Hi all,
A while back we had a client who was interested in funding some labelling
work to solve a problem they were having with labels being drawn over
external graphics. As an example:
https://skitch.com/jdeolive/fbiss/label-before
Andrea had the idea of introducing the concept of labelling obstacles. More
specifically marking a symbolizer as a "label obstacle" via a vendor option.
And when present such symbolizers would be factored into the labelling
routine. Basically it would mark the area taken by the symbolizer as "busy"
so that no label would be drawn over top of it.
I have taken a crack at implementing this. The initial results look
promising:
https://skitch.com/jdeolive/fbish/label-after
The current patch can be found on this jira issue:
http://jira.codehaus.org/browse/GEOT-3610
The patch is still rough at this point, but I wanted to post it to
supplement some of my questions:
1. I had to utilize the deprecated constructor on StyledShapePainter that
accepts the LabelCache as a parameter, however that constructor has been
deprecated. Is that because rendering is now multi threaded and that the
painting actually goes on in a separate thread? So access to the label cache
should be limited to the primary/data loading thread?
I am trying to analyze the rendering code to figure out if actually any race
conditions are introduced. And if I understand correctly I don't think there
are but I could definitely be missing something. With the new code the only
time the painting thread has to update the label cache is to put a new
reserved rectangle into the cache... which simply updates the reserved list.
And as far as I can tell this value is not accessed by the primary thread
until after it has joined with the paint thread...
Anyways, some guidance here on how best to proceed would be appreciated.
2. The patch adds support for marking a Line and Poly symbolizer as a label
obstacle. Not sure if this is a great idea since the method is bounding box
based hence we have to reserve the entire bounding box of lines and
polygons. Which you can imagine can lead to (depending on the shape of a
geometry) large spaces with no labels. So I am wondering if label obstacles
should be limited to point symbolizers?
That is about it for now... general feedback appreciated... but be gentle...
this is my first rendering patch :)
-Justin
--
Justin Deoliveira
OpenGeo - http://opengeo.org
Enterprise support for open source geospatial.
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