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"
 #include "base/logging.h"
 
 namespace gfx {
 
-// FrameTime::Now() should be used to get timestamps with a timebase that
-// is consistent across the graphics stack.
+// FrameTime should be used for getting the current timestamp in
+// the same timebase as DisplayTime and for representing things like deadlines
+// and animation start/end times, which may not occur exactly on a vsync
+// boundary.
 class FrameTime {
  public:
-  static base::TimeTicks Now() {
-    if (TimestampsAreHighRes())
-      return base::TimeTicks::HighResNow();
-    return base::TimeTicks::Now();
+  FrameTime() : ticks_(0) {
   }
 
 #if defined(OS_WIN)
   static base::TimeTicks FromQPCValue(LONGLONG qpc_value) {
-    DCHECK(TimestampsAreHighRes());
+    DCHECK(FrameTime::IsHighRes());
     return base::TimeTicks::FromQPCValue(qpc_value);
   }
 #endif
 
-  static bool TimestampsAreHighRes() {
+  static bool IsHighRes() {
     return base::TimeTicks::IsHighResNowFastAndReliable();
   }
+
+  static FrameTime Now() {
+    if (IsHighRes())
+      return FrameTime(base::TimeTicks::HighResNow().ToInternalValue());
+    return FrameTime(base::TimeTicks::Now().ToInternalValue());
+  }
+
+  // Returns true if this object has not been initialized.
+  bool is_null() const {
+    return ticks_ == 0;
+  }
+
+  double Unsafe_InSecondsF() const {
+    return static_cast<double>(ticks_) / base::Time::kMicrosecondsPerSecond;
+  }
+
+  double Unsafe_InMillisecondsF() const {
+    return static_cast<double>(ticks_) /
+        base::Time::kMicrosecondsPerMillisecond;
+  }
+
+  static FrameTime Unsafe_FromSecondsF(double seconds) {
+    return FrameTime(seconds * base::Time::kMicrosecondsPerSecond);
+  }
+
+  static FrameTime Unsafe_FromTimeTicks(base::TimeTicks time_ticks) {
+    return FrameTime(time_ticks.ToInternalValue());
+  }
+
+
+  FrameTime& operator=(FrameTime other) {
+    ticks_ = other.ticks_;
+    return *this;
+  }
+
+  // Compute the difference between two times.
+  base::TimeDelta operator-(FrameTime 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.
+  FrameTime& operator+=(base::TimeDelta delta) {
+    ticks_ += delta.ToInternalValue();
+    return *this;
+  }
+  FrameTime& operator-=(base::TimeDelta delta) {
+    ticks_ -= delta.ToInternalValue();
+    return *this;
+  }
+
+  // Return a new FrameTime modified by some delta.
+  FrameTime operator+(base::TimeDelta delta) const {
+    return FrameTime(ticks_ + delta.ToInternalValue());
+  }
+  FrameTime operator-(base::TimeDelta delta) const {
+    return FrameTime(ticks_ - delta.ToInternalValue());
+  }
+
+  // Comparison operators
+  bool operator==(FrameTime other) const {
+    return ticks_ == other.ticks_;
+  }
+  bool operator!=(FrameTime other) const {
+    return ticks_ != other.ticks_;
+  }
+  bool operator<(FrameTime other) const {
+    return ticks_ < other.ticks_;
+  }
+  bool operator<=(FrameTime other) const {
+    return ticks_ <= other.ticks_;
+  }
+  bool operator>(FrameTime other) const {
+    return ticks_ > other.ticks_;
+  }
+  bool operator>=(FrameTime 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 FrameTime(int64 ticks) : ticks_(ticks) {
+  }
+
+ friend class DisplayTime;
+};
+
+// DisplayTime should be used to represent a timestamp that should be aligned
+// with the display vsync phase.
+class DisplayTime : public FrameTime {
+ public:
+  DisplayTime() : FrameTime(0) {
+  }
+
+  static DisplayTime Unsafe_CreateFromTimeTicks(base::TimeTicks time_ticks) {
+    return DisplayTime(time_ticks.ToInternalValue());
+  }
+
+  static DisplayTime Unsafe_CreateFromFrameTime(FrameTime fractional) {
+    return DisplayTime(fractional.ticks_);
+  }
+
+ protected:
+  explicit DisplayTime(int64 ticks)
+  : FrameTime(ticks) {}
+
+ private:
+  // Hide non const methods of FrameTime
+  DisplayTime& operator+=(base::TimeDelta delta) {
+    NOTREACHED();
+    return *this;
+  }
+  DisplayTime& operator-=(base::TimeDelta delta) {
+    NOTREACHED();
+    return *this;
+  }
 };
 
 }
 
 #endif // UI_GFX_FRAME_TIME_H