Q: I have a car model; how do I make it follow the direction of the path smoothly?

A: Here's a simplified version of the code used in my car demo.

 

#define car_speed skill55

 

SOUND* aiskids1_wav = "aiskids1.wav";

SOUND* carai1_wav = "carai1.wav";

 

ENTITY* dummy1;

ENTITY* carai1_dummy;

ENTITY* carai1;

 

action car_ai()

{

       carai1 = my;

       var distance = 0;

       var previous_pan;

       var following_pan;

       var min_speed = 20;

       var max_speed;

       var carai_engine;

       var engine_factor;

       var dist_z;

       var skids_once = 0;

       VECTOR last_pos[3];

       VECTOR direction[3];

       VECTOR temp[3];

       max_speed = 35;

       dummy1 = ent_create(NULL, nullvector, NULL);

       // create another (carai1_dummy) dummy entity that will move on the path

       // the ai car will use the same x, y, pan, tilt and roll with the carai1_dummy entity that moves on the path

       // but will compute its own z using c_trace; this way, the nodes don't have to be place precisely above the ground

       carai1_dummy = ent_create(NULL, nullvector, NULL);

       path_set(dummy1, "path_001"); // make sure to name your path this way

       engine_factor = 2 + random(2); // start with a random engine sound frecquency each and every time

       carai_engine = ent_playloop(carai1, carai1_wav, 300); // start playing the car ai engine sound in a loop

       while(1)

       {

               previous_pan = carai1.pan;

               // place the carai1 entity on the path

               path_spline(dummy1, carai1_dummy.x, distance);

               distance += dummy1.car_speed * time_step;

               // let carai1 look ahead

               vec_diff(direction, carai1_dummy.x, last_pos);

               vec_to_angle(carai1_dummy.pan, direction);

               vec_set(last_pos, carai1_dummy.x);

               carai1.pan = carai1_dummy.pan;

               carai1.tilt = carai1_dummy.tilt;

               carai1.roll = carai1_dummy.roll;

               carai1.x = carai1_dummy.x;

               carai1.y = carai1_dummy.y;

               vec_set (temp.x, carai1_dummy.x);

               temp.z -= 2000;

               dist_z = c_trace(carai1_dummy.x, temp.x, IGNORE_ME | IGNORE_PASSABLE | IGNORE_MODELS); // ignore the "real" carai

               carai1.z = carai1_dummy.z - dist_z + 35; // 35 = experimental value

               // sets a variable car ai engine frequency, depending on the speed of the car

               snd_tune(carai_engine, 0, dummy1.car_speed * engine_factor, 0);

               wait(1);

               following_pan = carai1.pan;

               if (abs(following_pan - previous_pan) > 1) // sudden direction change? Then lower the speed of the AI car

               {

                       dummy1.car_speed -= 4 * time_step;

                       if (skids_once == 0)                        

                       {

                               skids_once = 1;

                               if (random(1) > 0.9)

                               {

                                       ent_playsound(dummy1, aiskids1_wav, 3000);

                               }

                       }

               }

               else

               {

                       skids_once = 0;

                       dummy1.car_speed += 2 * time_step;

               }

               dummy1.car_speed = clamp(dummy1.car_speed, min_speed, max_speed);

       }

}