Google지도 API V3에서 중심점을 오프셋하는 방법

'use strict';

const TILE_SIZE = {
  height: 256,
  width: 256
}; // google World tile size, as of v3.22
const ZOOM_MAX = 21; // max google maps zoom level, as of v3.22
const BUFFER = 15; // edge buffer for fitting markers within viewport bounds

const mapOptions = {
  zoom: 14,
  center: {
    lat: 34.075328,
    lng: -118.330432
  },
  options: {
    mapTypeControl: false
  }
};
const markers = [];
const mapDimensions = {};
const mapOffset = {
  x: 0,
  y: 0
};
const mapEl = document.getElementById('gmap');
const overlayEl = document.getElementById('overlay');
const gmap = new google.maps.Map(mapEl, mapOptions);

const updateMapDimensions = () => {
  mapDimensions.height = mapEl.offsetHeight;
  mapDimensions.width = mapEl.offsetWidth;
};

const getBoundsZoomLevel = (bounds, dimensions) => {
  const latRadian = lat => {
    let sin = Math.sin(lat * Math.PI / 180);
    let radX2 = Math.log((1 + sin) / (1 - sin)) / 2;
    return Math.max(Math.min(radX2, Math.PI), -Math.PI) / 2;
  };
  const zoom = (mapPx, worldPx, fraction) => {
    return Math.floor(Math.log(mapPx / worldPx / fraction) / Math.LN2);
  };
  const ne = bounds.getNorthEast();
  const sw = bounds.getSouthWest();
  const latFraction = (latRadian(ne.lat()) - latRadian(sw.lat())) / Math.PI;
  const lngDiff = ne.lng() - sw.lng();
  const lngFraction = ((lngDiff < 0) ? (lngDiff + 360) : lngDiff) / 360;
  const latZoom = zoom(dimensions.height, TILE_SIZE.height, latFraction);
  const lngZoom = zoom(dimensions.width, TILE_SIZE.width, lngFraction);
  return Math.min(latZoom, lngZoom, ZOOM_MAX);
};

const getBounds = locations => {
  let northeastLat;
  let northeastLong;
  let southwestLat;
  let southwestLong;
  locations.forEach(function(location) {
    if (!northeastLat) {
      northeastLat = southwestLat = location.lat;
      southwestLong = northeastLong = location.lng;
      return;
    }
    if (location.lat > northeastLat) northeastLat = location.lat;
    else if (location.lat < southwestLat) southwestLat = location.lat;
    if (location.lng < northeastLong) northeastLong = location.lng;
    else if (location.lng > southwestLong) southwestLong = location.lng;
  });
  const northeast = new google.maps.LatLng(northeastLat, northeastLong);
  const southwest = new google.maps.LatLng(southwestLat, southwestLong);
  const bounds = new google.maps.LatLngBounds();
  bounds.extend(northeast);
  bounds.extend(southwest);
  return bounds;
};

const zoomWithOffset = shouldZoom => {
  const currentzoom = gmap.getZoom();
  const newzoom = shouldZoom ? currentzoom + 1 : currentzoom - 1;
  const offset = {
    x: shouldZoom ? -mapOffset.x / 4 : mapOffset.x / 2,
    y: shouldZoom ? -mapOffset.y / 4 : mapOffset.y / 2
  };
  const newCenter = offsetLatLng(gmap.getCenter(), offset.x, offset.y);
  if (shouldZoom) {
    gmap.setZoom(newzoom);
    gmap.panTo(newCenter);
  } else {
    gmap.setCenter(newCenter);
    gmap.setZoom(newzoom);
  }
};

const setMapBounds = locations => {
  updateMapDimensions();
  const bounds = getBounds(locations);
  const dimensions = {
    width: mapDimensions.width - mapOffset.x - BUFFER * 2,
    height: mapDimensions.height - mapOffset.y - BUFFER * 2
  };
  const zoomLevel = getBoundsZoomLevel(bounds, dimensions);
  gmap.setZoom(zoomLevel);
  setOffsetCenter(bounds.getCenter());
};

const offsetLatLng = (latlng, offsetX, offsetY) => {
  offsetX = offsetX || 0;
  offsetY = offsetY || 0;
  const scale = Math.pow(2, gmap.getZoom());
  const point = gmap.getProjection().fromLatLngToPoint(latlng);
  const pixelOffset = new google.maps.Point((offsetX / scale), (offsetY / scale));
  const newPoint = new google.maps.Point(
    point.x - pixelOffset.x,
    point.y + pixelOffset.y
  );
  return gmap.getProjection().fromPointToLatLng(newPoint);
};

const setOffsetCenter = latlng => {
  const newCenterLatLng = offsetLatLng(latlng, mapOffset.x / 2, mapOffset.y / 2);
  gmap.panTo(newCenterLatLng);
};

const locations = [{
  name: 'Wilshire Country Club',
  lat: 34.077796,
  lng: -118.331151
}, {
  name: '301 N Rossmore Ave',
  lat: 34.077146,
  lng: -118.327805
}, {
  name: '5920 Beverly Blvd',
  lat: 34.070281,
  lng: -118.331831
}];

locations.forEach(function(location) {
  let marker = new google.maps.Marker({
    position: new google.maps.LatLng(location.lat, location.lng),
    title: location.name
  })
  marker.setMap(gmap);
  markers.push(marker);
});

mapOffset.x = overlayEl.offsetWidth;

document.zoom = bool => zoomWithOffset(bool);
document.setBounds = () => setMapBounds(locations);

section {
  height: 180px;
  margin-bottom: 15px;
  font-family: sans-serif;
  color: grey;
}
figure {
  position: relative;
  margin: 0;
  width: 100%;
  height: 100%;
}
figcaption {
  position: absolute;
  left: 15px;
  top: 15px;
  width: 120px;
  padding: 15px;
  background: white;
  box-shadow: 0 2px 5px rgba(0, 0, 0, .3);
}
gmap {
  display: block;
  height: 100%;
}

<script type="text/javascript" src="https://maps.googleapis.com/maps/api/js"></script>

<section>
  <figure>
    <gmap id="gmap"></gmap>
    <figcaption id="overlay">
      <h4>Tile Overlay</h4>
      <p>To be avoided by the map!</p>
    </figcaption>
  </figure>
</section>
<button onclick="zoom(true)">zoom in</button>
<button onclick="zoom(false)">zoom out</button>
<button onclick="setBounds()">set bounds</button>