private void present(){
  glUseProgram(quadProgram);
  glBindVertexArray(vao);
  glBindTexture(GL_TEXTURE_2D,tex);
  glBindSampler(0,this.sampler);
  glDrawArrays(GL_TRIANGLES,0,6);
  glBindSampler(0,0);
  glBindTexture(GL_TEXTURE_2D,0);
  glBindVertexArray(0);
  glUseProgram(0);
}

private void present ( ) { glUseProgram ( quadProgram ) ; glBindVertexArray ( vao ) ; glBindTexture ( GL_TEXTURE_2D , tex ) ; glBindSampler ( 0 , this . sampler ) ; glDrawArrays ( GL_TRIANGLES , 0 , 6 ) ; glBindSampler ( 0 , 0 ) ; glBindTexture ( GL_TEXTURE_2D , 0 ) ; glBindVertexArray ( 0 ) ; glUseProgram ( 0 ) ; }
present the final image on the screen / viewport .
