[Qgis-user] Understanding the rule-based renderer

[Martin Dobias]

On Fri, Apr 8, 2011 at 11:36 AM, Andreas Neumann <a.neumann at carto.net> wrote:
> Hi,
>
> I am trying to better understand the rule based renderer.
>
> Which version is correct?
>
> a) QGIS is rendering all features of the first rule, then the second rule,
> etc, Features of the first rule are rendered first, features of the second
> rule on top of features from the first rule
> b) QGIS is rendering each feature on by one and decides which rule applies.
>
> I hope it is not version b), I hoped it behaves like version a) but it
> behaves a bit odd with my data. For my data it seems like the order of the
> rule has no influence on the rendering order ;-(

Hi Andreas

the rule based renderer uses the b) option: it goes through the
features one by one and applies all matching rules (in the order in
which they appear). Mayeul Kaufmann has done some work in order to
support option a) by implementing support for symbol levels so that
the rendering order can be overridden.

My ultimate goal is to only support the option a) in a way how SLD
specifies it: rules are grouped and these groups are rendered one
after each other.

Regards
Martin