Visitor API for style entities #30522

nyalldawson · 2019-07-03T05:07:33Z

Adds a new visitor pattern API for creation of visitors which visit all the style entities (symbols, color ramps, text formats, and label styles) associated with different objects. Can be used on a renderer, map layer, or project wide level.

E.g. on a project wide level, allows collection of ALL the style symbols/color ramps/text settings inside a project, including those in layouts or annotations!

This opens up lots of possibilities. E.g. scripts (or processing algorithms!) which:

check for broken file references in symbols (e.g. missing svgs)
list all expressions from data defined properties in symbols, and check their validity
extract all symbols, color ramps, label settings from a project and saves them to a style database
extracts the unique colors from a project, and builds an automatic "project color scheme" from them
finds wherever you've used crappy fonts in a project (ms shell dlg anyone?)

...etc etc

(a nice follow up would be a visitor which allows symbols to be modified, but that's an order of magnitude more complex).

src/core/symbology/qgsstyleentityvisitor.h

src/core/qgsproject.cpp

src/core/layout/qgslayoutmanager.cpp

src/core/layout/qgsprintlayout.cpp

src/core/qgsrulebasedlabeling.cpp

src/core/symbology/qgsrulebasedrenderer.cpp

src/core/annotations/qgsannotation.cpp

src/core/annotations/qgsannotationmanager.cpp

src/core/layout/qgsabstractreportsection.cpp

m-kuhn · 2019-07-05T10:26:22Z

Good stuff!

One thing that I wonder is if it would be possible and useful to add nesting information / parent information to leafs and nodes, so you could see e.g. where in a nested rule structure you are which I think is currently not possible.

nyalldawson · 2019-07-05T23:20:21Z

@m-kuhn

One thing that I wonder is if it would be possible and useful to add nesting information / parent information to leafs and nodes, so you could see e.g. where in a nested rule structure you are which I think is currently not possible.

That was my intention with the enter/exit calls - but it's up to the visitor to utilise these and track the tree traversal if they need this info. I don't think there's a straightforward way to do this automatically. I guess we could have a built in "trackingvisitor" subclass which has a different virtual visit method which adds provides this extra info, but that's getting rather confusing!

Let's revisit this topic if/when there's a need for that.

m-kuhn · 2019-07-05T23:29:14Z

I was thinking of a parent in the node and leaf structs that would always be available. But no need really.

Adds a new visitor pattern API for creation of visitors which visit all the style entities (symbols, color ramps, text formats, and label styles) associated with different objects. Can be used on a renderer, map layer, or project wide level. E.g. on a project wide level, allows collection of ALL the style symbols/color ramps/text settings inside a project, including those in layouts or annotations!

nyalldawson added Feature API API improvement only, no visible user interface changes labels Jul 3, 2019

nyalldawson added this to the 3.10.0 milestone Jul 3, 2019

nyalldawson force-pushed the visitor branch 2 times, most recently from 6cc6baf to 808b624 Compare July 3, 2019 22:55