discard.glsl

// vertex shader
attribute vec4 a_position;
attribute vec2 a_tex_coord;
varying mediump vec2 v_tex_coord;
void main() {
  v_tex_coord = a_tex_coord;
  gl_Position = a_position;
}

// fragment shader
uniform lowp sampler2D u_texture;
varying mediump vec2 v_tex_coord;
void main() {
  if (texture2D(u_texture, v_tex_coord).a <= 0.05) {
    discard;
  }
}