LAOS Laser

The following code seems relevant. But this all seems to set target speed and accelerations, I'm not sure why the given speed would be ignored in engrave mode. I also don't understand the reason for queue emptying trick.

switch ( action.ActionType )
{
    case AT_MOVE: action.target.feed_rate = 60 * cfg->speed; break;
    case AT_LASER: action.target.feed_rate = 60 * mark_speed; break;
    case AT_BITMAP: action.target.feed_rate = 60 * cfg->xspeed; break;
}

if ( action.ActionType == AT_BITMAP )
{
    while ( queue() );// printf("-"); // wait for queue to empty
    plan_set_accel(cfg->xaccel);
    plan_buffer_line(&action);
    while ( queue() ); // printf("*"); // wait for queue to empty
    plan_set_accel(cfg->accel);
}
else
{
    plan_buffer_line(&action);
}