gfx: Add FrameTime and DisplayTime classes

ui/gfx/frame_time.h

 // Copyright 2013 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 UI_GFX_FRAME_TIME_H
 #define UI_GFX_FRAME_TIME_H
 
 #include "base/time/time.h"
 
 namespace gfx {
 
-// FrameTime::Now() should be used to get timestamps with a timebase that
-// is consistent across the graphics stack.
-namespace FrameTime {
-  static base::TimeTicks Now() {
-    if (base::TimeTicks::IsHighResNowFastAndReliable())
-      return base::TimeTicks::HighResNow();
-    return base::TimeTicks::Now();
+// FractionalFrameTime should be used for getting the current timestamp in
+// the same timebase as FrameTime and for representing things like deadlines,
+// which may not occur exactly on a frame boundary.
+class FractionalFrameTime {
+ public:
+  FractionalFrameTime() : ticks_(0) {
   }
 
-  static bool TimestampsAreHighRes() {
-    return base::TimeTicks::IsHighResNowFastAndReliable();
+  static FractionalFrameTime Now() {
+    if (base::TimeTicks::IsHighResNowFastAndReliable())
+      return FractionalFrameTime(
+          base::TimeTicks::HighResNow().ToInternalValue());
+    return FractionalFrameTime(base::TimeTicks::Now().ToInternalValue());
   }
-}
+
+  // Returns true if this object has not been initialized.
+  bool is_null() const {
+    return ticks_ == 0;
+  }
+
+  double Unsafe_InSecondsF() {
+    return static_cast<double>(ticks_) / base::Time::kMicrosecondsPerSecond;
+  }
+
+  double Unsafe_InMillisecondsF() const {
+    return static_cast<double>(ticks_) /
+        base::Time::kMicrosecondsPerMillisecond;
+  }
+
+  FractionalFrameTime& operator=(FractionalFrameTime other) {
+    ticks_ = other.ticks_;
+    return *this;
+  }
+
+  // Compute the difference between two times.
+  base::TimeDelta operator-(FractionalFrameTime other) const {
+    DCHECK(!other.is_null()) << "Please do not convert time to a float.";
+    return base::TimeDelta::FromInternalValue(ticks_ - other.ticks_);
+  }
+
+  // Modify by some time delta.
+  FractionalFrameTime& operator+=(base::TimeDelta delta) {
+    ticks_ += delta.ToInternalValue();
+    return *this;
+  }
+  FractionalFrameTime& operator-=(base::TimeDelta delta) {
+    ticks_ -= delta.ToInternalValue();
+    return *this;
+  }
+
+  // Return a new FractionalFrameTime modified by some delta.
+  FractionalFrameTime operator+(base::TimeDelta delta) const {
+    return FrameTime(ticks_ + delta.ToInternalValue());
+  }
+  FractionalFrameTime operator-(base::TimeDelta delta) const {
+    return FrameTime(ticks_ - delta.ToInternalValue());
+  }
+
+  // Comparison operators
+  bool operator==(FractionalFrameTime other) const {
+    return ticks_ == other.ticks_;
+  }
+  bool operator!=(FractionalFrameTime other) const {
+    return ticks_ != other.ticks_;
+  }
+  bool operator<(FractionalFrameTime other) const {
+    return ticks_ < other.ticks_;
+  }
+  bool operator<=(FractionalFrameTime other) const {
+    return ticks_ <= other.ticks_;
+  }
+  bool operator>(FractionalFrameTime other) const {
+    return ticks_ > other.ticks_;
+  }
+  bool operator>=(FractionalFrameTime other) const {
+    return ticks_ >= other.ticks_;
+  }
+
+ protected:
+  // Tick count in microseconds.
+  int64 ticks_;
+
+  // Please use Now() to create a new object. This is for internal use.
+  // Ticks is in microseconds.
+  explicit FractionalFrameTime(int64 ticks) : ticks_(ticks) {
+  }
+};
+
+// FrameTime should be used to represent an actual frame time.
+// If animations are using anything other than a FrameTime, there

[brianderson, 2013/10/17 18:42:20]

*there is something wrong.

+class FrameTime : public FractionalFrameTime {
+ public:
+  FrameTime Unsafe_CreateFromFractionalTime(FractionalFrameTime src) {
+    return FrameTime(src.ticks_);
+  }
+
+  FrameTime Unsafe_CreateFromTimeTicks(base::TimeTicks time_ticks) {
+    return FractionalFrameTime(time_ticks.ToInternalValue());
+  }
+
+ protected:
+  explicit FractionalFrameTime(int64 ticks)
+  : ticks_(ticks) {}
+};
 
 }
 
 #endif // UI_GFX_FRAME_TIME_H