precision mediump float;

varying vec4 v_color;
varying vec2 v_diffVector;
varying float v_radius;
varying float v_border;

const vec4 transparent = vec4(0.0, 0.0, 0.0, 0.0);

void main(void) {
  float dist = length(v_diffVector) - v_radius;

  float t = 0.0;
  if (dist > v_border)
    t = 1.0;
  else if (dist > 0.0)
    t = dist / v_border;

  gl_FragColor = mix(v_color, transparent, t);
}