[Qgis-developer] Legend refactoring - part II - ready for merge

[Marco Hugentobler]

Hi Martin

Thanks for your efforts to unify the legends. Few comments from my side:

- API break: is there a list of breaks inside the 2.x series? I recently 
came accross one in the provider API, and it would be good to provide 
some guidance for people porting code to newer versions. Regarding 'not 
used according to plugin analysis tool': most plugins are probably not 
in the plugin repo.

- For the legend graphics options layertitlespace and layerfontcolor, it 
says 'TODO'.

- qgswmsserver.cpp:671 : it seems a bit strange to iterate over all 
nodes to set the property. Can this be done inside some legend class 
(maybe legend renderer)?

Regards,
Marco

On 22.08.2014 13:02, Martin Dobias wrote:
> Hi all
>
> In recent weeks I have been busy with the second part of legend
> refactoring. The main goals were:
> - clean up the mess with legend - there are three different ways of
> legend presentation/rendering: 1. in legend widget (now layer tree
> view), 2. composer legend, 3. WMS legend
> - make legend rendering independent from composer - so it can be used
> elsewhere - in WMS or in GUI
> - allow different strategies how legend for a layer is created - until
> now the legend generation was hardcoded - this should allow things
> like data-defined legend, labeling / diagrams in legend
> - allow new types of legend items - for greater flexibility of item
> appearance - e.g. show a gradient color ramp for raster layer
>
> The code is in my repository:
> https://github.com/wonder-sk/QGIS/compare/legend-refactoring-part2
>
> To introduce the important new classes:
> - QgsLegendRenderer - takes care of rendering of the legend - similar
> to how QgsMapRenderer handles rendering of map
> - QgsLegendSettings - contains user configuration of the legend
> (fonts, colors, sizes, spacing) - similar to QgsMapSettings for map
> - QgsMapLayerLegend - base class for legend implementations. For a
> layer an implementation should return a list of legend nodes
> - QgsLayerTreeModelLegendNode - base class for legend node
> implementation. Provides data(), flags() methods used in the layer
> tree model and provides draw() method for rendering of legend in
> composer/WMS
>
> The QgsMapLayerLegend and QgsLayerTreeModelLegendNode classes are used
> by QgsLayerTreeModel to generate and display legend in a tree.
> QgsLegendRenderer makes use of QgsLayerTreeModel and allows the legend
> nodes do their legend rendering.
>
> An example of custom legend node:
> - screenshot: http://i.imgur.com/GtvTlQ7.png
> - code: https://gist.github.com/wonder-sk/c5d925833bcd54b9e401
>
> An example of custom dock widget using legend renderer:
> - screenshot: http://i.imgur.com/EAvE96u.png
> - code: https://gist.github.com/wonder-sk/211b7130b58e50d78e6d
> (in the screenshot above you can also see legend node icon embedded in
> layer node)
>
> There are not many changes visible to the user - the changes are
> mainly visible for developers. From the few user-visible changes:
> - in layer tree view - if a layer has just one legend item, it will be
> shown on the left side of the layer name instead of occupying another
> line. This is what already happens in composer.
> - in composer legend item settings - 1) there is tree view with just
> one column, label style is set in popup menu, 2) when auto-update is
> on, the tree view is synchronized with project's layer tree and it is
> read-only. When auto-update is off, it is possible to manipulate the
> source legend tree
>
> Regarding backward compatibility, there are two things worth mentioning:
> - QgsComposerLegend::model() will return QgsLegendModel which is not
> in use anymore. There is QgsComposerLegend::modelV2() as a
> replacement. The way how the models work is significantly different
> and I don't see a way of fixing that without a complex and fragile
> synchronization logic. Anyway, according to Nathan's plugin analyser
> tool there are no plugins using composer's legend model
> - reading of older projects with composer legend ignores the
> customization (e.g. renamed items, reordered items, removed items). If
> time allows, I will try to address this before the release
>
> So... please have a look if you are interested and enjoy the endless
> possibilities of new legends :-)
> If there are no objections I will merge it during the next week.
>
> Regards
> Martin
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-- 
Dr. Marco Hugentobler
Sourcepole -  Linux & Open Source Solutions
Weberstrasse 5, CH-8004 Zürich, Switzerland
marco.hugentobler at sourcepole.ch http://www.sourcepole.ch
Technical Advisor QGIS Project Steering Committee