From:	bigphil AT solutions DOT mb DOT ca (Mark Phillips)
Newsgroups:	comp.os.msdos.djgpp
Subject:	fractal
Message-ID:	<351ad99b.7246074@news>
Lines:	86
Date:	Thu, 26 Mar 1998 22:42:49 GMT
NNTP-Posting-Host:	207.161.165.50
NNTP-Posting-Date:	Thu, 26 Mar 1998 16:42:49 CST
To:	djgpp AT delorie DOT com
DJ-Gateway:	from newsgroup comp.os.msdos.djgpp

I was just playing around trying to write a fractal program using the
allegro library.  At least as far as I know, it's a fractal, I don't
even know the exact definition of what it a fractal, but it involves
recursion.  I won't bother to try to explain exactly what the program
does, but could someone tell me why it won't even compile?  I think
there is a good chance it has to do with the way I use the allegro
stuff.  Here is the complete source: (some of the comments may not
make sense but they were intended only for me)


#include "allegro.h"
#include <math.h>

struct point {
    int x;
    int y;
};

struct line {
  point p1;
  point p2;
};

class tri {
  public:
    point p1;
    point p2;
    point p3;

    void getTri(line);
    void draw(int);
};

void drawOneSide(line, int);

int main() {
  allegro_init();
  install_keyboard();
  set_gfx_mode(GFX_AUTODETECT, 640, 480, 0, 0);
  set_pallete(desktop_pallete);
  
  line l1, l2, l3;
  /***l1.p1=l3.p2    l1.p2=l2.p1    l2.p2=l3.p1***/

  l1.p1.x=320;     l1.p1.y=2;       l1.p2.x=120;

l1.p2.y=int(2+sqrt(400*400-200*200));
  l2.p1.x=l1.p2.x; l2.p1.y=l1.p2.y; l2.p2.x=520; l2.p2.y=l1.p2.y;

  l3.p1.x=l2.p2.x; l3.p1.y=l2.p2.y; l3.p2.x=l1.p1.x; l3.p2.y=l1.p1.y;


  drawOneSide(l1,1);
  drawOneSide(l2,1);
  drawOneSide(l3,1);
  
  exit(0);
} 

void drawOneSide(line l, int color) {
  tri triangl;
  line temp;

  if(l.p1.x==l.p2.x&&l.p1.y==l.p2.y)
    putpixel(screen, l.p1.x, l.p1.y, color);
  else {
    triangl.getTri(l);
    triangl.draw(color);
    color++; if(color>15) color=0;

    temp.p1.x = l.p1.x;       temp.p1.y = l.p1.y;
    temp.p2.x = triangl.p1.x; temp.p2.y = triangl.p1.y;
    drawOneSide(temp, color);

    temp.p1.x = triangl.p1.x; temp.p1.y = triangl.p1.y;
    temp.p2.x = triangl.p2.x; temp.p2.y = triangl.p2.y;
    drawOneSide(temp, color);

    temp.p1.x = triangl.p2.x; temp.p1.y = triangl.p2.y;
    temp.p2.x = triangl.p3.x; temp.p2.y = triangl.p3.y;
    drawOneSide(temp, color);

    temp.p1.x = triangl.p3.x; temp.p1.y = triangl.p3.y;
    temp.p2.x = l.p2.x;       temp.p2.y = l.p2.y;
    drawOneSide(temp, color);
    
  }
}

void tri::draw(int color) {
//  triangle(screen, p1.x, p1.y, p2.x, p2.y, p3.x, p3.y, color);
}

void tri::getTri(line l) {
  //new point = p2
  double slope;
  int length;
  point d, midpt;

  // get points 1 and 3 from points on line
  p1.x = l.p1.x +   (l.p2.x - l.p1.x) / 3;
  p1.y = l.p1.y +   (l.p2.y - l.p1.y) / 3;
  p3.x = l.p1.x + 2*(l.p2.x - l.p1.x) / 3;
  p3.y = l.p1.y + 2*(l.p2.y - l.p1.y) / 3;

  // get midpoint of points 1 and 3
  midpt.x = p1.x + (p3.x - p1.x) / 2;
  midpt.y = p1.y + (p3.y - p1.y) / 2;

  // calculate slope
  slope = (l.p1.y-l.p2.y)/(l.p1.x-l.p2.x);
  slope = -1/slope;

  length = int(sqrt( (l.p1.x-l.p2.x)*(l.p1.x-l.p2.x)+
                     (l.p1.y-l.p2.y)*(l.p1.y-l.p2.y) ));

  // d.x is some formula i worked out on paper from the distance
formula
  d.x = int(length/sqrt(1+sqrt(slope)));
  d.y = int(slope*d.x);

  // make sure new triangle is sticking out and not into previous
  if(p1.x>p3.x) d.x = -ABS(d.x);
  else          d.x =  ABS(d.x);
  if(p1.y>p3.y) d.y = -ABS(d.y);
  else          d.y =  ABS(d.y);

  // finally calculate point 2 (more trouble than it's worth)
  p2.x = midpt.x + d.x;
  p2.y = midpt.y + d.y;
}

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