[Qgis-developer] Question on inverted polygon renderer

[Régis Haubourg]

Hi Andreas, 
I'm the funder, Hugo Mercier from Oslandia is the developper. It's the right
time to do some teasing I guess ;-).

 The inverted polygon renderer idea appeared when writing specifications for
an improved mask tool . We will soon release new version of mask plugin that
allows the following:

- generate a ROI layer from current polygon selection, or from another
plugin's call.

- Label features of layers only for objects intersecting the mask region
(several spatial operators inside). Users wish that a lot to do professional
mapping. Unwanted side effect is that labeling is a lot more readable by
giving more affordable space to labeling engine. 

- Automagically reuse current mask style to generate a mask on the fly on
Atlas coverage feature. 

inverted style + shapeburst give crazy cool rendering!
Another positive point, instead of making a big bbox with a hole, as current
mask plugin does, an inverted style allowed a much cleaner solution, and
sounded a lot more reusable.  And now, it's much more clear for the user to
be able to zoom to the layer extent and not be zoomed out far away.

We were unsure about real performances of such spatial filtering, so we
decided to start with a plugin, and share with you..  And, we found that
filtering labels gives less work to pal engine, so the spatial intersection
seems to be less consuming than labeling, for average layers. 

Many thanks to Oslandia Team and Hugo for the hard work. We're about to
release the plugin, Hugo will launch a thread about this, and maybe a port
to core, if you like it.  

I already see what we could do next, like label features only on the parts
really intersecting that ROI.. 

Stay tuned! 
Régis



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