[Insight-developers] Template Meta Programming and itkImageBase

[Luis Ibanez]

Bill,

You are right, I had to manually change the value to ON.

BTW, the same probably happened for to the changes of
      ITK_IMAGE_BEHAVES_AS_ORIENTED_IMAGE

We may have to trigger a wave of clean builds.


    Luis


--------------------
Bill Lorensen wrote:
> Unfortunately, it seem that changing the default to ON does not change
> the value in the cache. I think a clean cache is required.
> 
> Bill
> 
> On Sun, Oct 19, 2008 at 10:39 AM, Bill Lorensen <bill.lorensen at gmail.com> wrote:
> 
>>Performance tests I did a while ago:
>>http://www.itk.org/Wiki/Proposals:Orientation#Recursive_Templates_for_fast_computation_of_Index-Point_transform
>> show a large difference between the use of recursive templates and
>>compiler optimized code.
>>
>>I'll try top resurrect these tests.
>>
>>Bill
>>
>>On Sun, Oct 19, 2008 at 10:03 AM, Luis Ibanez <luis.ibanez at kitware.com> wrote:
>>
>>>Bill,
>>>
>>>
>>>     Agree,
>>>     this was mostly a documentation issue.
>>>
>>>
>>>The previous implementation of the code had the expression:
>>>
>>>
>>>  #if 1
>>>       // template meta-programming implementation here
>>>  #else
>>>       // standard for loops implementation here
>>>  #endif
>>>
>>>
>>>which obviously was intended to be used temporarily for local debugging,
>>>but that unfortunately remained with the code...   for way too long.
>>>
>>>
>>>The consequence is that the "else" portion has not been tested recently,
>>>and therefore, it is broken, as probably illustrated by:
>>>
>>>http://www.cdash.org/CDash/testSummary.php?project=2&name=itkOrientedImage2DTest01&date=2008-10-19
>>>
>>>
>>>In addition, the "1" in the #if doesn't provide any indication
>>>of what the "if" is about. Which is an unfortunate lack of
>>>documentation for future maintenance of the code.
>>>
>>>
>>>Recent tests on gcc with -O3 illustrated that the compiler is
>>>actually able to unroll the for-loops and that the code with
>>>template meta-programming wasn't necessarily faster.
>>>
>>>
>>>By reconnecting this options to a CMake flag we can now:
>>>
>>>
>>>  1) Make sure that the "else" can be easily tested,
>>>     (maybe nightly, at least in some machines)
>>>
>>>  2) Re-evaluate the performance comparison of both
>>>     implementations.
>>>
>>>
>>>
>>>Your point of backward compatibility is well taken,
>>>therefore I'm turning the CMake flag:
>>>
>>>  ITK_USE_TEMPLATE_META_PROGRAMMING_LOOP_UNROLLING
>>>
>>>to be ON by default.
>>>
>>>http://www.itk.org/cgi-bin/viewcvs.cgi/CMakeLists.txt?root=Insight&view=log
>>>http://www.itk.org/cgi-bin/viewcvs.cgi/CMakeLists.txt?root=Insight&r1=1.318&r2=1.319
>>>
>>>
>>>This should bring the code back to behave just as when
>>>the  "#if 1"   was in place.
>>>
>>>
>>>We can now use the following Nightly tests:
>>>
>>>  itkOrientedImageProfileTest1.cxx
>>>  itkOrientedImageProfileTest2.cxx
>>>  itkOrientedImageProfileTest3.cxx
>>>
>>>to verify the computation time performance of the methods:
>>>
>>>  TransformIndexToPhysicalPoint()
>>>  TransformPhysicalPointToIndex(_
>>>
>>>in the
>>>
>>>  a) itk::OrientedImage  (test 1)
>>>  b) itk::Image          (test 2)
>>>  c) itk::VectorImage    (test 3)
>>>
>>>
>>>After running these profiling tests in multiple platforms
>>>we will be in a better informed position to decide whether
>>>we want to keep the option, or simply stick to one of the
>>>two implementations and remove the alternative code.
>>>
>>>
>>>My suggestion will be to base our test only on builds
>>>that use "Release" compilation mode, although one could
>>>argue that it may be desirable to have an option that could
>>>make Debug builds run faster...
>>>
>>>
>>>Thanks for any suggestions,
>>>
>>>
>>>    Luis
>>>
>>>
>>>---------------------
>>>Bill Lorensen wrote:
>>>
>>>>Luis,
>>>>
>>>>I noticed that the image helper methods are now enclosed within the
>>>>ITK_USE_TEMPLATE_META_PROGRAMMING_LOOP_UNROLLING  #ifdef. I suggest
>>>>that we do away with this cmake option. The image helper methods have
>>>>been the default behavior for oriented imaged from the beginning. I
>>>>see no reason to make that code optional now that we're also using it
>>>>in itkImage.
>>>>
>>>>Bill
>>>>
>>>
>