Added FluidProgram

src/osgParticle/FluidProgram.cpp

@@ -0,0 +1,47 @@
+#include <osgParticle/FluidProgram>
+
+osgParticle::FluidProgram::FluidProgram():
+    Program()
+{
+    setFluidToAir();
+}
+
+osgParticle::FluidProgram::FluidProgram(const FluidProgram& copy, const osg::CopyOp& copyop):
+    Program(copy, copyop),
+    _acceleration(copy._acceleration),
+    _viscosity(copy._viscosity),
+    _density(copy._density),
+    _wind(copy._wind),
+    _A(copy._A),
+    _B(copy._B)
+{
+}
+
+void osgParticle::FluidProgram::execute(double dt)
+{
+    const float four_over_three = 4.0f/3.0f;
+    ParticleSystem *ps = getParticleSystem();
+    int n = ps->numParticles();
+    for (int i=0; i<n; ++i)
+    {
+        Particle *particle = ps->getParticle(i);
+        if (particle->isAlive())
+        {
+            float radius = particle->getRadius();
+            float Area = osg::PI*radius*radius;
+            float Volume = Area*radius*four_over_three;
+        
+            // compute force due to gravity + boyancy of displacing the fluid that the particle is emersed in.
+            osg::Vec3 force = _acceleration * (particle->getMass() - _density*Volume);
+
+            // compute force due to friction
+            osg::Vec3 relative_wind = particle->getVelocity()-_wind;            
+            force -= relative_wind * Area * (_A + _B*relative_wind.length());            
+            
+            // divide force by mass to get acceleration.
+            force *= particle->getMassInv()*dt;
+            
+            particle->addVelocity(force);
+        }
+    }
+}