Make panner's doppler rate continuous as the source position approaches the listener position.

Source/modules/webaudio/PannerNode.cpp

 /*
  * Copyright (C) 2010, Google Inc. All rights reserved.
  *
  * Redistribution and use in source and binary forms, with or without
  * modification, are permitted provided that the following conditions
  * are met:
  * 1.  Redistributions of source code must retain the above copyright
  *    notice, this list of conditions and the following disclaimer.
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  *    notice, this list of conditions and the following disclaimer in the
@@ skipping 367 matching lines @@
 }
 
 void PannerNode::calculateAzimuthElevation(double* outAzimuth, double* outElevation)
 {
     double azimuth = 0.0;
 
     // Calculate the source-listener vector
     FloatPoint3D listenerPosition = listener()->position();
     FloatPoint3D sourceListener = m_position - listenerPosition;
 
     if (sourceListener.isZero()) {

[KhNo, 2014/05/28 13:57:20]

How do you think if we remove line from 388 to 394 although
sourceListener.isZero() is true.
It might create meaningful values even if distance is zero. outAzimuth and
outElevation might be meaningful after calculation with zero.

[Raymond Toy, 2014/05/28 17:19:16]

I think sourceListener.normalize() will fail (return NaN) because the length is
0 so you can't normalize it in any sane way.

[Raymond Toy, 2014/05/28 18:25:26]

Oh, wait.  normalize() does nothing if the length is 0. This might be ok.  Let
me check.

[Raymond Toy, 2014/05/29 18:22:13]

This is ok. The special case is removed.

-        // degenerate case if source and listener are at the same point
-        *outAzimuth = 0.0;
-        *outElevation = 0.0;
+        // Degenerate case if source and listener are at the same point. To preserve continuity,

[Ken Russell (switch to Gerrit), 2014/05/27 23:24:43]

Comparing against zero seems fragile. You're the expert, but wouldn't this be
more stable if there were an epsilon defined in this file and the comparison
happened against that?

[Raymond Toy, 2014/05/28 17:17:22]

I think this is ok here. If it's not zero, sourceListener.normalize() should
work fine and the rest of the computations should be ok.

+        // don't change anything; just use the cached values.
+        *outAzimuth = m_cachedAzimuth;
+        *outElevation = m_cachedElevation;
         return;
     }
 
     sourceListener.normalize();
 
     // Align axes
     FloatPoint3D listenerFront = listener()->orientation();
     FloatPoint3D listenerUp = listener()->upVector();
     FloatPoint3D listenerRight = listenerFront.cross(listenerUp);
     listenerRight.normalize();
@@ skipping 52 matching lines @@
         bool sourceHasVelocity = !sourceVelocity.isZero();
         bool listenerHasVelocity = !listenerVelocity.isZero();
 
         if (sourceHasVelocity || listenerHasVelocity) {
             // Calculate the source to listener vector
             FloatPoint3D listenerPosition = listener()->position();
             FloatPoint3D sourceToListener = m_position - listenerPosition;
 
             double sourceListenerMagnitude = sourceToListener.length();
 
-            double listenerProjection = sourceToListener.dot(listenerVelocity) / sourceListenerMagnitude;
-            double sourceProjection = sourceToListener.dot(sourceVelocity) / sourceListenerMagnitude;
+            if (!sourceListenerMagnitude) {

[Ken Russell (switch to Gerrit), 2014/05/27 23:24:43]

Same comment here.

[Raymond Toy, 2014/05/28 17:17:22]

I believe this is ok here too.  It's only a problem when the magnitude is
exactly zero. For any other value, we aren't dividing by zero and causing
problems.

+                // Source and listener are at the same position. Skip the computation of the doppler
+                // shift, and just return the cached value.
+                dopplerShift = m_cachedDopplerRate;
+            } else {
+                double listenerProjection = sourceToListener.dot(listenerVelocity) / sourceListenerMagnitude;
+                double sourceProjection = sourceToListener.dot(sourceVelocity) / sourceListenerMagnitude;
 
-            listenerProjection = -listenerProjection;
-            sourceProjection = -sourceProjection;
+                listenerProjection = -listenerProjection;
+                sourceProjection = -sourceProjection;
 
-            double scaledSpeedOfSound = speedOfSound / dopplerFactor;
-            listenerProjection = min(listenerProjection, scaledSpeedOfSound);
-            sourceProjection = min(sourceProjection, scaledSpeedOfSound);
+                double scaledSpeedOfSound = speedOfSound / dopplerFactor;
+                listenerProjection = min(listenerProjection, scaledSpeedOfSound);
+                sourceProjection = min(sourceProjection, scaledSpeedOfSound);
 
-            dopplerShift = ((speedOfSound - dopplerFactor * listenerProjection) / (speedOfSound - dopplerFactor * sourceProjection));
-            fixNANs(dopplerShift); // avoid illegal values
+                dopplerShift = ((speedOfSound - dopplerFactor * listenerProjection) / (speedOfSound - dopplerFactor * sourceProjection));
+                fixNANs(dopplerShift); // avoid illegal values
 
-            // Limit the pitch shifting to 4 octaves up and 3 octaves down.
-            if (dopplerShift > 16.0)
-                dopplerShift = 16.0;
-            else if (dopplerShift < 0.125)
-                dopplerShift = 0.125;
+                // Limit the pitch shifting to 4 octaves up and 3 octaves down.
+                if (dopplerShift > 16.0)
+                    dopplerShift = 16.0;
+                else if (dopplerShift < 0.125)
+                    dopplerShift = 0.125;
+            }
         }
     }
 
     return dopplerShift;
 }
 
 float PannerNode::calculateDistanceConeGain()
 {
     FloatPoint3D listenerPosition = listener()->position();
 
@@ skipping 81 matching lines @@
                     notifyAudioSourcesConnectedToNode(connectedNode, visitedNodes); // recurse
                 }
             }
         }
     }
 }
 
 } // namespace WebCore
 
 #endif // ENABLE(WEB_AUDIO)