Add helpers for creating UI components.

mojo/ui/choreographer.cc

Index: mojo/ui/choreographer.cc
diff --git a/mojo/ui/choreographer.cc b/mojo/ui/choreographer.cc
new file mode 100644
index 0000000000000000000000000000000000000000..7ea295b682aecc1d9c44c15d884aaa9f38c3d973
--- /dev/null
+++ b/mojo/ui/choreographer.cc
@@ -0,0 +1,119 @@
+// 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 "mojo/ui/choreographer.h"
+
+#include "base/bind.h"
+#include "base/logging.h"
+#include "mojo/public/cpp/system/functions.h"
+
+namespace mojo {
+namespace ui {
+
+Choreographer::Choreographer(mojo::gfx::composition::Scene* scene,
+                             ChoreographerDelegate* delegate)
+    : delegate_(delegate) {
+  DCHECK(delegate_);
+  scene->GetScheduler(mojo::GetProxy(&scene_scheduler_));
+}
+
+Choreographer::Choreographer(
+    mojo::gfx::composition::SceneSchedulerPtr scene_scheduler,
+    ChoreographerDelegate* delegate)
+    : scene_scheduler_(scene_scheduler.Pass()), delegate_(delegate) {
+  DCHECK(scene_scheduler_);
+  DCHECK(delegate_);
+}
+
+Choreographer::~Choreographer() {}
+
+void Choreographer::ScheduleDraw() {
+  if (!draw_scheduled_) {
+    draw_scheduled_ = true;
+    ScheduleFrame();
+  }
+}
+
+void Choreographer::ScheduleFrame() {
+  if (!frame_scheduled_) {
+    frame_scheduled_ = true;
+    scene_scheduler_->ScheduleFrame(
+        base::Bind(&Choreographer::DoFrame, base::Unretained(this)));
+  }
+}
+
+void Choreographer::DoFrame(mojo::gfx::composition::FrameInfoPtr frame_info) {
+  DCHECK(frame_info);
+  DCHECK(frame_scheduled_);
+  frame_scheduled_ = false;
+
+  if (draw_scheduled_) {
+    draw_scheduled_ = false;
+
+    // To reduce latency and jank, anticipate the next frame to be drawn by
+    // scheduling it early.
+    //
+    // TODO(jeffbrown): Reenable this once issue #604 is fixed.  Unfortunately
+    // this exacerbates starvation issues in the Mojo message pump.
+    // ScheduleFrame();
+
+    // Ensure frame info is sane since it comes from another service.
+    // TODO(jeffbrown): Would be better to report an error to the client
+    // who can shut things down if needed.
+    MojoTimeTicks now = MojoGetTimeTicksNow();
+    if (frame_info->frame_time > now) {
+      LOG(WARNING) << "Frame time is in the future: frame_time="
+                   << frame_info->frame_time << ", now=" << now;
+      frame_info->frame_time = now;
+    }
+    if (frame_info->frame_deadline < frame_info->frame_time) {
+      LOG(WARNING)
+          << "Frame deadline is earlier than frame time: frame_deadline="
+          << frame_info->frame_deadline
+          << ", frame_time=" << frame_info->frame_time << ", now=" << now;
+      frame_info->frame_deadline = frame_info->frame_time;
+    }
+    if (frame_info->presentation_time < frame_info->frame_deadline) {
+      LOG(WARNING) << "Presentation time is earlier than frame deadline: "
+                      "presentation_time="
+                   << frame_info->presentation_time
+                   << ", frame_deadline=" << frame_info->frame_deadline
+                   << ", now=" << now;
+      frame_info->presentation_time = frame_info->frame_deadline;
+    }
+
+    // Compensate for significant lag by adjusting the frame time if needed
+    // to step past skipped frames.
+    uint64_t lag = now - frame_info->frame_time;
+    if (frame_info->frame_interval > 0u && lag > frame_info->frame_interval) {
+      uint64_t offset = lag % frame_info->frame_interval;
+      uint64_t adjustment = now - offset - frame_info->frame_time;
+      frame_info->frame_time = now - offset;
+      frame_info->frame_deadline += adjustment;
+      frame_info->presentation_time += adjustment;
+
+      // Jank warning.
+      // TODO(jeffbrown): Suppress this once we're happy with things.
+      LOG(WARNING) << "Missed " << frame_info->frame_interval
+                   << " us frame deadline by " << lag << " us, skipping "
+                   << (lag / frame_info->frame_interval) << " frames";
+    }
+
+    // Ensure frame time isn't going backwards, just in case the compositor's
+    // timing is seriously broken.
+    base::TimeDelta time_delta;
+    if (last_frame_info_) {
+      DCHECK(frame_info->frame_time >= last_frame_info_->frame_time);
+      time_delta = base::TimeDelta::FromMicroseconds(
+          frame_info->frame_time - last_frame_info_->frame_time);
+    }
+
+    // Invoke the callback.
+    last_frame_info_ = frame_info.Pass();
+    delegate_->OnDraw(*last_frame_info_, time_delta);
+  }
+}
+
+}  // namespace ui
+}  // namespace mojo