QgsProcessing ParameterFeature Source

Quite a few native QGIS algorithms implement thread sensitive tasks in the prepareAlgorithm() method which should be called from the main thread. E.g. https://github.com/qgis/QGIS/blob/cd2944e57f98b434d7ab0643ecf7f909752cf970/src/analysis/processing/qgsalgorithmapplylayerstyle.cpp#L69 Note that this method returns a boolean, while processAlgorithm() returns a dictionary.

I want to create a script which will work inside QGIS (from toolbox). It should take as input multiple rasters and a vector layer (always 1 polygon). Check if raster overlaps with vector - if yes, add to list. Pass the list to virtual raster, then pass the virtual raster to rvt tools. The output is a folder containing the resulting rvt rasters. I got completely stuck at trying to pass the correct input parameters.

Based on the QGIS Processing API template I am trying to write a test script that calculates geodesic distances between point geometries using qgis:distancematrix. User selects the from- and to-point layer with the corresponding ID attribute fields, the matrix type and the output location via GUI analogous to the mentioned QGIS processing tool.