Refactors animation to allow for cleaner subclassing. I'm doing this

app/tween.cc

+// Copyright (c) 2010 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 "app/tween.h"
+
+#include <math.h>
+
+#if defined(OS_WIN)
+#include <float.h>
+#endif
+
+#include "gfx/rect.h"
+
+// static
+double Tween::CalculateValue(Tween::Type type, double state) {
+  DCHECK_GE(state, 0);
+  DCHECK_LE(state, 1);
+
+  switch (type) {
+    case EASE_IN:
+      return pow(state, 2);
+
+    case EASE_IN_OUT:
+      if (state < 0.5)
+        return pow(state * 2, 2) / 2.0;
+      return 1.0 - (pow((state - 1.0) * 2, 2) / 2.0);
+
+    case FAST_IN_OUT:
+      return (pow(state - 0.5, 3) + 0.125) / 0.25;
+
+    case LINEAR:
+      return state;
+
+    case EASE_OUT_SNAP:
+      state = 0.95 * (1.0 - pow(1.0 - state, 2));
+      break;
+
+    case EASE_OUT:
+      return 1.0 - pow(1.0 - state, 2);
+
+    case ZERO:
+      return 0;
+  }
+
+  NOTREACHED();
+  return state;
+}
+
+// static
+double Tween::ValueBetween(double value, double start, double target) {
+  return start + (target - start) * value;
+}
+
+// static
+int Tween::ValueBetween(double value, int start, int target) {
+  if (start == target)
+    return start;
+  double delta = static_cast<double>(target - start);
+  if (delta < 0)
+    delta--;
+  else
+    delta++;
+#if defined(OS_WIN)
+  return start + static_cast<int>(value * _nextafter(delta, 0));
+#else
+  return start + static_cast<int>(value * nextafter(delta, 0));
+#endif
+}
+
+// static
+gfx::Rect Tween::ValueBetween(double value,
+                              const gfx::Rect& start_bounds,
+                              const gfx::Rect& target_bounds) {
+  return gfx::Rect(ValueBetween(value, start_bounds.x(), target_bounds.x()),
+                   ValueBetween(value, start_bounds.y(), target_bounds.y()),
+                   ValueBetween(value, start_bounds.width(),
+                                target_bounds.width()),
+                   ValueBetween(value, start_bounds.height(),
+                                target_bounds.height()));
+}