fix midpoint

Simulations/MassSpringSystemSimulator.cpp

@@ -3,10 +3,6 @@
 
 MassSpringSystemSimulator::MassSpringSystemSimulator()
 {
-	m_iTestCase = 0;
-	m_fMass = 10;
-	m_fStiffness = 40;
-	m_iIntegrator = EULER;
 }
 
 const char* MassSpringSystemSimulator::getTestCasesStr()
@@ -310,43 +306,41 @@ void MassSpringSystemSimulator::Midpoint(Spring& spring, float timestep) {
 	auto massPoint1 = spring.mp1.lock();
 	auto massPoint2 = spring.mp2.lock();
 
-	//old Velocity
-	auto mOld_v = massPoint1->velocity;
-	auto m2Old_v = massPoint2->velocity;
-
 	Vec3 PosVector = massPoint1->position - massPoint2->position;
 	//Abstand ausrechnen
-	float length = LengthCalculator(PosVector);
+	float length = sqrtf(PosVector.x * PosVector.x + PosVector.y * PosVector.y + PosVector.z * PosVector.z);
 	//normalize
-	Vec3 normal1 = PosVector / length;
-	Vec3 normal2 = -1 * normal1;
+	Vec3 normal = PosVector / length;
 
 	//Midpoint calculator
-	auto midpointStep1 = MidPointStep(timestep / 2, spring, massPoint1->position, massPoint1->velocity, normal1, length);
-	auto midpointStep2 = MidPointStep(timestep / 2, spring, massPoint2->position, massPoint2->velocity, normal2, length);
+	std::tuple<Vec3, Vec3> midpointStep1 = MidPointHalfStep(timestep * .5, spring, massPoint1->position, massPoint1->velocity, normal, length);
+	std::tuple<Vec3, Vec3> midpointStep2 = MidPointHalfStep(timestep * .5, spring, massPoint2->position, massPoint2->velocity, -normal, length);
 
-	auto newPosVector = std::get<0>(midpointStep1) - std::get<0>(midpointStep2);
-	auto newLength = LengthCalculator(newPosVector);
-	auto newNormal1 = newPosVector / newLength;
-	auto newNormal2 = -1 * newNormal1;
+	Vec3 newPosVector = std::get<0>(midpointStep1) - std::get<0>(midpointStep2);
+	float newLength = sqrtf(newPosVector.x * newPosVector.x + newPosVector.y * newPosVector.y + newPosVector.z * newPosVector.z);
+	Vec3 newNormal = newPosVector / newLength;
 
-	auto midpoint1 = MidPointStep(timestep, spring, massPoint1->position, std::get<1>(midpointStep1), newNormal1, newLength);
-	auto midpoint2 = MidPointStep(timestep, spring, massPoint2->position, std::get<1>(midpointStep2), newNormal2, newLength);
+	std::tuple<Vec3, Vec3> midpoint1 = MidPointStep(timestep, spring, massPoint1->position, massPoint1->velocity, std::get<1>(midpointStep1), newNormal, newLength);
+	std::tuple<Vec3, Vec3> midpoint2 = MidPointStep(timestep, spring, massPoint2->position, massPoint2->velocity, std::get<1>(midpointStep2), -newNormal, newLength);
 	
-	//cout << NewPos;
-	//cout << NewVel;
 	massPoint1->position = std::get<0>(midpoint1);
 	massPoint1->velocity = std::get<1>(midpoint1);
 	massPoint2->position = std::get<0>(midpoint2);
 	massPoint2->velocity = std::get<1>(midpoint2);
 }
 
-std::tuple<Vec3, Vec3> MassSpringSystemSimulator::MidPointStep(float timestep, const Spring& spring, Vec3 position, Vec3 velocity, Vec3 normal, float length)
+std::tuple<Vec3, Vec3> MassSpringSystemSimulator::MidPointHalfStep(double timestep, const Spring& spring, Vec3 position, Vec3 velocity, Vec3 normal, double length)
 {
-	Vec3 force = -m_fStiffness * (length - spring.initialLength) * normal;
-	Vec3 acc = calculateAcceleration(force, m_fMass);
-	Vec3 pos = position + timestep  * velocity;
-	Vec3 vel = velocity + timestep * acc;
+	return MidPointStep(timestep, spring, position, velocity, velocity, normal, length);
+}
+
+
+std::tuple<Vec3, Vec3> MassSpringSystemSimulator::MidPointStep(double timestep, const Spring& spring, Vec3 position, Vec3 oldVelo,Vec3 velocity, Vec3 normal, double length)
+{
+	auto force = -m_fStiffness * (length - spring.initialLength) * normal;
+	auto acc = calculateAcceleration(force, m_fMass);
+	auto pos = position + timestep * velocity;
+	auto vel = oldVelo + timestep * acc;
 	return std::tuple<Vec3, Vec3>(pos, vel);
 }
 

Simulations/MassSpringSystemSimulator.h

@@ -40,7 +40,8 @@ public:
 	void applyExternalForce(Vec3 force);
 
 	void Midpoint(Spring& spring, float timestep);
-	std::tuple<Vec3, Vec3> MidPointStep(float timestep, const Spring& spring, Vec3 position, Vec3 velocity, Vec3 normal, float length);
+	std::tuple<Vec3, Vec3> MidPointHalfStep(double timestep, const Spring& spring, Vec3 position, Vec3 velocity, Vec3 normal, double length);
+	std::tuple<Vec3, Vec3> MassSpringSystemSimulator::MidPointStep(double timestep, const Spring& spring, Vec3 position, Vec3 oldVelo, Vec3 velocity, Vec3 normal, double length);
 	float LengthCalculator(Vec3 vector);
 
 	Vec3 calculatePositionTimestepEuler(Vec3 oldPosition, float timestep, Vec3 veloctiy);