Motown: Rename Ratio and LinearFunction classes

mojo/services/media/common/cpp/timeline_function.h

+// 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.
+
+#ifndef MOJO_SERVICES_MEDIA_COMMON_CPP_TIMELINE_FUNCTION_H_
+#define MOJO_SERVICES_MEDIA_COMMON_CPP_TIMELINE_FUNCTION_H_
+
+#include "mojo/public/cpp/environment/logging.h"
+#include "mojo/services/media/common/cpp/timeline_rate.h"
+
+namespace mojo {
+namespace media {
+
+// TODO(dalesat): Consider always allowing inexact results.
+
+// A linear function from int64_t to int64_t with non-negative slope that
+// translates reference timeline values into subject timeline values (the
+// 'subject' being the timeline that's represented by the function). The
+// representation is in point-slope form. The point is represented as two
+// int64_t time values (reference_time, subject_time), and the slope (rate) is
+// represented as a TimelineRate, the ratio of two uint32_t values
+// (subject_delta / reference_delta).
+class TimelineFunction {
+ public:
+  // Applies a timeline function.
+  static int64_t Apply(
+      int64_t reference_time,
+      int64_t subject_time,
+      const TimelineRate& rate,  // subject_delta / reference_delta
+      int64_t reference_input);
+
+  // Applies the inverse of a timeline function.
+  static int64_t ApplyInverse(
+      int64_t reference_time,
+      int64_t subject_time,
+      const TimelineRate& rate,  // subject_delta / reference_delta
+      int64_t subject_input) {
+    MOJO_DCHECK(rate.reference_delta() != 0u);
+    return Apply(subject_time, reference_time, rate.Inverse(), subject_input);
+  }
+
+  // Composes two timeline functions B->C and A->B producing A->C. If exact is
+  // true, DCHECKs on loss of precision.
+  static TimelineFunction Compose(const TimelineFunction& bc,
+                                  const TimelineFunction& ab,
+                                  bool exact = true);
+
+  TimelineFunction() : reference_time_(0), subject_time_(0) {}
+
+  TimelineFunction(int64_t reference_time,
+                   int64_t subject_time,
+                   uint32_t reference_delta,
+                   uint32_t subject_delta)
+      : reference_time_(reference_time),
+        subject_time_(subject_time),
+        rate_(subject_delta, reference_delta) {}
+
+  TimelineFunction(int64_t reference_time,
+                   int64_t subject_time,
+                   const TimelineRate& rate)  // subject_delta / reference_delta
+      : reference_time_(reference_time),
+        subject_time_(subject_time),
+        rate_(rate) {}
+
+  explicit TimelineFunction(
+      const TimelineRate& rate)  // subject_delta / reference_delta
+      : reference_time_(0),
+        subject_time_(0),
+        rate_(rate) {}
+
+  // Applies the function. Returns TimelineRate::kOverflow on overflow.
+  int64_t Apply(int64_t reference_input) const {
+    return Apply(reference_time_, subject_time_, rate_, reference_input);
+  }
+
+  // Applies the inverse of the function. Returns TimelineRate::kOverflow on
+  // overflow.
+  int64_t ApplyInverse(int64_t subject_input) const {
+    MOJO_DCHECK(rate_.reference_delta() != 0u);
+    return ApplyInverse(reference_time_, subject_time_, rate_, subject_input);
+  }
+
+  // Applies the function.  Returns TimelineRate::kOverflow on overflow.
+  int64_t operator()(int64_t reference_input) const {
+    return Apply(reference_input);
+  }
+
+  // Returns a timeline function that is the inverse if this timeline function.
+  TimelineFunction Inverse() const {
+    MOJO_DCHECK(rate_.reference_delta() != 0u);
+    return TimelineFunction(subject_time_, reference_time_, rate_.Inverse());
+  }
+
+  int64_t reference_time() const { return reference_time_; }
+
+  int64_t subject_time() const { return subject_time_; }
+
+  const TimelineRate& rate() const { return rate_; }
+
+  uint32_t reference_delta() const { return rate_.reference_delta(); }
+
+  uint32_t subject_delta() const { return rate_.subject_delta(); }
+
+ private:
+  int64_t reference_time_;
+  int64_t subject_time_;
+  TimelineRate rate_;  // subject_delta / reference_delta
+};
+
+// Tests two timeline functions for equality. Equality requires equal basis
+// values.
+inline bool operator==(const TimelineFunction& a, const TimelineFunction& b) {
+  return a.reference_time() == b.reference_time() &&
+         a.subject_time() == b.subject_time() && a.rate() == b.rate();
+}
+
+// Tests two timeline functions for inequality. Equality requires equal basis
+// values.
+inline bool operator!=(const TimelineFunction& a, const TimelineFunction& b) {
+  return !(a == b);
+}
+
+// Composes two timeline functions B->C and A->B producing A->C. DCHECKs on
+// loss of precision.
+inline TimelineFunction operator*(const TimelineFunction& bc,
+                                  const TimelineFunction& ab) {
+  return TimelineFunction::Compose(bc, ab);
+}
+
+}  // namespace media
+}  // namespace mojo
+
+#endif  // MOJO_SERVICES_MEDIA_COMMON_CPP_TIMELINE_FUNCTION_H_