[vtk-developers] bounds calculation in vtkActor

[David Gobbi]

It all looks good to me.  Your comments about ComputeMatrix are valid.
>From my inspection of vtkProp3D, the main purpose of this->Transform
is to hold the orientation.  However, this->Transform is also used for
several other things, usually by expediently pushing and popping it.
That, as far as I am concerned, is bad coding.  If the purpose of
this->Transform to hold the orientation, then it should be used for
that purpose only.  It should not also be used as "scratch space" for
matrix computations.

  David

On Tue, Nov 2, 2010 at 11:10 AM, Rusty Blue <rusty.blue at kitware.com> wrote:
> Changes and a test pushed to gerrit... (finally).  Without the changes, the
> test result would have incorrectly set clipping planes.
>
> Rusty
>
> -----Original Message-----
> From: Bill Lorensen [mailto:bill.lorensen at gmail.com]
> Sent: Thursday, October 28, 2010 12:18 AM
> To: Aashish Chaudhary
> Cc: Rusty Blue; vtk-developers at vtk.org
> Subject: Re: [vtk-developers] bounds calculation in vtkActor
>
> I would push both the changes and the test to gerrit.
>
> Bill
>
> On Wed, Oct 27, 2010 at 10:12 PM, Aashish Chaudhary
> <aashish.chaudhary at kitware.com> wrote:
>> Bill,
>>
>> On Wed, Oct 27, 2010 at 8:35 PM, Bill Lorensen <bill.lorensen at gmail.com>
> wrote:
>>
>> What Rusty (in his reply) +
>>
>>> Rusty,
>>>
>>> I would think it should be consistent across ImageActor and Volume.
>>
>> I agree but I guess it would be nice to know if someone else ran into
>> similar issues (yes / no). It is hard to imagine though but not
>> impossible. When I worked on a project (8 months back with Rusty) I
>> took control over the matrix multiplication and division by
>> homogeneous coordinate and hence this problem never showed up.
>>
>>> I
>>> also suggest you push it to Gerrit for code review. And you should
>>> provide or modify a test to illustrate it.
>>
>> Would you prefer test to go to the Gerrit or  in the email thread?
>>>
>>> Bill
>>>
>>> On Wed, Oct 27, 2010 at 8:29 PM, Rusty Blue <rusty.blue at kitware.com>
> wrote:
>>>> Folks,
>>>>
>>>>
>>>>
>>>> We're setting the UserMatrix of an actor to... surprise, surprise...
>>>> transform the actor.  Nothing exciting, right?
>>>>
>>>>
>>>>
>>>> Wrong, because the last row of our matrix is not the trivial [0 0 0 1].
>>>> This is handled well enough in OpenGL, but the bounds calculation (in
>>>> vtkActor::GetBounds()) is seriously wrong because it is doing a linear
>>>> transformation of the bbox it gets from the mapper (Transform is a
>>>> vtkLinearTransform):
>>>>
>>>>
>>>>
>>>>     fptr = bbox;
>>>>
>>>>     for (n = 0; n < 8; n++)
>>>>
>>>>       {
>>>>
>>>>       this->Transform->TransformPoint(fptr,fptr);
>>>>
>>>>       fptr += 3;
>>>>
>>>>       }
>>>>
>>>>
>>>>
>>>> The easiest fix I found for the issue was the following (force call to
>>>> InternalTransformPoint of vtkHomogeneousTransform):
>>>>
>>>>
>>>>
>>>>     fptr = bbox;
>>>>
>>>>     this->Transform->Update();
>>>>
>>>>     for (n = 0; n < 8; n++)
>>>>
>>>>       {
>>>>
>>>>
>>>>
> this->Transform->vtkHomogeneousTransform::InternalTransformPoint(fptr,fptr);
>>>>
>>>>       fptr += 3;
>>>>
>>>>       }
>>>>
>>>>
>>>>
>>>> The change doesn't cause any tests to fail (for me)... and it seems like
> a
>>>> reasonable change (perhaps should be made in vtkImageActor and vtkVolume
> as
>>>> well?)... but I wanted to put it out there (before I committed and
> pushed
>>>> the change), because it is seriously likely that I'm not considering
> some
>>>> other special "situations", or perhaps the "right" way to fix this, or
> ????
>>>>
>>>>
>>>>
>>>> Rusty
>>>>
>>>>
>>>>
>>>>
>>>>
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>>>
>>
>>
>>
>> --
>> | Aashish Chaudhary
>> | R&D Engineer
>> | Kitware Inc.
>> | www.kitware.com
>>
>
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