Add support for inverse transform animations.

ui/compositor/transform_animation_curve_adapter_unittest.cc

+// Copyright (c) 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.
+
+#include "ui/compositor/transform_animation_curve_adapter.h"
+
+#include "base/time/time.h"
+#include "testing/gtest/include/gtest/gtest.h"
+#include "ui/compositor/test/test_utils.h"
+
+namespace ui {
+
+namespace {
+
+// Check that the counter transform curve gives the gives a transform that when
+// applied on top of the parent transform gives the original transform

[Ian Vollick, 2013/08/23 12:45:19]

Nice test!

[avallee, 2013/08/23 15:01:19]

Thanks.

+TEST(CounterTransformCurveAdapterTest, InversesTransform) {
+  gfx::Transform parent_start, parent_target;
+  parent_start.Scale(0.5, 3);
+  parent_start.Translate(-20, 30);
+  parent_target.Translate(0, 100);
+
+  gfx::Transform child_transform;
+  child_transform.Rotate(-30.0);
+
+  base::TimeDelta duration = base::TimeDelta::FromSeconds(1);
+
+  const gfx::Transform effective_child_transform =
+      parent_start * child_transform;
+
+  TransformAnimationCurveAdapter parent_curve(Tween::LINEAR,
+                                              parent_start,
+                                              parent_target,
+                                              duration);
+
+  CounterTransformCurveAdapter child_curve(parent_curve,
+                                           child_transform,
+                                           duration);
+  const int steps = 1000;
+  double step = 1.0/steps;
+  for (int i = 0; i != steps; ++i) {
+    gfx::Transform progress_parent_transform =
+            parent_curve.GetValue(i*step);
+    gfx::Transform progress_child_transform =
+            child_curve.GetValue(i*step);
+    CheckApproximatelyEqual(effective_child_transform,
+                            progress_parent_transform *
+                            progress_child_transform);
+  }
+}
+
+} // namespace
+
+} // namespace ui