The FileProvider documentation lists these locations as places where it can serve files from:
the files/ subdirectory of an app's internal storage area
the cache subdirectory of an app's internal storage area
the root of the external storage area
the root of an app's external storage area
the root of an app's external cache area
There are FileProvider descendants, such as Commonsware's CWAC Provider, which also allow files to be served from:
an app's raw resources folder
an app's assets folder
the folder returned by getDir()
the folder returned by Environment.getExternalStoragePublicDirectory()
But (if it doesn't have some fatal drawback) how would one write a FileProvider that grants access to an app's existing drawables (without first making copies of those drawables in another folder)?