import graphics.*;

//handles low level rendering
class RayTracerApplet extends MISApplet
{
  protected int[][][] framebuffer, bgbuffer; //2D array of RGB values

  protected Sphere[] spheres;
  protected Light[] lights;
  protected int[] ambient = {0,0,0};

  protected double F = 10;

  public void initialize()
  {
    super.initialize();

    framebuffer = new int[H][W][3]; //rgb values
    bgbuffer = new int[H][W][3]; //rgb values
  }

  public void initFrame(long time)
  {
    for (int w=0; w<W; w++)
    for (int h=0; h<H; h++)
    {
      //copy from background buffer to framebuffer
      framebuffer[h][w][0] = bgbuffer[h][w][0]; framebuffer[h][w][1] = bgbuffer[h][w][1]; framebuffer[h][w][2] = bgbuffer[h][w][2];
    }

    animate(time);
    doRayTrace();
  }

  //just copy from framebuffer...
  public void setPixel(int x, int y, int rgb[])
  {
    rgb[0] = framebuffer[y][x][0];
    rgb[1] = framebuffer[y][x][1];
    rgb[2] = framebuffer[y][x][2];
  }

  //OVERRIDE THIS
  protected void animate(long time) {}

  private int[] rayTrace(Vector3 v, Vector3 w)
  {
    int[] rgb = {0, 0, 0};

    //"infinity"
    double t = 9999999;

    //loop invariants
    double a = w.dotProduct(w);
    double a2 = 2*a;

    //since w is normalized, "a" should always be = 1

    for (int i=0; i<spheres.length; i++)
    {
      //vc = v - c
      Vector3 vc = new Vector3(spheres[i].center);
      vc.scale(-1);
      vc.add(v);

      double b = 2 * vc.dotProduct(w);
      double c = vc.dotProduct(vc) - spheres[i].radius*spheres[i].radius;

      double disc = b*b - 4.0*a*c;

      if (disc < 0) continue; //no roots = no intersection

      double root1 = (-1*b - disc)/a2, root2 = (-1*b + disc)/a2;

      //pick smaller (nearer) root
      double t1 = root1 < root2 ? root1 : root2;

      //is this the closest sphere so far?
      if (t1 >= t) continue; //if not, skip it

      t = t1;
      //calculate intersection point
      double[] pos = new double[3];

      pos[0] = v.get(0) + t * w.get(0);
      pos[1] = v.get(1) + t * w.get(1);
      pos[2] = v.get(2) + t * w.get(2);
//System.err.println("pos pt: ("+pos[0]+", "+pos[1]+", "+pos[2]+")");

      rgb = spheres[i].shade(pos, lights, ambient);
    }

    return rgb;
  }

  private void doRayTrace()
  {
    double w2 = W/2.0;
    double h2 = H/2.0;

    Vector3 v = new Vector3(0, 0, 0);

    for (int i = 0 ; i < W ; i++)
    for (int j = 0 ; j < H ; j++)
    {
      Vector3 w = new Vector3(
        (i - w2) / w2, // x
        (h2 - j) / h2, // y
        -F             // z
      );
//System.err.println(w);

      w.normalize();

      int[] rgb = rayTrace(v, w);

      framebuffer[j][i][0] = rgb[0]; framebuffer[j][i][1] = rgb[1]; framebuffer[j][i][2] = rgb[2];
    }
  }
}