[vtkusers] Problem with vtkActor->SetOrigin()

[王君臣]

Hi, sorry for my uncompleted explanation. Now let's study the
underlying mechanism of "SetOrigin etc." together.
here is the source code of vtkProp3D::ComputeMatrix (vtk 5.4)

void vtkProp3D::ComputeMatrix()
{
  if (this->IsIdentity)
    {
    return;
    }
  // check whether or not need to rebuild the matrix
  if ( this->GetMTime() > this->MatrixMTime )
    {
    this->GetOrientation();
    this->Transform->Push();
    this->Transform->Identity();
    this->Transform->PostMultiply();
     //* Notice This Code segment*
    // begin {
    // shift back to actor's origin
    this->Transform->Translate(-this->Origin[0],
                              -this->Origin[1],
                              -this->Origin[2]);
    // scale
    this->Transform->Scale(this->Scale[0],
                          this->Scale[1],
                          this->Scale[2]);
    // rotate
    this->Transform->RotateY(this->Orientation[1]);
    this->Transform->RotateX(this->Orientation[0]);
    this->Transform->RotateZ(this->Orientation[2]);
    // move back from origin and translate
    this->Transform->Translate(this->Origin[0] + this->Position[0],
                              this->Origin[1] + this->Position[1],
                              this->Origin[2] + this->Position[2]);
    //}end ==> it means: at first, the actor frame is an identity (same with
the world frame), then you have a chance to rotate or/and scale the identity
frame with respect to a point (specified by setorigin) in the world frame.
after that, the usermatrix takes efforts.
    // apply user defined transform last if there is one
    if (this->UserTransform)
      {
      this->Transform->Concatenate(this->UserTransform->GetMatrix());
      }
    this->Transform->PreMultiply();
    this->Transform->GetMatrix(this->Matrix);
    this->MatrixMTime.Modified();
    this->Transform->Pop();
    }
}
2010/5/26 Anant Vemuri <ajar108 at gmail.com>

> Hi,
>
> I had posted a problem a few days back that I am still having with using
> vtkActor->SetOrigin(). The documentation of vtkProp3D says that
> SetOrigin(pos) function sets the point of rotation to the point specified by
> pos. However, when I apply SetOrigin(pos), my actor moves in the scene such
> that his point is at the world origin. For example, if I do SetOrigin(100,
> 100, 100), the actor moves such that the previous (100,100,100) is now at
> (0,0,0) initially before I apply any other transform to it. The effect is
> similar to when I do
>
> m_transform->Translate( -100,-100,-100 );
> m_actor->SetUserTransform( m_transform );
>
>
> Is this what is expected? Becase from the documentation, I understood that
> it should do translate(-newOrigin) [rotations, scaling etc]
> translate(newOrigin). Should I expect that when I do
> vtkActor->SetOrigin(newOrigin), the newOrigin moves to the world (0,0,0).
> Can someone explain this to me?
>
> Thank you.
> Anant.
>
>
> On Mon, May 24, 2010 at 11:27 PM, Anant Vemuri <ajar108 at gmail.com> wrote:
>
>> Thanks... But doesn't SetUserTransform() do that already... the vtk
>> documentation says as below...
>>
>> I think I understand the problem, but not sure how to correct it... I
>> am attaching a transform as the base transform which means that all
>> the other operations such as SetOrigin(), SetScale() get overridden.
>>
>>
>> On 5/24/10, 王君臣 <wangjunchen at gmail.com> wrote:
>> > what you need is a multiplication (PostMultiply) of m_defaultTrf to the
>> > current actor transform not a replacement.
>> >
>> >
>> > 2010/5/24 Anant Vemuri <ajar108 at gmail.com>
>> >
>> >> Hi,
>> >>
>> >> I am trying to use myVtkActor->SetOrigin(origin) to set the origin so
>> that
>> >> any rotations I apply is done about this point. This is what I do to
>> build
>> >> the pipeline
>> >>
>> >>
>> >> void buildPipeline( )
>> >> {
>> >>     m_actor->SetMapper( m_mapper );
>> >>     m_actor->SetOrigin( 100, 100, 100 );
>> >>     m_defaultTrf->Scale(m_scale, m_scale, m_scale);
>> >>     m_defaultTrf->PostMultiply();
>> >>     m_defaultTrf->Concatenate( this->getTransform() );
>> >>     /// I add some more things to the m_defaultTrf
>> >>     .
>> >>     .
>> >>     .
>> >>     m_actor->SetUserTransform( m_defaultTrf );
>> >>     }
>> >>     std::cout << "\n\n\nOrigin = [" << m_actor->GetOrigin()[0] << ", "
>> <<
>> >> m_actor->GetOrigin()[1] << ", " << m_actor->GetOrigin()[2] <<
>> "]\n\n\n";
>> >> }
>> >>
>> >> But when I apply the transform in the scene, it is not being about some
>> >> other point entirely. I noticed that this is the same point when I
>> remove
>> >> the SetOrigin() line. But in the last line it gives me the origin as
>> the
>> >> one
>> >> that I set a few line earlier. I am not able to figure out what is the
>> >> mistake. Can anyone help me?
>> >>
>> >> Thank you.
>> >> Anant.
>> >>
>> >> _______________________________________________
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>> >>
>> >
>> >
>> > --
>> >
>>
>>
>> --
>> -----------
>> Anant S. Vemuri
>> email: ajar108 at gmail.com
>>
>
>
> _______________________________________________
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>
> Visit other Kitware open-source projects at
> http://www.kitware.com/opensource/opensource.html
>
> Please keep messages on-topic and check the VTK FAQ at:
> http://www.vtk.org/Wiki/VTK_FAQ
>
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