uniform vec2 u_resolution;
uniform vec2 u_mouse;
uniform float u_time;

#define PI 3.14159265358979323846

vec2 rotate2D(vec2 st, float angle, float view_at=0.5, float origin=0.5) {
  st -= view_at;
  st = mat2(cos(angle), -sin(angle),
      sin(angle), cos(angle)) * st;
  st += origin;
  return st;
}

float box(vec2 st, vec2 size, float smoothEdges) {
  size = vec2(0.5) - size * 0.5;
  vec2 aa = vec2(smoothEdges * 0.5);
  vec2 uv = smoothstep(size, size + aa, st);
  uv *= smoothstep(size, size+aa, vec2(1.0) - st);
  return uv.x * uv.y;
}

vec2 tile(vec2 st, float zoom) {
  st *= zoom;
  return fract(st);
}

float circle(vec2 st, float radius) {
  vec2 l = st - vec2(0.5);
  return 1.0 - smoothstep(radius - (radius * 0.01),
      radius+(radius * 0.01),
      dot(l,l) * 4.0);
}

void main() {
  vec2 st = gl_FragCoord.xy/u_resolution;
  vec3 color = vec3(0.0);
  vec2 mouse_at = smoothstep(0.1, 0.9, u_mouse/u_resolution);

  st = tile(st, 4.0);

  st = rotate2D(st, PI * sin(u_time) / 4, 0.5, mouse_at);

  color = vec3(box(st, vec2(0.7), 0.01));

  gl_FragColor = vec4(color, 1.0);
}