part2.cl

#define STRINGIFY(A) #A

std::string kernel_source = STRINGIFY(
__kernel void part2(__global float4* pos, __global float4* color, __global float4* vel, __global float4* pos_gen, __global float4* vel_gen, float dt)
{
    //get our index in the array
    unsigned int i = get_global_id(0);
    //copy position and velocity for this iteration to a local variable
    //note: if we were doing many more calculations we would want to have opencl
    //copy to a local memory array to speed up memory access (this will be the subject of a later tutorial)
    float4 p = pos[i];
    float4 v = vel[i];

    //we've stored the life in the fourth component of our velocity array
    float life = vel[i].w;
    //decrease the life by the time step (this value could be adjusted to lengthen or shorten particle life
    life -= dt;
    //if the life is 0 or less we reset the particle's values back to the original values and set life to 1
    if(life <= 0)
    {
        p = pos_gen[i];
        v = vel_gen[i];
        life = 1.0;    
    }

    //we use a first order euler method to integrate the velocity and position (i'll expand on this in another tutorial)
    //update the velocity to be affected by "gravity" in the z direction
    v.z -= 9.8*dt;
    //update the position with the new velocity
    p.z += v.z*dt;
    //store the updated life in the velocity array
    v.w = life;

    //update the arrays with our newly computed values
    pos[i] = p;
    vel[i] = v;

    //you can manipulate the color based on properties of the system
    //here we adjust the alpha
    color[i].w = life;

}
);