Add support for WaveShaperNode.oversample

Add support for WaveShaperNode.oversample

Please see specification for details:
https://dvcs.w3.org/hg/audio/raw-file/tip/webaudio/specification.html#WaveShaperNode

.oversample specifies what type of oversampling (if any) should be used when applying the shaping curve.
The default value is "none", meaning the curve will be applied directly to the input samples.
A value of "2x" or "4x" can improve the quality of the processing by avoiding some aliasing,
with the "4x" value yielding the highest quality.

TEST=webaudio/waveshaper-oversample-2x.html, webaudio/waveshaper-oversample-4x.html
R=kbr@chromium.org

Committed: https://src.chromium.org/viewvc/blink?view=rev&revision=151686

[Chris Rogers, 2013-05-22 00:05:29]

Ken, I'll be happy to chat with you in person to help give you an overview here.

[Ken Russell (switch to Gerrit), 2013-05-23 02:29:25]

Thanks for the in-person chat today. Some questions.

https://codereview.chromium.org/15619003/diff/19001/Source/core/platform/audi...
File Source/core/platform/audio/DownSampler.cpp (right):

https://codereview.chromium.org/15619003/diff/19001/Source/core/platform/audi...
Source/core/platform/audio/DownSampler.cpp:107:
m_convolver.process(&m_reducedKernel, oddSamplesP, destP, destFramesToProcess);
Checks are needed around the size of the reduced kernel. Currently it's based on
DefaultKernelSize, but the rest of the buffers are sized around the
inputBlockSize. Assertions and run-time checks are needed to make sure these
match up.

https://codereview.chromium.org/15619003/diff/19001/Source/core/platform/audi...
Source/core/platform/audio/DownSampler.cpp:119: memcpy(m_inputBuffer.data(),
inputP, sizeof(float) * sourceFramesToProcess);
I don't understand why m_inputBuffer is needed. It doesn't seem to be exposed
outside this class, and all it's used for is temporary storage for the source
data. Could you please explain this to me?

https://codereview.chromium.org/15619003/diff/19001/Source/core/platform/audi...
File Source/core/platform/audio/DownSampler.h (right):

https://codereview.chromium.org/15619003/diff/19001/Source/core/platform/audi...
Source/core/platform/audio/DownSampler.h:2: * Copyright (C) 2013 Google Inc. All
rights reserved.
The copyright notice on these new files is the wrong version. I'm not 100% sure
what's the right text to use for new files in Blink but I think it's
http://src.chromium.org/viewvc/chrome/trunk/src/LICENSE , same as Chromium.
Please double-check with the program managers.

https://codereview.chromium.org/15619003/diff/19001/Source/core/platform/audi...
File Source/core/platform/audio/UpSampler.cpp (right):

https://codereview.chromium.org/15619003/diff/19001/Source/core/platform/audi...
Source/core/platform/audio/UpSampler.cpp:89: destP[i * 2] = inputP[i -
halfSize];
Checks and assertions are needed to ensure that "i - halfSize" is always within
the range of m_inputBuffer. In particular, the kernel is sized based on
DefaultKernelSize but all of the buffers are sized based on inputBlockSize.

https://codereview.chromium.org/15619003/diff/19001/Source/core/platform/audi...
Source/core/platform/audio/UpSampler.cpp:99: memcpy(m_inputBuffer.data(),
inputP, sizeof(float) * sourceFramesToProcess);
Again could you please explain to me why m_inputBuffer is necessary? It doesn't
look like it's exposed outside this class, and the convolver is operating
directly on the source data, not m_inputBuffer's data.

https://codereview.chromium.org/15619003/diff/19001/Source/modules/webaudio/W...
File Source/modules/webaudio/WaveShaperDSPKernel.cpp (right):

https://codereview.chromium.org/15619003/diff/19001/Source/modules/webaudio/W...
Source/modules/webaudio/WaveShaperDSPKernel.cpp:34: const unsigned
RenderingQuantum = 128;
Should be in an anonymous namespace.

https://codereview.chromium.org/15619003/diff/19001/Source/modules/webaudio/W...
Source/modules/webaudio/WaveShaperDSPKernel.cpp:130:
m_upSampler->process(source, tempP, framesToProcess);
Some assertions and checks are needed to ensure that framesToProcess is properly
related to RenderingQuantum.

https://codereview.chromium.org/15619003/diff/19001/Source/modules/webaudio/W...
Source/modules/webaudio/WaveShaperDSPKernel.cpp:143:
m_upSampler->process(source, tempP, framesToProcess);
Same here regarding framesToProcess.

[Chris Rogers, 2013-05-24 20:09:04]

PTAL

https://codereview.chromium.org/15619003/diff/19001/Source/core/platform/audi...
File Source/core/platform/audio/DownSampler.cpp (right):

https://codereview.chromium.org/15619003/diff/19001/Source/core/platform/audi...
Source/core/platform/audio/DownSampler.cpp:107:
m_convolver.process(&m_reducedKernel, oddSamplesP, destP, destFramesToProcess);
On 2013/05/23 02:29:25, kbr wrote:
> Checks are needed around the size of the reduced kernel. Currently it's based
on
> DefaultKernelSize, but the rest of the buffers are sized around the
> inputBlockSize. Assertions and run-time checks are needed to make sure these
> match up.

Added ASSERTS to check all (I think) necessary conditions.  The input buffer
size is now checked versus halfSize (half of kernel size), which is the
important check for the kernel size since the actual convolver can accept any
kernel size unrelated to the input block size, etc.

https://codereview.chromium.org/15619003/diff/19001/Source/core/platform/audi...
Source/core/platform/audio/DownSampler.cpp:119: memcpy(m_inputBuffer.data(),
inputP, sizeof(float) * sourceFramesToProcess);
On 2013/05/23 02:29:25, kbr wrote:
> I don't understand why m_inputBuffer is needed. It doesn't seem to be exposed
> outside this class, and all it's used for is temporary storage for the source
> data. Could you please explain this to me?

Added comment in header file for this.

https://codereview.chromium.org/15619003/diff/19001/Source/core/platform/audi...
File Source/core/platform/audio/DownSampler.h (right):

https://codereview.chromium.org/15619003/diff/19001/Source/core/platform/audi...
Source/core/platform/audio/DownSampler.h:2: * Copyright (C) 2013 Google Inc. All
rights reserved.
On 2013/05/23 02:29:25, kbr wrote:
> The copyright notice on these new files is the wrong version. I'm not 100%
sure
> what's the right text to use for new files in Blink but I think it's
> http://src.chromium.org/viewvc/chrome/trunk/src/LICENSE , same as Chromium.
> Please double-check with the program managers.

Done.

https://codereview.chromium.org/15619003/diff/19001/Source/core/platform/audi...
File Source/core/platform/audio/UpSampler.cpp (right):

https://codereview.chromium.org/15619003/diff/19001/Source/core/platform/audi...
Source/core/platform/audio/UpSampler.cpp:89: destP[i * 2] = inputP[i -
halfSize];
On 2013/05/23 02:29:25, kbr wrote:
> Checks and assertions are needed to ensure that "i - halfSize" is always
within
> the range of m_inputBuffer. In particular, the kernel is sized based on
> DefaultKernelSize but all of the buffers are sized based on inputBlockSize.

Done.

https://codereview.chromium.org/15619003/diff/19001/Source/core/platform/audi...
Source/core/platform/audio/UpSampler.cpp:99: memcpy(m_inputBuffer.data(),
inputP, sizeof(float) * sourceFramesToProcess);
On 2013/05/23 02:29:25, kbr wrote:
> Again could you please explain to me why m_inputBuffer is necessary? It
doesn't
> look like it's exposed outside this class, and the convolver is operating
> directly on the source data, not m_inputBuffer's data.

Added comment in header file.

https://codereview.chromium.org/15619003/diff/19001/Source/modules/webaudio/W...
File Source/modules/webaudio/WaveShaperDSPKernel.cpp (right):

https://codereview.chromium.org/15619003/diff/19001/Source/modules/webaudio/W...
Source/modules/webaudio/WaveShaperDSPKernel.cpp:34: const unsigned
RenderingQuantum = 128;
On 2013/05/23 02:29:25, kbr wrote:
> Should be in an anonymous namespace.

This is const, so should already be limited to file scope in terms of linkage,
and also matches many other constants in the web audio code.

https://codereview.chromium.org/15619003/diff/19001/Source/modules/webaudio/W...
Source/modules/webaudio/WaveShaperDSPKernel.cpp:130:
m_upSampler->process(source, tempP, framesToProcess);
On 2013/05/23 02:29:25, kbr wrote:
> Some assertions and checks are needed to ensure that framesToProcess is
properly
> related to RenderingQuantum.

Done.

https://codereview.chromium.org/15619003/diff/19001/Source/modules/webaudio/W...
Source/modules/webaudio/WaveShaperDSPKernel.cpp:143:
m_upSampler->process(source, tempP, framesToProcess);
On 2013/05/23 02:29:25, kbr wrote:
> Same here regarding framesToProcess.

Done.

[Ken Russell (switch to Gerrit), 2013-05-28 21:01:50]

Thanks for the enhanced asserts and explanation of m_inputBuffer. LGTM

[Chris Rogers, 2013-06-03 19:45:03]

Committed patchset #9 manually as r151686.