This is a clean up commit prior to the subsystem API standardisation to simplify
the diffs. It includes all SGSubsystem and SGSubsystemGroup derived classes.
Not every xml-autopilot filter needs to run at the update rate
of the FDM. This only makes sense for the autpilot filters. Those,
who update instrument needles or environment properties for example
may run at frame rate.
This patch (thanks to ThorstenB, who is the author) forces those
filters defined in /sim/systems/autopilot into the FDM loop and those
defined in /sim/systems/property-rule into the default loop. They
show up as xml-autopilot and xml-proprules in the performance monitor
The autopilot has grown beyond being just an autopilot. It's
components, filters and controllers could be used to set property
values based on complex rules and driven from other property values.
That's why I chose to give it the name "property-rule".
This patch allows to define an arbitrary number of property rules under
a/sim/property-rule[n]/path
using the same syntax as autopilot configurations.
Split the former single-file-implementation in xmlauto.?xx into multiple
files and use some OO techniques. Started with documentation to be used
with doxygen.
