Source/WebCore/Modules/webaudio/AudioParamTimeline.cpp - WebKit - Git at Google

 /*
  * Copyright (C) 2011 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.
  * 2.  Redistributions in binary form must reproduce the above copyright
  *     notice, this list of conditions and the following disclaimer in the
  *     documentation and/or other materials provided with the distribution.
  *
  * THIS SOFTWARE IS PROVIDED BY APPLE AND ITS CONTRIBUTORS "AS IS" AND ANY
  * EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE IMPLIED
  * WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE ARE
  * DISCLAIMED. IN NO EVENT SHALL APPLE OR ITS CONTRIBUTORS BE LIABLE FOR ANY
  * DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES
  * (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES;
  * LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND
  * ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT
  * (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE OF
  * THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
  */

 #include "config.h"

 #if ENABLE(WEB_AUDIO)

 #include "AudioParamTimeline.h"

 #include "AudioUtilities.h"
 #include "FloatConversion.h"
 #include <algorithm>
 #include <wtf/MathExtras.h>

 namespace WebCore {

 void AudioParamTimeline::setValueAtTime(float value, float time)
 {
     insertEvent(ParamEvent(ParamEvent::SetValue, value, time, 0, 0, 0));
 }

 void AudioParamTimeline::linearRampToValueAtTime(float value, float time)
 {
     insertEvent(ParamEvent(ParamEvent::LinearRampToValue, value, time, 0, 0, 0));
 }

 void AudioParamTimeline::exponentialRampToValueAtTime(float value, float time)
 {
     insertEvent(ParamEvent(ParamEvent::ExponentialRampToValue, value, time, 0, 0, 0));
 }

 void AudioParamTimeline::setTargetAtTime(float target, float time, float timeConstant)
 {
     insertEvent(ParamEvent(ParamEvent::SetTarget, target, time, timeConstant, 0, 0));
 }

 void AudioParamTimeline::setValueCurveAtTime(Float32Array* curve, float time, float duration)
 {
     insertEvent(ParamEvent(ParamEvent::SetValueCurve, 0, time, 0, duration, curve));
 }

 static bool isValidNumber(float x)
 {
     return !std::isnan(x) && !std::isinf(x);
 }

 void AudioParamTimeline::insertEvent(const ParamEvent& event)
 {
     // Sanity check the event. Be super careful we're not getting infected with NaN or Inf.
     bool isValid = event.type() < ParamEvent::LastType
         && isValidNumber(event.value())
         && isValidNumber(event.time())
         && isValidNumber(event.timeConstant())
         && isValidNumber(event.duration())
         && event.duration() >= 0;

     ASSERT(isValid);
     if (!isValid)
         return;

     auto locker = holdLock(m_eventsMutex);

     unsigned i = 0;
     float insertTime = event.time();
     for (auto& paramEvent : m_events) {
         // Overwrite same event type and time.
         if (paramEvent.time() == insertTime && paramEvent.type() == event.type()) {
             paramEvent = event;
             return;
         }

         if (paramEvent.time() > insertTime)
             break;

         ++i;
     }

     m_events.insert(i, event);
 }

 void AudioParamTimeline::cancelScheduledValues(float startTime)
 {
     auto locker = holdLock(m_eventsMutex);

     // Remove all events starting at startTime.
     for (unsigned i = 0; i < m_events.size(); ++i) {
         if (m_events[i].time() >= startTime) {
             m_events.remove(i, m_events.size() - i);
             break;
         }
     }
 }

 float AudioParamTimeline::valueForContextTime(AudioContext& context, float defaultValue, bool& hasValue)
 {
     {
         std::unique_lock<Lock> lock(m_eventsMutex, std::try_to_lock);
         if (!lock.owns_lock() || !m_events.size() || context.currentTime() < m_events[0].time()) {
             hasValue = false;
             return defaultValue;
         }
     }

     // Ask for just a single value.
     float value;
     double sampleRate = context.sampleRate();
     double startTime = context.currentTime();
     double endTime = startTime + 1.1 / sampleRate; // time just beyond one sample-frame
     double controlRate = sampleRate / AudioNode::ProcessingSizeInFrames; // one parameter change per render quantum
     value = valuesForTimeRange(startTime, endTime, defaultValue, &value, 1, sampleRate, controlRate);

     hasValue = true;
     return value;
 }

 float AudioParamTimeline::valuesForTimeRange(double startTime, double endTime, float defaultValue, float* values, unsigned numberOfValues, double sampleRate, double controlRate)
 {
     // We can't contend the lock in the realtime audio thread.
     std::unique_lock<Lock> lock(m_eventsMutex, std::try_to_lock);
     if (!lock.owns_lock()) {
         if (values) {
             for (unsigned i = 0; i < numberOfValues; ++i)
                 values[i] = defaultValue;
         }
         return defaultValue;
     }

     float value = valuesForTimeRangeImpl(startTime, endTime, defaultValue, values, numberOfValues, sampleRate, controlRate);

     return value;
 }

 float AudioParamTimeline::valuesForTimeRangeImpl(double startTime, double endTime, float defaultValue, float* values, unsigned numberOfValues, double sampleRate, double controlRate)
 {
     ASSERT(values);
     if (!values)
         return defaultValue;

     // Return default value if there are no events matching the desired time range.
     if (!m_events.size() || endTime <= m_events[0].time()) {
         for (unsigned i = 0; i < numberOfValues; ++i)
             values[i] = defaultValue;
         return defaultValue;
     }

     // Maintain a running time and index for writing the values buffer.
     double currentTime = startTime;
     unsigned writeIndex = 0;

     // If first event is after startTime then fill initial part of values buffer with defaultValue
     // until we reach the first event time.
     double firstEventTime = m_events[0].time();
     if (firstEventTime > startTime) {
         double fillToTime = std::min(endTime, firstEventTime);
         unsigned fillToFrame = AudioUtilities::timeToSampleFrame(fillToTime - startTime, sampleRate);
         fillToFrame = std::min(fillToFrame, numberOfValues);
         for (; writeIndex < fillToFrame; ++writeIndex)
             values[writeIndex] = defaultValue;

         currentTime = fillToTime;
     }

     float value = defaultValue;

     // Go through each event and render the value buffer where the times overlap,
     // stopping when we've rendered all the requested values.
     // FIXME: could try to optimize by avoiding having to iterate starting from the very first event
     // and keeping track of a "current" event index.
     int n = m_events.size();
     for (int i = 0; i < n && writeIndex < numberOfValues; ++i) {
         ParamEvent& event = m_events[i];
         ParamEvent* nextEvent = i < n - 1 ? &(m_events[i + 1]) : 0;

         // Wait until we get a more recent event.
         if (nextEvent && nextEvent->time() < currentTime)
             continue;

         float value1 = event.value();
         double time1 = event.time();
         float value2 = nextEvent ? nextEvent->value() : value1;
         double time2 = nextEvent ? nextEvent->time() : endTime + 1;

         double deltaTime = time2 - time1;
         float k = deltaTime > 0 ? 1 / deltaTime : 0;
         double sampleFrameTimeIncr = 1 / sampleRate;

         double fillToTime = std::min(endTime, time2);
         unsigned fillToFrame = AudioUtilities::timeToSampleFrame(fillToTime - startTime, sampleRate);
         fillToFrame = std::min(fillToFrame, numberOfValues);

         ParamEvent::Type nextEventType = nextEvent ? static_cast<ParamEvent::Type>(nextEvent->type()) : ParamEvent::LastType /* unknown */;

         // First handle linear and exponential ramps which require looking ahead to the next event.
         if (nextEventType == ParamEvent::LinearRampToValue) {
             for (; writeIndex < fillToFrame; ++writeIndex) {
                 float x = (currentTime - time1) * k;
                 value = (1 - x) * value1 + x * value2;
                 values[writeIndex] = value;
                 currentTime += sampleFrameTimeIncr;
             }
         } else if (nextEventType == ParamEvent::ExponentialRampToValue) {
             if (value1 <= 0 || value2 <= 0) {
                 // Handle negative values error case by propagating previous value.
                 for (; writeIndex < fillToFrame; ++writeIndex)
                     values[writeIndex] = value;
             } else {
                 float numSampleFrames = deltaTime * sampleRate;
                 // The value goes exponentially from value1 to value2 in a duration of deltaTime seconds (corresponding to numSampleFrames).
                 // Compute the per-sample multiplier.
                 float multiplier = powf(value2 / value1, 1 / numSampleFrames);

                 // Set the starting value of the exponential ramp. This is the same as multiplier ^
                 // AudioUtilities::timeToSampleFrame(currentTime - time1, sampleRate), but is more
                 // accurate, especially if multiplier is close to 1.
                 value = value1 * powf(value2 / value1,
                                       AudioUtilities::timeToSampleFrame(currentTime - time1, sampleRate) / numSampleFrames);

                 for (; writeIndex < fillToFrame; ++writeIndex) {
                     values[writeIndex] = value;
                     value *= multiplier;
                     currentTime += sampleFrameTimeIncr;
                 }
             }
         } else {
             // Handle event types not requiring looking ahead to the next event.
             switch (event.type()) {
             case ParamEvent::SetValue:
             case ParamEvent::LinearRampToValue:
             case ParamEvent::ExponentialRampToValue:
                 {
                     currentTime = fillToTime;

                     // Simply stay at a constant value.
                     value = event.value();
                     for (; writeIndex < fillToFrame; ++writeIndex)
                         values[writeIndex] = value;

                     break;
                 }

             case ParamEvent::SetTarget:
                 {
                     currentTime = fillToTime;

                     // Exponential approach to target value with given time constant.
                     float target = event.value();
                     float timeConstant = event.timeConstant();
                     float discreteTimeConstant = static_cast<float>(AudioUtilities::discreteTimeConstantForSampleRate(timeConstant, controlRate));

                     for (; writeIndex < fillToFrame; ++writeIndex) {
                         values[writeIndex] = value;
                         value += (target - value) * discreteTimeConstant;
                     }

                     break;
                 }

             case ParamEvent::SetValueCurve:
                 {
                     Float32Array* curve = event.curve();
                     float* curveData = curve ? curve->data() : 0;
                     unsigned numberOfCurvePoints = curve ? curve->length() : 0;

                     // Curve events have duration, so don't just use next event time.
                     float duration = event.duration();
                     float durationFrames = duration * sampleRate;
                     float curvePointsPerFrame = static_cast<float>(numberOfCurvePoints) / durationFrames;

                     if (!curve || !curveData || !numberOfCurvePoints || duration <= 0 || sampleRate <= 0) {
                         // Error condition - simply propagate previous value.
                         currentTime = fillToTime;
                         for (; writeIndex < fillToFrame; ++writeIndex)
                             values[writeIndex] = value;
                         break;
                     }

                     // Save old values and recalculate information based on the curve's duration
                     // instead of the next event time.
                     unsigned nextEventFillToFrame = fillToFrame;
                     float nextEventFillToTime = fillToTime;
                     fillToTime = std::min(endTime, time1 + duration);
                     fillToFrame = AudioUtilities::timeToSampleFrame(fillToTime - startTime, sampleRate);
                     fillToFrame = std::min(fillToFrame, numberOfValues);

                     // Index into the curve data using a floating-point value.
                     // We're scaling the number of curve points by the duration (see curvePointsPerFrame).
                     float curveVirtualIndex = 0;
                     if (time1 < currentTime) {
                         // Index somewhere in the middle of the curve data.
                         // Don't use timeToSampleFrame() since we want the exact floating-point frame.
                         float frameOffset = (currentTime - time1) * sampleRate;
                         curveVirtualIndex = curvePointsPerFrame * frameOffset;
                     }

                     // Render the stretched curve data using nearest neighbor sampling.
                     // Oversampled curve data can be provided if smoothness is desired.
                     for (; writeIndex < fillToFrame; ++writeIndex) {
                         // Ideally we'd use round() from MathExtras, but we're in a tight loop here
                         // and we're trading off precision for extra speed.
                         unsigned curveIndex = static_cast<unsigned>(0.5 + curveVirtualIndex);

                         curveVirtualIndex += curvePointsPerFrame;

                         // Bounds check.
                         if (curveIndex < numberOfCurvePoints)
                             value = curveData[curveIndex];

                         values[writeIndex] = value;
                     }

                     // If there's any time left after the duration of this event and the start
                     // of the next, then just propagate the last value.
                     for (; writeIndex < nextEventFillToFrame; ++writeIndex)
                         values[writeIndex] = value;

                     // Re-adjust current time
                     currentTime = nextEventFillToTime;

                     break;
                 }
             }
         }
     }

     // If there's any time left after processing the last event then just propagate the last value
     // to the end of the values buffer.
     for (; writeIndex < numberOfValues; ++writeIndex)
         values[writeIndex] = value;

     return value;
 }

 } // namespace WebCore

 #endif // ENABLE(WEB_AUDIO)
	/*
	* Copyright (C) 2011 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.
	* 2. Redistributions in binary form must reproduce the above copyright
	* notice, this list of conditions and the following disclaimer in the
	* documentation and/or other materials provided with the distribution.
	*
	* THIS SOFTWARE IS PROVIDED BY APPLE AND ITS CONTRIBUTORS "AS IS" AND ANY
	* EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE IMPLIED
	* WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE ARE
	* DISCLAIMED. IN NO EVENT SHALL APPLE OR ITS CONTRIBUTORS BE LIABLE FOR ANY
	* DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES
	* (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES;
	* LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND
	* ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT
	* (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE OF
	* THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
	*/

	#include "config.h"

	#if ENABLE(WEB_AUDIO)

	#include "AudioParamTimeline.h"

	#include "AudioUtilities.h"
	#include "FloatConversion.h"
	#include <algorithm>
	#include <wtf/MathExtras.h>

	namespace WebCore {

	void AudioParamTimeline::setValueAtTime(float value, float time)
	{
	insertEvent(ParamEvent(ParamEvent::SetValue, value, time, 0, 0, 0));
	}

	void AudioParamTimeline::linearRampToValueAtTime(float value, float time)
	{
	insertEvent(ParamEvent(ParamEvent::LinearRampToValue, value, time, 0, 0, 0));
	}

	void AudioParamTimeline::exponentialRampToValueAtTime(float value, float time)
	{
	insertEvent(ParamEvent(ParamEvent::ExponentialRampToValue, value, time, 0, 0, 0));
	}

	void AudioParamTimeline::setTargetAtTime(float target, float time, float timeConstant)
	{
	insertEvent(ParamEvent(ParamEvent::SetTarget, target, time, timeConstant, 0, 0));
	}

	void AudioParamTimeline::setValueCurveAtTime(Float32Array* curve, float time, float duration)
	{
	insertEvent(ParamEvent(ParamEvent::SetValueCurve, 0, time, 0, duration, curve));
	}

	static bool isValidNumber(float x)
	{
	return !std::isnan(x) && !std::isinf(x);
	}

	void AudioParamTimeline::insertEvent(const ParamEvent& event)
	{
	// Sanity check the event. Be super careful we're not getting infected with NaN or Inf.
	bool isValid = event.type() < ParamEvent::LastType
	&& isValidNumber(event.value())
	&& isValidNumber(event.time())
	&& isValidNumber(event.timeConstant())
	&& isValidNumber(event.duration())
	&& event.duration() >= 0;

	ASSERT(isValid);
	if (!isValid)
	return;

	auto locker = holdLock(m_eventsMutex);

	unsigned i = 0;
	float insertTime = event.time();
	for (auto& paramEvent : m_events) {
	// Overwrite same event type and time.
	if (paramEvent.time() == insertTime && paramEvent.type() == event.type()) {
	paramEvent = event;
	return;
	}

	if (paramEvent.time() > insertTime)
	break;

	++i;
	}

	m_events.insert(i, event);
	}

	void AudioParamTimeline::cancelScheduledValues(float startTime)
	{
	auto locker = holdLock(m_eventsMutex);

	// Remove all events starting at startTime.
	for (unsigned i = 0; i < m_events.size(); ++i) {
	if (m_events[i].time() >= startTime) {
	m_events.remove(i, m_events.size() - i);
	break;
	}
	}
	}

	float AudioParamTimeline::valueForContextTime(AudioContext& context, float defaultValue, bool& hasValue)
	{
	{
	std::unique_lock<Lock> lock(m_eventsMutex, std::try_to_lock);
	if (!lock.owns_lock() \|\| !m_events.size() \|\| context.currentTime() < m_events[0].time()) {
	hasValue = false;
	return defaultValue;
	}
	}

	// Ask for just a single value.
	float value;
	double sampleRate = context.sampleRate();
	double startTime = context.currentTime();
	double endTime = startTime + 1.1 / sampleRate; // time just beyond one sample-frame
	double controlRate = sampleRate / AudioNode::ProcessingSizeInFrames; // one parameter change per render quantum
	value = valuesForTimeRange(startTime, endTime, defaultValue, &value, 1, sampleRate, controlRate);

	hasValue = true;
	return value;
	}

	float AudioParamTimeline::valuesForTimeRange(double startTime, double endTime, float defaultValue, float* values, unsigned numberOfValues, double sampleRate, double controlRate)
	{
	// We can't contend the lock in the realtime audio thread.
	std::unique_lock<Lock> lock(m_eventsMutex, std::try_to_lock);
	if (!lock.owns_lock()) {
	if (values) {
	for (unsigned i = 0; i < numberOfValues; ++i)
	values[i] = defaultValue;
	}
	return defaultValue;
	}

	float value = valuesForTimeRangeImpl(startTime, endTime, defaultValue, values, numberOfValues, sampleRate, controlRate);

	return value;
	}

	float AudioParamTimeline::valuesForTimeRangeImpl(double startTime, double endTime, float defaultValue, float* values, unsigned numberOfValues, double sampleRate, double controlRate)
	{
	ASSERT(values);
	if (!values)
	return defaultValue;

	// Return default value if there are no events matching the desired time range.
	if (!m_events.size() \|\| endTime <= m_events[0].time()) {
	for (unsigned i = 0; i < numberOfValues; ++i)
	values[i] = defaultValue;
	return defaultValue;
	}

	// Maintain a running time and index for writing the values buffer.
	double currentTime = startTime;
	unsigned writeIndex = 0;

	// If first event is after startTime then fill initial part of values buffer with defaultValue
	// until we reach the first event time.
	double firstEventTime = m_events[0].time();
	if (firstEventTime > startTime) {
	double fillToTime = std::min(endTime, firstEventTime);
	unsigned fillToFrame = AudioUtilities::timeToSampleFrame(fillToTime - startTime, sampleRate);
	fillToFrame = std::min(fillToFrame, numberOfValues);
	for (; writeIndex < fillToFrame; ++writeIndex)
	values[writeIndex] = defaultValue;

	currentTime = fillToTime;
	}

	float value = defaultValue;

	// Go through each event and render the value buffer where the times overlap,
	// stopping when we've rendered all the requested values.
	// FIXME: could try to optimize by avoiding having to iterate starting from the very first event
	// and keeping track of a "current" event index.
	int n = m_events.size();
	for (int i = 0; i < n && writeIndex < numberOfValues; ++i) {
	ParamEvent& event = m_events[i];
	ParamEvent* nextEvent = i < n - 1 ? &(m_events[i + 1]) : 0;

	// Wait until we get a more recent event.
	if (nextEvent && nextEvent->time() < currentTime)
	continue;

	float value1 = event.value();
	double time1 = event.time();
	float value2 = nextEvent ? nextEvent->value() : value1;
	double time2 = nextEvent ? nextEvent->time() : endTime + 1;

	double deltaTime = time2 - time1;
	float k = deltaTime > 0 ? 1 / deltaTime : 0;
	double sampleFrameTimeIncr = 1 / sampleRate;

	double fillToTime = std::min(endTime, time2);
	unsigned fillToFrame = AudioUtilities::timeToSampleFrame(fillToTime - startTime, sampleRate);
	fillToFrame = std::min(fillToFrame, numberOfValues);

	ParamEvent::Type nextEventType = nextEvent ? static_cast<ParamEvent::Type>(nextEvent->type()) : ParamEvent::LastType /* unknown */;

	// First handle linear and exponential ramps which require looking ahead to the next event.
	if (nextEventType == ParamEvent::LinearRampToValue) {
	for (; writeIndex < fillToFrame; ++writeIndex) {
	float x = (currentTime - time1) * k;
	value = (1 - x) * value1 + x * value2;
	values[writeIndex] = value;
	currentTime += sampleFrameTimeIncr;
	}
	} else if (nextEventType == ParamEvent::ExponentialRampToValue) {
	if (value1 <= 0 \|\| value2 <= 0) {
	// Handle negative values error case by propagating previous value.
	for (; writeIndex < fillToFrame; ++writeIndex)
	values[writeIndex] = value;
	} else {
	float numSampleFrames = deltaTime * sampleRate;
	// The value goes exponentially from value1 to value2 in a duration of deltaTime seconds (corresponding to numSampleFrames).
	// Compute the per-sample multiplier.
	float multiplier = powf(value2 / value1, 1 / numSampleFrames);

	// Set the starting value of the exponential ramp. This is the same as multiplier ^
	// AudioUtilities::timeToSampleFrame(currentTime - time1, sampleRate), but is more
	// accurate, especially if multiplier is close to 1.
	value = value1 * powf(value2 / value1,
	AudioUtilities::timeToSampleFrame(currentTime - time1, sampleRate) / numSampleFrames);

	for (; writeIndex < fillToFrame; ++writeIndex) {
	values[writeIndex] = value;
	value *= multiplier;
	currentTime += sampleFrameTimeIncr;
	}
	}
	} else {
	// Handle event types not requiring looking ahead to the next event.
	switch (event.type()) {
	case ParamEvent::SetValue:
	case ParamEvent::LinearRampToValue:
	case ParamEvent::ExponentialRampToValue:
	{
	currentTime = fillToTime;

	// Simply stay at a constant value.
	value = event.value();
	for (; writeIndex < fillToFrame; ++writeIndex)
	values[writeIndex] = value;

	break;
	}

	case ParamEvent::SetTarget:
	{
	currentTime = fillToTime;

	// Exponential approach to target value with given time constant.
	float target = event.value();
	float timeConstant = event.timeConstant();
	float discreteTimeConstant = static_cast<float>(AudioUtilities::discreteTimeConstantForSampleRate(timeConstant, controlRate));

	for (; writeIndex < fillToFrame; ++writeIndex) {
	values[writeIndex] = value;
	value += (target - value) * discreteTimeConstant;
	}

	break;
	}

	case ParamEvent::SetValueCurve:
	{
	Float32Array* curve = event.curve();
	float* curveData = curve ? curve->data() : 0;
	unsigned numberOfCurvePoints = curve ? curve->length() : 0;

	// Curve events have duration, so don't just use next event time.
	float duration = event.duration();
	float durationFrames = duration * sampleRate;
	float curvePointsPerFrame = static_cast<float>(numberOfCurvePoints) / durationFrames;

	if (!curve \|\| !curveData \|\| !numberOfCurvePoints \|\| duration <= 0 \|\| sampleRate <= 0) {
	// Error condition - simply propagate previous value.
	currentTime = fillToTime;
	for (; writeIndex < fillToFrame; ++writeIndex)
	values[writeIndex] = value;
	break;
	}

	// Save old values and recalculate information based on the curve's duration
	// instead of the next event time.
	unsigned nextEventFillToFrame = fillToFrame;
	float nextEventFillToTime = fillToTime;
	fillToTime = std::min(endTime, time1 + duration);
	fillToFrame = AudioUtilities::timeToSampleFrame(fillToTime - startTime, sampleRate);
	fillToFrame = std::min(fillToFrame, numberOfValues);

	// Index into the curve data using a floating-point value.
	// We're scaling the number of curve points by the duration (see curvePointsPerFrame).
	float curveVirtualIndex = 0;
	if (time1 < currentTime) {
	// Index somewhere in the middle of the curve data.
	// Don't use timeToSampleFrame() since we want the exact floating-point frame.
	float frameOffset = (currentTime - time1) * sampleRate;
	curveVirtualIndex = curvePointsPerFrame * frameOffset;
	}

	// Render the stretched curve data using nearest neighbor sampling.
	// Oversampled curve data can be provided if smoothness is desired.
	for (; writeIndex < fillToFrame; ++writeIndex) {
	// Ideally we'd use round() from MathExtras, but we're in a tight loop here
	// and we're trading off precision for extra speed.
	unsigned curveIndex = static_cast<unsigned>(0.5 + curveVirtualIndex);

	curveVirtualIndex += curvePointsPerFrame;

	// Bounds check.
	if (curveIndex < numberOfCurvePoints)
	value = curveData[curveIndex];

	values[writeIndex] = value;
	}

	// If there's any time left after the duration of this event and the start
	// of the next, then just propagate the last value.
	for (; writeIndex < nextEventFillToFrame; ++writeIndex)
	values[writeIndex] = value;

	// Re-adjust current time
	currentTime = nextEventFillToTime;

	break;
	}
	}
	}
	}

	// If there's any time left after processing the last event then just propagate the last value
	// to the end of the values buffer.
	for (; writeIndex < numberOfValues; ++writeIndex)
	values[writeIndex] = value;

	return value;
	}

	} // namespace WebCore

	#endif // ENABLE(WEB_AUDIO)