Dynamically enable/disable navit.xml items

[mvglasow]

It would be nice to have the possibility to enable/disable items defined in navit.xml dynamically while navit is running.

This could be done through a condition attribute, similar to the menu items in the internal GUI. Conditions could be based on variables (e.g. as used in OSD text labels); support for expressions would be helpful.

This would open up a host of possibilities:

• Showing OSD items only when meaningful: The next maneuver, ETA and other navigation-related items are empty and thus useless in tracking mode; a condition could be defined to make them visible only when a route is planned. Similarly, the speed and compass make sense only when a valid GPS position is received.

• Logging could be enabled/disabled within Navit, e.g. through an OSD button, through the internal GUI menu or event-driven.

• Maps could be enabled/disabled at run-time; this would allow the user to switch between different maps for the same area.

• Tracked vehicles could be enabled or disabled

Variables should include:

• Navigation active (boolean) or route_status

• GPS data available (boolean) or position_sats_used

• User-defined variables (to be defined in navit.xml) that can be changed through OSD buttons or the internal GUI menu, preferably both (e.g. to switch logging on/off, switch between maps or enable/disable tracked vehicles)

• Tracking data (following a road, off-road in map area, outside of map area)

• osd_configuration, in which case the related attribute would become obsolete and identical functionality could be implemented through the condition attribute

A possible application of this would be to start logging vehicle position as soon as the vehicle is no longer on a known road - which would be very useful for OSM mapping.

A problem might be how to update the items whenever their condition changes between true and false. Maybe this can be done in a similar way text labels in OSD get updated (I haven't looked in the code how this is done) or create a hook for each variable used in a condition which causes the condition to be re-evaluated as soon as the variable changes.

[mvglasow (2)]

Having familiarized myself with the code I would now suggest the following:

• Implement commands to enable or disable items (I see some work is being done for OSD items, and I am working on a command that will turn logging on and off, others may be done in a similar way).

• Introduce user-defined callbacks to the config file. Each callback consists of a condition (format similar to text attribute of OSD text item) and a command (similar to those used in OSD buttons and menu items.

For example:

<callback cond="${!tracking.item}" command="vehicle.start_log()">

which would start logging as soon as the vehicle is no longer on a known road.

The basic structure for the condition can probably be copied from the OSD text labels (or maybe we can move the related code to a new component which can be used by all and extend it to fit our needs).

[usul]

This mixes a lot of requests, some are already implemented:

• Android port can enable/disable POI layers
• osd items have speed conditions
• some routing related OSD items appear only if navit is in routing mode

What remains is:

• Can logging already be toggled from the OSD?
• Can (and should?) map styles switched from OSD?
• Can (and should?) vehicles switched from OSD?