CodeIgniter的anchor_popup弹出界面居中显示

 <?php

$attributes = array(
    'class'     =>  'blue-button',
    'width'     =>  '800',
    'height'    =>  '600',
    'screenx'   =>  '\'+((parseInt(screen.width) - 800)/2)+\'',
    'screeny'   =>  '\'+((parseInt(screen.height) - 600)/2)+\'',
);
echo anchor_popup('program/start_worksheet/8', 'Start Worksheet', $attributes);
?>