50 . Shades of Grey for GLSL

shaders_of_gray.frag

uniform vec2 u_resolution;
void main(){
  vec2 st = gl_FragCoord.xy/u_resolution.xy;
  vec3 color;
  float shaders = 50.0;
  for(float i = 0.0; i < shaders; i++){
    float left = step(1.0/shaders*(shaders - i), st.x);
    color += vec3(left * 1.0/shaders);
    gl_FragColor = vec4(color,1.0);
  }
}