Implement StereoPannerNode for robust stereo panning

Source/platform/audio/Spatializer.h

Index: Source/platform/audio/Spatializer.h
diff --git a/Source/platform/graphics/GraphicsContextStateSaver.h b/Source/platform/audio/Spatializer.h
similarity index 58%
copy from Source/platform/graphics/GraphicsContextStateSaver.h
copy to Source/platform/audio/Spatializer.h
index 7134a98d938e44a9e0041b120a4cebc24238a54d..69b68d5a926fe9a9f5d4b9d4c34385797b5f0d5a 100644
--- a/Source/platform/graphics/GraphicsContextStateSaver.h
+++ b/Source/platform/audio/Spatializer.h
@@ -1,4 +1,4 @@
-// Copyright (C) 2013 Google Inc. All rights reserved.
+// Copyright 2014 The Chromium Authors. All rights reserved.
 //
 // Redistribution and use in source and binary forms, with or without
 // modification, are permitted provided that the following conditions are
@@ -26,60 +26,45 @@
 // (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE
 // OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
 
-#ifndef GraphicsContextStateSaver_h
-#define GraphicsContextStateSaver_h
+#ifndef Spatializer_h
+#define Spatializer_h
 
 #include "platform/PlatformExport.h"
-#include "platform/graphics/GraphicsContext.h"
+#include "platform/heap/Handle.h"
 
 namespace blink {
 
-class PLATFORM_EXPORT GraphicsContextStateSaver {
-    WTF_MAKE_FAST_ALLOCATED;
+class AudioBus;
+
+// Abstract base class for spatializing a mono or stereo source.
+class PLATFORM_EXPORT Spatializer : public GarbageCollectedFinalized<Spatializer> {
 public:
-    GraphicsContextStateSaver(GraphicsContext& context, bool saveAndRestore = true)
-        : m_context(context)
-        , m_saveAndRestore(saveAndRestore)
-    {
-        if (m_saveAndRestore)
-            m_context.save();
-    }
+    enum {
+        PanningModelEqualPower = 0
+    };
+
+    typedef unsigned PanningModel;
+
+    static Spatializer* create(PanningModel, float sampleRate);
 
-    ~GraphicsContextStateSaver()
-    {
-        if (m_saveAndRestore)
-            m_context.restore();
-    }
+    virtual ~Spatializer() { };
 
-    void save()
-    {
-        ASSERT(!m_saveAndRestore);
-        m_context.save();
-        m_saveAndRestore = true;
-    }
+    // Handle sample-accurate panning by AudioParam automation.
+    virtual void panWithSampleAccurateValues(const AudioBus* inputBus, AudioBus* outputBuf, const float* panValues, size_t framesToProcess) = 0;
 
-    void saveIfNeeded()
-    {
-        if (saved())
-            return;
-        save();
-    }
+    // Handle de-zippered panning to a target value.
+    virtual void panToTargetValue(const AudioBus* inputBus, AudioBus* outputBuf, float panValue, size_t framesToProcess) = 0;
 
-    void restore()
-    {
-        ASSERT(m_saveAndRestore);
-        m_context.restore();
-        m_saveAndRestore = false;
-    }
+    virtual void reset() = 0;
+    virtual double tailTime() const = 0;
+    virtual double latencyTime() const = 0;
 
-    GraphicsContext* context() const { return &m_context; }
-    bool saved() const { return m_saveAndRestore; }
+    virtual void trace(Visitor*) { }
 
-private:
-    GraphicsContext& m_context;
-    bool m_saveAndRestore;
+protected:
+    Spatializer(PanningModel model) { }
 };
 
 } // namespace blink
 
-#endif // GraphicsContextStateSaver_h
+#endif // Spatializer_h