mess.js

Is a stylesheet renderer for Mapnik. It's an evolution of the Cascadenik idea and language, with an emphasis on speed and flexibility.

Installation

Follow the directions to install node-zipfile and then:

npm install mess

note: possibly broken on ubuntu

MML

incompatibility

• MML files are assumed to be JSON, not XML. The files are near-identical to the XML files accepted by Cascadenik, just translated into JSON.
• Like Cascadenik, you can also include remote stylesheets, by including their URLs as simple strings in the Stylesheet array.

mess.js MML:

{
    "srs": "+proj=merc +a=6378137 +b=6378137 +lat_ts=0.0 +lon_0=0.0 +x_0=0.0 +y_0=0 +k=1.0 +units=m +nadgrids=@null +no_defs",
    "Stylesheet": [{"id":"style.mss","data":"Map {\n  background-color: #fff;\n}\n\n#world {\n  line-color: #ccc;\n  line-width: 0.5;\n  polygon-fill: #eee;\n}"}],
    "Layer": [{
        "id": "world",
        "name": "world",
        "srs": "+proj=latlong +ellps=WGS84 +datum=WGS84 +no_defs",
        "Datasource": {
            "file": "world_borders",
            "type": "shape"
        }
    }]
}

Cascadenik MML

<Stylesheet><![CDATA[
    Map
    {
        map-bgcolor: #69f;
    }

    Layer
    {
        line-width: 1;
        line-color: #696;
        polygon-fill: #6f9;
    }
]]></Stylesheet>
<Layer srs="+proj=latlong +ellps=WGS84 +datum=WGS84 +no_defs">
    <Datasource>
        <Parameter name="type">shape</Parameter>
        <Parameter name="file">world_borders</Parameter>
    </Datasource>
</Layer>
</Map>

Attachments

new

In CSS, a certain object can only have one instance of a property. A <div> has a specific border width and color, rules that match better than others (#id instead of .class) override previous definitions. mess.js acts the same way normally for the sake of familiarity and organization, but Mapnik itself is more powerful.

Layers in Mapnik can have multiple borders and multiple copies of other attributes. This ability is useful in drawing line outlines, like in the case of road borders or 'glow' effects around coasts. mess.js makes this accessible by allowing attachments to styles:

#world {
  line-color: #fff;
  line-width: 3;
  }

  #world::outline {
    line-color: #000;
    line-width: 6;
    }

Attachments are optional: if you don't define them, mess.js does overriding of styles just like Cascadenik.

This brings us to another incompatibility: line-inline and line-outline have been removed from the language, because attachments are capable of the same trick.

text-name

incompatibility

Instead of the name attribute of the TextSymbolizer and ShieldSymbolizer being a part of the selector, it is a property of a rule. Thus the evaluation is less complex and one can use expressions in names.

cascadenik	mess.js
#world NAME { text-face-name: "Arial"; }	#world { text-name: "NAME"; text-face-name: "Arial"; }

Mapnik2

new

mess.js is only compatible with Mapnik2. Compatibility with Mapnik 0.7.x is not planned.

Rasters and Buildings

new

Rasters are supported in mess.js - it knows how to download .vrt, .tiff, and soon other raster formats, and the properties of the RasterSymbolizer are exposed in the language.

The BuildingSymbolizer is also supported in mess.js. The code stores symbolizer types and properties in a JSON file (in tree/reference.js), so new Mapnik features can be quickly implemented here.

Variables & Expressions

new

mess.js inherits from its basis in less.js some new features in CSS. One can define variables in stylesheets, and use expressions to modify them.

@mybackground: #2B4D2D;

Map {
  background-color: @mybackground
}

#world {
  polygon-fill: @mybackground + #222;
  line-color: darken(@mybackground, 10%);
}

Nested Styles

new

mess.js also inherits nesting of rules from less.js.

/* Applies to all layers with .land class */
.land {
  line-color: #ccc;
  line-width: 0.5;
  polygon-fill: #eee;
  /* Applies to #lakes.land */
  #lakes {
    polygon-fill: #000;
  }
}

This can be a convenient way to group style changes by zoom level:

[zoom > 1] {
  /* Applies to all layers at zoom > 1 */
  polygon-gamma: 0.3;
  #world {
    polygon-fill: #323;
  }
  #lakes {
    polygon-fill: #144;
  }
}

FontSets

new

By defining multiple fonts in a text-face-name definition, you create FontSets in mess.js. These are useful for supporting multiple character sets and fallback fonts for distributed styles.

mess	XML
<pre>#world { text-name: "[NAME]"; text-size: 11; text-face-name: "Georgia Regular", "Arial Italic"; }	<FontSet name="fontset-0"> <Font face_name="Georgia Regular"/> <Font face_name="Arial Italic"/> </FontSet> <Style name="world-text"> <Rule> <TextSymbolizer fontset_name="fontset-0" size="11" name="[NAME]"/> </Rule> </Style>

Usage

Using the binary

messc map_file.json

Using the code

Currently mess.js is designed to be invoked from node.js. The Renderer interface is the main API for developers, and it takes an MML file as a string as input.

// defined variables:
// - input (the name or identifier of the file being parsed)
// - data (a string containing the MML or an object of MML)
var mess = require('mess');

new mess.Renderer({
        filename: input,
        local_data_dir: path.dirname(input),
    }).render(data, function(err, output) {
        if (err) {
            if (Array.isArray(err)) {
                err.forEach(function(e) {
                    mess.writeError(e, options);
                });
            } else { throw err; }
        } else {
            sys.puts(output);
        }
    });

Credits

mess.js is based on less.js, a CSS compiler written by Alexis Sellier.

It depends on

• underscore.js
• zipfile
• srs
• step
• xml2js

Authors

• Tom MacWright (tmcw)
• Konstantin Käfer (kkaefer)
• AJ Ashton (ajashton)