@mathieubossaert (and anyone else trying out offline tiles over Mapbox basemaps), offline raster layers are currently displayed with 50% transparency when using a Mapbox basemap whereas they are displayed with no manipulation with other basemaps. Which do you prefer?
I'm also interested in what @Ivangayton has to say. You described the "reference layer" as a "semi-transparent layer" here. I took that to mean that someone creating this layer will generally want to either use transparent PNG rasters or vectors with a style that doesn't fill everything in. Did you instead mean that ODK should take whatever file the user provides and render it semi-transparently?
I think some colleagues will want transparency (for example to show tracks or oteher things), some other will want opacity.
The best would be to able transparency setting of the offline data layer in the mapping settings screen.
Anyway I think that 50% transparency is too transparent, maybe (20%-25% would be better)
Thanks for the feedback! The transparency is easy to adjust.
One aspect that is a bit awkward right now is that we have clearly separated the "Reference layer" from the "Basemap", which is a change.
Previously, the basemap options and the offline tile files would all be shown together in one menu, even though the offline tiles did not truly replace the basemap (which you can see if the tiles have transparent areas, for example); and the layers button in the activity would let you choose a different offline file, but not let you change the basemap. So it was a little bit fuzzy before as to whether the offline file was a replacement for the basemap or a layer on top of the basemap.
Separating the basemap and the reference layer will make things clearer in the future, but right now it feels like a shift from what we did before.
Based on the discussion starting at Geo: Using the Mapbox SDK for Android - #26 by Ivangayton, I'm thinking that eventually we will want to allow you to choose an offline file at the Basemap level (where you could use fully opaque tiles) and also, if you want, at the Reference layer (where you could apply transparent tiles on top).
But we're not there yet, and are still open to feedback and suggestions on the ultimate model we offer to users!