The following shows a sample shader code for the particle system.

You can find an explanation for this example from the following link.
(for different types of particles)
http://msdn.microsoft.com/en-us/library/bb205329(VS.85).aspx

NOTE: this sample code uses a Geometry shader -- a Geometry shader
is not needed for Project 1.


//
// Explanation of different particle types
//
#define PT_LAUNCHER 0 //Firework Launcher - launches a PT_SHELL every
so many seconds
#define PT_SHELL    1 //Unexploded shell - flies from the origin and
explodes into many PT_EMBERXs
#define PT_EMBER1   2 //basic particle - after it's emitted from the
shell, it dies
#define PT_EMBER2   3 //after it's emitted, it explodes again into
many PT_EMBER1s
#define PT_EMBER3   4 //just a differently colored ember1

//
// Generic particle motion handler
//

void GSGenericHandler( VSParticleIn input, inout
PointStream<VSParticleIn> ParticleOutputStream )
{
    input.pos += input.vel*g_fElapsedTime;
    input.vel += g_vFrameGravity;
    input.Timer -= g_fElapsedTime;
    ParticleOutputStream.Append( input );
}

//
// Shell type particle handler
//
void GSShellHandler( VSParticleIn input, inout
PointStream<VSParticleIn> ParticleOutputStream )
{
    if(input.Timer <= 0)
    {
        VSParticleIn output;
        float3 vRandom = float3(0,0,0);

        //time to emit a series of new Ember1s
        for(int i=0; i<g_iNumEmber1s; i++)
        {
            vRandom = normalize( RandomDir( input.Type + i ) );
            output.pos = input.pos + input.vel*g_fElapsedTime;
            output.vel = input.vel + vRandom*15.0;
            output.Timer = P_EMBER1LIFE;
            output.Type = PT_EMBER1;
            ParticleOutputStream.Append( output );
        }

        //find out how many Ember2s to emit
        for(int i=0; i<abs(vRandom.x)*g_fMaxEmber2s; i++)
        {
            vRandom = normalize( RandomDir( input.Type + i ) );
            output.pos = input.pos + input.vel*g_fElapsedTime;
            output.vel = input.vel + vRandom*10.0;
            output.Timer = P_EMBER2LIFE + 0.4*vRandom.x;
            output.Type = PT_EMBER2;
            ParticleOutputStream.Append( output );
        }

    }
    else
    {
        GSGenericHandler( input, ParticleOutputStream );
    }
}