move ExplititEuler cloth solver to its own file, so it can be replaced by PDB, implicit euler etc

add wireframe toggle ('w' key)
add --paused command-line option to start simulation in paused mode
render cloth using drawPoints method

Demos3/CpuDemos/deformable/ExplicitEuler.cpp

@@ -0,0 +1,106 @@
+#include "ExplicitEuler.h"
+	
+#include "CpuSoftClothDemoInternalData.h"
+
+
+
+
+
+void ExplicitEuler::computeForces(struct CpuSoftClothDemoInternalData* clothData, char* vertexPositions, int vertexStride, float dt)
+{
+	
+	B3_PROFILE("computeForces");
+	int numPoints = clothData->m_particleMasses.size();
+
+	b3Vector3 gravityAcceleration = b3MakeVector3(0,-9.8,0);
+	//f=m*a
+	for (int i=0;i<numPoints;i++)
+	{
+		{
+			float	particleMass = clothData->m_particleMasses[i];
+
+			b3Vector3 particleMassVec = b3MakeVector3(particleMass,particleMass,particleMass,0);
+			clothData->m_forces[i] = gravityAcceleration*particleMass;
+		}
+	}
+
+	
+	
+
+
+
+	//add spring forces
+	for(int i=0;i<clothData->m_springs.size();i++) 
+	{
+
+		int indexA = clothData->m_springs[i].m_particleIndexA;
+		int indexB = clothData->m_springs[i].m_particleIndexB;
+		float restLength = clothData->m_springs[i].m_restLength;
+		const ClothMaterial& mat = clothData->m_materials[clothData->m_springs[i].m_material];
+
+		const b3Vector3& posA = (const b3Vector3&)vertexPositions[indexA*vertexStride];
+		const b3Vector3& posB = (const b3Vector3&)vertexPositions[indexB*vertexStride];
+		const b3Vector3& velA = clothData->m_velocities[indexA];
+		const b3Vector3& velB = clothData->m_velocities[indexB];
+
+		b3Vector3 deltaP = posA-posB;
+		b3Vector3 deltaV = velA-velB;
+		float dist = deltaP.length();
+		b3Vector3 deltaPNormalized = deltaP/dist;
+
+		float spring = -mat.m_stiffness * (dist-restLength)*100000;
+		float damper = mat.m_damping * b3Dot(deltaV,deltaPNormalized)*100;
+
+		b3Vector3 springForce = (spring+damper)*deltaPNormalized;
+		float particleMassA = clothData->m_particleMasses[indexA];
+		float particleMassB = clothData->m_particleMasses[indexB];
+
+		//if (springForce.length())
+		{
+			if (particleMassA)
+			{
+				clothData->m_forces[indexA] += springForce*particleMassA;
+			}
+
+			if (particleMassB)
+			{
+				clothData->m_forces[indexB] -= springForce*particleMassB;
+			}
+		}
+	}
+	
+}
+	
+void ExplicitEuler::integrateExplicitEuler(struct CpuSoftClothDemoInternalData* clothData, char* vertexPositions, int vertexStride,float deltaTime)
+{
+	B3_PROFILE("integrateEuler");
+	b3Vector3 deltaTimeVec = b3MakeVector3(deltaTime,deltaTime,deltaTime,0);
+
+	int numPoints = clothData->m_particleMasses.size();
+	
+	for (int i=0;i<numPoints;i++)
+	{
+		float mass = clothData->m_particleMasses[i];
+		if (mass)
+		{
+			
+
+
+			b3Vector3 dv = (clothData->m_forces[i]/mass)*deltaTimeVec;
+			clothData->m_velocities[i]+= dv;
+			clothData->m_velocities[i]*=0.999;
+
+			b3Vector3& pos = (b3Vector3&)vertexPositions[i*vertexStride];
+			
+			pos += clothData->m_velocities[i]*deltaTimeVec;
+		}
+	}
+	
+}
+
+void ExplicitEuler::solveConstraints(struct CpuSoftClothDemoInternalData* data, char* vertexPositions, int vertexStride,float deltaTime)
+{
+	computeForces(data,vertexPositions,vertexStride,deltaTime);
+
+	integrateExplicitEuler(data,vertexPositions,vertexStride,deltaTime);
+}