+/**
+ * Built-in command: interpolate a property value over time
+ *
+ * property: the name of the property value to interpolate.
+ * value[0..n] any number of constant values to interpolate
+ * time/rate[0..n] time between each value, number of time elements must
+ * match those of value elements. Instead of time also rate can
+ * be used which automatically calculates the time to change
+ * the property value at the given speed.
+ * -or-
+ * property[1..n] any number of target values taken from named properties
+ * time/rate[0..n] time between each value, number of time elements must
+ * match those of value elements. Instead of time also rate can
+ * be used which automatically calculates the time to change
+ * the property value at the given speed.
+ */
+static bool
+do_property_interpolate (const SGPropertyNode * arg)
+{
+ SGPropertyNode * prop = get_prop(arg);
+
+ simgear::PropertyList valueNodes = arg->getChildren( "value" );
+ simgear::PropertyList timeNodes = arg->getChildren( "time" );
+ simgear::PropertyList rateNodes = arg->getChildren( "rate" );
+
+ if( !timeNodes.empty() && !rateNodes.empty() )
+ // mustn't specify time and rate
+ return false;
+
+ simgear::PropertyList::size_type num_times = timeNodes.empty()
+ ? rateNodes.size()
+ : timeNodes.size();
+
+ boost::scoped_array<double> value;
+ boost::scoped_array<double> time;
+
+ if( valueNodes.size() > 0 ) {
+ // must match
+ if( num_times != valueNodes.size() )
+ return false;
+
+ value.reset( new double[valueNodes.size()] );
+ for( simgear::PropertyList::size_type n = 0; n < valueNodes.size(); n++ ) {
+ value[n] = valueNodes[n]->getDoubleValue();
+ }
+ } else {
+ valueNodes = arg->getChildren("property");
+ // must have one more property node
+ if( valueNodes.size() - 1 != num_times )
+ return false;
+
+ value.reset( new double[valueNodes.size()-1] );
+ for( simgear::PropertyList::size_type n = 0; n < valueNodes.size()-1; n++ ) {
+ value[n] = fgGetNode(valueNodes[n+1]->getStringValue(), "/null")->getDoubleValue();
+ }
+
+ }
+
+ time.reset( new double[num_times] );
+ if( !timeNodes.empty() ) {
+ for( simgear::PropertyList::size_type n = 0; n < num_times; n++ ) {
+ time[n] = timeNodes[n]->getDoubleValue();
+ }
+ } else {
+ for( simgear::PropertyList::size_type n = 0; n < num_times; n++ ) {
+ double delta = value[n]
+ - (n > 0 ? value[n - 1] : prop->getDoubleValue());
+ time[n] = fabs(delta / rateNodes[n]->getDoubleValue());
+ }
+ }
+
+ ((SGInterpolator*)globals->get_subsystem_mgr()
+ ->get_group(SGSubsystemMgr::INIT)->get_subsystem("interpolator"))
+ ->interpolate(prop, num_times, value.get(), time.get() );
+
+ return true;
+}