How to switch rule-based styles in loop?

Question

I'm a working on a QGIS script that could activate/deactivate rule-based styles of the vector layer in a loop (one active layer per iteration). On the every iteration this scenario should:

1. Activate one of the prearranged style rules for a given vector layer and deactivate all other;
2. Save current view as JPEG screenshot;

In my particular case the vector layer is a PostGIS table that contains the contours derived from some raster layer. Rules are based on the distinct values of the isolines. I take screenshot of the map for the every activated rule and finally put them all into the animated gif.

Since list of the rule-based styles can be very long, I'm looking torward the PyQGIS code snippet that could go through the one in a loop.

Answer 1

Even without programming, I think it should be possible to achieve this using the idea presented in http://nathanw.net/2014/09/23/qgis-atlas-on-non-geometry-tables/: use the Atlas functionality to loop through a coverage layer containing values for the rule-based rendering of e.g. your contours.

I imagine you will want to compare one of the contour attributes to a value in the coverage layer and control e.g. the line color transparency. To do that, you can expand on the example Nathan showed in his post:

CASE WHEN "contour_value" = attribute($atlasfeature,'value') 
     THEN color_rgba(0,0,255,255)
     ELSE color_rgba(0,0,255,0)
END