precision mediump float;

#endif

​

varying vec2 pos;

​

uniform sampler2D filter_background;

uniform vec2 filter_res;

​

void main() {

  vec4 col = texture2D(filter_background, pos);

  // Step function returns

  // 0 if colour is less than 0.01

  // 1 otherwise

  // so we make the colour 0 (black), if it's less than 0.01

  col = col * step(0.1, col);

  gl_FragColor = col;

}