How to enforce provider limits on interaction and tile loading in Modest Maps JS

See issue 57 for discussion and planned improvements.

<!DOCTYPE html>
<html>
<head>
<title>Modest Maps JS</title>
<script type="text/javascript" src="https://cdn.jsdelivr.net/gh/stamen/modestmaps-js/v0.18.4/modestmaps.min.js"></script>
<script type="text/javascript">
window.onload = function() {

// "import" the namespace
    var MM = com.modestmaps;
    
    var provider = new MM.TemplatedMapProvider("https://otile1.mqcdn.com/tiles/1.0.0/osm/{Z}/{X}/{Y}.png");

// override provider limits so that tiles are not loaded unless they are inside these bounds:
    var minZoom = 2;
    var maxZoom = 10;
    var topLeft = new MM.Location(51.4, -131.8);
    var bottomRight = new MM.Location(21.5, -50.5);

provider.bottomRightInnerLimit = provider.locationCoordinate(bottomRight).zoomTo(maxZoom);
    provider.topLeftOuterLimit = provider.locationCoordinate(topLeft).zoomTo(minZoom);

// override sourceCoordinate so that it doesn't use coord limits to wrap tiles
    // but so that it rejects any tile coordinates that lie outside the limits
    provider.sourceCoordinate = function(coord) {
        // don't need .container() stuff here but it means *something* will get loaded at low zoom levels
        // e.g. at level 0 the base tile could contain the entire extent
        // skip the .container() stuff if you don't want to load/render tiles outside the extent *at all*
        var TL = this.topLeftOuterLimit.zoomTo(coord.zoom).container();
        var BR = this.bottomRightInnerLimit.zoomTo(coord.zoom).container().right().down();
        if (coord.row < TL.row || coord.row >= BR.row || coord.column < TL.column || coord.column >= BR.column) {
            // it's too high or too low or too lefty or too righty:
            return null;
        }
        // otherwise it's cool, let it through
        return coord;
    }
    
    var map = new MM.Map(document.body, provider);

// override enforceLimits so that you can't pan outside the given limits
    // Prevent the user from navigating the map outside the `outerLimits`
    // of the map's provider.
    map.enforceLimits = function(coord) {
        coord = coord.copy();
        var limits = this.provider.outerLimits();
        if (limits) {
            var minZoom = limits[0].zoom;
            var maxZoom = limits[1].zoom;
            if (coord.zoom < minZoom) {
                coord = coord.zoomTo(minZoom);
            }
            else if (coord.zoom > maxZoom) {
                coord = coord.zoomTo(maxZoom);
            }
    
            // this generally does the *intended* thing,
            // but it's not always desired behavior so it's disabled for now
    
            var topLeftLimit = limits[0].zoomTo(coord.zoom);
            var bottomRightLimit = limits[1].zoomTo(coord.zoom);
            var currentTopLeft = this.pointCoordinate(new MM.Point(0,0));
            var currentBottomRight = this.pointCoordinate(this.dimensions);
    
            if (bottomRightLimit.row - topLeftLimit.row < currentBottomRight.row - currentTopLeft.row) {
                // if the limit is smaller than the current view center it
                coord.row = (bottomRightLimit.row + topLeftLimit.row) / 2;
            }
            else {
                if (currentTopLeft.row < topLeftLimit.row) {
                    coord.row += topLeftLimit.row - currentTopLeft.row;
                }
                else if (currentBottomRight.row > bottomRightLimit.row) {
                    coord.row -= currentBottomRight.row - bottomRightLimit.row;
                }
            }
            if (bottomRightLimit.column - topLeftLimit.column < currentBottomRight.column - currentTopLeft.column) {
                // if the limit is smaller than the current view, center it
                coord.column = (bottomRightLimit.column + topLeftLimit.column) / 2;                    
            }
            else {
                if (currentTopLeft.column < topLeftLimit.column) {
                    coord.column += topLeftLimit.column - currentTopLeft.column;
                }
                else if (currentBottomRight.column > bottomRightLimit.column) {
                    coord.column -= currentBottomRight.column - bottomRightLimit.column;
                }
            }
    
        }
        return coord;
    }

map.setCenterZoom(new MM.Location(37.811530, -122.2666097), 5);
    
}
</script>
<style>
html, body {
  width: 100%;
  height: 100%;
  margin: 0;
  padding: 0;
  border: 0;
}
</style>
</head>
<body>
</body>
</html>

Updated missing url https://raw.github.com/stamen/modestmaps-js/v0.18.4/modestmaps.min.js to https://cdn.jsdelivr.net/gh/stamen/modestmaps-js/v0.18.4/modestmaps.min.js

https://raw.github.com/stamen/modestmaps-js/v0.18.4/modestmaps.min.js