[vtk-developers] A weird 6.x specific bug with ModifiedEvents

[Bill Lorensen]

Itkarsh,

Now I see the old/new code. I guess this logic has been there for a
whiole. We are stuck witk it.

I think it is bad practice to have a Get, change the Set value.

Bill


On Mon, Apr 14, 2014 at 1:51 PM, Utkarsh Ayachit
<utkarsh.ayachit at kitware.com> wrote:
> I am not entire surely sure why that change was done, but I think
> here's a potential explanation:
>
> - SetColor is really a "convenience" method. It's a shortcut to set
> AmbientColor, SpecularColor, DiffuseColor. The Color ivar on
> vtkProperty is not used by vtkOpenGLProperty at all when passing the
> color to OpenGL.
> - Since the "effective" color used by the property is the value
> computed similar to what vtkProperty::ComputeCompositeColor does,
> GetColor was changed to return that value.
> - In fact, looking at the commit 52fd8ad8, GetColor() always returned
> the "computed" value. Kyle just made that a static method and made
> vtkProperty::GetColor() call that method instead.
>
> Utkarsh
>
>
> On Mon, Apr 14, 2014 at 12:57 PM, Bill Lorensen <bill.lorensen at gmail.com> wrote:
>> Ooops, I think Kyle has left Kitware...
>>
>> On Mon, Apr 14, 2014 at 12:54 PM, Bill Lorensen <bill.lorensen at gmail.com> wrote:
>>> GetColor should return the value set by SetColor. If we need the
>>> composite color then we should explicitly ask for it.
>>>
>>> I'm not sure why this change was made. Kyle made it.
>>>
>>> Bill
>>>
>>>
>>> On Mon, Apr 14, 2014 at 12:52 PM, Bill Lorensen <bill.lorensen at gmail.com> wrote:
>>>> So here is the bug the sample code uncovers:
>>>>
>>>> SetColor
>>>> 1) Sets the Color ivar to the requested color
>>>> 2) SetColor calls SetAmbientColor which triggers the Modified event
>>>>     The Modified event call GetColor which calls ComputeCompositeColor
>>>> and computes a composite color
>>>>     The composite color is not correct
>>>> 3) Color continues to get corrupted with SetDiffuseColor and SetSpecularColor.
>>>>
>>>>
>>>>
>>>> On Mon, Apr 14, 2014 at 12:40 PM, Bill Lorensen <bill.lorensen at gmail.com> wrote:
>>>>> I do not think that GetColor should change the value of Color. If we
>>>>> need the composite color, we could have a method GetCompositeColor().
>>>>> No SetCompositeColor.
>>>>>
>>>>> Bill
>>>>>
>>>>>
>>>>> On Mon, Apr 14, 2014 at 12:24 PM, Bill Lorensen <bill.lorensen at gmail.com> wrote:
>>>>>> Really bad stuff. ComputeCompositeColor "sets" this->Color directly.
>>>>>> ComputeCompositeColor was added about a year ago...
>>>>>>
>>>>>>
>>>>>>
>>>>>> On Mon, Apr 14, 2014 at 12:18 PM, Bill Lorensen <bill.lorensen at gmail.com> wrote:
>>>>>>> This is indeed weird.
>>>>>>>
>>>>>>> GetColor does not return the value set by SetColor. It calls
>>>>>>> ComputeCompositeColor.
>>>>>>>
>>>>>>> Also, SetColor calls SetAmbientColor, SetDiffuseColor and
>>>>>>> SetSpecularColor. Each should cause a Modified event. In fact if you
>>>>>>> remove the o.GetColor() call in the Modified callback, you will see
>>>>>>> three modified events and each call will change one more of the color
>>>>>>> s (ambeint, diffuse, specular).
>>>>>>>
>>>>>>>
>>>>>>> Very strange.
>>>>>>>
>>>>>>> Bill
>>>>>>>
>>>>>>>
>>>>>>> On Mon, Apr 14, 2014 at 11:35 AM, Prabhu Ramachandran
>>>>>>> <prabhu at aero.iitb.ac.in> wrote:
>>>>>>>> Hi everyone,
>>>>>>>>
>>>>>>>> I just discovered a weird bug with VTK 6.1 and 6.0 that doesn't happen with
>>>>>>>> VTK 5.x.  Here is a tiny Python script:
>>>>>>>>
>>>>>>>> ##################################################
>>>>>>>> import vtk
>>>>>>>> def f(o, e):
>>>>>>>>     print e, o.GetAmbientColor(), o.GetColor(),
>>>>>>>>     print o.GetDiffuseColor(), o.GetSpecularColor()
>>>>>>>>
>>>>>>>> p = vtk.vtkProperty()
>>>>>>>> p.AddObserver('ModifiedEvent', f)
>>>>>>>> p.SetColor(0,0,0)
>>>>>>>> print p.GetColor()
>>>>>>>> ##################################################
>>>>>>>>
>>>>>>>> If you comment out the AddObserver line, everything works correctly but with
>>>>>>>> it, you can never set the color of the property!  This doesn't seem to be
>>>>>>>> specific to Python and happens with a small C++ example as well.
>>>>>>>>
>>>>>>>> Thoughts?
>>>>>>>>
>>>>>>>> cheers,
>>>>>>>> Prabhu
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>>>>>>>
>>>>>>>
>>>>>>>
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>>>>>>
>>>>>>
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