Add helpers for creating UI components.

mojo/ui/choreographer.h

Index: mojo/ui/choreographer.h
diff --git a/mojo/ui/choreographer.h b/mojo/ui/choreographer.h
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+// 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.
+
+#ifndef MOJO_UI_CHOREOGRAPHER_H_
+#define MOJO_UI_CHOREOGRAPHER_H_
+
+#include "base/time/time.h"
+#include "mojo/public/cpp/system/macros.h"
+#include "mojo/services/gfx/composition/interfaces/scenes.mojom.h"
+#include "mojo/services/gfx/composition/interfaces/scheduling.mojom.h"
+
+namespace mojo {
+namespace ui {
+
+class ChoreographerDelegate;
+
+// Coordinates drawing a frame of a scene.
+//
+// This class is intended to be included as a member of a View that wants to
+// schedule drawing using the following pattern.
+//
+// class MyView : public mojo::ui::BaseView,
+//                public mojo::ui::ChoreographerDelegate {
+//  public:
+//   MyView(mojo::ApplicationImpl* app_impl,
+//          const mojo::ui::ViewProvider::CreateViewCallback&
+//              create_view_callback)
+//          : BaseView(app_impl, "MyView", create_view_callback),
+//            choreographer_(scene_scheduler(), this) {}
+//   ~MyView() override {}
+//
+//  private:
+//   // |ChoreographerDelegate|:
+//   void OnDraw(const mojo::gfx::composition::FrameInfo& frame_info) override;
+//
+//   mojo::ui::Choreographer choreographer_;
+//
+//   MOJO_DISALLOW_COPY_AND_ASSIGN(MyView);
+// };
+class Choreographer {
+ public:
+  Choreographer(mojo::gfx::composition::Scene* scene,
+                ChoreographerDelegate* delegate);
+  Choreographer(mojo::gfx::composition::SceneSchedulerPtr scene_scheduler,
+                ChoreographerDelegate* delegate);
+  ~Choreographer();
+
+  // Gets the scene scheduler.
+  mojo::gfx::composition::SceneScheduler* scene_scheduler() {
+    return scene_scheduler_.get();
+  }
+
+  // Gets the most recent frame info, or null if none.
+  mojo::gfx::composition::FrameInfo* last_frame_info() {
+    return last_frame_info_.get();
+  }
+
+  // Schedules a call to the delegate's |OnDraw| using the scene scheduler.
+  void ScheduleDraw();
+
+ private:
+  mojo::gfx::composition::SceneSchedulerPtr scene_scheduler_;
+  ChoreographerDelegate* delegate_;
+  mojo::gfx::composition::FrameInfoPtr last_frame_info_;
+
+  void ScheduleFrame();
+  void DoFrame(mojo::gfx::composition::FrameInfoPtr frame_info);
+
+  bool draw_scheduled_ = false;
+  bool frame_scheduled_ = false;
+
+  MOJO_DISALLOW_COPY_AND_ASSIGN(Choreographer);
+};
+
+// An abstract class that the view may subclass to handle choreographer events.
+class ChoreographerDelegate {
+ public:
+  ChoreographerDelegate() = default;
+  virtual ~ChoreographerDelegate() = default;
+
+  // Called when it is time to draw the next frame and provides timing
+  // information for the frame.
+  //
+  // The |frame_info| provides information about the frame timing.
+  // The |time_delta| is the time interval since the last draw occurred,
+  // guaranteed to be non-negative.  Always zero for the first draw.
+  virtual void OnDraw(const mojo::gfx::composition::FrameInfo& frame_info,
+                      const base::TimeDelta& time_delta) = 0;
+
+ private:
+  MOJO_DISALLOW_COPY_AND_ASSIGN(ChoreographerDelegate);
+};
+
+}  // namespace ui
+}  // namespace mojo
+
+#endif  // MOJO_UI_CHOREOGRAPHER_H_