Support list placement for text

[gravitystorm]

Since mapnik 2.1 you can provide a list of placement options for the textsymbolizer. This is an alternative to the "simple" placement type.

<TextSymbolizer face-name="DejaVu Sans Book" size="16" placement="point" dy="8" fill="blue" placement-type="list">[name]
    <Placement size="10" dy="-8" fill="red"/><!-- Reduces text size and changes offset -->
    <Placement fill="green">[abbreviated_name]</Placement> <!-- size="10", dy="-8", fill="green", shorter text -->
    <Placement fill="orange" dy="8">[nr]</Placement> <!-- size="10", dy="8", fill="orange", shortest text -->
</TextSymbolizer>

(from https://github.com/mapnik/mapnik/wiki/TextSymbolizer )

I don't have a particularly clear idea what the carto syntax would look like for this!

See also mapnik/mapnik-reference#45 , since it's not yet in mapnik-reference either.

[tmcw]

Cool, need to read up Mapnik's source for this - kind of looks like the <Placement> element can take the same attributes as TextSymbolizer, except for placement, I'd assume? /cc @springmeyer

[springmeyer]

sounds right @tmcw - its basically a list of multiple text symbolizers. Not sure whether you can, on the fly, switch from something like line placement to point. @herm would.

[gravitystorm]

You can't currently flick between placement types (e.g. line -> point), see mapnik/mapnik#1152

[petzlux]

Would love to see this supported in CartoCSS (and by extension in Tilemill). At the moment, need to edit XML after export from Tilemill to make use of this feature.

[gravitystorm]

@petzlux there's a hack you can use, by writing XML inline within carto, e.g.

      [...]
      text-size: 24;
      text-placement-type: list;
      text-name: "[name]<Placement size='20' /><Placement size='16' />";
      [...]

See also:

• Support Mapnik's text-name Formatter #196 (comment)

• carto/lib/carto/tree/definition.js

  Line 143 in 74fa914

  if (tagcontent.indexOf('<') != -1) {

[springmeyer]

btw, landed in mapnik-reference now and carto 0.9.6 now includes this which will go out with next tilemill (> 0.10.1).

[petzlux]

Okay I am a bit confused as I cant find any doc in carto for this feature, is it included in the latest nightlies of tilemill ? And how is the syntax in Carto ?

[springmeyer]

it is a hack and therefore is intentionally undocumented. The only documentation is #238 (comment). #347 is what it is going to take to make this officially supported.

[kocio-pl]

Is there a chance to add this support into the Carto? It allows to fine tune the style.

[nebulon42]

Definitely. The main shortcoming for CartoCSS here at the moment are developers who are willing to submit patches. However, for this specifically it will be first necessary to find a proper way to represent this in CartoCSS (see #347). There is a unfinished PR that needs to be picked up and probably rewritten from scratch.

Current plans are to release 1.0 in early 2018 without this and tackle this afterwards.