From 82f103758dc806faef11f3216db508524172625f Mon Sep 17 00:00:00 2001
From: Okay Uenal <okay.uenal@tum.de>
Date: Wed, 8 Nov 2023 15:19:29 +0100
Subject: [PATCH] merge stuff demo 2

---
 Simulations/MassSpringSystemSimulator.cpp | 55 ++++++++++++++++++++---
 Simulations/MassSpringSystemSimulator.h   |  5 +++
 2 files changed, 53 insertions(+), 7 deletions(-)

diff --git a/Simulations/MassSpringSystemSimulator.cpp b/Simulations/MassSpringSystemSimulator.cpp
index 4a4b155..0ea12ac 100644
--- a/Simulations/MassSpringSystemSimulator.cpp
+++ b/Simulations/MassSpringSystemSimulator.cpp
@@ -7,12 +7,10 @@ MassSpringSystemSimulator::MassSpringSystemSimulator()
 	m_fStiffness = 40;
 	int m_iIntegrater = 0;
 
-
-	//Test only
-	auto first = addMassPoint(Vec3(0, 0, 1), Vec3(0, 0, 0), true);
-	auto second = addMassPoint(Vec3(0, 0, 0), Vec3(0, 0, 0), true);
-	addSpring(first, second, 2.0);
-
+	auto first = addMassPoint(Vec3(0, 0, 0), Vec3(-1, 0, 0), true);
+	auto second = addMassPoint(Vec3(0, 2, 0), Vec3(1, 0, 0), true);
+	addSpring(first, second, 1.0);
+	m_fStiffness = 40;
 }
 
 const char* MassSpringSystemSimulator::getTestCasesStr()
@@ -94,7 +92,7 @@ void MassSpringSystemSimulator::notifyCaseChanged(int testCase)
 	}
 }
 
-void MassSpringSystemSimulator::externalForcesCalculations(float timeElapsed)
+void MassSpringSystemSimulator::externalForcesCalculations(float timeElapsed) 
 {
 	Point2D mouseDiff;
 	mouseDiff.x = m_trackmouse.x - m_oldtrackmouse.x;
@@ -137,6 +135,8 @@ void MassSpringSystemSimulator::simulateTimestep(float timeStep)
 		break;
 	default: break;
 	}
+
+	Euler(0, 1, 0, timeStep);
 }
 
 void MassSpringSystemSimulator::onClick(int x, int y)
@@ -218,3 +218,44 @@ void MassSpringSystemSimulator::applyExternalForce(Vec3 force)
 {
 
 }
+
+Vec3 MassSpringSystemSimulator::calcualtePositionTimestepEuler(Vec3 oldPosition, float timestep, Vec3 velocity)
+{
+	return oldPosition + timestep * velocity;
+}
+
+Vec3 MassSpringSystemSimulator::calcualteVelocityTimestepEuler(Vec3 oldVelocity, float timestep, Vec3 acceleration)
+{
+	return oldVelocity + acceleration * timestep;
+}
+
+Vec3 MassSpringSystemSimulator::calculateAcceleration(Vec3 force, float mass)
+{
+	return force / mass;
+}
+
+void MassSpringSystemSimulator::Euler(int index1, int index2, int indexSpring, float timestep)
+{
+	//take old position and send to calculatePositionTimestepEuler
+	auto mp = masspoints.at(index1);
+	auto mp2 = masspoints.at(index2);
+	Vec3 PosVector = mp->position - mp2->position;
+	auto lengthVector = sqrt(PosVector.x * PosVector.x + PosVector.y * PosVector.y + PosVector.z * PosVector.z);
+	auto normalized = PosVector / lengthVector;
+
+	// Actual Calculation
+	// Force of spring is -k * (l - L) * normalizedVector [for P2 we can take -F1)
+	auto force = -m_fStiffness * (lengthVector - springs.at(0).initialLength) * normalized;
+	auto foreP2 = -1 * force;
+	auto veloc = calcualteVelocityTimestepEuler(mp->velocity, timestep, calculateAcceleration(force, 10.));
+	auto pos = calcualtePositionTimestepEuler(mp->position, timestep, veloc);
+
+	auto veloc2 = calcualteVelocityTimestepEuler(mp2->velocity, timestep, calculateAcceleration(foreP2, 10.));
+	auto pos2 = calcualtePositionTimestepEuler(mp2->position, timestep, veloc2);
+
+	// Update Positions and Velocity
+	mp->position = pos;
+	mp->velocity = veloc;
+	mp2->position = pos2;
+	mp2->velocity = veloc2;
+}
diff --git a/Simulations/MassSpringSystemSimulator.h b/Simulations/MassSpringSystemSimulator.h
index d6f968e..d40aee9 100644
--- a/Simulations/MassSpringSystemSimulator.h
+++ b/Simulations/MassSpringSystemSimulator.h
@@ -38,6 +38,11 @@ public:
 	Vec3 getPositionOfMassPoint(int index);
 	Vec3 getVelocityOfMassPoint(int index);
 	void applyExternalForce(Vec3 force);
+
+	Vec3 calcualtePositionTimestepEuler(Vec3 oldPosition, float timestep, Vec3 veloctiy);
+	Vec3 calcualteVelocityTimestepEuler(Vec3 oldVelocity, float timestep, Vec3 acceleration);
+	Vec3 calculateAcceleration(Vec3 acceleration, float mass);
+	void Euler(int index1, int index2, int indexSpring, float timestep);
 	
 	// Do Not Change
 	void setIntegrator(int integrator) {