Use frames instead of time for running AudioParam timelines.

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

 /*
  * 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
@@ skipping 68 matching lines @@
 
     exceptionState.throwDOMException(
         InvalidAccessError,
         message + " must be a finite positive number: " + String::number(time));
     return false;
 }
 
 String AudioParamTimeline::eventToString(const ParamEvent& event)
 {
     // The default arguments for most automation methods is the value and the time.
     String args = String::number(event.value()) + ", " + String::number(event.time(), 16);

[hongchan, 2015/10/01 20:20:52]

Just out of curiosity, why 16?

[Raymond Toy, 2015/10/01 20:31:23]

That was done in a different CL, unrelated to this.  But 16 is about the number
of significant digits in a double precision number.  Without this, event.time()
is printed with 6 or 7 digits at most.

 
     // Get a nice printable name for the event and update the args if necessary.
     String s;
     switch (event.type()) {
     case ParamEvent::SetValue:
         s = "setValueAtTime";
         break;
     case ParamEvent::LinearRampToValue:
         s = "linearRampToValueAtTime";
         break;
@@ skipping 152 matching lines @@
         MutexTryLocker tryLocker(m_eventsLock);
         if (!tryLocker.locked() || !context || !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
+    size_t startFrame = context->currentSampleFrame();
     double controlRate = sampleRate / AudioHandler::ProcessingSizeInFrames; // one parameter change per render quantum
-    value = valuesForTimeRange(startTime, endTime, defaultValue, &value, 1, sampleRate, controlRate);
+    value = valuesForFrameRange(startFrame, startFrame + 1, defaultValue, &value, 1, sampleRate, controlRate);
 
     hasValue = true;
     return value;
 }
 
-float AudioParamTimeline::valuesForTimeRange(
-    double startTime,
-    double endTime,
+float AudioParamTimeline::valuesForFrameRange(
+    size_t startFrame,
+    size_t endFrame,
     float defaultValue,
     float* values,
     unsigned numberOfValues,
     double sampleRate,
     double controlRate)
 {
     // We can't contend the lock in the realtime audio thread.
     MutexTryLocker tryLocker(m_eventsLock);
     if (!tryLocker.locked()) {
         if (values) {
             for (unsigned i = 0; i < numberOfValues; ++i)
                 values[i] = defaultValue;
         }
         return defaultValue;
     }
 
-    return valuesForTimeRangeImpl(startTime, endTime, defaultValue, values, numberOfValues, sampleRate, controlRate);
+    return valuesForFrameRangeImpl(startFrame, endFrame, defaultValue, values, numberOfValues, sampleRate, controlRate);
 }
 
-float AudioParamTimeline::valuesForTimeRangeImpl(
-    double startTime,
-    double endTime,
+float AudioParamTimeline::valuesForFrameRangeImpl(
+    size_t startFrame,
+    size_t endFrame,
     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()) {
+    if (!m_events.size() || (endFrame / sampleRate <= 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;
+    // Maintain a running time (frame) and index for writing the values buffer.
+    size_t currentFrame = startFrame;
     unsigned writeIndex = 0;
 
-    // If first event is after startTime then fill initial part of values buffer with defaultValue
+    // If first event is after startFrame 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);
+    if (firstEventTime > startFrame / sampleRate) {
+        // |fillToFrame| is an exclusive upper bound, so use ceil() to compute the bound from the
+        // firstEventTime.
+        size_t fillToFrame = std::min(endFrame, static_cast<size_t>(ceil(firstEventTime * sampleRate)));
+        ASSERT(fillToFrame >= startFrame);
+        fillToFrame -= startFrame;
+        fillToFrame = std::min(fillToFrame, static_cast<size_t>(numberOfValues));
         for (; writeIndex < fillToFrame; ++writeIndex)
             values[writeIndex] = defaultValue;
 
-        currentTime = fillToTime;
+        currentFrame += fillToFrame;
     }
 
     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;
+        if (nextEvent && nextEvent->time() < currentFrame / sampleRate) {
+            // But if the current event is a SetValue event and the event time is between
+            // currentFrame - 1 and curentFrame (in time). we don't want to skip it.  If we do skip
+            // it, the SetValue event is completely skipped and not applied, which is wrong.  Other
+            // events don't have this problem.  (Because currentFrame is unsigned, we do the time
+            // check in this funny, but equivalent way.)
+            double eventFrame = event.time() * sampleRate;
+
+            // Condition is currentFrame - 1 < eventFrame <= currentFrame, but currentFrame is
+            // unsigned and could be 0, so use currentFrame < eventFrame + 1 instead.
+            if (!((event.type() == ParamEvent::SetValue
+                && (eventFrame <= currentFrame)
+                && (currentFrame < eventFrame + 1))))
+                continue;
+        }
 
         float value1 = event.value();
         double time1 = event.time();
         float value2 = nextEvent ? nextEvent->value() : value1;
-        double time2 = nextEvent ? nextEvent->time() : endTime + 1;
+        double time2 = nextEvent ? nextEvent->time() : endFrame / sampleRate + 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);
+        // |fillToEndFrame| is the exclusive upper bound of the last frame to be computed for this
+        // event.  It's either the last desired frame (|endFrame|) or derived from the end time of
+        // the next event (time2). We compute ceil(time2*sampleRate) because fillToEndFrame is the
+        // exclusive upper bound.  Consider the case where |startFrame| = 128 and time2 = 128.1
+        // (assuming sampleRate = 1).  Since time2 is greater than 128, we want to output a value
+        // for frame 128.  This requires that fillToEndFrame be at least 129.  This is achieved by
+        // ceil(time2).
+        size_t fillToEndFrame = std::min(endFrame, static_cast<size_t>(ceil(time2 * sampleRate)));
+        ASSERT(fillToEndFrame >= startFrame);
+        size_t fillToFrame = fillToEndFrame - startFrame;
+        fillToFrame = std::min(fillToFrame, static_cast<size_t>(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) {
             const float valueDelta = value2 - value1;
 #if CPU(X86) || CPU(X86_64)
             // Minimize in-loop operations. Calculate starting value and increment. Next step: value += inc.
-            //  value = value1 + (currentTime - time1) * k * (value2 - value1);
-            //  inc = sampleFrameTimeIncr * k * (value2 - value1);
+            //  value = value1 + (currentFrame/sampleRate - time1) * k * (value2 - value1);
+            //  inc = 4 / sampleRate * k * (value2 - value1);
             // Resolve recursion by expanding constants to achieve a 4-step loop unrolling.
-            //  value = value1 + ((currentTime - time1) + i * sampleFrameTimeIncr) * k * (value2 -value1), i in 0..3
-            __m128 vValue = _mm_mul_ps(_mm_set_ps1(sampleFrameTimeIncr), _mm_set_ps(3, 2, 1, 0));
-            vValue = _mm_add_ps(vValue, _mm_set_ps1(currentTime - time1));
+            //  value = value1 + ((currentFrame/sampleRate - time1) + i * sampleFrameTimeIncr) * k * (value2 -value1), i in 0..3
+            __m128 vValue = _mm_mul_ps(_mm_set_ps1(1 / sampleRate), _mm_set_ps(3, 2, 1, 0));
+            vValue = _mm_add_ps(vValue, _mm_set_ps1(currentFrame / sampleRate - time1));
             vValue = _mm_mul_ps(vValue, _mm_set_ps1(k * valueDelta));
             vValue = _mm_add_ps(vValue, _mm_set_ps1(value1));
-            __m128 vInc = _mm_set_ps1(4 * sampleFrameTimeIncr * k * valueDelta);
+            __m128 vInc = _mm_set_ps1(4 / sampleRate * k * valueDelta);
 
             // Truncate loop steps to multiple of 4.
             unsigned fillToFrameTrunc = writeIndex + ((fillToFrame - writeIndex) / 4) * 4;
             // Compute final time.
-            currentTime += sampleFrameTimeIncr * (fillToFrameTrunc - writeIndex);
+            currentFrame += fillToFrameTrunc - writeIndex;
+
             // Process 4 loop steps.
             for (; writeIndex < fillToFrameTrunc; writeIndex += 4) {
                 _mm_storeu_ps(values + writeIndex, vValue);
                 vValue = _mm_add_ps(vValue, vInc);
             }
 #endif
             // Serially process remaining values.
             for (; writeIndex < fillToFrame; ++writeIndex) {
-                float x = (currentTime - time1) * k;
+                float x = (currentFrame / sampleRate - time1) * k;
                 // value = (1 - x) * value1 + x * value2;
                 value = value1 + x * valueDelta;
                 values[writeIndex] = value;
-                currentTime += sampleFrameTimeIncr;
+                ++currentFrame;
             }
         } 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).
+                // The value goes exponentially from value1 to value2 in a duration of deltaTime
+                // seconds according to
+                //
+                //  v(t) = v1*(v2/v1)^((t-t1)/(t2-t1))
+                //
+                // Let c be currentFrame and F be the sampleRate.  Then we want to sample v(t)
+                // at times t = (c + k)/F for k = 0, 1, ...:
+                //
+                //   v((c+k)/F) = v1*(v2/v1)^(((c/F+k/F)-t1)/(t2-t1))
+                //              = v1*(v2/v1)^((c/F-t1)/(t2-t1))
+                //                  *(v2/v1)^((k/F)/(t2-t1))
+                //              = v1*(v2/v1)^((c/F-t1)/(t2-t1))
+                //                  *[(v2/v1)^(1/(F*(t2-t1)))]^k
+                //
+                // Thus, this can be written as
+                //
+                //   v((c+k)/F) = V*m^k
+                //
+                // where
+                //   V = v1*(v2/v1)^((c/F-t1)/(t2-t1))
+                //   m = (v2/v1)^(1/(F*(t2-t1)))
+
                 // 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.
+                // Set the starting value of the exponential ramp.
                 value = value1 * powf(value2 / value1,
-                    AudioUtilities::timeToSampleFrame(currentTime - time1, sampleRate) / numSampleFrames);
+                    (currentFrame / sampleRate - time1) / deltaTime);
 
                 for (; writeIndex < fillToFrame; ++writeIndex) {
                     values[writeIndex] = value;
                     value *= multiplier;
-                    currentTime += sampleFrameTimeIncr;
+                    ++currentFrame;
                 }
             }
         } 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;
+                    currentFrame = fillToEndFrame;
 
                     // 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.
+                    //
+                    //   v(t) = v2 + (v1 - v2)*exp(-(t-t1/tau))
+                    //
 
-                    // 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));
 
+                    // Set the starting value correctly.  This is only needed when the current time
+                    // is "equal" to the start time of this event.  This is to get the sampling
+                    // correct if the start time of this automation isn't on a frame boundary.
+                    // Otherwise, we can just continue from where we left off from the previous
+                    // rendering quantum.
+
+                    {
+                        double rampStartFrame = time1 * sampleRate;
+                        // Condition is c - 1 < r <= c where c = currentFrame and r =
+                        // rampStartFrame.  Compute it this way because currentFrame is unsigned and
+                        // could be 0.
+                        if (rampStartFrame <= currentFrame && currentFrame < rampStartFrame + 1)
+                            value = target + (value - target) * exp(-(currentFrame / sampleRate - time1) / timeConstant);
+                    }
 #if CPU(X86) || CPU(X86_64)
                     // Resolve recursion by expanding constants to achieve a 4-step loop unrolling.
                     // v1 = v0 + (t - v0) * c
                     // v2 = v1 + (t - v1) * c
                     // v2 = v0 + (t - v0) * c + (t - (v0 + (t - v0) * c)) * c
                     // v2 = v0 + (t - v0) * c + (t - v0) * c - (t - v0) * c * c
                     // v2 = v0 + (t - v0) * c * (2 - c)
                     // Thus c0 = c, c1 = c*(2-c). The same logic applies to c2 and c3.
                     const float c0 = discreteTimeConstant;
                     const float c1 = c0 * (2 - c0);
@@ skipping 17 matching lines @@
                         // Update value for next iteration.
                         value += delta * c3;
                     }
 #endif
                     // Serially process remaining values
                     for (; writeIndex < fillToFrame; ++writeIndex) {
                         values[writeIndex] = value;
                         value += (target - value) * discreteTimeConstant;
                     }
 
+                    currentFrame = fillToEndFrame;
+
                     break;
                 }
 
             case ParamEvent::SetValueCurve:
                 {
                     DOMFloat32Array* 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.
                     double duration = event.duration();
                     double durationFrames = duration * sampleRate;
                     // How much to step the curve index for each frame.  We want the curve index to
                     // be exactly equal to the last index (numberOfCurvePoints - 1) after
                     // durationFrames - 1 frames.  In this way, the last output value will equal the
                     // last value in the curve array.
                     double curvePointsPerFrame;
 
                     // If the duration is less than a frame, we want to just output the last curve
                     // value.  Do this by setting curvePointsPerFrame to be more than number of
                     // points in the curve.  Then the curveVirtualIndex will always exceed the last
                     // curve index, so that the last curve value will be used.
                     if (durationFrames > 1)
                         curvePointsPerFrame = (numberOfCurvePoints - 1) / (durationFrames - 1);
                     else
                         curvePointsPerFrame = numberOfCurvePoints + 1;
 
                     if (!curve || !curveData || !numberOfCurvePoints || duration <= 0 || sampleRate <= 0) {
                         // Error condition - simply propagate previous value.
-                        currentTime = fillToTime;
+                        currentFrame = fillToEndFrame;
                         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;
-                    double nextEventFillToTime = fillToTime;
-                    fillToTime = std::min(endTime, time1 + duration);
-                    // |fillToTime| can be less than |startTime| when the end of the
+                    size_t nextEventFillToFrame = fillToFrame;
+
+                    // Use ceil here for the same reason as using ceil above: fillToEndFrame is an
+                    // exclusive upper bound of the last frame to be computed.
+                    fillToEndFrame = std::min(endFrame, static_cast<size_t>(ceil(sampleRate*(time1 + duration))));
+                    // |fillToFrame| can be less than |startFrame| when the end of the
                     // setValueCurve automation has been reached, but the next automation has not
-                    // yet started. In this case, |fillToTime| is clipped to |time1|+|duration|
-                    // above, but |startTime| will keep increasing (because the current time is
+                    // yet started. In this case, |fillToFrame| is clipped to |time1|+|duration|
+                    // above, but |startFrame| will keep increasing (because the current time is
                     // increasing).
-                    fillToFrame = AudioUtilities::timeToSampleFrame(std::max(0.0, fillToTime - startTime), sampleRate);
-                    fillToFrame = std::min(fillToFrame, numberOfValues);
+                    fillToFrame = (fillToEndFrame < startFrame) ? 0 : fillToEndFrame - startFrame;
+                    fillToFrame = std::min(fillToFrame, static_cast<size_t>(numberOfValues));
 
                     // Index into the curve data using a floating-point value.
                     // We're scaling the number of curve points by the duration (see curvePointsPerFrame).
                     double curveVirtualIndex = 0;
-                    if (time1 < currentTime) {
+                    if (time1 < currentFrame / sampleRate) {
                         // Index somewhere in the middle of the curve data.
                         // Don't use timeToSampleFrame() since we want the exact floating-point frame.
-                        double frameOffset = (currentTime - time1) * sampleRate;
+                        double frameOffset = currentFrame - time1 * sampleRate;
                         curveVirtualIndex = curvePointsPerFrame * frameOffset;
                     }
 
                     // Set the default value in case fillToFrame is 0.
                     value = curveData[numberOfCurvePoints - 1];
 
                     // Render the stretched curve data using linear interpolation.  Oversampled
                     // curve data can be provided if sharp discontinuities are desired.
                     unsigned k = 0;
 #if CPU(X86) || CPU(X86_64)
@@ skipping 53 matching lines @@
                         } else {
                             curveIndex0 = numberOfCurvePoints - 1;
                         }
 
                         unsigned curveIndex1 = std::min(curveIndex0 + 1, numberOfCurvePoints - 1);
 
                         // Linearly interpolate between the two nearest curve points.  |delta| is
                         // clamped to 1 because currentVirtualIndex can exceed curveIndex0 by more
                         // than one.  This can happen when we reached the end of the curve but still
                         // need values to fill out the current rendering quantum.
+                        ASSERT(curveIndex0 < numberOfCurvePoints);
+                        ASSERT(curveIndex1 < numberOfCurvePoints);
                         float c0 = curveData[curveIndex0];
                         float c1 = curveData[curveIndex1];
                         double delta = std::min(currentVirtualIndex - curveIndex0, 1.0);
 
                         value = c0 + (c1 - c0) * delta;
 
                         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.
+                    // of the next, then just propagate the last value of the curveData.
+                    value = curveData[numberOfCurvePoints - 1];
                     for (; writeIndex < nextEventFillToFrame; ++writeIndex)
                         values[writeIndex] = value;
 
                     // Re-adjust current time
-                    currentTime = nextEventFillToTime;
+                    currentFrame = nextEventFillToFrame;
 
                     break;
                 }
             case ParamEvent::LastType:
                 ASSERT_NOT_REACHED();
                 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 blink
 
 #endif // ENABLE(WEB_AUDIO)