//overlay setting tutorial http://www.netzgesta.de/busy/
//ctrl = getBusyOverlay(parent[, overlay[, busy]]);
function block_viewport() {
    getBusyOverlay('viewport',
                        { color: '#000000',
                            opacity: 0.34,
                            text: '處理中...',
                            style: 'text-shadow: 0 0 3px black;font-weight:bold;font-size:16px;color:white'
                        },
                        { color: '#fff200',
                            size: 151,
                            radius: 16,
                            weight: 16,
                            count: 12,
                            speed: 124,
                            min: 25,
                            type: 'o'
                        }
                       );
}