source: binary-improvements/webserver_legacy/js/leaflet.regionlayer.js@ 501

function GetRegionLayer (mapinfo) {
        var FormatRegionFileName = function(latlng) {
                return "r." + latlng.lat + "." + latlng.lng + ".7rg";
        }

        var regionLayer = L.gridLayer({
                maxZoom: mapinfo.maxzoom + 1,
                minZoom: 0,
                maxNativeZoom: mapinfo.maxzoom + 1,
                tileSize: mapinfo.tilesize,
        });

        regionLayer.createTile = function(tilePoint) {
                var blockWorldSize = mapinfo.tilesize * Math.pow(2, mapinfo.maxzoom - tilePoint.z);
                var tileLeft = tilePoint.x * blockWorldSize;
                var tileBottom = (-1-tilePoint.y) * blockWorldSize;
                var blockPos = L.latLng(tileLeft, tileBottom);

                var canvas = L.DomUtil.create('canvas', 'leaflet-tile');
                canvas.width = mapinfo.tilesize;
                canvas.height = mapinfo.tilesize;
                var ctx = canvas.getContext('2d');

                ctx.strokeStyle = "lightblue";
                ctx.fillStyle = "lightblue";
                ctx.lineWidth = 1;
                ctx.font="14px Arial";

                var lineCount = blockWorldSize / mapinfo.regionsize;
                if (lineCount >= 1) {
                        var pos = 0;
                        while (pos < mapinfo.tilesize) {
                                // Vertical
                                ctx.beginPath();
                                ctx.moveTo(pos, 0);
                                ctx.lineTo(pos, mapinfo.tilesize);
                                ctx.stroke();
                
                                // Horizontal
                                ctx.beginPath();
                                ctx.moveTo(0, pos);
                                ctx.lineTo(mapinfo.tilesize, pos);
                                ctx.stroke();

                                pos += mapinfo.tilesize / lineCount;
                        }
                        ctx.fillText(FormatRegionFileName(CoordToRegion(blockPos)), 4, mapinfo.tilesize-5);
                } else {
                        if ((tileLeft % mapinfo.regionsize) == 0) {
                                // Vertical
                                ctx.beginPath();
                                ctx.moveTo(0, 0);
                                ctx.lineTo(0, mapinfo.tilesize);
                                ctx.stroke();
                        }
                        if ((tileBottom % mapinfo.regionsize) == 0) {
                                // Horizontal
                                ctx.beginPath();
                                ctx.moveTo(0, mapinfo.tilesize);
                                ctx.lineTo(mapinfo.tilesize, mapinfo.tilesize);
                                ctx.stroke();
                        }
                        if ((tileLeft % mapinfo.regionsize) == 0 && (tileBottom % mapinfo.regionsize) == 0) {
                                ctx.fillText(FormatRegionFileName(CoordToRegion(blockPos)), 4, mapinfo.tilesize-5);
                        }
                }
                return canvas;
        }
        
        return regionLayer;
}