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add documentation about symbolizer instances

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Konstantin Käfer 2011-09-12 11:05:49 +02:00
parent 79abfa1436
commit bdf65ac8f0
2 changed files with 17 additions and 1 deletions
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5
CHANGELOG.md
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@ -1,5 +1,10 @@
## Changelog ## Changelog
### 0.3.0 (NOT YET RELEASED)
* Add "name/" prefix for creating multiple instances of a symbolizer in the same
attachment
### 0.2.3 ### 0.2.3
* Fixes many bugs * Fixes many bugs

13
README.md
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@ -52,7 +52,7 @@ Cascadenik MML
</Layer> </Layer>
&lt;/Map&gt;</pre> &lt;/Map&gt;</pre>
## Attachments ## Attachments and Instances
_new_ _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. 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.
@ -73,6 +73,17 @@ Attachments are optional: if you don't define them, carto.js does overriding of
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. 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.
While attachments allow creating implicit "layers" with the same data, using **instances** allows you to create multiple symbolizers in the same style/layer:
#roads {
casing/line-width: 6;
casing/line-color: #333;
line-width: 4;
line-color: #666;
}
This makes Mapnik first draw the line of color #333 with a width of 6, and then immediately afterwards, it draws the same line again with width 4 and color #666. Contrast that to attachments: Mapnik would first draw all casings before proceeding to the actual lines.
## text-name ## text-name
_incompatibility_ _incompatibility_