Javascript hexmap display

hexagon map

After a good bit of head-scratching I’ve managed to make some progress on what I assumed was going to be one of the more difficult aspects of the hex-map project: actually displaying the hexes in a browser.  This also turned out to be a good opportunity to finally dig into jQuery a little more deeply, too.  I’ve come up with a rough idea of how to proceed from here, too; I’ll have the page make Ajax calls out to Scala to retrieve map details in JSON and it should be pretty easy to dynamically construct the hex grids from there.

Github, probably wisely, doesn’t display checked-in HTML directly in the browser, but I’ll attach a screenshot here; interested parties can check out the code on github under src/main/webapp.  Currently the page generates a new random map on every page refresh, with each map being a mixture of roughly 2/3 desert tiles and 1/3 ocean tiles.  The data structure is a simple 2-dimensional array:

 var map = [["desert", "ocean", "desert"],
            ["desert", "ocean", "desert"],
            ["desert", "desert", "ocean"]]

Obviously for a full game implementation the elements would be complex JSON structures, not strings, but this suffices for now.  To tile the hexes together, I’m simply laying them on top of one another via CSS absolute positioning; each image is a rectangle (actually, a square) with the diagonal edges cut out of the sides.  I was a little worried this would make it cumbersome to attach jQuery event handlers to the right places, but I currently have a handler that displays the (x,y) coordinates of a hex when a user mouses over one and it seems very usable, if not perfect around the edges of hexes.

The code I’m using to position the tiles looks roughly like this (note: some cleanup is still pending in the actual code; what follows is the gist but see the code itself for details).  Here tile is a string from the previous array, and x and y are row / column numbers.

function placeTile(tile, x, y) {
  var tile$ = $("." + tile, "#templates").children().clone();

  tile$.hexMapPosition(x, y).appendTo($('#hexmap'));
}

This code clones images based on the tile name from the map data structure. The images themselves are stored in a hidden div:

<div id="templates" class="hidden">
  <div class="tiles desert">
    <img src="images/tiles/desert.png" width="72" height="72"/>
  </div>
  <div class="tiles ocean">
    <img src="images/tiles/ocean.png" width="72" height="72"/>
  </div>
</div>

It then positions them via a jQuery extension, hexMapPosition(), which examines the image’s height and width and then calculates an absolute position for the top left pixel.

  (function($) {
    $.fn.hexMapPosition = function(row, column) {
      var tile_width = this.attr("width");
      var tile_height = this.attr("height");

      // Haven't done the math to check these but they work
      var y_offset = tile_height / 2;
      var x_offset = tile_width / 4;

      var xpos = row * (tile_width - x_offset));
      var ypos = column * tile_height);

      if (row % 2 == 0) {
        ypos -= y_offset;    // Every other row, offset down
      }

      return this.css({"position": "absolute", "top": ypos, "left": xpos});
    }
  })(jQuery);

This isn’t perfect, but it’s a good place to start. Some problems I’ve got with it:

  • The hexagon pngs are ones I’ve borrowed from the Battle for Wesnoth project, and are a bit irregular (literally – the top edges are shorter than those on the sides). This does seem to make the math easy, though. I should note here that the PNGs are published under the GPLv2, though to be honest, I have no clue how the GPLv2 could possibly apply to images.
  • I’m a little worried that overlaying further PNGs on top of these ones (for map highlighting, roads, player markers, etc) will interfere with the mouseover events, but I’ll need to experiment.
  • I had a lot of trouble trying to get little borders to appear between hexes by monkeying with the positioning values above.

Edit: having recently discovered jsfiddle, I uploaded a fiddle of this there. I’ve also manage to clean up the code so that it is currently in much better shape on jsfiddle than it is in github, but the github version will be changing and it will be nice to keep a clean version of the basic idea around.

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2 Comments

  1. Pedro

     /  September 18, 2013

    Hi Tim, great post. Do you have any pointers as to how would I get a Java generated map in..say, a List to be usable in your JavaScript code? Thanks in advance.

    Reply
  2. Hi Pedro… For Java / JavaScript interoperability you have a lot of options and it depends somewhat on what your web server architecture is like. The most straightforward way would probably be to expose your Java List as a web service, then have your JavaScript code call the service and use the data it provides to make the hexmap. It might look something like this:

    $ curl http://localhost:3333/map
    [[“desert”, “ocean”, “desert” ], [“ocean”, “ocean”, “desert”]] // etc…

    From the Java side the simplest way to convert your List to JSON that the javascript can read might be with something like Jackson (for the web server) and Jersey or Jackson or MOXy (for the JSON conversion). I personally like Google’s Gson library for doing java -> json mapping.

    Reply

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