bullets and collisions

function fire_bullets() // includes the code that animates the weapon as well
{
       VECTOR temp;
       VECTOR temp1;
       proc_kill(4); // don't allow more than 1 copy of this function to run
       while (mouse_left) // this loop runs for as long as the left mouse button is pressed
       {
               vec_set(temp.x,gun_fire_ent.x); // get the coordinates for the bullets' origin
               vec_set(temp1.x, gun_fire2_ent.x);
                // create the bullet at camera's position and attach it the "move_bullets" function
               ent_create ("bullet.mdl", temp1.x, move_bullets);
               ent_create ("gun_fire.tga", temp1.x, display_muzzle);
               ent_create ("bullet.mdl", temp.x, move_bullets);
               ent_create ("gun_fire.tga", temp.x, display_muzzle); // create the gun muzzle
              // snd_play (bullet_wav, 100, 0); // play the bullet sound at a volume of 100
               wait (-0.2); // number of bullets, 6 bullets per second, if 0.1 - 10 bullets per second
       }
}

function p_alphafade(PARTICLE *p)
{
    p.alpha -= 1*time_step;
    if (p.alpha <= 0) p.lifespan = 0;
}

function p_trace(PARTICLE *p)
{
   set(p, BRIGHT|TRANSLUCENT|STREAK);
   p.alpha = 10;
   p.size = 10;
   //p.skill_a = 1; // fade factor
   p.event = p_alphafade;
}
ENTITY* bullet_ent;
function move_bullets()
{
		 VECTOR last_pos;
       VECTOR bullet_speed; // stores the speed of the bullet
       bullet_ent = me;
       my.scale_x = 0.2;
       my.scale_y = my.scale_x;
       my.scale_z = my.scale_x;
       my.skill30 = 1; // I'm a bullet
       my.emask |= (ENABLE_IMPACT | ENABLE_ENTITY | ENABLE_BLOCK);
       set(me,BRIGHT|LIGHT); 
       set(my,PASSABLE);
       my.event = remove_bullets; // when it collides with something, its event function (remove_bullets) will run
       my.pan = player.pan; // the bullet has the same pan
       my.tilt = player.tilt; // and tilt with the camera
       bullet_speed.x = 100 * time_step; // adjust the speed of the bullet here
       bullet_speed.y = 0; // the bullet doesn't move sideways
       bullet_speed.z = 0; // then don't allow the gravity to have its ways with the bullet
       while (my) // this loop will run for as long as the bullet exists (it isn't "null")
       {
               // move the bullet ignoring the passable entities and store the result in distance_covered
               vec_set(last_pos.x,my.x);
               c_move (my, bullet_speed, nullvector, IGNORE_PASSABLE);
               effect(p_trace,1,my.x,vec_sub(last_pos.x,my.x));
               wait (1);
       }
}
function remove_bullets() // this function runs when the bullet collides with something
{
       wait (1); // wait a frame to be sure (don't trigger engine warnings)
       ent_create ("gun_fire.tga", my.x, explosion_sprite); // create the explosion sprite
       set (my, INVISIBLE | PASSABLE);
       wait (-2); // wait until the explosion_sprite() function is over
       ent_remove (my); // and then remove the bullet
}
function display_muzzle()
{
       set (my, PASSABLE | LIGHT);
       my.roll = 0.01;
       my.ambient = 100; // and this line makes it even brighter
       my.pan = player.pan; // has the same pan and tilt
       my.tilt = player.tilt; // with the weapon
       my.roll = random(360); // and a random roll angle (looks nicer)
       my.scale_x = 0.05; // we scale it down
       my.scale_y = my.scale_x; // on all the axis
       my.scale_z = my.scale_z; // this would only be needed for a 3D (model-based) muzzle
       player.ambient = 100; // highlight the weapon (makes it look more realistic)
       wait (2); // show the muzzle sprite for 2 frames
       player.ambient = 0; // restore the normal weapon ambient value
       ent_remove (my); // and then remove it
}
function explosion_sprite()
{
       set (my, PASSABLE | BRIGHT | TRANSLUCENT);
       my.scale_x = 0.15; // we scale it down to 0.15
       my.scale_y = my.scale_x; // on both axis
       my.ambient = 100; // and we give it an ambient of 100
       my.roll = random(360); // we set a random roll angle
       my.alpha = 100; // but we set it to be completely opaque for now
    //   while (my.frame < 5) // go through all the animation frames
    //   {
    //           my.frame += 2 * time_step; // animation speed
    //           wait (1);
    //   }
       while (my.alpha > 0) // now fade the last frame quickly
       {
               my.alpha -= 50 * time_step; // 50 = fading speed
               wait (1);
       }
       ent_remove (my);
}