/* Fractal na tela */
#include "us.h"

#define NTLINHAS     786    // n£mero de linhas na tela
#define NTCOLUNAS   1024    // n£mero de colunas na tela
#define NFLINHAS     480    // n£mero de linhas no fractal
#define NFCOLUNAS    640    // n£mero de colunas no fractal

typedef byte tela[NTLINHAS][NTCOLUNAS];

// variaveis
float xini,yini;   // coordenadas do ponto dentro do fractal
dword xpix,ypix;   // posi‡„o do pixel na tela do video

// prototypes
void desenhar_fractal();

// A primeira rotina deve ser o main
void main() {
   desenhar_fractal();
   terminate();
}

void desenhar_fractal() {
/*
 Calculation of Julia set
 ------------------------
 Written by Kiselev Y. 1994

 Definitions of complex numbers:
   z = x + i*y  screen coordinates   xini <= x < xini+1024*xstep
   u = s + i*t  parameter         \  yini <= y < yini+768*ystep
 Equation used:
   f(z) = z^2 - u
 Iteration:
   f(z), f(f(z)), f(f(f(z))), ...
   until |f(...)| > 2  or  max_it iterations
 Result:
   pixel value at (x,y) is the number of iterations.
*/

   tela far *video = VIDEO_FP(0);
   byte pix;          // valor do pixel
   
   for(yini=-1.15, ypix=120; ypix<120+NFLINHAS; yini+=0.005, ypix++) {
     if(ypix==120+NFLINHAS/2) carrega('b');
     for(xini=-1.55, xpix=250; xpix<250+NFCOLUNAS; xini+=0.005, xpix++) {
       float x,x2,y,y2,xy;
       x=xini;
       y=yini;
       for(pix=0; pix<255; pix++) {  // max_it=255
         x2=x*x;
         y2=y*y;
         if(x2+y2>4.0) break;  // |z|=sqrt(x^2+y^2) < 2
         xy = x*y;
         x = x2-y2-0.76;  // -s
         y = xy+xy-0.09;  // -t
       }
       if (pix>2) (*video)[ypix][xpix] = pix;
       // for(i=1; i<100; i++);
     }
   }
}