6.1 KiB
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.
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.
| Cascadenik | Mess.js |
|---|---|
<Stylesheet><![CDATA[
Map
{
map-bgcolor: #69f;
}
|
{
"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"
}
}]
}
|
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 |
|---|---|
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>
|
Credits
mess.js is based on less.js, a CSS compiler written by Alexis Sellier. It depends on underscore.js.
Usage
Using the binary
messc map_file.json
Authors
- Tom MacWright (tmcw)
- Konstantin Käfer (kkaefer)
- AJ Ashton (ajashton)