thebookofshaders/09/dots1.frag

// Author @patriciogv ( patriciogonzalezvivo.com ) - 2015

#ifdef GL_ES
precision mediump float;
#endif

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

vec2 tile(vec2 _st, float _zoom){
  _st *= _zoom;
  return fract(_st);
}

float circle(vec2 _st, float _radius){
  vec2 pos = vec2(0.5)-_st;
  _radius *= 0.75;
  return 1.-smoothstep(_radius-(_radius*0.05),_radius+(_radius*0.05),dot(pos,pos)*3.14);
}

void main(){

  vec2 st = gl_FragCoord.xy/u_resolution.xy;
  st.x *= u_resolution.x/u_resolution.y;
  st = tile(st,5.);
  vec3 color = vec3(circle(st+vec2(0.,-.5), 0.35)+
                    circle(st+vec2(0.,.5), 0.35)+
                    circle(st+vec2(-.5,0.), 0.35)+
                    circle(st+vec2(.5,0.), 0.35));

  gl_FragColor = vec4(color,1.0);
}