question: 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 ) ; }
target:  Present the final image on the screen/viewport.