Pepper: Add an example/test plugin for audio input (a.k.a. microphone).

ppapi/examples/audio_input/audio_input.cc

+// Copyright (c) 2011 The Chromium Authors. All rights reserved.
+// Use of this source code is governed by a BSD-style license that can be
+// found in the LICENSE file.
+
+#include <string.h>
+
+#include <algorithm>
+
+#include "ppapi/cpp/audio_config.h"
+#include "ppapi/cpp/completion_callback.h"
+#include "ppapi/cpp/dev/audio_input_dev.h"
+#include "ppapi/cpp/graphics_2d.h"
+#include "ppapi/cpp/image_data.h"
+#include "ppapi/cpp/instance.h"
+#include "ppapi/cpp/logging.h"
+#include "ppapi/cpp/module.h"
+#include "ppapi/cpp/rect.h"
+#include "ppapi/cpp/size.h"
+
+class MyInstance : public pp::Instance {
+ public:
+  explicit MyInstance(PP_Instance instance)
+      : pp::Instance(instance),
+        callback_factory_(this),
+        sample_count_(0),
+        channel_count_(0),
+        samples_(NULL),
+        timer_interval_(0),
+        pending_paint_(false),
+        waiting_for_flush_completion_(false) {
+  }
+  virtual ~MyInstance() {
+    audio_input_.StopCapture();
+    delete[] samples_;
+  }
+
+  virtual bool Init(uint32_t argc, const char* argn[], const char* argv[]) {
+    // This sample frequency is guaranteed to work.
+    const PP_AudioSampleRate kSampleFrequency = PP_AUDIOSAMPLERATE_44100;
+    const uint32_t kSampleCount = 1024;
+    const uint32_t kChannelCount = 1;
+
+    sample_count_ = pp::AudioConfig::RecommendSampleFrameCount(kSampleFrequency,
+                                                               kSampleCount);
+    PP_DCHECK(sample_count_ > 0);
+    channel_count_ = kChannelCount;
+    pp::AudioConfig config = pp::AudioConfig(this,
+                                             kSampleFrequency,
+                                             sample_count_);
+    samples_ = new int16_t[sample_count_ * channel_count_];
+    memset(samples_, 0, sample_count_ * channel_count_ * sizeof(int16_t));
+    audio_input_ = pp::AudioInput_Dev(this, config, CaptureCallback, this);
+    if (!audio_input_.StartCapture())
+      return false;
+
+    // Try to ensure that we pick up a new set of samples between each
+    // timer-generated repaint.
+    timer_interval_ = 44100 / sample_count_ + 5;

[dmichael (off chromium), 2011/11/23 20:15:52]

This doesn't make sense to me. timer_interval_ is used as ms, but the units here
are more like 1/s. Imagine if you had a higher sample frequency or lower sample
count. The timer_interval_ would then be bigger, but you should want it to be
smaller, I'd think.

Maybe should be something like:
timer_interval_ = (sample_count_ * 1000) / kSampleFrequency + 5;
(where 5 is apparently a fudge factor?)

[viettrungluu, 2011/11/23 21:06:25]

Right, good catch. Fixed.

+    ScheduleNextTimer();
+
+    return true;
+  }
+
+  virtual void DidChangeView(const pp::Rect& position, const pp::Rect& clip) {
+    if (position.size() == size_)
+      return;
+
+    size_ = position.size();
+    device_context_ = pp::Graphics2D(this, size_, false);
+    if (!BindGraphics(device_context_))
+      return;
+
+    Paint();
+  }
+
+ private:
+  void ScheduleNextTimer() {
+    PP_DCHECK(timer_interval_ > 0);
+    pp::Module::Get()->core()->CallOnMainThread(
+        timer_interval_,
+        callback_factory_.NewRequiredCallback(&MyInstance::OnTimer),
+        0);
+  }
+
+  void OnTimer(int32_t) {
+    ScheduleNextTimer();
+    Paint();
+  }
+
+  void DidFlush(int32_t result) {
+    waiting_for_flush_completion_ = false;
+    if (pending_paint_) {
+      pending_paint_ = false;
+      Paint();
+    }
+  }
+
+  void Paint() {
+    if (size_.IsEmpty()) {
+      pending_paint_ = false;
+      return;
+    }
+
+    if (waiting_for_flush_completion_) {
+      pending_paint_ = true;
+      return;
+    }
+
+    pp::ImageData image = PaintImage(size_,
+                                     samples_,
+                                     sample_count_,
+                                     channel_count_);
+    if (!image.is_null()) {
+      device_context_.ReplaceContents(&image);
+      waiting_for_flush_completion_ = true;
+      device_context_.Flush(
+          callback_factory_.NewRequiredCallback(&MyInstance::DidFlush));
+    }
+  }
+
+  pp::ImageData PaintImage(const pp::Size& size,
+                           const int16_t* samples,
+                           uint32_t sample_count,
+                           uint32_t channel_count) {

[dmichael (off chromium), 2011/11/23 20:15:52]

nit: Is there a reason to use parameters for these last 3 instead of accessing
them directly? Just making it less coupled with the rest? As written, it could
probably be made static.

[viettrungluu, 2011/11/23 21:06:25]

No good reason; I got rid of the last three parameters.

+    pp::ImageData image(this, PP_IMAGEDATAFORMAT_BGRA_PREMUL, size, false);
+    if (image.is_null())
+      return image;
+
+    // Clear to dark grey.
+    for (int y = 0; y < size.height(); y++) {
+      for (int x = 0; x < size.width(); x++)
+        *image.GetAddr32(pp::Point(x, y)) = 0xff202020;
+    }
+
+    int mid_height = size.height() / 2;
+    int max_amplitude = size.height() * 4 / 10;
+
+    // Draw some lines.
+    for (int x = 0; x < size.width(); x++) {
+      *image.GetAddr32(pp::Point(x, mid_height)) = 0xff606060;
+      *image.GetAddr32(pp::Point(x, mid_height + max_amplitude)) = 0xff404040;
+      *image.GetAddr32(pp::Point(x, mid_height - max_amplitude)) = 0xff404040;
+    }
+
+    // Draw our samples.
+    for (int x = 0, i = 0;
+         x < std::min(size.width(), static_cast<int>(sample_count));
+         x++, i += channel_count) {
+      int y = samples[i] * max_amplitude / 32768 + mid_height;

[dmichael (off chromium), 2011/11/23 20:15:52]

nit: std::numeric_limits<int16_t>::max()+1 might look less magical than 32768.

[viettrungluu, 2011/11/23 21:06:25]

Done.

+      *image.GetAddr32(pp::Point(x, y)) = 0xffffffff;
+    }
+
+    return image;
+  }
+
+  // TODO(viettrungluu): Danger! We really should lock, but which thread

[dmichael (off chromium), 2011/11/23 20:15:52]

I have some threading primitive wrappers sitting somewhere locally, if you want.
I ended up not needing them yet, but I'm saving them for when I do need to write
a test or example with locking.

+  // primitives to use? In any case, the |StopCapture()| in the destructor
+  // shouldn't return until this callback is done, so at least we should be
+  // writing to a valid region of memory.

[dmichael (off chromium), 2011/11/23 20:15:52]

But I agree... in this case, the worst that will happen (and it's very likely it
will happen) is drawing a bad frame, which will probably never look so bad as to
be noticed.

Of course, it is an example, so we should ultimately fix it lest it be
copied/pasted this way.

[viettrungluu, 2011/11/23 21:06:25]

Yeah, we should fix it, but let's hold off on it for the moment, if that sounds
okay to you.

+  static void CaptureCallback(const void* samples,
+                              uint32_t num_bytes,
+                              void* ctx) {
+    MyInstance* thiz = reinterpret_cast<MyInstance*>(ctx);

[dmichael (off chromium), 2011/11/23 20:15:52]

static_cast

[viettrungluu, 2011/11/23 21:06:25]

Done.

+    PP_DCHECK(num_bytes ==
+              thiz->sample_count_ * channel_count_ * sizeof(int16_t));
+    memcpy(thiz->samples_, samples, num_bytes);
+  }
+
+  pp::CompletionCallbackFactory<MyInstance> callback_factory_;
+
+  uint32_t sample_count_;
+  uint32_t channel_count_;
+  int16_t* samples_;
+
+  int32_t timer_interval_;
+
+  // Painting stuff.
+  pp::Size size_;
+  pp::Graphics2D device_context_;
+  bool pending_paint_;
+  bool waiting_for_flush_completion_;
+
+

[yzshen1, 2011/11/23 21:21:17]

One redundant empty line could be removed.

[viettrungluu, 2011/11/23 21:31:30]

Done.

+  // Allocated in |Init()|, freed on destruction.
+  pp::AudioInput_Dev audio_input_;

[yzshen1, 2011/11/23 21:21:17]

nit: Allocated / freed may not be accurate. It sounds like |audio_input_| is an
object on the heap.
Maybe this comment is for |samples_|?

[viettrungluu, 2011/11/23 21:31:30]

I removed this misleading comment (which I forgot to remove when
cutting-and-pasting from examples/audio.cc).

+};
+
+class MyModule : public pp::Module {
+ public:
+  virtual pp::Instance* CreateInstance(PP_Instance instance) {
+    return new MyInstance(instance);
+  }
+};
+
+namespace pp {
+
+// Factory function for your specialization of the Module object.
+Module* CreateModule() {
+  return new MyModule();
+}
+
+}  // namespace pp