--- /dev/null
+// Written by Andrew J. Ross, started December 2003
+//
+// Copyright (C) 2003 Andrew J. Ross - andy@plausible.org
+//
+// This library is free software; you can redistribute it and/or
+// modify it under the terms of the GNU Library General Public
+// License as published by the Free Software Foundation; either
+// version 2 of the License, or (at your option) any later version.
+//
+// This library is distributed in the hope that it will be useful,
+// but WITHOUT ANY WARRANTY; without even the implied warranty of
+// MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU
+// Library General Public License for more details.
+//
+// You should have received a copy of the GNU Library General Public
+// License along with this library; if not, write to the
+// Free Software Foundation, Inc., 59 Temple Place - Suite 330,
+// Boston, MA 02111-1307, USA.
+
+#include "interpolator.hxx"
+
+void SGInterpolator::addNew(SGPropertyNode* prop, int nPoints)
+{
+ // Set the property type to a double, if it isn't already, and
+ // make sure we aren't already managing this node.
+ prop->setDoubleValue(prop->getDoubleValue());
+ cancel(prop);
+
+ Interp* iterp = new Interp();
+ iterp->target = prop;
+ iterp->nPoints = nPoints;
+ iterp->curve = new double[2*nPoints];
+
+ // Dirty trick: leave the new value sitting in _list to avoid
+ // having to return a pointer to a private type.
+ iterp->next = _list;
+ _list = iterp;
+}
+
+void SGInterpolator::interpolate(SGPropertyNode* prop, int nPoints,
+ double* values, double* deltas)
+{
+ addNew(prop, nPoints);
+ for(int i=0; i<nPoints; i++) {
+ _list->dt(i) = deltas[i];
+ _list->val(i) = values[i];
+ }
+}
+
+void SGInterpolator::interpolate(SGPropertyNode* prop, double val, double dt)
+{
+ addNew(prop, 1);
+ _list->dt(0) = dt;
+ _list->val(0) = val;
+}
+
+//
+// Delete all the list elements where "expr" is true.
+//
+// Silly preprocessor hack to avoid writing the linked list code in
+// two places. You would think that an STL set would be the way to
+// go, but I had terrible trouble getting it to work with the
+// dynamically allocated "curve" member. Frankly, this is easier to
+// write, and the code is smaller to boot...
+//
+#define DELETE_WHERE(EXPR)\
+Interp *p = _list, **last = &_list; \
+while(p) { \
+ if(EXPR) { \
+ *last = p->next; \
+ delete p; \
+ p = (*last) ? (*last)->next : 0; \
+ } else { \
+ last = &(p->next); \
+ p = p->next; } }
+
+void SGInterpolator::cancel(SGPropertyNode* prop)
+{
+ DELETE_WHERE(p->target == prop)
+}
+
+void SGInterpolator::update(double dt)
+{
+ DELETE_WHERE(interp(p, dt))
+}
+
+// This is the where the only "real" work happens. Walk through the
+// data points until we find one with some time left, slurp it up and
+// repeat until we run out of dt.
+bool SGInterpolator::interp(Interp* rec, double dt)
+{
+ double val = rec->target->getDoubleValue();
+ int i;
+ for(i=0; i < rec->nPoints; i++) {
+ if(rec->dt(i) > 0 && dt < rec->dt(i)) {
+ val += (dt / rec->dt(i)) * (rec->val(i) - val);
+ rec->dt(i) -= dt;
+ break;
+ }
+ dt -= rec->dt(i);
+ val = rec->val(i);
+ }
+ rec->target->setDoubleValue(val);
+
+ // Return true if this one is done
+ return i == rec->nPoints;
+}
--- /dev/null
+#ifndef __SG_INTERPOLATOR_HXX
+#define __SG_INTERPOLATOR_HXX
+
+// SGInterpolator
+// Subsystem that manages smooth linear interpolation of property
+// values across multiple data points and arbitrary time intervals.
+
+// Written by Andrew J. Ross, started December 2003
+//
+// Copyright (C) 2003 Andrew J. Ross - andy@plausible.org
+//
+// This library is free software; you can redistribute it and/or
+// modify it under the terms of the GNU Library General Public
+// License as published by the Free Software Foundation; either
+// version 2 of the License, or (at your option) any later version.
+//
+// This library is distributed in the hope that it will be useful,
+// but WITHOUT ANY WARRANTY; without even the implied warranty of
+// MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU
+// Library General Public License for more details.
+//
+// You should have received a copy of the GNU Library General Public
+// License along with this library; if not, write to the
+// Free Software Foundation, Inc., 59 Temple Place - Suite 330,
+// Boston, MA 02111-1307, USA.
+
+#include <simgear/props/props.hxx>
+#include <simgear/structure/subsystem_mgr.hxx>
+
+// TODO: support a callback upon interpolation completion so that user
+// code can register another one immediately without worrying about
+// timer aliasing.
+
+class SGInterpolator : public SGSubsystem {
+public:
+ SGInterpolator() { _list = 0; }
+ virtual void init() {}
+ virtual void update(double delta_time_sec);
+
+ // Simple method that interpolates a double property value from
+ // its current value (default of zero) to the specified target
+ // over the specified time.
+ void interpolate(SGPropertyNode* prop, double value, double dt_sec);
+
+ // More elaborate version that takes a pointer to lists of
+ // arbitrary size.
+ void interpolate(SGPropertyNode* prop, int nPoints,
+ double* values, double* deltas);
+
+ // Cancels any interpolation of the specified property, leaving
+ // its value at the current (mid-interpolation) state.
+ void cancel(SGPropertyNode* prop);
+
+private:
+ struct Interp {
+ SGPropertyNode_ptr target;
+ int nPoints;
+ double* curve; // time0, val0, time1, val1, ...
+ Interp* next;
+
+ ~Interp() { delete[] curve; }
+ double& dt(int i) { return curve[2*i]; }
+ double& val(int i) { return curve[2*i + 1]; }
+ };
+ Interp* _list;
+
+ bool interp(Interp* rec, double dt);
+ void addNew(SGPropertyNode* prop, int nPoints);
+};
+
+#endif // __SG_INTERPOLATOR_HXX
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