[Qgis-developer] Plugin layer and labelling

[Martin Dobias]

On Sun, Jan 27, 2013 at 10:53 PM, Chris Crook <ccrook at linz.govt.nz> wrote:
> More generally though having labels plotting after the layers can be a bit weird.  For example if I have a point layer underneath a polygon layer I end up seeing a polygon with a whole lot of labels on top of it (which come from the point layer hidden beneath it).  That doesn't seem right?

In such situation the result may not look good. But in general I think
we have no other choice: first one has to be aware of all features
(from all layers) that should be labeled. Once all layers have been
rendered, the labeling algorithm is able to produce candidate labels
(for each feature), compute their costs and finally resolve the label
placement problem, returning a set of labels that do not overlap.
Also, by default features act as obstacles to labels, so such
candidates covered by other features would get higher cost (and may
not be considered at all).

Martin