/* 2024-03-09
 * rewrite of https://shadertoy.com/view/X3l3Rr
 *
 * gcc -Wall -o increment-tan increment-tan.c -lm
 * ./increment-tan | ffmpeg -f rawvideo -s 512x256 -r 25 -pix_fmt gray -i - -vf palettegen /tmp/palette.png
 * ./increment-tan | ffmpeg -f rawvideo -s 512x256 -r 25 -pix_fmt gray -i - -i /tmp/palette.png -filter_complex paletteuse /tmp/increment-tan.gif
 */

#if 0
/* original shader */
#define rotation(angle) mat2(cos(angle), -sin(angle), sin(angle), cos(angle));

float PI = 3.14159;
float TAU = 2.*3.14159;

void mainImage( out vec4 fragColor, in vec2 fragCoord )
{
   vec2 uv = ( fragCoord - .5* iResolution.xy ) /iResolution.y;
   uv *= .7;
   vec3 col = vec3(0.);
   float a = (3.*PI/2.)*pow(1.-length(uv),5.);
   uv *= rotation(tan(a));   
   uv.y += .2*sin(iTime+3.*TAU*uv.x)*(1.1-pow(length(uv),.25));
   col += .01/(10.*pow(uv.y,2.));
   fragColor = vec4(col,1.0);
}
#endif

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

                                     int main
                                           (void
                                               ){for
                                                 (int
                            n=0;n<9830400;         n++
                          ){float u=256-(n&511      ),v
                        =(n>>9&255)     -128,l       =sqrt
                       (u*u+v*v)/          333,      a=tan
                      ((1.5*M_PI            )*pow    (1-
                     l,5)),c=cos            (a),    s=sin
                     (a  );a=u              *s+v* c+67*
                     sin (M_PI            /50*(u*c-v*s-
                     (    n>>            17)/.75))*(1.1
                          -pow             (l,.25))
                           ;a=
                            28333
                             /a/a
                               ;putchar
                                  (a>255?255:a);}return
                                        0;}