Early terminate flings when scrolling impossible

ui/gfx/android/scroller_unittest.cc

 // Copyright 2014 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 "base/time/time.h"
 #include "testing/gtest/include/gtest/gtest.h"
 #include "ui/gfx/android/scroller.h"
 
 namespace gfx {
 
@@ skipping 45 matching lines @@
   EXPECT_LT(kDefaultStartY, scroller.GetCurrY());
   EXPECT_LT(scroller.GetFinalX(), scroller.GetCurrX());
   EXPECT_GT(scroller.GetFinalY(), scroller.GetCurrY());
   EXPECT_FALSE(scroller.IsFinished());
 
   // Ensure our velocity is non-zero and in the same direction as the delta.
   EXPECT_GT(0.f, scroller.GetCurrVelocityX() * kDefaultDeltaX);
   EXPECT_GT(0.f, scroller.GetCurrVelocityY() * kDefaultDeltaY);
   EXPECT_TRUE(scroller.IsScrollingInDirection(kDefaultDeltaX, kDefaultDeltaY));
 
+  // Repeated offset computations at the same timestamp should yield identical
+  // results.
+  float curr_x = scroller.GetCurrX();
+  float curr_y = scroller.GetCurrY();
+  float curr_velocity_x = scroller.GetCurrVelocityX();
+  float curr_velocity_y = scroller.GetCurrVelocityY();
+  scroller.ComputeScrollOffset(start_time + scroll_duration / 2);
+  EXPECT_EQ(curr_x, scroller.GetCurrX());
+  EXPECT_EQ(curr_y, scroller.GetCurrY());
+  EXPECT_EQ(curr_velocity_x, scroller.GetCurrVelocityX());
+  EXPECT_EQ(curr_velocity_y, scroller.GetCurrVelocityY());
+
   // Advance to the end.
   scroller.ComputeScrollOffset(start_time + scroll_duration);
   EXPECT_EQ(scroller.GetFinalX(), scroller.GetCurrX());
   EXPECT_EQ(scroller.GetFinalY(), scroller.GetCurrY());
   EXPECT_TRUE(scroller.IsFinished());
   EXPECT_EQ(scroll_duration, scroller.GetTimePassed());
   EXPECT_NEAR(0.f, scroller.GetCurrVelocityX(), kEpsilon);
   EXPECT_NEAR(0.f, scroller.GetCurrVelocityY(), kEpsilon);
 
   // Try to advance further; nothing should change.
@@ skipping 40 matching lines @@
   EXPECT_GT(scroller.GetFinalY(), scroller.GetCurrY());
   EXPECT_FALSE(scroller.IsFinished());
 
   // Ensure our velocity is non-zero and in the same direction as the original
   // velocity.
   EXPECT_LT(0.f, scroller.GetCurrVelocityX() * kDefaultVelocityX);
   EXPECT_LT(0.f, scroller.GetCurrVelocityY() * kDefaultVelocityY);
   EXPECT_TRUE(
       scroller.IsScrollingInDirection(kDefaultVelocityX, kDefaultVelocityY));
 
+  // Repeated offset computations at the same timestamp should yield identical
+  // results.
+  float curr_x = scroller.GetCurrX();
+  float curr_y = scroller.GetCurrY();
+  float curr_velocity_x = scroller.GetCurrVelocityX();
+  float curr_velocity_y = scroller.GetCurrVelocityY();
+  scroller.ComputeScrollOffset(start_time + scroll_duration / 2);
+  EXPECT_EQ(curr_x, scroller.GetCurrX());
+  EXPECT_EQ(curr_y, scroller.GetCurrY());
+  EXPECT_EQ(curr_velocity_x, scroller.GetCurrVelocityX());
+  EXPECT_EQ(curr_velocity_y, scroller.GetCurrVelocityY());
+
   // Advance to the end.
   scroller.ComputeScrollOffset(start_time + scroll_duration);
   EXPECT_EQ(scroller.GetFinalX(), scroller.GetCurrX());
   EXPECT_EQ(scroller.GetFinalY(), scroller.GetCurrY());
   EXPECT_TRUE(scroller.IsFinished());
   EXPECT_EQ(scroll_duration, scroller.GetTimePassed());
   EXPECT_NEAR(0.f, scroller.GetCurrVelocityX(), kEpsilon);
   EXPECT_NEAR(0.f, scroller.GetCurrVelocityY(), kEpsilon);
 
   // Try to advance further; nothing should change.
   scroller.ComputeScrollOffset(start_time + scroll_duration * 2);
   EXPECT_EQ(scroller.GetFinalX(), scroller.GetCurrX());
   EXPECT_EQ(scroller.GetFinalY(), scroller.GetCurrY());
   EXPECT_TRUE(scroller.IsFinished());
   EXPECT_EQ(scroll_duration, scroller.GetTimePassed());
 }
 
 }  // namespace gfx