uniform vec2 u_resolution;
uniform vec2 u_mouse;
uniform float u_duration;
uniform float u_time;
uniform float u_time_end;

void main() {
  float tick = (u_time_end - u_time) / u_duration;
  float blink = smoothstep(1.0, 0.5, tick);
  vec4 color = vec4(blink, blink, blink, 1.0);
  gl_FragColor = gl_Color * color;
}