Make symbolizers editable in memory (allowing application of scaling factors)

[artemp]

Symbolizers are currently not editable from python (once created and attached to the Map), and fully const inside of a boost variant container in C++.

We need a way to support variable output resolutions and a key part of supporting this is allowing a scale factor to be applied to all line widths, font sizes, symbol sizes, and dash-spacing for each relevant symbolizer.

This could either be done by allowing a scale factor to be applied to all in memory symbolizer object properties or by applying a scale factor to the symbolizer processor at rendering for both agg and cairo.

The latter approach was recently taken by Mapserver:

http://trac.osgeo.org/mapserver/changeset/8843

The former approach has it benefits since all modified symbolizers could then be serialized to xml and saved.

The latter approach may be more flexible and avoids hardcoding scaled sized inside the xml.

[artemp]

[springmeyer] Fixed title.

[artemp]

[springmeyer] conversion on #mapnik about this ticket: http://mapnik.dbsgeo.com/days/2009-01-26

[artemp]

[springmeyer] The idea behind this ticket is to be able to globally tweak relevant sizes of symbolizers, such as fonts, line width, symbols, etc.

A discussion today on the mapserver list about this is being termed 'magnification': http://lists.osgeo.org/pipermail/mapserver-dev/2009-February/008266.html

Perhaps a c++ function to internally magnify all object properties would be even more useful than python access to them to do it from the bindings.

[artemp]

[springmeyer] 23:12:54 it might be a good idea to consider implementing all symbolizers as 'property maps'
23:13:18 name=value containers or something similar
23:15:05 keep internal impl as it is but provide user-friendly way to set/get properties .. needs some thinking

[artemp]

[springmeyer] renaming this ticket so it serves as umbrella for edibility of symbolizers (esp from python).

[artemp]

[springmeyer] Noting here that mapserver ended up going with a scale_factor applied at rendering time in agg and gd renderers:

http://trac.osgeo.org/mapserver/changeset/8843

[artemp]

[springmeyer] closing as duplicate since there are at least two ideas going on here that we'll now cover in other tickets..

1. allowing symbolizers to be created from python with a set of **kwargs: see now Symbolizers via python accepting **kwargs in constructor #319

2. Allowing for a way to scale font sizes, symbol sizes, and line widths for variable resolution output: see now Allow memory-mapping of shapefiles to be optional param for shape.input #342