carto/README.md

# carto

Is a stylesheet renderer for Mapnik. It's an evolution of the [Cascadenik](https://github.com/mapnik/Cascadenik) idea and language, with an emphasis on speed and flexibility.

## Installation

Follow the directions to install [node-zipfile](https://github.com/springmeyer/node-zipfile) and then:

    npm install carto

_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.

carto.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

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

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

## 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. `carto.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](http://trac.mapnik.org/wiki/LineSymbolizer) 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. `carto.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, carto.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](http://trac.mapnik.org/wiki/TextSymbolizer) and [ShieldSymbolizer](http://trac.mapnik.org/wiki/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.

<table>
  <tr>
    <th>cascadenik</th>
    <th>carto.js</th>
  </tr>
  <tr>
    <td valign='top'>
      <pre>
#world NAME {
  text-face-name: "Arial";
}</pre>
    </td>
    <td valign='top'>
      <pre>
#world {
  text-name: "NAME";
  text-face-name: "Arial";
}</pre>
    </td>
  </tr>
</table>

## Mapnik2
_new_

`carto.js` is only compatible with [Mapnik2](http://trac.mapnik.org/wiki/Mapnik2). Compatibility with Mapnik 0.7.x is not planned.

## Rasters and Buildings
_new_

Rasters are supported in carto.js - it knows how to download `.vrt`, `.tiff`, and soon other raster formats, and the properties of the [RasterSymbolizer](http://trac.mapnik.org/wiki/RasterSymbolizer) are exposed in the language.

The [BuildingSymbolizer](http://trac.mapnik.org/wiki/BuildingSymbolizer) is also supported in `carto.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_

`carto.js` inherits from its basis in [less.js](http://lesscss.org/) 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_

`carto.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](http://trac.mapnik.org/wiki/FontSet) in `carto.js`. These are useful for supporting multiple character sets and fallback fonts for distributed styles.

<table>
  <tr>
    <th>carto</th><th>XML</th>
    </tr>
    <tr>
    <td valign='top'>

    <pre>#world {
  text-name: "[NAME]";
  text-size: 11;
  text-face-name: "Georgia Regular", "Arial Italic";
}</pre>

</td>
<td valign='top'>
<pre>&lt;FontSet name=&quot;fontset-0&quot;&gt;
  &lt;Font face_name=&quot;Georgia Regular&quot;/&gt;
  &lt;Font face_name=&quot;Arial Italic&quot;/&gt;
&lt;/FontSet&gt;
&lt;Style name=&quot;world-text&quot;&gt;
  &lt;Rule&gt;
    &lt;TextSymbolizer fontset_name=&quot;fontset-0&quot;
      size=&quot;11&quot;
      name=&quot;[NAME]&quot;/&gt;
  &lt;/Rule&gt;
&lt;/Style&gt;</pre>
</td>
<tr>
</table>


## Usage

#### Using the binary

    cartoc map_file.json

#### Using the code

Currently `carto.js` is designed to be invoked from [node.js](http://nodejs.org/).
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 carto = require('carto');
    
    new carto.Renderer({
            filename: input,
            local_data_dir: path.dirname(input),
        }).render(data, function(err, output) {
            if (err) {
                if (Array.isArray(err)) {
                    err.forEach(function(e) {
                        carto.writeError(e, options);
                    });
                } else { throw err; }
            } else {
                sys.puts(output);
            }
        });

## Credits

`carto.js` is based on [less.js](https://github.com/cloudhead/less.js), a CSS compiler written by Alexis Sellier.

It depends on:

* [underscore.js](https://github.com/documentcloud/underscore/)
* [zipfile](https://github.com/springmeyer/node-zipfile)
* [srs](https://github.com/springmeyer/node-srs)
* [step](https://github.com/creationix/step)

Only for running tests:

* [expresso](https://github.com/visionmedia/expresso)
* [sax-js](https://github.com/isaacs/sax-js/)
* [xml2js](https://github.com/maqr/node-xml2js)


## Authors

* Tom MacWright (tmcw)
* Konstantin Käfer (kkaefer)
* AJ Ashton (ajashton)
* Dane Springmeyer (springmeyer)