i4_image_class *im;
  float *z_buffer;
  i4_transform_class t;
  int iw,ih;
  i4_3d_vector light;
  int mouse_x, mouse_y;
  float theta;
  
  float get_z(int x, int y) { return z_buffer[x+y*iw]; }
  void set_z(int x, int y, float z) 
  {
    z_buffer[ x + y*iw ]=z; 
  }

  void clear_z() 
  { 
    for (int i=0; i<iw*ih; i++)
      z_buffer[i]=100000;
  }

  void render()
  {
    srand(0);
    i4_draw_context_class context(0,0, im->width()-1, im->height()-1);
    
    i4_3d_vector circles[3]={i4_3d_vector(0,0,0), i4_3d_vector(0.5,1,0), i4_3d_vector(-2,-2,4)};

    im->clear(0x4f0000, context);
    clear_z();

    float sx=width()/2, sy=height()/2;
    float cx=sx,cy=sy;
   

    for (int j=0; j<3; j++)    
    {
      for (int i=0; i<50000; i++)
      {   
        float x=frand(),
              y=frand();
        float z=frand();

        i4_3d_vector p(x,y,z);
        p.normalize();


        float c1=-p.dot(light);
        i4_3d_vector reflect=i4_3d_vector(light.x + 2*p.x*c1,
                                          light.y + 2*p.y*c1,
                                          light.z + 2*p.z*c1);
                                          


        float light_v=-light.dot(p)*0.7;

        i4_3d_vector pixel_pos(circles[j].x+p.x,circles[j].y+p.y, circles[j].z+p.z);
        i4_3d_vector t_p;
        t.transform(pixel_pos, t_p);

        
        i4_3d_vector view_dir=t_p;
        view_dir.normalize();
        float view_dot_r=-view_dir.dot(reflect);
        if (view_dot_r>=0)
        {
          light_v += pow(view_dot_r, 0.4)*0.2;
        }
    

        if (light_v<0) 
          light_v=0;
        if (light_v>1)
          light_v=1;

        
        float ooz=1.0/t_p.z;

        float px=t_p.x * ooz * sx;
        float py=t_p.y * ooz * sy;

        int ix=(int)(px+cx), iy=(int)(py+cy);
        if (ix>=0 && iy>=0 && ix<w && iy<h)
        {
          if (t_p.z<get_z(ix,iy))
          {
            im->put_pixel(ix, iy, (int)(light_v*255.0));
            set_z(ix,iy, t_p.z);
          }
        }

      }
    }

  }

  void calc_transform()
  {
    t.identity();
    t.mult_translate(0,0,8);
    t.mult_rotate_x(theta);
    t.mult_rotate_y(theta);
  }


  char *name() { return "trace_view"; }
  trace_view(int w, int h) : i4_window_class(w,h)
  {
    theta=0;

    i4_pixel_format fmt;
    fmt.default_format();
    fmt.alpha_mask=0;
    fmt.calc_shift();

    iw=w; ih=h;
    z_buffer=(float *)i4_malloc(w*h*sizeof(float), "");
    im=i4_create_image(w,h, i4_pal_man.register_pal(&fmt));

    calc_transform();
    light=i4_3d_vector(0,0,1);

    render();
  
  }


  i4_bool project_point(i4_3d_vector v, i4_3d_vector &t_v)
  {
    t.transform(v, t_v);
    if (t_v.z>0)
    {
      float ooz=1.0/t_v.z;
      t_v.x=t_v.x * ooz * width()/2.0 + width()/2.0;
      t_v.y=t_v.y * ooz * height()/2.0 + height()/2.0;
      return i4_T;
    }
    return i4_F;

  }

  void draw_3d_line(i4_3d_vector p1, i4_3d_vector p2, 
                    w32 color,
                    i4_draw_context_class &context)
  {
    i4_3d_vector t_p1, t_p2;

    if (project_point(p1, t_p1) &&
        project_point(p2, t_p2))
      local_image->line((int)t_p1.x, (int)t_p1.y,
                        (int)t_p2.x, (int)t_p2.y, color, context);

  }


  void receive_event(i4_event *ev)
  {
    if (ev->type()==i4_event::MOUSE_BUTTON_DOWN)
    {
      CAST_PTR(bev, i4_mouse_button_event_class, ev);
      float fw=width(), fh=height();
      light=i4_3d_vector((bev->x-fw/2)/(fw/2),
                         (bev->y-fh/2)/(fh/2),
                         1);
      light.normalize();
                         
      render();
      request_redraw();
      
      mouse_x=bev->x;
      mouse_y=bev->y;
    }
    else if (ev->type()==i4_event::KEY_PRESS)
    {
      theta+=0.2;
      calc_transform();
      render();
      request_redraw();
    }

    i4_window_class::receive_event(ev);
  }

  void draw(i4_draw_context_class &context)
  {
    im->put_image(local_image, 0,0, context);

    i4_float mx=(mouse_x - width()/2);
    i4_float my=(mouse_y - height()/2);  

    i4_3d_vector c_pos, c_dir; 
    t.inverse_transform(i4_3d_vector(0,0,0),c_pos);
    t.inverse_transform(i4_3d_vector(mx,my, width()),c_dir);  

    c_dir -= c_pos;


    draw_3d_line(i4_3d_vector(-1,0,0),
                 i4_3d_vector(1,0,0),
                 0x00ff00, context);
    draw_3d_line(i4_3d_vector(0,-1,0),
                 i4_3d_vector(0,1,0),
                 0x00ff00, context);
    draw_3d_line(i4_3d_vector(0,0,-1),
                 i4_3d_vector(0,0,1),
                 0x00ff00, context);
                 

   
    draw_3d_line(i4_3d_vector(c_pos.x + mx,
                              c_pos.y + my,
                              c_pos.z),
                 i4_3d_vector(0,0,0),
                 0xffffff, context);
                 




  }