Sub-sample accurate start of OscillatorNode

third_party/WebKit/Source/modules/webaudio/OscillatorNode.cpp

Index: third_party/WebKit/Source/modules/webaudio/OscillatorNode.cpp
diff --git a/third_party/WebKit/Source/modules/webaudio/OscillatorNode.cpp b/third_party/WebKit/Source/modules/webaudio/OscillatorNode.cpp
index ca484863958c8b70f9ba754a57702524fb52278e..25d724381734dea9e73c497c88add39840681ec2 100644
--- a/third_party/WebKit/Source/modules/webaudio/OscillatorNode.cpp
+++ b/third_party/WebKit/Source/modules/webaudio/OscillatorNode.cpp
@@ -239,9 +239,10 @@ void OscillatorHandler::process(size_t framesToProcess) {
 
   size_t quantumFrameOffset;
   size_t nonSilentFramesToProcess;
+  double startFrameOffset;
 
   updateSchedulingInfo(framesToProcess, outputBus, quantumFrameOffset,
-                       nonSilentFramesToProcess);
+                       nonSilentFramesToProcess, startFrameOffset);
 
   if (!nonSilentFramesToProcess) {
     outputBus->zero();
@@ -286,6 +287,19 @@ void OscillatorHandler::process(size_t framesToProcess) {
   destP += quantumFrameOffset;
   int n = nonSilentFramesToProcess;
 
+  // If startFrameOffset is not 0, that means the oscillator doesn't actually
+  // start at quantumFrameOffset, but just past that time.  Adjust destP and n
+  // to reflect that, and adjust virtualReadIndex to start the value at
+  // startFrameOffset.
+  if (startFrameOffset > 0) {
+    ++destP;
+    --n;
+    virtualReadIndex += (1 - startFrameOffset) * frequency * rateScale;
+    DCHECK(virtualReadIndex < periodicWaveSize);
+  } else if (startFrameOffset < 0) {
+    virtualReadIndex = -startFrameOffset * frequency * rateScale;
+  }
+
   while (n--) {
     unsigned readIndex = static_cast<unsigned>(virtualReadIndex);
     unsigned readIndex2 = readIndex + 1;