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Unified Diff: third_party/WebKit/Source/modules/webaudio/AudioParamTimeline.cpp

Issue 1485003002: Make setTarget followed by linear or exponential ramp continuous. (Closed) Base URL: https://chromium.googlesource.com/chromium/src.git@master
Patch Set: Rebase and fix test failures Created 4 years, 8 months ago
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Index: third_party/WebKit/Source/modules/webaudio/AudioParamTimeline.cpp
diff --git a/third_party/WebKit/Source/modules/webaudio/AudioParamTimeline.cpp b/third_party/WebKit/Source/modules/webaudio/AudioParamTimeline.cpp
index be242483b7738a578b20925345fa49205d00b2dd..a2c5f457501a6780e817c33802e721d133bb983d 100644
--- a/third_party/WebKit/Source/modules/webaudio/AudioParamTimeline.cpp
+++ b/third_party/WebKit/Source/modules/webaudio/AudioParamTimeline.cpp
@@ -420,6 +420,46 @@ float AudioParamTimeline::valuesForFrameRangeImpl(
continue;
}
+ // If there's no next event, set nextEventType to LastType to indicate that.
+ ParamEvent::Type nextEventType = nextEvent ? static_cast<ParamEvent::Type>(nextEvent->getType()) : ParamEvent::LastType;
+
+ // If the current event is SetTarget and the next event is a LinearRampToValue or
+ // ExponentialRampToValue, special handling is needed. In this case, the linear and
+ // exponential ramp should start at wherever the SetTarget processing has reached.
+ if (event.getType() == ParamEvent::SetTarget
+ && (nextEventType == ParamEvent::LinearRampToValue
+ || nextEventType == ParamEvent::ExponentialRampToValue)) {
+ // Replace the SetTarget with a SetValue to set the starting time and value for the ramp
+ // using the current frame. We need to update |value| appropriately depending on
+ // whether the ramp has started or not.
+ //
+ // If SetTarget starts somewhere between currentFrame - 1 and currentFrame, we directly
+ // compute the value it would have at currentFrame. If not, we update the value from
+ // the value from currentFrame - 1.
+ //
+ // Can't use the condition currentFrame - 1 <= t0 * sampleRate <= currentFrame because
+ // currentFrame is unsigned and could be 0. Instead, compute the condition this way,
+ // where f = currentFrame and Fs = sampleRate:
+ //
+ // f - 1 <= t0 * Fs <= f
+ // 2 * f - 2 <= 2 * Fs * t0 <= 2 * f
+ // -2 <= 2 * Fs * t0 - 2 * f <= 0
+ // -1 <= 2 * Fs * t0 - 2 * f + 1 <= 1
+ // abs(2 * Fs * t0 - 2 * f + 1) <= 1
+ if (fabs(2 * sampleRate * event.time() - 2 * currentFrame + 1) <= 1) {
+ // SetTarget is starting somewhere between currentFrame - 1 and
+ // currentFrame. Compute the value the SetTarget would have at the currentFrame.
+ value = event.value() + (value - event.value()) * exp(-(currentFrame / sampleRate - event.time()) / event.timeConstant());
+ } else {
+ // SetTarget has already started. Update |value| one frame because it's the value from
+ // the previous frame.
+ float discreteTimeConstant = static_cast<float>(AudioUtilities::discreteTimeConstantForSampleRate(
+ event.timeConstant(), controlRate));
+ value += (event.value() - value) * discreteTimeConstant;
+ }
+ m_events[i] = ParamEvent::createSetValueEvent(value, currentFrame / sampleRate);
+ }
+
float value1 = event.value();
double time1 = event.time();
@@ -448,8 +488,6 @@ float AudioParamTimeline::valuesForFrameRangeImpl(
size_t fillToFrame = fillToEndFrame - startFrame;
fillToFrame = std::min(fillToFrame, static_cast<size_t>(numberOfValues));
- ParamEvent::Type nextEventType = nextEvent ? static_cast<ParamEvent::Type>(nextEvent->getType()) : 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;
@@ -536,6 +574,11 @@ float AudioParamTimeline::valuesForFrameRangeImpl(
// computed value.
if (writeIndex >= 1)
value /= multiplier;
+
+ // Due to roundoff it's possible that value exceeds value2. Clip value to value2 if
+ // we are within 1/2 frame of time2.
+ if (currentFrame > time2 * sampleRate - 0.5)
+ value = value2;
}
} else {
// Handle event types not requiring looking ahead to the next event.
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