Particle Systems - Introduction to 3D Game Programming with DirectX 9.0 - page 247

_device->SetTexture(0, _tex);
_device->SetFVF(Particle::FVF);
_device->SetStreamSource(0, _vb, 0, sizeof(Particle));
// start at beginning if we're at the end of the vb
if(_vbOffset >= _vbSize)
_vbOffset = 0;
Particle*v=0;
_vb->Lock(
_vbOffset * sizeof( Particle ),
_vbBatchSize * sizeof( Particle ),
(void**)&v,
_vbOffset ? D3DLOCK_NOOVERWRITE : D3DLOCK_DISCARD);
DWORD numParticlesInBatch = 0;
//
// Until all particles have been rendered.
//
std::list<Attribute>::iterator i;
for(i = _particles.begin(); i != _particles.end(); i++)
{
if( i->_isAlive )
{
//
// Copy a batch of the living particles to the
// next vertex buffer segment
//
v->_position = i->_position;
v->_color = (D3DCOLOR)i->_color;
v++; // next element;
numParticlesInBatch++; //increase batch counter
// is this batch full?
if(numParticlesInBatch == _vbBatchSize)
{
//
// Draw the last batch of particles that was
// copied to the vertex buffer.
//
_vb->Unlock();
_device->DrawPrimitive(
D3DPT_POINTLIST,
_vbOffset,
_vbBatchSize);
//
// While that batch is drawing, start filling the
// next batch with particles.
//
// move the offset to the start of the next batch