Fix for bug where composited rotate3d should SLERP

cc/animation/transform_operations.cc

 // 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.
 
 #include "cc/animation/transform_operations.h"
 
 #include <algorithm>
 
 #include "ui/gfx/animation/tween.h"
 #include "ui/gfx/geometry/box_f.h"
@@ skipping 259 matching lines @@
   if (from_identity && to_identity)
     return true;
 
   if (MatchesTypes(from)) {
     size_t num_operations =
         std::max(from_identity ? 0 : from.operations_.size(),
                  to_identity ? 0 : operations_.size());
     for (size_t i = 0; i < num_operations; ++i) {
       gfx::Transform blended;
       if (!TransformOperation::BlendTransformOperations(
-          from_identity ? 0 : &from.operations_[i],
-          to_identity ? 0 : &operations_[i],
-          progress,
-          &blended))
+              from.operations_.size() <= i ? 0 : &from.operations_[i],
+              operations_.size() <= i ? 0 : &operations_[i], progress,

[ajuma, 2015/06/24 14:47:45]

Please add a test for this change too.

[soonm, 2015/06/26 07:48:38]

The new tests I've added for the corrected shareSameAxis checks depend on this
behavior.

So they will correctly fail if this part is reverted. The identity transform
tests currently in the
transform_operations_unittest does test this code part.

I think the original code is an optimization on figuring out if the whole list
of transform operations
are already identity, if so, then just use a 0. However, this is bad for
rotations because rotate axis
does not get encoded into the matrix representations when the rotation angle is
0 deg. (ie no rotation)

so isIdentity will return true...which is sort of correct.

In this change, I allow the for-loop to use those functions even though they
could possibly be identity.
I suspect only a performance test with many transforms will be able to pick it
up.

[ajuma, 2015/06/26 13:13:31]

Ah, of course, thanks for the explanation!

+              &blended))
           return false;
       result->PreconcatTransform(blended);
     }
     return true;
   }
 
   if (!ComputeDecomposedTransform() || !from.ComputeDecomposedTransform())
     return false;
 
   gfx::DecomposedTransform to_return;
@@ skipping 13 matching lines @@
       decomposed_transform_.reset(new gfx::DecomposedTransform());
     gfx::Transform transform = Apply();
     if (!gfx::DecomposeTransform(decomposed_transform_.get(), transform))
       return false;
     decomposed_transform_dirty_ = false;
   }
   return true;
 }
 
 }  // namespace cc