class Marble {
  float radius;
  float[] x,y,z;
  float xm=0, ym=0, zm=0;
  int TRACE_LENGTH=5;

  Marble(float _radius, float _spd) {
    radius = _radius;
    float rd=random(TWO_PI);
    xm=_spd*cos(rd);
    zm=_spd*sin(rd);
    x=new float[TRACE_LENGTH];
    y=new float[TRACE_LENGTH];
    z=new float[TRACE_LENGTH];
  }
  
  void centerOn(Terrain _ter) {
    for (int i=0;i<TRACE_LENGTH;i++) {
      x[i] = _ter.fullWid/2.0;
      z[i] = _ter.fullDep/2.0;
      y[i] = _ter.getAltitudeAt(x[i],z[i]);
    }
  }
  
  void putSomewhereOn(Terrain _ter) {
    float xr =random(_ter.fullWid);
    float zr =random(_ter.fullDep);
    for (int i=0;i<TRACE_LENGTH;i++) {
      x[i] = xr;
      z[i] = zr;
      y[i] = _ter.getAltitudeAt(x[i],z[i]) - random(100);
    }
  }
  
  void shiftTail() {
    for (int i=TRACE_LENGTH-1;i>0;i--) {
      x[i]=x[i-1];
      y[i]=y[i-1];
      z[i]=z[i-1];
    }
  }
  
  void move(Terrain _ter) {
    xm+=random(-0.1,0.1);
    zm+=random(-0.1,0.1);
    ym+=0.2;
    if (x[0]+xm-radius<0||x[0]+xm+radius>=_ter.fullWid) xm*=-1;
    if (z[0]+zm-radius<0||z[0]+zm+radius>=_ter.fullDep) zm*=-1;
    shiftTail();
    x[0]+=xm;
    z[0]+=zm;
    y[0]+=ym;
    float ylim = _ter.getAltitudeAt(x[0],z[0]);
    if (y[0]>ylim) {
      y[0] -= (y[0]-ylim);
      ym*=-0.4;
    }
    //y[0] = _ter.getAltitudeAt(x[0],z[0]);
  }
  
  void draw() {
    //noStroke();
    //fill(255,0,0);
    //pushMatrix();
    //translate(x,y-radius,z);
    //sphere(radius);
    //box(radius);
    
    //stroke(255,255,255,128);
    for (int i=0;i<TRACE_LENGTH;i++) {
      stroke(255,255,255,128*(1-i/float(TRACE_LENGTH)));
      point(x[i],y[i],z[i]);
    }
    //popMatrix();
  }
  
}