precision mediump float;
varying vec2 v_texcoord;
#define PI 3.14159265358979323846

float plotX(vec2 _st, float _pct,float _antia){
  return  smoothstep( _pct-_antia, _pct, _st.x) - 
          smoothstep( _pct, _pct+_antia, _st.x);
}

float plotY(vec2 _st, float _pct,float _antia){
  return  smoothstep( _pct-_antia, _pct, _st.y) - 
          smoothstep( _pct, _pct+_antia, _st.y);
}