TileLayer.Overzoom.js

L.TileLayer.Overzoom = {
    
    overzoomOptions: {
        // List of available server zoom levels in ascending order. Empty means all  
        // client zooms are available (default). Allows to only request tiles at certain
        // zooms and resizes tiles on the other zooms.
        serverZooms: []
    },

    // override _getTileSize to add serverZooms (when maxNativeZoom is not defined)
    _getTileSize: function() {
        var map = this._map,
            options = this.options,
            zoom = map.getZoom() + options.zoomOffset,
            zoomN = options.maxNativeZoom || this._getServerZoom(zoom);

        // increase tile size when overscaling
        //return zoomN && zoom > zoomN ?
        var tileSize = zoomN && zoom !== zoomN ?
            Math.round(map.getZoomScale(zoom) / map.getZoomScale(zoomN) * options.tileSize) :
            options.tileSize;

        //console.log('tileSize = ' + tileSize + ', zoomOffset = ' + this.options.zoomOffset + ', serverZoom = ' + zoomN + ', zoom = ' + zoom);
        return tileSize;
    },

    _getZoomForUrl: function () {
        var zoom = L.TileLayer.prototype._getZoomForUrl.call(this);
        var result = this._getServerZoom(zoom);
        //console.log('zoomForUrl = ' + result);
        return result;
    },

    // Returns the appropriate server zoom to request tiles for the current zoom level.
    // Next lower or equal server zoom to current zoom, or minimum server zoom if no lower 
    // (should be restricted by setting minZoom to avoid loading too many tiles).
    _getServerZoom: function(zoom) {
        var serverZooms = this.options.serverZooms || [],
            result = zoom;
        // expects serverZooms to be sorted ascending
        for (var i = 0, len = serverZooms.length; i < len; i++) {
            if (serverZooms[i] <= zoom) {
                result = serverZooms[i];
            } else {
                if (i === 0) {
                    // zoom < smallest serverZoom
                    result = serverZooms[0];
                }
                break;
            }
        }
        return result;
    }
};

if (typeof L.TileLayer.Vector !== 'undefined') {
    L.TileLayer.Vector.include(L.TileLayer.Overzoom);
    L.TileLayer.Vector.mergeOptions(L.TileLayer.Overzoom.overzoomOptions);
}

if (typeof L.TileLayer.Div !== 'undefined') {
    L.TileLayer.Div.include(L.TileLayer.Overzoom);
    L.TileLayer.Div.mergeOptions(L.TileLayer.Overzoom.overzoomOptions);
}