[vtk-developers] DoublePi proposal

[David Gobbi]

Hi J-C,

All of those are good examples of why vtkMath:Pi() should be
returning double instead of float... in each of those four locations,
a double-precision Pi should be used instead of a single-precision Pi.
So don't changed them to FloatPi().

I've also noticed that many of the vtkParametricFunction subclasses in
VTK are using vtkMath::Pi() when they should be using  double-precision pi.

 - David


On Wed, Feb 29, 2012 at 4:44 PM, Jean-Christophe Fillion-Robin
<jchris.fillionr at kitware.com> wrote:
> Within Slicer vtkMath::Pi() is called at four location.  See details below.
>
> We will make sure to use vtkMath::FloatPi() when we will integrate VTK 5.10.
>
> Thanks
> Jc
>
>
>
> Modules/Loadable/Annotations/VTKWidgets/vtkAnnotationGlyphSource2D.cxx
> 352:  theta = 2.0 * vtkMath::Pi() / 8.0;
>
> Libs/MRML/Logic/vtkMRMLSliceLogic.cxx
> 2128:    double axisMisalignmentDegrees=acos(dotProd)*180.0/vtkMath::Pi();
>
> Libs/vtkTeem/vtkPreciseHyperStreamline.cxx
> 591:  vtkFloatingPointType theta=2.0*vtkMath::Pi()/this->NumberOfSides;
>
> Base/Logic/vtkSlicerGlyphSource2D.cxx
> 346:  theta = 2.0 * vtkMath::Pi() / 8.0
>
>
> On Wed, Feb 29, 2012 at 6:41 PM, Jean-Christophe Fillion-Robin
> <jchris.fillionr at kitware.com> wrote:
>>
>> +1 :)
>>
>>
>> On Wed, Feb 29, 2012 at 4:57 PM, David Gobbi <david.gobbi at gmail.com>
>> wrote:
>>>
>>> Hi All,
>>>
>>> I'm wondering if, for VTK 6, we can make the vtkMath::Pi() return a
>>> double instead of a float.  Currently, most VTK code is calling
>>> vtkMath::DoublePi() and, in my opinion, vtkMath::Pi() is more
>>> readable.
>>>
>>> Here's my proposal:
>>>
>>> 1) In VTK 5.10, a vtkMath::FloatPi() method would be added.  Any VTK
>>> 5.10 code that calls vtkMath::Pi() would be changed to call
>>> vtkMath::FloatPi() instead.
>>>
>>> 2) In VTK 6, vtkMath::Pi() would be changed so that it returns double,
>>> and then all instances of vtkMath::DoublePi() can be changed to
>>> vtkMath::Pi() to improve readability.
>>>
>>> If anyone thinks this is a good idea, I can submit a patch for the VTK
>>> 5.10 changes to gerrit.
>>>
>>>
>>> To reiterate what I'm proposing, in VTK 5.10, the following methods would
>>> exist:
>>>
>>> double vtkMath::DoublePi();
>>> float vtkMath::Pi();
>>> float vtkMath::FloatPi();  - new method for single precision
>>>
>>> In VTK 6.0, the following methods would exist:
>>>
>>> double vtkMath::DoublePi();
>>> double vtkMath::Pi();
>>> float vtkMath::FloatPi();
>>>
>>>  - David
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>>
>>
>>
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