PHP + CodeIgniter + Canvas // PARTE PHP

//Controller file
    public function sketch($idWork = null) {
        $this->load->helper('rocks');

        if ( ! file_exists(APPPATH.'/views/pages/sketch.php')) {
            show_404();
        }

        $session_data = $this->session->userdata('logged_in');

        if ( !$session_data) {
            set_log("Accesso alla vista 'rocks' non consentito.");
            show_403();
        }

        $sketch = get_rock_sketch_by_work($this->uri->segment('3'));
        $data['saved'] = get_saved_sketch($this->uri->segment('3'));

        $data['email'] = $session_data['email'];

        if(isset($sketch) && $sketch != "") {
            $data['background'] = $sketch;
        } else {
            $data['background'] = "";
        }

        $this->load->view('templates/header', $data);
        $this->load->view('pages/sketch', $data);
        $this->load->view('templates/footer', $data);
    }

    function save_sketch() {
        $this->load->helper('form');

        $data = array(
            'canvas' => $this->input->post('sketch')
        );

        $this->db->where('id', $this->input->post('segment'));
        $this->db->update('manager_works', $data);

        $this->session->set_flashdata('msg', '<div class="alert alert-success text-center">Sketch aggiornato correttamente!</div>');
        redirect('pages/sketch/' . $this->input->post('segment'));
    }



// --------------------------------------------------
// Helper

function get_rock_sketch_by_work($idWork) {
    $CI = &get_instance();
    $CI->db->select('rock');
    $CI->db->from('manager_works');
    $CI->db->where('id', $idWork);
    $query = $CI->db->get();

    if($query->num_rows() > 0) {
        $idRock = $query->result();

        $CI->db->select('sketch');
        $CI->db->from('manager_rocks');
        $CI->db->where('id', $idRock[0]->rock);
        $query = $CI->db->get();
        $sketch = $query->result();
        return "/uploads/" . $sketch[0]->sketch;
    } else {
        return null;
    }
}

function get_saved_sketch($idWork) {
    $CI = &get_instance();
    $CI->db->select('canvas');
    $CI->db->from('manager_works');
    $CI->db->where('id', $idWork);
    $query = $CI->db->get();

    if($query->num_rows() > 0) {
        $saved = $query->result();

        return $saved[0]->canvas;
    } else {
        return null;
    }
}