Map attributes parsing

[springmeyer]

We should respect map level attributes like 'min_version' when an mml parsed by python, and stuff like 'font_directory' which will be available in mapnik2.

I'll take this on, but it can happen after initial release.

[gravitystorm]

Making this issue easier to find: cascadenik support for "minimum_version"

[migurski]

Is this still a thing? Did "font_directory" get added?

[springmeyer]

Yes, it did. And before the 2.0.0 release all parameters were made to use consistent dashes (instead of underscores), so its now font-directory, and it can be passed a directory or a single file:

https://github.com/mapnik/mapnik/blob/master/tests/data/good_maps/extra_known_map_attributes.xml

[mojodna]

So, I'm trying to fix this because I'm off in the weeds on a Friday evening...

I've gotten as far as getting font-directory to pass through as a URI: mojodna/Cascadenik@b4e1385

However, I'm having trouble associating it with a mapnik.Map here:

Cascadenik/cascadenik/output.py

Line 32 in 82f6685

def to_mapnik(self, mmap, dirs=None):

It's an "extra param" (i.e. not directly part of the public API, along with minimum_version per extra_known_map_attributes.xml), so it should be attached to mmap.parameters, which is a mapnik._mapnik.Parameters instance and appears to be read-only, but I'm probably missing something.

Ideas?

[mojodna]

mmap.parameters.append(mapnik._mapnik.Parameter("font-directory", "fonts/"))
mapnik.save_map(mmap, "style.xml")

outputs:

<?xml version="1.0" encoding="utf-8"?>
<Map srs="+proj=longlat +ellps=WGS84 +datum=WGS84 +no_defs">
    <Parameters>
        <Parameter name="font-directory" type="string">fonts/</Parameter>
    </Parameters>
</Map>

This what I was expecting (https://github.com/mapnik/mapnik/blob/master/tests/data/good_maps/extra_known_map_attributes.xml, effectively):

<Map srs="+proj=longlat +ellps=WGS84 +datum=WGS84 +no_defs" font-directory="fonts/" />

@springmeyer are these intended to be interchangeable? https://github.com/mapnik/mapnik/blob/49feda9b13e6db416647afad8204b8d7d6c22024/src/load_map.cpp#L263 makes me think that they're not (since it's reading font-directory from the <Map> node).

Is this a bug in the Python bindings?

[springmeyer]

Yes, a bug in the bindings resulting from the oddity of this parameter. Basically, font-directory only matters at the time the xml is loaded so it did not make sense to add it as a new property. So, I think my reasoning was to push it into the extra attributes so that it would not get lost and could be serialized still. But it has gotten lost.

[springmeyer]

hmm, forgot that I actually did away with this support (mapnik/mapnik@ea5a46f#diff-bc721da090a4fdd48972b8aad7f14ec8). So, font-directory is not able to be round tripped and there is no way to add it via python.

[mojodna]

Well, crap. Thanks for looking into it.

[springmeyer]

it this lack of round tripping a major problem?

[mojodna]

No, I think I've got a better way of dealing with it that doesn't involve Cascadenik.

[springmeyer]

great. so I'll close this. Ping back if you have reservations. I'm planning on reworking the behavior of font-directory in Mapnik master soon (consider making it apply fonts locally to map rather than to global cache) - in this case it would again be round-trippable.