/* 2022-11-04
 *
 * inspired by https://arxiv.org/abs/2210.17320
 *     The Kochawave curve, a variant of the Koch curve
 *     Rémy Sigrist
 *
 * gcc -Wall -o koch koch.c -lm
 * ./koch |./gui -w 160 -h 90 -scale4 -bgra -stdout > XX
 * ffmpeg -f rawvideo -s 640x360 -r 25 -pix_fmt bgra -i XX -vf palettegen palette.png
 * ffmpeg -f rawvideo -s 640x360 -r 25 -pix_fmt bgra -i XX -i palette.png -filter_complex paletteuse koch.gif
 *
 * gui.c is at http://sedcore.eu.org/small/gui.c
 */

#include <stdio.h>
#include <math.h>

typedef struct {
  unsigned char r, g, b;
} color_t;

unsigned char screen[160*90*4];

void point(int x, int y, color_t color)
{
  y = 90 - y;
  if (x < 0 || x > 159 || y < 0 || y > 89) return;
  screen[(y * 160 + x) * 4] = color.b;
  screen[(y * 160 + x) * 4 + 1] = color.g;
  screen[(y * 160 + x) * 4 + 2] = color.r;
}

void koch(float x1, float y1, float x2, float y2, int frame)
{
  float x3, y3;
  float x4, y4;
  float x5, y5;

  if (fabs(x1-x2) < .5 && fabs(y1-y2) < .5) {
    point(x1, y1, (color_t){192,0,0});
    return;
  }

  x3 = x1 + (x2 - x1) / 3;
  y3 = y1 + (y2 - y1) / 3;

  x5 = x2 - (x2 - x1) / 3;
  y5 = y2 - (y2 - y1) / 3;

  x4 = x5 - x3;
  y4 = y5 - y3;
  /* cos + isin *  x + iy =   cos x - sin y + i sin x + cos y */
  float c = 1. / 2;
  float s = sqrt(3) / 2;
  float x4n = c * x4 - s * y4;
  float y4n = s * x4 + c * y4;
  x4 = x4n + x3;
  y4 = y4n + y3;

  double angle = atan2(y2-y1, x2-x1);
  double length = sqrt((y2-y1)*(y2-y1) + (x2-x1)*(x2-x1)) * 2./3;

  float f = cos(2 * M_PI * frame / 100);
  float g = sin(2 * M_PI * frame*2 / 100);
  float x = f * length / 2;
  float y = g * length / 2. / 4.;
  c = cos(angle);
  s = sin(angle);
  float xn = c * x - s * y;
  float yn = s * x + c * y;
  x4 += xn;
  y4 += yn;

  koch(x1, y1, x3, y3, frame);
  koch(x3, y3, x4, y4, frame);
  koch(x4, y4, x5, y5, frame);
  koch(x5, y5, x2, y2, frame);
}

void clear(void)
{
  unsigned char *s = screen;
  int i;
  for (i = 0; i < 160*90; i++, s+=4) { s[0] = 203; s[1] = 192; s[2] = 255; s[3] = 255; }
}

void dump(void)
{
  fwrite(screen, 160*90*4, 1, stdout);
}

int main(void)
{
  int frame = 0;
  while (frame < 100) {
    clear();
    koch(0, 10, 160, 10, frame);
    dump();
    frame++;
  }
  fflush(stdout);
  return 0;
}