/* -------------------------------------------------------
                          colvalue
                    nimmt RGB-Farben auf
   ------------------------------------------------------- */
struct colvalue
{
  uint8_t r;
  uint8_t g;
  uint8_t b;
};


#define graphwidth     160
#define graphheight    128

/* -------------------------------------------------------
                         mandelbrot

                      Fraktalgenerator
   ------------------------------------------------------- */
void mandelbrot(uint16_t ofsx, uint16_t ofsy)
{
  uint16_t k, kt, x, y;
  float    dx, dy, xmin, xmax, ymin, ymax;
  float    jx, jy, wx, wy, tx, ty, r, m;
  struct   colvalue mrgb;

  kt= 100; m= 4.0;

  xmin= 1.7; xmax= -0.8; ymin= -1.0; ymax= 1.0;

//  alternative Zahlenwerte

//  xmin= -0.5328; xmax= -0.2078; ymin= 0.3742; ymax= 0.892;

  dx= (float)(xmax-xmin) / graphwidth;
  dy= (float) (ymax-ymin) / graphheight;

  for (x= 0; x< graphwidth; x++)
  {
    jx= xmin + ((float)x*dx);

    for (y= 0; y< graphheight; y++)
    {
      jy= ymin+((float)y*dy);

      k= 0; wx= 0.0; wy= 0.0;
      do
      {
        tx= wx*wx-(wy*wy+jx);
        ty= 2.0*wx*wy+jy;
        wx= tx;
        wy= ty;
        r= wx*wx+wy+wy;

        k++;
      } while ((r < m) & (k < kt));

      if (k< 3) {mrgb.b= k * 20; }
      if ((k> 2) && (k< 35)) { mrgb.b= k * 9; mrgb.g = k; mrgb.r= k*2 ; }
      if (k> 34) { mrgb.r= ( 128 ); mrgb.g= (k * 3 ); mrgb.b= (k); }
      if (k> 90) { mrgb.r= 0, mrgb.g= 0; mrgb.b= 0; }

      putpixel(ofsx+x,ofsy+y,rgbfromvalue(mrgb.r, mrgb.g, mrgb.b));

    }
  }
}