#ifdef GL_ES
precision mediump float;
#endif

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

float circle(in vec2 _st,in float _radius){
  vec2 dist=_st-vec2(.5);
  return 1.-smoothstep(_radius-(_radius*.01),
  _radius+(_radius*.01),
  dot(dist,dist)*25.*(1.-.5*abs(sin(u_time))));
}

void main(){
  vec2 st=gl_FragCoord.xy/u_resolution.xy;
  st.x*=u_resolution.x/u_resolution.y;
  vec3 color=vec3(0.);
  float r=step(.7,sin(10.*u_time+10.*(sin(st.y)/sin(st.x))));
  color=circle(st,r)*vec3(st.yxx);
  gl_FragColor=vec4(color,1.);
}