[SoC] QGIS label placement, week 11

[Martin Dobias]

Hi,

since the server with qgis site is still unavailable, I'm posting my
report to the list:

I've added saving of layer labeling settings into project file. For
this I've added "custom properties" for map layers - basically a
key-value map of values assigned by plugins to the layers. This map is
saved to project and loaded back during the project load.

Another feature I've added is the ability to remove duplicate labels
of connected lines. If turned on, the features with equal label text
are grouped and the algorithm tries to merge the lines into one: this
helps also to generate better label candidate positions.

Among other developments I've tweaked cost evaluation of label candidates:
- candidates further from the line's center point are penalized so the
label is now mostly put on center (for better readability)
- short lines / small polygons are penalized to increase possibility
of labeling greater (and thus more important) map features

The SoC is rapidly coming to the end, but there's still quite some
work that could be done, which I won't manage to do during the last
days of the program. The next week I'd like to finish some smaller
features, squash some bugs and maybe try to do some speed improvements
and documentation. Shortly after the end of SoC 2009 I'm travelling
abroad for several weeks, then I'm going to bring the labeling (and
new symbology) ready for QGIS 1.3 release.

Cheers
Martin