Format.SLD: add support for TextSymbolizer

[bartvde]

I'll create a patch to add support for TextSymbolizer.

[bartvde]

It does not really make sense to implement read support right now, since vector layers can't render labels as yet.

Write support makes sense IMHO as you can now easily label a WMS layer using SLD.

An example useage is:

    var symbolizer = {};
    symbolizer["Text"] = {property: propertyName, fontFamily: fontFamily,
        fontSize: fontSize, fillColor: color};

Which will create something like (when used in an SLD document):

<StyledLayerDescriptor xmlns="http://www.opengis.net/sld" version="1.0.0" xsi:schemaLocation="http://www.opengis.net/sld http://schemas.opengis.net/sld/1.0.0/StyledLayerDescriptor.xsd" xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"><NamedLayer><Name>AAA64</Name><UserStyle><FeatureTypeStyle><Rule><Name>default</Name><TextSymbolizer><Label><ogc:PropertyName xmlns:ogc="http://www.opengis.net/ogc">ROUTE</ogc:PropertyName></Label><Font><CssParameter name="font-family">Arial</CssParameter><CssParameter name="font-size">10</CssParameter></Font><Fill><CssParameter name="fill">#FFFF00</CssParameter></Fill></TextSymbolizer></Rule></FeatureTypeStyle></UserStyle></NamedLayer></StyledLayerDescriptor>

[bartvde]

patch implementing write support for TextSymbolizer

[tschaub]

write text symbolizers with support for label expressions

[tschaub]

Hey Bart - This is a nice addition. I think we'll eventually want to support more ogc:expressions. With that in mind, I decided a "label" property in the text symbolizer would more closely fit the sld:Label element. This parser has support for limited expression handling, so you can do something like:

var symbolizer = {
    "Text": {
        "label": "There are ${population} people in ${state}.",
        "fontFamily": "Arial" // etc
    }
};

I also added a test to demonstrate it working. Let me know if this works for you.

[ahocevar]

Great work Bart and Tim! I can confirm that tests pass in FF2 and IE7, and that the patch does not interfer with existing code. Also, is an important contribution to make SLD read/write support more complete. Tim, please commit.

[tschaub]

(In [7333]) Adding support for TextSymbolizer writing in the SLD format. Thanks to Bart for the original patch. This provides basic expression handling for text labels. Read support later. r=ahocevar (closes #1542)