Add the option to define volume and pitch using an expression

simgear/sound/xmlsound.cxx

@@ -140,7 +140,12 @@ SGXmlSound::init( SGPropertyNode *root,
    float v = 0.0;
    std::vector<SGPropertyNode_ptr> kids = node->getChildren("volume");
    for (i = 0; (i < kids.size()) && (i < SGXmlSound::MAXPROP); i++) {
-      _snd_prop volume = {NULL, NULL, NULL, 1.0, 0.0, 0.0, 0.0, false};
+      _snd_prop volume = {NULL, NULL, NULL, NULL, 1.0, 0.0, 0.0, 0.0, false};
+
+      SGPropertyNode *n = kids[i]->getChild("expression");
+      if (n != NULL) {
+         volume.expr = SGReadDoubleExpression(root, n->getChild(0));
+      }
 
       propval = kids[i]->getStringValue("property", "");
       if ( propval != "" )
@@ -198,7 +203,12 @@ SGXmlSound::init( SGPropertyNode *root,
    float p = 0.0;
    kids = node->getChildren("pitch");
    for (i = 0; (i < kids.size()) && (i < SGXmlSound::MAXPROP); i++) {
-      _snd_prop pitch = {NULL, NULL, NULL, 1.0, 1.0, 0.0, 0.0, false};
+      _snd_prop pitch = {NULL, NULL, NULL, NULL, 1.0, 1.0, 0.0, 0.0, false};
+
+      SGPropertyNode *n = kids[i]->getChild("expression");
+      if (n != NULL) {
+         pitch.expr = SGReadDoubleExpression(root, n->getChild(0));
+      }
 
       propval = kids[i]->getStringValue("property", "");
       if (propval != "")
@@ -401,15 +411,27 @@ SGXmlSound::update (double dt)
    int max = _volume.size();
    double volume = 1.0;
    double volume_offset = 0.0;
+   bool expr = false;
 
    for(i = 0; i < max; i++) {
       double v = 1.0;
 
-      if (_volume[i].prop)
+      if (_volume[i].expr) {
-         v = _volume[i].prop->getDoubleValue();
+         v = _volume[i].expr->getValue(NULL);
+         expr = true;
+         continue;
+      }
 
-      else if (_volume[i].intern)
+      if (_volume[i].prop) {
+         // do not process if there was an expression defined
+         if (expr) continue;
+
+         v = _volume[i].prop->getDoubleValue();
+      }
+      else if (_volume[i].intern) {
+         // intern sections always get processed.
          v = *_volume[i].intern;
+      }
 
       if (_volume[i].fn)
          v = _volume[i].fn(v);
@@ -438,14 +460,26 @@ SGXmlSound::update (double dt)
    double pitch = 1.0;
    double pitch_offset = 0.0;
 
+   expr = false;
    for(i = 0; i < max; i++) {
       double p = 1.0;
 
-      if (_pitch[i].prop)
+      if (_volume[i].expr) {
-         p = _pitch[i].prop->getDoubleValue();
+         p = _pitch[i].expr->getValue(NULL);
+         expr = true;
+         continue;
+      }
 
-      else if (_pitch[i].intern)
+      if (_pitch[i].prop) {
+         // do not process if there was an expression defined
+         if (expr) continue;
+
+         p = _pitch[i].prop->getDoubleValue();
+      }
+      else if (_pitch[i].intern) {
+         // intern sections always get processed.
          p = *_pitch[i].intern;
+      }
 
       if (_pitch[i].fn)
          p = _pitch[i].fn(p);

simgear/sound/xmlsound.hxx

@@ -33,6 +33,7 @@
 
 #include <simgear/props/propsfwd.hxx>
 #include <simgear/structure/SGSharedPtr.hxx>
+#include <simgear/structure/SGExpression.hxx>
 
 // forward decls
 class SGSampleGroup;
@@ -126,8 +127,9 @@ protected:
   enum { ONCE=0, LOOPED, IN_TRANSIT };
   enum { LEVEL=0, INVERTED, FLIPFLOP };
 
-  // SGXmlSound properties
+  // SGXmlSound properties for
   typedef struct {
+        SGSharedPtr<SGExpressiond> expr;	// sound system version 2.0
         SGPropertyNode_ptr prop;
         double (*fn)(double);
         double *intern;
@@ -147,6 +149,7 @@ private:
   SGPropertyNode_ptr _property;
 
   bool _active;
+  float _version;
   std::string _name;
   int _mode;
   double _prev_value;
@@ -157,6 +160,7 @@ private:
                         // This is useful for lost packets in in-transit mode.
   bool _initialized;
 
+  // sound system version 1.0
   std::vector<_snd_prop> _volume;
   std::vector<_snd_prop> _pitch;
 };