, b3MassType type)
+{
+	B3_ASSERT(i < m_massCount);
+	m_massTypes[i] = type;
+}
+
+inline const b3SpringClothStep& b3SpringCloth::GetStep() const
+{
+	return m_step;
+}
+
+#endif