Fix frozen particles affected by gravity when using Projective Fluids (#373)

* applying gravity to active particles only in 'clearAccelerations'

* setting acceleration of non-active particles to zero

* fixed non-active particles advected in PF

Author: lukashof

SPlisHSPlasH/PF/TimeStepPF.cpp

@@ -183,9 +183,16 @@ void TimeStepPF::initialGuessForPositions(const unsigned int fluidModelIndex)
 	for (int i = 0; i < (int)numParticles; i++)
 	{
 		m_simulationData.setOldPosition(fluidModelIndex, i, model->getPosition(i));
-		const auto newPos = (model->getPosition(i) + h * model->getVelocity(i) + (h * h) * model->getAcceleration(i)).eval();
-		model->setPosition(i, newPos);
-		m_simulationData.setS(fluidModelIndex, i, newPos);
+		if (model->getParticleState(i) == ParticleState::Active)
+		{
+			const auto newPos = (model->getPosition(i) + h * model->getVelocity(i) + (h * h) * model->getAcceleration(i)).eval();
+			model->setPosition(i, newPos);
+			m_simulationData.setS(fluidModelIndex, i, newPos);
+		}
+		else
+		{
+			m_simulationData.setS(fluidModelIndex, i, model->getPosition(i));
+		}
 	}
 }
 

SPlisHSPlasH/TimeStep.cpp

@@ -41,11 +41,15 @@ void TimeStep::clearAccelerations(const unsigned int fluidModelIndex)
 	for (unsigned int i=0; i < count; i++)
 	{
 		// Clear accelerations of dynamic particles
-		if (model->getMass(i) != 0.0)
+		Vector3r& a = model->getAcceleration(i);
+		if (model->getMass(i) != 0.0 && model->getParticleState(i) == ParticleState::Active)
 		{
-			Vector3r &a = model->getAcceleration(i);
 			a = grav;
 		}
+		else
+		{
+			a.setZero();
+		}
 	}
 }