Mozart: Move frame lag compensation to new class.

mojo/services/gfx/composition/cpp/frame_tracker.cc

Index: mojo/services/gfx/composition/cpp/frame_tracker.cc
diff --git a/mojo/services/gfx/composition/cpp/frame_tracker.cc b/mojo/services/gfx/composition/cpp/frame_tracker.cc
new file mode 100644
index 0000000000000000000000000000000000000000..d85246aa117afcc792696795dcd6ab409635771b
--- /dev/null
+++ b/mojo/services/gfx/composition/cpp/frame_tracker.cc
@@ -0,0 +1,88 @@
+// Copyright 2016 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/services/gfx/composition/cpp/frame_tracker.h"
+
+#include "mojo/public/cpp/environment/logging.h"
+
+namespace mojo {
+namespace gfx {
+namespace composition {
+
+FrameTracker::FrameTracker() {}
+
+FrameTracker::~FrameTracker() {}
+
+void FrameTracker::Clear() {
+  frame_count_ = 0u;
+  frame_info_ = mojo::gfx::composition::FrameInfo();
+}
+
+uint64_t FrameTracker::Update(
+    const mojo::gfx::composition::FrameInfo& raw_frame_info,
+    MojoTimeTicks now) {
+  const int64_t old_frame_time = frame_info_.frame_time;
+  const int64_t old_presentation_time = frame_info_.presentation_time;
+  frame_info_ = raw_frame_info;
+
+  // Ensure frame info is sane since it comes from another service.
+  if (frame_info_.frame_time > now) {
+    MOJO_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) {
+    MOJO_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) {
+    MOJO_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.
+    MOJO_LOG(WARNING) << "Missed " << frame_info_.frame_interval
+                      << " us frame deadline by " << lag << " us, skipping "
+                      << (lag / frame_info_.frame_interval) << " frames";
+  }
+
+  // Ensure monotonicity.
+  if (frame_count_++ == 0u)
+    return 0u;
+  if (frame_info_.frame_time < old_frame_time) {
+    MOJO_LOG(WARNING) << "Frame time is going backwards: new="
+                      << frame_info_.frame_time << ", old=" << old_frame_time
+                      << ", now=" << now;
+    frame_info_.frame_time = old_frame_time;
+  }
+  if (frame_info_.presentation_time < old_presentation_time) {
+    MOJO_LOG(WARNING) << "Presentation time is going backwards: new="
+                      << frame_info_.presentation_time
+                      << ", old=" << old_presentation_time << ", now=" << now;
+    frame_info_.presentation_time = old_presentation_time;
+  }
+  return frame_info_.frame_time - old_frame_time;
+}
+
+}  // namespace composition
+}  // namespace gfx
+}  // namespace mojo