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

[Tim Sutton]

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Hi Martin

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.


Ah wow - I've been playing with it here and it is so much nicer from
the UI point of view. Two things I picked up though.

* I don't know how to reproduce it exactly but it seems that when I
change the text for a layer name in general properties it updates the
legend fine but after using QGIS a little more I notice that the layer
name reverts to its previous state. I will post more details if I
figure out how to replicate this.

* Do you have any strategy for dealing with symbols larger than the
thumbnail in the legend? e.g. if you set the size of a circle  to 8 it
basically draws a square. This is not a regression as the old legend
implementation suffered the same thing, but I was hoping a new
implementation could offer a fix for this. I know there are limits to
what we can do in the space of the legend but perhaps having some
simple system whereby symbol previews are proportionally scaled such
that the largest icon will always fit into the space provided and the
smaller ones are relatively reduced in scale? Perhaps someone else has
some creative ideas on how to improve their visual representation in
the legend?

Great stuff as always Martin!

Regards

Tim


> 
> Regards Martin _______________________________________________ 
> Qgis-developer mailing list Qgis-developer at lists.osgeo.org 
> http://lists.osgeo.org/mailman/listinfo/qgis-developer
> 

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Tim Sutton
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