Use sphere mesh. Add soft body test.

examples/testbed/tests/soft_body.h

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+/*
+* Copyright (c) 2016-2019 Irlan Robson https://irlanrobson.github.io
+*
+* 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 SOFT_BODY_H
+#define SOFT_BODY_H
+
+#include <testbed/framework/sphere_mesh.h>
+
+struct b3SphereClothMesh : public b3ClothMesh
+{
+	b3StackArray<b3Vec3, 256> sphereVertices;
+	b3StackArray<b3ClothMeshTriangle, 256> sphereTriangles;
+	b3ClothMeshMesh sphereMesh;
+
+	b3SphereClothMesh()
+	{
+		smMesh mesh;
+		smCreateMesh(mesh, 1);
+
+		sphereVertices.Resize(mesh.vertices.Count());
+		for (u32 i = 0; i < mesh.vertices.Count(); ++i)
+		{
+			sphereVertices[i] = mesh.vertices[i];
+		}
+		
+		sphereTriangles.Resize(mesh.triangleIndices.Count() / 3);
+		for (u32 i = 0; i < mesh.triangleIndices.Count() / 3; ++i)
+		{
+			sphereTriangles[i].v1 = mesh.triangleIndices[3 * i + 0];
+			sphereTriangles[i].v2 = mesh.triangleIndices[3 * i + 1];
+			sphereTriangles[i].v3 = mesh.triangleIndices[3 * i + 2];
+		}
+
+		sphereMesh.startTriangle = 0;
+		sphereMesh.triangleCount = sphereTriangles.Count();
+		sphereMesh.startVertex = 0;
+		sphereMesh.vertexCount = sphereVertices.Count();
+
+		vertexCount = sphereVertices.Count();
+		vertices = sphereVertices.Begin();
+		triangleCount = sphereTriangles.Count();
+		triangles = sphereTriangles.Begin();
+		meshCount = 1;
+		meshes = &sphereMesh;
+		sewingLineCount = 0;
+		sewingLines = nullptr;
+	}
+};
+
+class SoftBody : public Test
+{
+public:
+	SoftBody()
+	{
+		// Scale and translate the cloth mesh upwards
+		for (u32 i = 0; i < m_mesh.vertexCount; ++i)
+		{
+			m_mesh.vertices[i] *= 2.0f;
+			m_mesh.vertices[i].y += 10.0f;
+		}
+
+		// Create cloth
+		b3ClothDef def;
+		def.mesh = &m_mesh;
+		def.density = 0.2f;
+		def.structural = 10000.0f;
+		def.bending = 0.0f;
+		def.damping = 0.0f;
+
+		m_cloth = new b3Cloth(def);
+
+		for (b3Particle* p = m_cloth->GetParticleList().m_head; p; p = p->GetNext())
+		{
+			p->SetRadius(0.05f);
+			p->SetFriction(0.5f);
+		}
+
+		b3Vec3 gravity(0.0f, -9.8f, 0.0f);
+		
+		m_cloth->SetGravity(gravity);
+
+		// Attach a world to the cloth
+		m_cloth->SetWorld(&m_world);
+
+		// Create static shapes
+		{
+			b3BodyDef bd;
+			bd.type = e_staticBody;
+
+			b3Body* b = m_world.CreateBody(bd);
+
+			static b3BoxHull boxHull(10.0f, 1.0f, 10.0f);
+
+			b3HullShape boxShape;
+			boxShape.m_hull = &boxHull;
+
+			b3ShapeDef sd;
+			sd.shape = &boxShape;
+			sd.friction = 0.5f;
+
+			b->CreateShape(sd);
+		}
+
+		m_clothDragger = new b3ClothDragger(&m_ray, m_cloth);
+	}
+
+	~SoftBody()
+	{
+		delete m_clothDragger;
+		delete m_cloth;
+	}
+
+	// Compute the volume of soft body
+	float32 ComputeVolume() const
+	{
+		const b3ClothMesh* mesh = m_cloth->GetMesh();
+		
+		b3StackArray<b3Vec3, 256> positions;
+		positions.Resize(mesh->vertexCount);
+		
+		for (u32 i = 0; i < mesh->vertexCount; ++i)
+		{
+			b3Particle* p = m_cloth->GetVertexParticle(i);
+			positions[i] = p->GetPosition();
+		}
+
+		b3AABB3 aabb;
+		aabb.Compute(positions.Begin(), positions.Count());
+
+		return aabb.Volume();
+	}
+
+	// Apply pressure forces
+	// Explanation available in the paper 
+	// "Pressure Model of Soft Body Simulation"
+	void ApplyPressureForces()
+	{
+		const b3ClothMesh* mesh = m_cloth->GetMesh();
+
+		// Volume in m^3
+		float32 V = ComputeVolume();
+		
+		// Inverse volume
+		float32 invV = V > 0.0f ? 1.0f / V : 0.0f;
+
+		// Apply pressure forces on particles
+		for (u32 i = 0; i < m_mesh.triangleCount; ++i)
+		{
+			u32 i1 = m_mesh.triangles[i].v1;
+			u32 i2 = m_mesh.triangles[i].v2;
+			u32 i3 = m_mesh.triangles[i].v3;
+
+			b3Particle* p1 = m_cloth->GetVertexParticle(i1);
+			b3Particle* p2 = m_cloth->GetVertexParticle(i2);
+			b3Particle* p3 = m_cloth->GetVertexParticle(i3);
+
+			b3Vec3 v1 = p1->GetPosition();
+			b3Vec3 v2 = p2->GetPosition();
+			b3Vec3 v3 = p3->GetPosition();
+
+			b3Vec3 n = b3Cross(v2 - v1, v3 - v1);
+			
+			// Triangle area
+			float32 A = n.Normalize();
+			A *= 0.5f;
+
+			// Ideal Gas Approximation
+
+			// Number of gas moles
+			const float32 k_n = 1.0f;
+			
+			// Ideal Gas Constant [J / K mol]
+			const float32 k_R = 8.31f;
+			
+			// Gas temperature in Kelvin
+			const float32 k_T = 100.0f;
+
+			// Pressure in Pascals
+			float32 P = invV * k_n * k_R * k_T;
+
+			// Pressure vector
+			b3Vec3 Pn = P * n;
+
+			// Pressure force
+			b3Vec3 FP = Pn * A;
+
+			// Distribute
+			p1->ApplyForce(FP);
+			p2->ApplyForce(FP);
+			p3->ApplyForce(FP);
+		}
+	}
+
+	void Step()
+	{
+		Test::Step();
+
+		ApplyPressureForces();
+
+		m_cloth->Step(g_testSettings->inv_hertz);
+
+		m_cloth->Draw();
+
+		if (m_clothDragger->IsDragging())
+		{
+			b3Vec3 pA = m_clothDragger->GetPointA();
+			b3Vec3 pB = m_clothDragger->GetPointB();
+
+			g_draw->DrawPoint(pA, 2.0f, b3Color_green);
+
+			g_draw->DrawPoint(pB, 2.0f, b3Color_green);
+
+			g_draw->DrawSegment(pA, pB, b3Color_white);
+		}
+
+		extern u32 b3_clothSolverIterations;
+		g_draw->DrawString(b3Color_white, "Iterations = %d", b3_clothSolverIterations);
+
+		float32 E = m_cloth->GetEnergy();
+		g_draw->DrawString(b3Color_white, "E = %f", E);
+	}
+
+	void MouseMove(const b3Ray3& pw)
+	{
+		Test::MouseMove(pw);
+
+		if (m_clothDragger->IsDragging() == true)
+		{
+			m_clothDragger->Drag();
+		}
+	}
+
+	void MouseLeftDown(const b3Ray3& pw)
+	{
+		Test::MouseLeftDown(pw);
+
+		if (m_clothDragger->IsDragging() == false)
+		{
+			m_clothDragger->StartDragging();
+		}
+	}
+
+	void MouseLeftUp(const b3Ray3& pw)
+	{
+		Test::MouseLeftUp(pw);
+
+		if (m_clothDragger->IsDragging() == true)
+		{
+			m_clothDragger->StopDragging();
+		}
+	}
+
+	static Test* Create()
+	{
+		return new SoftBody();
+	}
+
+	b3SphereClothMesh m_mesh;
+	b3Cloth* m_cloth;
+	b3ClothDragger* m_clothDragger;
+};
+
+#endif