[Portugal] [Fwd: [Qgis-developer] Rule-based renderer updates]

[Giovanni Manghi]

-------- Forwarded Message --------
> From: Martin Dobias <wonder.sk at gmail.com>
> To: qgis-dev <qgis-developer at lists.osgeo.org>
> Subject: [Qgis-developer] Rule-based renderer updates
> Date: Tue, 24 Jan 2012 13:58:28 +0100
> 
> Hi all
> 
> I have just merged improved rule-based renderer to master branch.
> There are various changes in both backend and GUI:
> 
> * Rules now form a hierarchical structure: any rule can contain
> further "child" rules. When rendering, child rules are applied only
> when their parent rule matches. This allows users to build a logical
> trees of rules instead of keeping all rules in a flat list with
> complex filters.
> 
> * The options "use only first rule" and "use symbol levels" have been
> removed: now all the matching rules and applied and at the same time
> the rendering order is given by the symbol levels.
> 
> * GUI: rules are shown as a tree. They can be organized easily with
> drag and drop (multiple selection is supported, too). Let me emphasize
> again that the tree of rules does not say anything about the rendering
> order (because in SLD and Mapnik the order of rules matters). The
> rendering order can be set by the button in bottom-right corner of the
> renderer widget - it triggers the same dialog as used for setting
> symbol levels.
> 
> * GUI: inline editing of labels, filters and scale range is now
> possible - use F2 -or- click again a selected item to enter inline
> editing.
> 
> * Rules may not contain a symbol: usually parent rules are not
> assigned a symbol because their child rules take care of rendering.
> 
> * symbol levels dialog for other renderers is now accessible from a
> menu from their "advanced" button - to avoid some clutter,
> additionally renderers indicate whether they support symbol levels or
> not.
> 
> Originally I wanted to design the rule-based renderer to follow SLD /
> Mapnik logic - the order of rules (and group of rules) determines the
> rendering order. However this is not very user friendly: the user has
> to prepare the rules in a way that is convenient to a software, not
> the user. For example, when drawing a map of roads with nicely
> rendered road outlines and varying Z-levels (bridges / tunnels), the
> user has to split the road symbols into multiple rules and move them
> away from each other - further editing of rules and symbols becomes
> complex. In our approach the user can keep the rules in a hierarchy
> that is most convenient and then define the rendering order
> independently. So there is not a 1:1 relation between QGIS rule-based
> rendering and SLD (or Mapnik) rules, however the import/export
> capabilities can be implemented without problems.
> 
> Please test, I would like to hear your comments, suggestions and bug
> reports. I am especially interested to hear any notes related to
> usability - I have some doubts regarding GUI, e.g.:
> - expand all rules when GUI is opened?
> - delete parent rule's symbol when refining it? or completely forbid
> rules to contain a symbol if they have children?
> 
> There are still some smaller things that might be added in future:
> - cloning of rules
> - filtering of rules in GUI - by label / filter expression / scale
> - "else" rule - will be used only if no other sibling rule matches
> - checkable rules?
> - better item delegates for inline editing - e.g. filter editor with
> "..." button to open query builder
> 
> Finally, I would like to thank Ville de Morges, Switzerland for
> sponsoring this work.
> 
> Regards
> Martin
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