unnamed.glsl

$HEADER$

float PI = 3.1415926535;
uniform vec2 resolution;
uniform float time;

vec2 rotate(vec2 pos, float angle, vec2 center){
  pos -= center;
  pos *= mat2(cos(angle), sin(-angle), sin(angle), cos(angle));
  pos += center;
  return pos;
}

vec2 scale(vec2 pos, float scale, vec2 center){
  pos -= center;
  pos *= scale;
  pos += center;
  return pos;
}

float nsin(float v){
  return .5 + .5 * sin(v);
}

void main(){
  vec2 pos = gl_FragCoord.xy / resolution.xy;
  vec2 center = vec2(.5, .5);
  float line_width = 4. / resolution.x;
  float r = 0.; float g = 0.; float b = 0.;
  float d = distance(pos, center);

  pos = rotate(pos, -time + 30. * log(sin(d)) / 10., center);
  pos = scale(pos, nsin(time), center);

  if (min(mod(pos.x, .1), mod(pos.y, .1)) < line_width) {
    r = 1.0;
    g = 1.0;
    b = 1.0;
  }

  gl_FragColor = vec4( r, g, b, 1.0);
}