Add a multi-threaded rendering example.

examples/ui/noodles/noodles_view.cc

Index: examples/ui/noodles/noodles_view.cc
diff --git a/examples/ui/noodles/noodles_view.cc b/examples/ui/noodles/noodles_view.cc
new file mode 100644
index 0000000000000000000000000000000000000000..86517c038b7bd51f7b8b816c6e464dd632956c98
--- /dev/null
+++ b/examples/ui/noodles/noodles_view.cc
@@ -0,0 +1,189 @@
+// Copyright 2015 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 "examples/ui/noodles/noodles_view.h"
+
+#include <math.h>
+
+#include <cstdlib>
+
+#include "base/bind.h"
+#include "base/logging.h"
+#include "base/message_loop/message_loop.h"
+#include "examples/ui/noodles/frame.h"
+#include "examples/ui/noodles/rasterizer.h"
+#include "third_party/skia/include/core/SkCanvas.h"
+#include "third_party/skia/include/core/SkColor.h"
+#include "third_party/skia/include/core/SkPath.h"
+#include "third_party/skia/include/core/SkPicture.h"
+#include "third_party/skia/include/core/SkPictureRecorder.h"
+
+namespace examples {
+
+static constexpr double kSecondsBetweenChanges = 10.0;
+
+template <typename T>
+static void Drop(scoped_ptr<T> ptr) {}

[abarth, 2016/01/10 03:25:56]

There's a declaration in base for this.  base::Ignored or something like that.

[jeffbrown, 2016/01/26 08:30:37]

I thought so too but there's only IgnoreResult, not anything to ignore an
argument.

+
+static scoped_ptr<base::MessagePump> CreateMessagePumpMojo() {
+  return base::MessageLoop::CreateMessagePumpForType(
+      base::MessageLoop::TYPE_DEFAULT);
+}
+
+static void Lissajous(SkPath* path,
+                      double ax,
+                      double ay,
+                      int wx,
+                      int wy,
+                      double p) {
+  uint32_t segments = ceil(fabs(ax) + fabs(ay)) / 2u + 1u;
+  for (uint32_t i = 0; i < segments; ++i) {
+    double t = M_PI * 2.0 * i / segments;
+    double x = ax * sin(t * wx);
+    double y = ay * sin(t * wy + p);
+    if (i == 0u)
+      path->moveTo(x, y);
+    else
+      path->lineTo(x, y);
+  }
+  path->close();
+}
+
+NoodlesView::NoodlesView(
+    mojo::ApplicationImpl* app_impl,
+    const mojo::ui::ViewProvider::CreateViewCallback& create_view_callback)
+    : BaseView(app_impl, "Noodles", create_view_callback),
+      choreographer_(scene(), this),
+      frame_queue_(std::make_shared<FrameQueue>()),
+      rasterizer_delegate_(
+          make_scoped_ptr(new RasterizerDelegate(frame_queue_))) {
+  base::Thread::Options options;
+  options.message_pump_factory = base::Bind(&CreateMessagePumpMojo);
+
+  rasterizer_thread_.reset(new base::Thread("noodles_rasterizer"));
+  rasterizer_thread_->StartWithOptions(options);
+  rasterizer_task_runner_ = rasterizer_thread_->message_loop()->task_runner();
+
+  rasterizer_task_runner_->PostTask(
+      FROM_HERE,
+      base::Bind(&RasterizerDelegate::CreateRasterizer,
+                 base::Unretained(rasterizer_delegate_.get()),
+                 base::Passed(app_impl->CreateApplicationConnector()),
+                 base::Passed(TakeScene().PassInterface())));
+}
+
+NoodlesView::~NoodlesView() {
+  // Ensure destruction happens on the correct thread.
+  rasterizer_task_runner_->PostTask(
+      FROM_HERE, base::Bind(&Drop<RasterizerDelegate>,
+                            base::Passed(&rasterizer_delegate_)));
+}
+
+void NoodlesView::OnLayout(mojo::ui::ViewLayoutParamsPtr layout_params,
+                           mojo::Array<uint32_t> children_needing_layout,
+                           const OnLayoutCallback& callback) {
+  size_.width = layout_params->constraints->max_width;
+  size_.height = layout_params->constraints->max_height;
+
+  // Submit the new layout information.
+  auto info = mojo::ui::ViewLayoutResult::New();
+  info->size = size_.Clone();
+  callback.Run(info.Pass());
+
+  choreographer_.ScheduleDraw();
+}
+
+void NoodlesView::OnDraw(const mojo::gfx::composition::FrameInfo& frame_info,
+                         const base::TimeDelta& time_delta) {
+  // Update the animation.
+  alpha_ += time_delta.InSecondsF();
+
+  // Create and post a new frame to the renderer.
+  auto metadata = mojo::gfx::composition::SceneMetadata::New();
+  metadata->presentation_time = frame_info.presentation_time;
+  std::unique_ptr<Frame> frame(
+      new Frame(size_, CreatePicture(), metadata.Pass()));
+  if (frame_queue_->PutFrame(std::move(frame))) {

[abarth, 2016/01/10 03:25:56]

This isn't great for perf, but I guess that's not the point of this example.

[jeffbrown, 2016/01/26 08:30:37]

Yeah we should really have more backpressure here.

+    rasterizer_task_runner_->PostTask(
+        FROM_HERE, base::Bind(&RasterizerDelegate::PublishNextFrame,
+                              base::Unretained(rasterizer_delegate_.get())));
+  }
+
+  // Loop!
+  choreographer_.ScheduleDraw();

[abarth, 2016/01/10 03:25:56]

This should go at the top of the function.

[jeffbrown, 2016/01/26 08:30:37]

Done.  Note that Choreographer also contains an optimization to achieve the same
effect by speculatively scheduling one frame ahead.

+}
+
+skia::RefPtr<SkPicture> NoodlesView::CreatePicture() {
+  constexpr int count = 4;
+  constexpr int padding = 1;

[abarth, 2016/01/10 03:25:56]

Why not just const ?

[jeffbrown, 2016/01/26 08:30:37]

Eh?  constexpr is my new favorite keyword.  I'll abuse it until I get bored, I
guess.  ;)

+
+  if (alpha_ > kSecondsBetweenChanges) {
+    alpha_ = 0.0;
+    wx_ = rand() % 9 + 1;
+    wy_ = rand() % 9 + 1;
+  }
+
+  SkPictureRecorder recorder;
+  SkCanvas* canvas = recorder.beginRecording(size_.width, size_.height);
+
+  double cx = size_.width * 0.5;
+  double cy = size_.height * 0.5;
+  canvas->translate(cx, cy);
+
+  double phase = alpha_;
+  for (int i = 0; i < count; i++, phase += 0.1) {
+    SkPaint paint;
+    SkScalar hsv[3] = {fmod(phase * 120, 360), 1, 1};
+    paint.setColor(SkHSVToColor(hsv));
+    paint.setStyle(SkPaint::kStroke_Style);
+    paint.setAntiAlias(true);
+
+    SkPath path;
+    Lissajous(&path, cx - padding, cy - padding, wx_, wy_, phase);
+    canvas->drawPath(path, paint);
+  }
+
+  canvas->flush();

[abarth, 2016/01/10 03:25:56]

I don't think you need to flush here.  endRecordingAsPicture is basically a
finish.

[jeffbrown, 2016/01/26 08:30:37]

Removed, here and in other places.

+  return skia::AdoptRef(recorder.endRecordingAsPicture());
+}
+
+NoodlesView::FrameQueue::FrameQueue() {}
+
+NoodlesView::FrameQueue::~FrameQueue() {}
+
+bool NoodlesView::FrameQueue::PutFrame(std::unique_ptr<Frame> frame) {
+  std::lock_guard<std::mutex> lock(mutex_);
+  bool was_empty = !next_frame_.get();
+  next_frame_.swap(frame);
+  return was_empty;
+}
+
+std::unique_ptr<Frame> NoodlesView::FrameQueue::TakeFrame() {
+  std::lock_guard<std::mutex> lock(mutex_);
+  return std::move(next_frame_);
+}
+
+NoodlesView::RasterizerDelegate::RasterizerDelegate(
+    const std::shared_ptr<FrameQueue>& frame_queue)
+    : frame_queue_(frame_queue) {
+  DCHECK(frame_queue_);
+}
+
+NoodlesView::RasterizerDelegate::~RasterizerDelegate() {}
+
+void NoodlesView::RasterizerDelegate::CreateRasterizer(
+    mojo::InterfacePtrInfo<mojo::ApplicationConnector> connector_info,
+    mojo::InterfacePtrInfo<mojo::gfx::composition::Scene> scene_info) {
+  rasterizer_.reset(
+      new Rasterizer(mojo::MakeProxy(connector_info.Pass()).Pass(),
+                     mojo::MakeProxy(scene_info.Pass()).Pass()));
+}
+
+void NoodlesView::RasterizerDelegate::PublishNextFrame() {
+  std::unique_ptr<Frame> frame(frame_queue_->TakeFrame());
+  DCHECK(frame);
+  rasterizer_->PublishFrame(std::move(frame));
+}
+
+}  // namespace examples