OSM Geoservice plugin improvements, including offline data support

This patch contains improvements for the OSM geoservice plugin, in form
of property-controllable disk cache, and the support for a directory
containing an offline dataset.

The offline directory can contain subdirectories also in form of
symlinks. If duplicate tiles are present, the newest is used.

The population of the offline tiles registry is offloaded to a
thread to prevent blocking the startup of the application.
No synchronization is used (except on cache destruction),
so that, as the tiles are being indexed, they can be used in
the application.

For the time being, no support is given to populate such directory
(mostly due to current API limitations), but tiles can be placed
manually, for example copying them from the disk cache directory.

Task-number: QTBUG-45284
Change-Id: I518980669a3ee474545025adf05adc69cdd29781
Reviewed-by: Paolo Angelelli <paolo.angelelli@theqtcompany.com>
Reviewed-by: Alex Blasche <alexander.blasche@theqtcompany.com>

1 files changed, 23 insertions, 0 deletions

diff --git a/src/location/doc/src/plugins/osm.qdoc b/src/location/doc/src/plugins/osm.qdoc
index 1c924fd3..9f4979b5 100644
--- a/src/location/doc/src/plugins/osm.qdoc
+++ b/src/location/doc/src/plugins/osm.qdoc
@@ -86,6 +86,29 @@ a prefix.
         If not specified the default  \l {http://nominatim.openstreetmap.org/search}{url}
         will be used.
         \note The API documentation is available at \l {https://wiki.openstreetmap.org/wiki/Nominatim}{Project OSM Nominatim}.
+\row
+    \li osm.mapping.cache.directory
+    \li Absolute path to map tile cache directory used as network disk cache.
+
+    The default place for the cache is \c{QtLocation/osm} directory in \l {QStandardPaths::writableLocation()} {QStandardPaths::writableLocation}(\l{QStandardPaths::GenericCacheLocation}).
+    On systems that have no concept of a shared cache, the application-specific \l{QStandardPaths::CacheLocation} is used instead.
+\row
+    \li osm.mapping.offline.directory
+    \li Absolute path to a directory containing map tiles used as an offline storage. If specified, it will work together with the network disk cache, but tiles won't get automatically
+    inserted, removed or updated. The format of the tiles is the same used by the network disk cache.
+
+    There is no default value, and if this property is not set, no directory will be indexed and only the network disk cache will be used
+    to reduce network usage or to act as an offline storage for the currently cached tiles.
+\row
+    \li osm.mapping.cache.disk.size
+    \li Map tile disk cache size in bytes. Default size of the cache is 100MB.
+\row
+    \li osm.mapping.cache.memory.size
+    \li Map tile memory cache size in bytes. Default size of the cache is 3MB.
+\row
+    \li osm.mapping.cache.texture.size
+    \li Map tile texture cache size in bytes. Default size of the cache is 6MB. Note that the texture cache has a hard minimum size which depends on the size of the map viewport (it must contain enough data to display the tiles currently visible on the display). This value is the amount of cache to be used in addition to the bare minimum.
+
 \endtable
 
 \section1 Parameter Usage Example