Calculate shifted area of google map

gistfile1.js

/**
 * Calculate bounds for the whole map or just the shifted area
 * @param  {Boolean} reset Force calculation for the whole map
 * @return {Array} Array of map bounds arrays
 */
function calculateNewBounds(reset) {

  var curSW  = currentBounds.getSouthWest(),
    curNE    = currentBounds.getNorthEast(),
    curNW    = new google.maps.LatLng(curNE.lat(), curSW.lng()),
    curSE    = new google.maps.LatLng(curSW.lat(), curNE.lng()),
    
    preSW    = previousBounds.getSouthWest(),
    preNE    = previousBounds.getNorthEast(),
    preNW    = new google.maps.LatLng(preNE.lat(), preSW.lng()),
    preSE    = new google.maps.LatLng(preSW.lat(), preNE.lng()),
    
    shiftSE  = currentBounds.contains(preNW),
    shiftSW  = currentBounds.contains(preNE),
    shiftNE  = currentBounds.contains(preSW),
    shiftNW  = currentBounds.contains(preSE),
    shiftN   = shiftNE && shiftNW,
    shiftS   = shiftSE && shiftSW,
    shiftW   = shiftNE && shiftSE,
    shiftE   = shiftNW && shiftSW,
    
    roundNum = Utils.roundNum;
  
  // Initial request, zoom in or zoom out, forced reset
  // We need bounds for whole map
  if (reset ||
    (shiftNE && shiftSE && shiftNW && shiftSW) ||
    (!shiftNE && !shiftSE && !shiftNW && !shiftSW) ||
    (curSW.lng() > curNE.lng())) {
    return [
      [roundNum(curSW.lat(), 6), roundNum(curSW.lng(), 6)],
      [roundNum(curNE.lat(), 6), roundNum(curNE.lng(), 6)]
    ];
  } 

  // Map is dragged - we need bounds only for the new area
  if (shiftS) {
    return [
      [roundNum(curNE.lat(), 6), roundNum(curNE.lng(), 6)],
      [roundNum(preNW.lat(), 6), roundNum(preNW.lng(), 6)]
    ];      
  }

  if (shiftN) {
    return [
      [roundNum(curSW.lat(), 6), roundNum(curSW.lng(), 6)],
      [roundNum(preSE.lat(), 6), roundNum(preSE.lng(), 6)]
    ];      
  }

  if (shiftE) {
    return [
      [roundNum(curSW.lat(), 6), roundNum(curSW.lng(), 6)],
      [roundNum(preNW.lat(), 6), roundNum(preNW.lng(), 6)]
    ];      
  }

  if (shiftW) {
    return [
      [roundNum(preSE.lat(), 6), roundNum(preSE.lng(), 6)],
      [roundNum(curNE.lat(), 6), roundNum(curNE.lng(), 6)]
    ];      
  }

  if (shiftSE) {
    return [
      [roundNum(curNW.lat(), 6), roundNum(curNW.lng(), 6)],
      [roundNum(curNE.lat(), 6), roundNum(curNE.lng(), 6)],
      [roundNum(preNE.lat(), 6), roundNum(curNE.lng(), 6)],
      [roundNum(preNW.lat(), 6), roundNum(preNW.lng(), 6)],
      [roundNum(curSW.lat(), 6), roundNum(preSW.lng(), 6)],
      [roundNum(curSW.lat(), 6), roundNum(curSW.lng(), 6)]
    ];
  } 

  if (shiftSW) {
    return [
      [roundNum(curNW.lat(), 6), roundNum(curNW.lng(), 6)],
      [roundNum(curNE.lat(), 6), roundNum(curNE.lng(), 6)],
      [roundNum(curSE.lat(), 6), roundNum(curSE.lng(), 6)],
      [roundNum(curSW.lat(), 6), roundNum(preNE.lng(), 6)],
      [roundNum(preNE.lat(), 6), roundNum(preNE.lng(), 6)],
      [roundNum(preNE.lat(), 6), roundNum(curSW.lng(), 6)]
    ];
  }

  if (shiftNE) {
    return [
      [roundNum(curNW.lat(), 6), roundNum(curNW.lng(), 6)],
      [roundNum(curNE.lat(), 6), roundNum(preSW.lng(), 6)],
      [roundNum(preSW.lat(), 6), roundNum(preSW.lng(), 6)],
      [roundNum(preSW.lat(), 6), roundNum(curNE.lng(), 6)],
      [roundNum(curSE.lat(), 6), roundNum(curSE.lng(), 6)],
      [roundNum(curSW.lat(), 6), roundNum(curSW.lng(), 6)]
    ];
  }

  if (shiftNW) {
    return [
      [roundNum(curNE.lat(), 6), roundNum(preNE.lng(), 6)],
      [roundNum(curNE.lat(), 6), roundNum(curNE.lng(), 6)],
      [roundNum(curSE.lat(), 6), roundNum(curSE.lng(), 6)],
      [roundNum(curSW.lat(), 6), roundNum(curSW.lng(), 6)],
      [roundNum(preSW.lat(), 6), roundNum(curSW.lng(), 6)],
      [roundNum(preSE.lat(), 6), roundNum(preSE.lng(), 6)]
    ];
  }

}