//do the downsampling
  tex.bind();
  glTexParameteri( GL_TEXTURE_2D, GL_TEXTURE_MIN_FILTER, GL_LINEAR_MIPMAP_LINEAR );
  glTexParameteri( GL_TEXTURE_2D, GL_TEXTURE_MAG_FILTER, GL_LINEAR );
  glTexParameteri( GL_TEXTURE_2D, GL_TEXTURE_WRAP_S, GL_CLAMP_TO_EDGE );
  glTexParameteri( GL_TEXTURE_2D, GL_TEXTURE_WRAP_T, GL_CLAMP_TO_EDGE );
  glGenerateMipmap( GL_TEXTURE_2D );

  //process the half res texture
  glViewport( 0, 0, o->conf.SCREEN_WIDTH / 2, o->conf.SCREEN_HEIGHT / 2 );

  half_fbo.bind();
  shader->bind();

  shader->pass_m4x4( o->ppl.get_projection_matrix(), "proj" );
  shader->pass_m4x4( o->ppl.get_model_view_matrix(), "modelview" );
  shader->pass_int( 0, "texture0" );

  tex.bind();
//how do I select the desired mipmap level here?
  quad.render();

  shader->unbind();
  half_fbo.unbind();

  //do the downsampling
  tex.bind();
  glTexParameteri( GL_TEXTURE_2D, GL_TEXTURE_MIN_FILTER, GL_LINEAR_MIPMAP_LINEAR );
  glTexParameteri( GL_TEXTURE_2D, GL_TEXTURE_MAG_FILTER, GL_LINEAR );
  glTexParameteri( GL_TEXTURE_2D, GL_TEXTURE_WRAP_S, GL_CLAMP_TO_EDGE );
  glTexParameteri( GL_TEXTURE_2D, GL_TEXTURE_WRAP_T, GL_CLAMP_TO_EDGE );
  glGenerateMipmap( GL_TEXTURE_2D );
  //process the half res texture
  glViewport( 0, 0, o->conf.SCREEN_WIDTH / 2, o->conf.SCREEN_HEIGHT / 2 );
  half_fbo.bind();
  shader->bind();
  shader->pass_m4x4( o->ppl.get_projection_matrix(), "proj" );
  shader->pass_m4x4( o->ppl.get_model_view_matrix(), "modelview" );
  shader->pass_int( 0, "texture0" );
  tex.bind();
//how do I select the desired mipmap level here?
  quad.render();
  shader->unbind();
  half_fbo.unbind();

  //do the downsampling
  tex.bind();
  glTexParameteri( GL_TEXTURE_2D, GL_TEXTURE_MIN_FILTER, GL_LINEAR_MIPMAP_LINEAR );
  glTexParameteri( GL_TEXTURE_2D, GL_TEXTURE_MAG_FILTER, GL_LINEAR );
  glTexParameteri( GL_TEXTURE_2D, GL_TEXTURE_WRAP_S, GL_CLAMP_TO_EDGE );
  glTexParameteri( GL_TEXTURE_2D, GL_TEXTURE_WRAP_T, GL_CLAMP_TO_EDGE );
  glGenerateMipmap( GL_TEXTURE_2D );
 
  //process the half res texture
  glViewport( 0, 0, o->conf.SCREEN_WIDTH / 2, o->conf.SCREEN_HEIGHT / 2 );

  half_fbo.bind();
  shader->bind();

  shader->pass_m4x4( o->ppl.get_projection_matrix(), "proj" );
  shader->pass_m4x4( o->ppl.get_model_view_matrix(), "modelview" );
  shader->pass_int( 0, "texture0" );

  tex.bind();
//how do I select mipmap level here?
  quad.render();

  shader->unbind();
  half_fbo.unbind();